MSc Program Renewable Energy in Central & Eastern

The Brenner Base (BBT): A Source of Renewable Energy

A Survey on the Geothermal Energy Potential of the Tunnel Water at the BBT’s South Portal and its Utilization Possibilities for District Heating Purposes

Master Thesis submitted for the degree of

“Master of Science”

supervised by

O.Univ.Prof. Dipl.-Ing. MSc Dr.phil. Dr.techn. Konrad Bergmeister

and

Ao.Univ.Prof. Dipl.-Ing. Dr.nat.techn. Bernhard Pelikan

BSc Andreas Kostner

Vienna, November 2011

AFFIDAVIT

I, Andreas Kostner, hereby declare

1. that I am the sole author of the present Master Thesis, "The Brenner Base Tunnel (BBT): A Source of Renewable Energy – A Survey on the Geothermal Energy Potential of the Tunnel Water at the BBT’s South Portal and its Utilization Possibilities for District Heating Purposes", 107 pages, bound, and that I have not used any source or tool other than those referenced or any other illicit aid or tool, and 2. that I have not prior to this date submitted this Master Thesis as an examination paper in any form in or abroad.

Vienna, ______Date Signature

ii ACKNOWLEDGMENT

Many thanks to Prof. Dipl.-Ing. Dr. Bernhard Pelikan and Prof. Dipl.-Ing. MSc. DDr. Konrad Bergmeister for supervising my master thesis. The team of the Continuing Education Centre has been of great help especially the program manager Dipl.-Ing. Andrea Würz and the program assistant Martin Schestag. Special thanks to Michael Bergmeister from Ingenieurteam Bergmeister for his professional input, to Dipl.-Ing. Dr. Anton Rieder and Ing. Ugo Bacchiega from BBT- SE for providing the data of the Brenner Base Tunnel project and to Dr. Paul Seidemann and Dr. Robert Schiffregger, Amt für Gewässerschutz – Province of , for the data of the River. Thanks also to Dr. Ing. Leszek Wojtan of Friotherm/ Winterthur (CH) and Walter Schläpfer of CTA/ Bern (CH) for spending their time to design feasible heat pumps for the investigated district heating systems. Dipl.-Ing. Stephan Hasse, SEL AG, provided data on the planned district heating system in and Mr. Wolfgang Plank, Director Stadtwerke , the data set for Brixen/Vahrn. Thanks.

I also want to thank the stuff of the companies Ekos GmbH and Kostner GmbH, particularly Mr. David Leitner, for replacing me in my absence. Furthermore, I want to thank my family, in particular my partner Prof. DDr. Mag. MSc Annemarie Profanter, for her patience and her professional inputs in writing my master thesis. Last but not least I want to send a big thank you to my mother. She supported me in all my decisions although she was concerned about the extensive traveling for professional and educational purposes. Sadly she passed away in November 2009 while I was still in the midst of writing this thesis. I am so sorry that she can’t witness this moment.

iii ABSTRACT

The projected Brenner Base Tunnel (BBT), with its continuous warm tunnel water outflow at its tunnel portals, represents a considerable geothermal, renewable energy source. At the BBT’s south portal the expected stabilized tunnel water outflow rate is approximately 745 liters per second with temperatures of 22° C to 26° C, which corresponds to a geothermal capability of 68 MW to 81 MW year-round. The focus of this master thesis is on the geothermal capability of the tunnel water at the south portal of the BBT’s exploratory tunnel in Aicha and its utilization possibilities. It analyzes the usable geothermal potential of the tunnel water and its specific utilization possibilities in a planned and in an existing district heating system of different sizes near the southern tunnel portal. For the tunnel water heat utilization in the relatively small planned district heating system of Franzensfeste (heat demand of 4,195 MWh/ year), a pump system has to be installed to overcome the height difference to the exploratory tunnel portal where the BBT’s tunnel water is discharged. The existing large district heating system of Brixen/ Vahrn (heat production of over 100,000 MWh/ year) can be supplied with tunnel water by inherent pressure. Since this district heating system is located few kilometers farther than Franzensfeste, the pipeline to be installed is much longer. The calculations of profitability show that the tunnel water heat utilization by heat pumps for the small district heating system of Franzensfeste is not feasible economically. In contrast, tunnel water heat exploitation by a heat pump system for the large district heating of Brixen/ Vahrn is reasonable and competitive with alternative energy sources. Apart from the tunnel water pipe length, the two identified key factors for the profitability of tunnel water heat utilization by district heating systems are: the amount of heat demand and the electricity price for driving the heat pumps. Assuming the lowest expected geothermal output of the BBT’s tunnel water and its utilization by the three district heat systems near the tunnel south portal (Franzensfeste, Schabs, Brixen/ Vahrn), the heat surplus referring to the required cooling of the tunnel water for surface water discharge, is still over 100,000 MWh per year.

iv TABLE OF CONTENT

Affidavit...... ii

Acknowledgment...... iii

Abstract ...... iv

Table of Content...... v

List of Figures...... viii

List of Tables...... x

1. INTRODUCTION ...... 1

1.1 Motivation...... 1

1.2 Objective ...... 2

1.3 Literature ...... 2

1.4 Structure of work ...... 3

2. METHODOLOGY ...... 4

3. BACKGROUND INFORMATION ...... 5

3.1 The Brenner Base Tunnel Project...... 5

3.2 Geothermal Energy in Tunneling...... 7

3.3 Geothermal Energy from Tunnel Water in Deep Tunneling ...... 10

3.3.1 Tunnel Water in Deep Tunneling ...... 10

3.3.2 The Geothermal Potential of Tunnel Water and Discharge

Conditions ...... 13

3.3.3 Tunnel Water Outflow and Temperature Prognosis in Tunneling ..... 15

v 3.4 The Indirect Use of Geothermal Energy – Heat Pump Systems ...... 18

3.4.1 Heat Source Loop of Indirect Geothermal Energy Use...... 20

3.4.2 The Heat Pump...... 23

3.4.2.1 Compression Heat Pumps...... 23

3.4.2.2 Absorption Heat Pumps ...... 30

3.4.2.3 The Performance of Heat Pumps...... 31

3.4.3 The Heat Sink ...... 37

3.5 District Heating Systems ...... 38

3.5.1 Heat Production/ Distribution/ Consumption ...... 39

3.5.2 Geothermal District Heating...... 43

3.5.3 Combined Heat and Power and Heat Pump Systems for

Residential Use...... 44

3.6 Utilization Possibilities of Tunnel Water Heat...... 46

3.6.1 Heating of Buildings (Conventional Heating vs.

Low Temperature Heating) ...... 47

3.6.2 Process Heat for Commerce and Industry...... 49

3.6.3 Process Heat for Agriculture ...... 50

3.6.4 Process Heat for Animal Husbandry and Aquaculture...... 51

3.6.5 Suitability of Tunnel Heat Utilization for Different Utilization Forms

and Heat Sources ...... 53

3.7 Operating Examples of Tunnel Water Heat Utilization ...... 55

3.7.1 Tunnel Water Heat Utilization in Switzerland...... 55

3.7.2 Tunnel Water Heat Utilization Projects at Lötschberg

and Gotthard Railway Base Tunnel ...... 57

vi

4. GEOTHERMAL HEAT POTENTIAL OF THE BBT’S TUNNEL WATER

AT THE SOUTH PORTAL AND ITS UTILIZATION POSSIBILITIES ...... 64

4.1 Analysis of the Geothermal Energy Potential of the BBT’s Tunnel Water .. 64

4.1.1 Conceptual Hydrogeological Model of the BBT Project ...... 64

4.1.2 Forecast of BBT’s Tunnel Water Flow Rates and Temperatures ..... 66

4.1.3 Geothermal Potential of the BBT’s Tunnel Water ...... 68

4.1.3.1 Flow Rates and Temperatures of the Eisack River...... 68

4.1.3.2 Tunnel Water Discharge Condition/ Environmental

Regulations ...... 69

4.1.3.3 The Usable Geothermal Energy ...... 72

4.2 Evaluation of different Tunnel Heat Utilization Possibilities for District

Heating Purposes...... 75

4.2.1 Municipality of Franzensfeste...... 76

4.2.1.1 Prognosticated Heat Demand ...... 77

4.2.1.2 Heat Supply – Heat Pump System Design ...... 79

4.2.1.3 Energy and Environmental Balance...... 80

4.2.1.4 Investments and Economy...... 83

4.2.2 Municipality of Vahrn/Brixen...... 87

4.2.2.1 Existent Heat Supply System...... 87

4.2.2.2 Heat Pump System Design ...... 89

4.2.2.3 Energy and Environmental Balance...... 91

4.2.2.4 Investments and Economy...... 94

5. SUMMARY & CONCLUSION ...... 97

6. LITERATURE ...... 103

vii LIST OF FIGURES

Fig. 1: TEN1 axis from to ...... 5

Fig. 2: Profile of the Brenner Base Tunnel ...... 6

Fig. 3: Base slab of station „U2/4 Messe“ Vienna equipped with absorber pipes ... 7

Fig. 4: „Energy Geotextile“ with absorber loops ...... 7

Fig. 5: Profile of the geothermal experimental plant Haderdorf-Weidlingau...... 8

Fig. 6: Typical dewatering system of a rail tunnel ...... 10

Fig. 7: Tunnel water intrusion ...... 11

Fig. 8: Comparison of prognosticated rock temperatures and in-situ measurements

in the ...... 16

Fig. 9: Rock temperature vs. temperature of inflowing water at the Simplon railway

and the Gotthard highway tunnel ...... 17

Fig. 10: The Lindal Diagramm with different applications for geothermal energy

according to the temperature of the heat source...... 19

Fig. 11: Schematic diagram of indirect geothermal heat exploitation with 3

loops/circuits...... 20

Fig. 12: Horizontal closed absorber system ...... 21

Fig. 13: Vertical closed absorber system ...... 21

Fig. 14: Reinforcement cage for diaphragm wall equipped with absorbers...... 22

Fig. 15: Reinforcement cage for bored pile equipped with absorbers...... 22

Fig. 16: Scheme of a compression heat pump with temperatures and pressures for

the refrigerant medium R290...... 24

Fig. 17: Heat exchange in the evaporator (schematic)...... 25

Fig. 18: Compression action of a piston compressor cylinder...... 26

Fig. 19: Compression action function of a scroll compressor...... 26

viii Fig. 20: Compressing action of a screw compressor ...... 27

Fig. 21: Centrifugal compressor ...... 27

Fig. 22: Properties of refrigerants...... 29

Fig. 23: Thermodynamic cycle of R134a...... 29

Fig. 24: The principle of absorption heat pumps ...... 30

Fig. 25: Ideal thermodynamic cycle (Carnot cylce) ...... 34

Fig. 26: Real thermodynamic cycle ...... 34

Fig. 27: Energy efficiency respectively the primary energy input of different

heating methods...... 36

Fig. 28: Screw plate heat exchanger...... 37

Fig. 29: Main distribution networks of heatings systems...... 40

Fig. 30: Transmission routings of district heating ...... 40

Fig. 31: Simplified indirect substation...... 41

Fig. 32: Operating principles of geothermal heating stations ...... 43

Fig. 33: Energy flow of a CHP - HP system ...... 45

Fig. 34: The overall efficiency of a CHP-HP system depending on the heat

pump's seasonal performance factor ...... 45

Fig. 35: The principle of the tunnel water utilization for heating purposes of

Lötschberg and Gotthard Base Tunnel ...... 60

Fig. 36: Cascade use of tunnel water heat at Tropic House Frutigen ...... 62

Fig. 37: Flow diagram illustrating the conceptual process for hydrogeological

interpretation of the BBT project...... 64

Fig. 38: Municipalities around the tunnel portal of the BBT exploratory gallery

at Aicha ...... 76

Fig. 39: Annual load duration curve of Franzensfeste...... 78

Fig. 40: Air pollutant and greenhouse gas emissions of a district heating system

Franzensfeste for different heat plants...... 83

ix Fig. 41: Heat generation costs of a heat pump system for a district heating

Franzensfeste as a function of the net heat demand ...... 87

Fig. 42: Load curve of the district heating Brixen/Vahrn – 2010...... 88

Fig. 43: Annual load duration curve of the district heating Brixen/Vahrn – 2010..... 89

Fig. 44: Heat pump design of Unitop 33C-6145U/ Friotherm ...... 89

Fig. 45: Heat pump data of Unitop 33C-6145/ Friotherm ...... 90

Fig. 46: Air pollutant and greenhouse gas emissions of the district heating system

Brixen/Vahrn with heat pump system and with actual heat plants ...... 93

Fig. 47: Heat generation costs of a heat pump system for the district heating

Brixen/Vahrn as a function of the electricity price ...... 96

LIST OF TABLES

Tab. 1: Basic Data of BBT ...... 6

Tab. 2: Geothermal utilization forms of tunnel water and its temperature levels.... 47

Tab. 3: Different tunnel heat sources and their characteristics ...... 53

Tab. 4: Suitability of tunnel heat utilization for different utilization forms and tunnel

heat sources...... 54

Tab. 5: Geothermal potential and current thermal utilization of rail and road

in Switzerland ...... 55

Tab. 6: Overview of operating and planned geothermal plants for tunnel water

utilization in Suisse...... 56

Tab. 7: Tunnel water heat estimations, potentials and its utilization possibilities

of Lötschberg and Gotthard Base Tunnel ...... 60

Tab. 8: Forcasted discharge rates and temperatures of the BBT’s tunnel water

at the south portal in Aicha...... 67

x Tab. 9: Thermal potential in kWh of the tunnel water of Brenner Base Tunnel

depending on outflow rate and temperature...... 68

Tab. 10: Temperatures and flow rates of the Eisack River and the influence

of tunnel water discharge without cooling ...... 69

Tab. 11: Maximal dischargeable tunnel water amount and maximal discharge

temperature of tunnel water into Eisack River...... 71

Tab. 12: Required cooling power for discharging the tunnel water into Eisack

River at Aicha ...... 71

Tab. 13: Usable thermal potential of the BBT tunnel water at the south portal for

different scenarios with maximal possible and minimal required cooling... 72

Tab. 14: Maximal dischargeable tunnel water amount and maximal discharge

temperature of tunnel water into Eisack at reservoir of Franzensfeste ...... 74

Tab. 15: Analyzed heat demand of Franzensfeste ...... 78

Tab. 16: Heat supply and efficiency of a heat pump system for Franzensfeste...... 79

Tab. 17: Energetic data and assumptions for a heat pump system utilizing the

BBT’s tunnel water heat for a district heating Franzensfeste ...... 80

Tab. 18: Non-renewable primary energy factor of a district heating

system for Franzensfeste powered by a heat pump system and

the tunnel water heat...... 81

Tab. 19: Non-renewable primary energy factors of a district heating system for

Franzensfeste powerd by a gas CHP-plant and a biomass heat plant ...... 82

Tab. 20: Air pollutant and greenhouse gas emissions of a district heating system

Franzensfeste for different heat plants...... 83

Tab. 21: Investment costs and annuities for a heat pump district heating

system Franzensfeste ...... 84

Tab. 22: Economic assumptions for annuity and heat generation cost calculation.. 85

xi Tab. 23: Heat generation costs for a heat pump district heating system

Franzensfeste...... 85

Tab. 24: Comparison of heating costs for different combustibles ...... 86

Tab. 25: Heat generation costs of a heat pump system for DH Franzensfeste

dependent on the energy input prices...... 86

Tab. 26: Heat pump system for the district heating Brixen/ Vahrn with

two heat pumps UNITOP 33C/ Friotherm ...... 91

Tab. 27: Non-renewable primary energy factor of heat production for the district

heating Brixen/ Vahrn with heat pump system utilizing tunnel water heat . 92

Tab. 28: Non-renewable primary energy factor of heat production for the district

heating Brixen/ Vahrn with actual heat plants ...... 92

Tab. 29: Air pollutant and greenhouse gas emissions of a district heating system

Brixen/Vahrn with a heat pump system and with actual heat plants ...... 93

Tab. 30: Investment costs and annuities for a heat pump system supplying

the district heating of Brixen/ Vahrn ...... 94

Tab. 31: Heat generation costs for a heat pump system supplying the district

heating of Brixen/ Vahrn...... 95

Tab. 32: Comparison of heat generation costs for heat pump systems for

Brixen/ Vahrn and Franzensfeste...... 100

Tab. 33: Degree of BBT’s tunnel water heat utilization by the district heatings at

south portal...... 101

xii 1. INTRODUCTION

In tunneling there is considerable potential for geothermal heat energy generation caused by increased temperatures under ground. Deep tunnel projects in existence give evidence that tunnel water and surrounding rock can reach 30-40° C or higher. A deep tunnel project is the Brenner Base Tunnel (BBT), a 64 kilometers long alpine-crossing railway tunnel connecting to Austria to be constructed from 2011 to 2025. When completed, it will be one of the longest railway tunnels worldwide. Because of the BBT’s length and prolonged contact with overlapping rock surfaces, there is a significant potential for geothermal energy allowing this to be a major source of renewable energy.

1.1 Motivation

The tunnel water is part of Earth’s hydrological cycle; underground it absorbs the heat of Earth’s interior. Thus, flow rates and temperatures of tunnel water are constant for an infinitely long time period. Ecologically it is necessary to cool down elevated temperatures of the drained tunnel water before discharging it to the surface waters. In most of the cases the water is cooled down in basins and towers, without making use of the extracted heat. For a sustainable energy system it is vital to harness a renewable energy resource as it presents the tunnel water, for heating, agricultural and commercial purposes. The technology necessary to exploit the tunnel water’s heat is similar to the one for low enthalpy geothermal heat generation from ambient air and ground water. The systems do include heat pumps, which are widely applied and well developed.

At the south portal of the Brenner Base Tunnel the predicted tunnel water flow rate is 745 liters per second with temperatures between 22 and 26° C. This represents an enormous geothermal heat capability. Additionally, more than 20,000 people with a considerable heat demand for space heating and domestic hot water live in the range of a few kilometers near the south portal. By supplying the heat demand with the heat capacity of the Brenner Base Tunnel water, tons of fossil fuel could be substituted and unnecessary CO2 emissions could be avoided.

1 1.2 Objective

This master thesis represents a preliminary study for the utilization of the geothermal energy of the tunnel water at the south portal of the Brenner Base Tunnel. The goals of the study are: (1) to explore the geothermal potential of the tunnel water at the BBT’s south portal; and (2) to indentify and evaluate different possibilities for utilization of the heat energy extracted. The research questions to be addressed are as follows: What volume of geothermal energy can be extracted from the tunnel water at the BBT south portal? How can the extracted heat energy be used in a technologically efficient, economically feasible and, last but not least, ecologically reasonable way? The research results should make it possible to draw conclusions for planning an efficient geothermal system to utilize the heat of tunnel water of the BBT at the south portal. Based on the huge geothermal potential and the absence of agricultural and commercial applications, this pre-study is limited to the use of the tunnel water heat in district heating systems. Single building applications, as heating and cooling purposes of tunnel infrastructures, are not dealt with.

1.3 Literature

The main literatures reviewed for this thesis are papers of Rybach and Wilhelm about tunnel water heat exploitation in Switzerland and papers of Adam and Brandl on surface geothermal energy in tunneling and concrete building foundations. The technical principles on geothermal heat systems, heat pumps and district heating systems are based on “Renewable Energy: Technology, Economics and Environment” by Kaltschmitt et al. (2007) and “Handbuch Wärmepumpen – Planung und Projektierung” by Bonin (2009). The economical part of the thesis was designed according the principles of energetic and economic evaluation of energy systems described in “Energieeffiziente Nahwärmesysteme – Grundwissen, Auslegung, Technik für Energieberater und Planer” by Krimmling (2011).

2 1.4 Structure of Work

After the introduction section (Chapter 1) and the description of the methodology of how the defined objectives will be achieved (Chapter 2),

Chapter 3 gives background information on the Brenner Base Tunnel project, on geothermal energy in tunneling and on systems for exploiting geothermal heat. Since the tunnel water is of low enthalpy, i.e. of low temperatures, and temperatures need to be lifted for heating applications, a special emphasis is placed on the description of indirect geothermal heat systems with heat pumps. A detailed description of the function of heat pumps and their efficiency factors should underline the importance of the optimal design of a geothermal low enthalpy system for this economy. An important part of the chapter is the identification of utilization possibilities of the tunnel water heat. By comparing the tunnel water temperature levels and the temperature needs on the demand side, benefits and drawbacks can be figured out for the different applications. In the last part of the chapter realized tunnel water heat exploitation projects in Switzerland and planned tunnel water heat utilization projects for the Gotthard Base Railway and the Lötschberg Base Railway Tunnel are presented.

In Chapter 4 background information is used to evaluate different tunnel water heat exploitation possibilities at the south portal of the Brenner Base Tunnel. Chapter 4.1 estimates the geothermal potential of the tunnel water at the BBT’s south portal; Chapter 4.2 identifies different probable heat customers. Since presently there do not exist agricultural and commercial applications for the tunnel water heat near the tunnel portal, heat exploitation possibilities at the south portal are limited to space heating and domestic hot water production. In the surrounding area of the south portal, three different municipalities and district heating systems with considerable heat demand can be identified: Franzensfeste, Natz/ Schabs and Vahrn/ Brixen. For two municipalities, Franzensfeste and Vahrn/ Brixen, heat demand is determined, heat systems for the integration of the tunnel water heat are roughly designed, and finally evaluated in their economy and efficiency.

Chapter 5 draws conclusions on the tunnel water heat exploitation possibilities for district heating systems and highlights the key factors for a future economical and ecological geothermal heat system.

3

2. METHODOLOGY

To fulfill the objectives a literature review in the online database of the library – TU Vienna was carried out complemented by a detailed web research for papers on the topic. There is a substantial canon of literature on geothermal energy and geothermal energy generation systems; however, when it comes to tunnel water heat exploitation, there are hardly any books and guidelines describing how to design such energy systems. As mentioned already, papers by Rybach and Wilhelm give an overview of existing tunnel water heat utilization systems and their outcomes.

To determine the geothermal heat potential of the tunnel water at the south portal, studies on the BBT project with predictions of tunnel water out flow rates and temperatures have been used. By taking into account the discharge condition of the environmental impact assessment (EIA) and the flow rates and temperatures of the Eisack River recorded by the “Amt für Gewässerschutz” of the Province of Bolzano, the theoretical geothermal potential of the tunnel water was calculated. Given that the tunnel water predictions are of a partial uncertainty, calculations of the geothermal potential were made for three different scenarios with different flow rates and temperatures.

The first step to evaluate the different possibilities of the tunnel water heat utilization for space heating and domestic hot water production in the surrounding municipalities and district heating systems was to determine their heat demands and requested heat potentials. For this, recent studies and actual data of existing district heating systems have been taken into account. To plan efficient geothermal energy systems with heat pumps, energy experts and heat pump manufacturers have been contacted. With their expertise heat pump systems have been roughly designed for Franzensfeste and Brixen/ Vahrn, taking into account the heat supply of the tunnel water and the defined heat demand of the municipalities and district heating systems. To identify the investments and the costs of these geothermal energy systems, economical and financial valuations have been made by the net present value and the annuity method.

4 3. BACKGROUND INFORMATIONS

3.1 The Brenner Base Tunnel Project

The Brenner Base Tunnel (BBT) is a 55 km long planned Railway Tunnel crossing the at the Brenner Massif, connecting /Austria in the North with Franzensfeste/Italy in the South. The Tunnel is part of the new line from Munich to and the European TEN-1 axis from Berlin to Palermo (see fig. 1). Including the railway bypass tunnel of Innsbruck, which ends in Tulfes, the BBT with a total length of 64 km will be the longest railway tunnel in the world. The Brenner Base Tunnel consists of two main tubes, one for each direction. The tubes have a width of 8.1 m and run 70 m apart from one another (see fig. 2). Every 333 m they are connected by side tunnels, which in emergency cases can be used as escape routes. Before excavating the main tunnels, an exploratory tunnel with a width of 5 m will be constructed 12 m beneath the main ones. The exploratory tunnel, on which construction started in 2007, should give information on the rock mass and thereby help to Fig. 1: TEN1 axis from Berlin to Palermo (Source: www.bbt-se.com/projekt/) reduce construction costs and minimize construction times. When the BBT becomes operational, the exploratory tunnel will be essential for the drainage of the tunnel water. Basic data on the BBT project are presented in table 1 (Bergmeister, 2011).

5 20 Österreich Austria Tunnel 2/2011

• Regulatory principles and technical speci!cations for the lot-based tendering and executive planning • Principles for the design and construction detailing for a service lifetime of 200 years • Creation of detailed interface and type plans • Tolerances (surveying and construction method-de- pendent tolerances), taking into account the subsequent works • Measures for development of the railway infrastructure.

In addition, the entire UTM-based route planning was placed in a project-speci!c coordinate system: BBT-TM, produced by a transverse Mercator projection. Thus, the ave- 2 rage orthometric height of 720 m for the project was determined, Fig.Regelquerschnitt 2: Profile durch of TBM the Brenner Base Tunnel (Source: Bergmeister, 2011) which is about a 770 m ellipsoidal Standard cross-section of the TBM height. The project lies therefore in an area about 10 km east and thometrische Höhe festgelegt, sich dabei der internationa- planning for environmental com- west of the central meridian. The was ca. 770 m ellipsoidischer len Vereinbarung, bei der die patibility were completed. distance distortion in this case is Tab.Höhe entspricht.1: Basic DasData Projekt of BBT Projektion (Source: der ellipsoidischen www.bbt- se.com/projekt/On November 18) th, 2010 further less than 2 to 3 mm/km. liegt somit in einem Gebiet ca. geographischen Koordinaten !nancing and the start of phase Thus, for this reference sys- 10 km östlich und westlich vom WGS84 nach Gauss erfolgt. III (building phase) in Italy were tem, no further rotation must Mittelmeridian.Basic In diesem Data Fall ofMittels the querachsiger Brenner Zylinder Base- approved Tunnel by CIPE. (BBT) On February be performed, as the meridian beträgt die Streckenverzerrung projektion wurde mit einem 1st,2011 Austria´s federal Cabinet convergence is easy to calcu- TENweniger 1 alsaxis: 2 bis Berlin3 mm/km.–Palermo,Massstabsfaktor Milan–Bologna von 0.9996 approved2,400 further ! nancingkm of pre- late and the resulting reduction TENIm so1 geschaaxis !inenen operation Bezugs- undor under unter Verwendung construction des paratory construction65% works and e"ect on the directions is insig- system muss keine weitere Ro- Streifens 32 gerechnet; bei die- in-depth prospection. The start ni!cant (the convergence angle Length of the new Brenner railway line from Munich tation durchgeführt werden, da sem Ansatz ist der Mittelmeridi- of construction work425 in the km main is about 4‘). todie Verona Meridiankonvergenz ein- an bei 9° Länge und besitzt eine construction lots is scheduled for Totalfach zu tunnelberechnen length ist und fromder E-Koordinate the Innsbruck von 500 bypasskm, wäh- to 2016 and the completion of the 2.3 Geo-referenced data sich daraus ergebende Reduk- rend die N-Koordinaten ihren Brenner Base Tunnel64 for 2025.km and WebGis Fortezzationse!ekt auf die Richtungen Ursprung am Äquator haben. The entire planning of the Brenner Lengthunbedeutend of the ist (der base Konver tunnel- Dasfrom Projektgebiet the Innsbruck liegt am portal2.2 Cross-project system plan- Base Tunnel was based on geo- 55 km togenzwinkel the Fortezza beträgt ca. portal 4’). östlichen Punkt 2°40’ vom ning (guide design) referenced data. The project was Mittelmeridian des Streifens In February 2011, the cross-project developed with UTM -WGS84 co- Internal2.3 Georeferenzierte diameter of mainentfernt; tunnels daher ist auch die system planning was8.1 tendered m ordinates, using the international InternalPlanungsgrundlagen diameter of exploratoryMeridiankonvergenz, tunnel sprich Europe-wide, to min.create a5 solid, m agreement for the projection of Die gesamte Planung des Bren- der Unterschied zwischen dem uniform basis for subsequent the WGS84 ellipsoidal geographic Longitudinalner Basistunnels wurde grade auf geo- geographischen und dem Git- planning. The essential4.0 ‰ elements–6.7 ‰ coordinates according to Gauss. Operatingreferenzierten speed Daten aufgefor goods- ternord, beträchtlich. Daher ist of this integratedmax. planning 120 are:km/hCalculation was done by means of baut [2]. Das Projekt wurde mit es vorteilhaft, die Projektdaten • Revision of the route planning a transverse cylindrical projection, Operatingden Koordinaten speed UTM-WGS84 for passenger in ein ebenes trains Bezugssystem zu incorporatingmax. all 160 optimiza km/h- applying a scale factor of 0.9996 Elevationausgearbeitet. at Man the bediente upper surfacetransformieren, of the das rails den atTras the- tions for strip 32; using this approach 608.80 m Innsbruck portal Elevation at the upper surface of the rails at the 794 m highest point Elevation at the upper surface of the rails at the 747.20 m Fortezza portal Expected costs (price basis: 01.01.2010) 7,460 Mio. € Expected costs including risks that are presumed to occur but are not quantifiable (price basis: 8,062 Mio. € 01.01.2010) Planning and construction phases: Phase I: preliminary project and prospection 1999–2003 Phase II: final project and Environmental Impact 2003–2010 Assessment Phase IIa: exploratory section 2007–2013 Phase III: main tunnel 2011–2025

6 84 Geothermie Europe

Tunnels as Energy Sources Tunnelwärmenutzung mit Absorber- Utilisation de la géothermie des tunnels 83 Elementen: Technologie und Fallbeispiele avec des éléments d’absorption: technologies et exemples d’application Betonkonstruktionen von Tunneln in offener Bauweise und Tunnelauskleidungen von Les constructions de tunnels en béton de Tunneln in bergmännischer Bauweise können type ouvert et les habillages des tunnels als Absorberelemente für den Bodenwärme- peuvent être utilisés comme éléments Tunnels as Energyaustausch genutzt Sources: werden. Solche Tunnel absorbeurs pour l’échange de chaleur wurden in Österreich für die U-Bahn-Strecke géothermique. Ce type d’ouvrage a été conçu der U2 in Wien und beim Lainzer Tunnel et construit en Autriche pour la section de la

Technology andkonstruiert Case und gebaut. Histories ligne de métro U2 à Vienne et pour le tunnel 3.2 Geothermal Energy in Tunneling de Lainz. Univ. Doz. Dr. D. Adam Sfruttamento dell’energia geotermica dei tunnel tramite elementi assorbenti: pipes in the concrete structure While the existing methods can The ground under the surface of the Earthof a t exhibitsunnel is di ere annt for enormous cut- be app lie potentiald for the insta llafortion of tecnologia e casi esemplifi cativi Concrete structures of cut-and-cover tunnels and tunnel linings ofa nminedd-cover tu ntunnelsnels and mi ncaned abebso rusedber syste mass in the tunnel geothermal energy, generated by sun insulationtunnels. Fo r atcut -athend-c ov Earth’ser tun- i nvsurface,ert, a compl etandely ne wby tec h- absorber elements for groundLe costruzioni heat exchange. in cemento nei Such tunnel tunnels a were ndesignedels, the we landl-exper ieconstructednced nology had tino b e developed for element heat from earth formation and radioactivemethods alrea dy decay used in d ineep theth e l depthining of tshe. tu Tunnelnnel. Austria at the Vienna metrostruttura U2 and aperta at ethe i rivestimenti Lainzer Tunnel. dei tunnel a foundations can be used: instal- constructions are directly influenced by this energy and can be used for ground heat struttura mineraria possono essere utilizzati lation of absorber pipes in bored 2 Geothermal Tunnel piles, diaphragm walls and in or exchangecome elementi purpo assorbentises. In per deep lo scambio tunneling the elevatedunder base sla b temperaturess. However, the Projects of water in Austria inflows 1 Introduction and termico con il suolo. Questo tipo di tunnel è use of mined tunnels as thieoant exw- ith heSiantcien gth ea ynedar c20o0o0l isnegve ral can be used for energy recovery. principles of stato progettato e costruito in Austria per il changer elements has sbtoeerna gae . geothermal projects in com- new challenge for engineers. bination with infrastructure geothermal heat tronco ferroviario della metropolitana U2 a For exclusive geothermal en- Vienna e nel Lainzer Tunnel. ergy extraction the energy ow utilization The Use of Near-surface Geothermal takes place only in 1 direction, The subsurface of Earth con- e.g. for heating purposes during Energy tains an enormous potential of a substantially larger ground ing in a better performance of winter. The seasonal operation volume can be activated for the geothermal system. How- geothermal energy that can be geTemperaturesothermal heat exc hatang thee. eEarth’sver, shallow surfacetunnels, i.e. m andetro however uses the thermody- used for heating and cooling Additionally, tunnels with a high tunnels, can also be used pro t- namic inertia of the soil in order purposes. In particular with the ovtheerbu rd firsten ca n metershave a sign i of - theably f orE gearthother m crustal heat e xt arerac- to store thermal energy in the development of the earth- cantly higher temperature of tion due to their urban location. ground for a later operation thmainlye surround ing g influencedround, result- The by in stalla thetion of energyabsorber coupled heat pump it became with reversed energy ow. possible to open up the geo- exchange between the sun, ground and Consequently, the seasonal op- thermal energy present in the atmosphere. Because of the seasonal eration can produce energy ground. 1 Extracted energy and consumption of electricity of testing plant LT24 equilibrium in the ground over In the 1980s deep founda- variations of insulation and atmosphere a complete heating/cooling pe- tions were rst used for geo- temperatures,Heat pumps an d they/or c oo fluctuateling tio ovn, erCO P) the of a t least 4, meaning riod of a year. A geothermal thermal heat extraction by plac- machines are connected be- that ¼ of electric energy and ¾ cooling system extracts heat ing heat absorber pipes in year.tween the Depth absorb er pip rangees with - whereof g eoth thiserma l energy can be energy from the building either 4 concrete elements which are in in the concrete elements (pri- added up to /4 directly usable via an air-cooling system or a temperature variation does not occur any close contact with the ground. mary circuit) and the heating/ energy (for heating operation). water-based cooling system, At rst foundation slabs, then morecoolin g is sy thestem sos o-calledf the b u neutralild- zone.2 Thisdi er ent operation which can be integrated in ceil- driven precast piles and later 3 Einnegrgsy g(esoetcexotinled ata lroyt LTc2i2r couf tihte) Lwainhziecr hTu nnel schemes for the u 4s eB aosef sglaebo otf hstaetrio-n “U2/i4n Mgess saen” edqu wippaellds w. Tith aeb scoorboelri npigpe sma- bored piles and diaphragm zoneadap t startsthe te m fromperat u 10re tom a to 40m aml e ndepthergy fr omFig. dee p3: f oBaseunda -slabc hofin statione acts l ik„U2/4e a “r eMesse“verse” h eat walls have been successfully ac- belowsuitabl e theleve l fosurface,r HVAC ap pdependinglica- tio nson are ptheoss ibleVienna: equippedp uwithmp absorberand the th pipesermal e(Source:nergy tivated for heating and cooling tions (around 6 to 50° C). ˾ Exclusive geotAdam,hermal e2008)nergy can be stored in the ground. local thermal conductivity of the ground purposes [1–3]. Modern heat pumps have an extraction or ene rgy input Geothermal energy applica- The basic requirement for ande c itheenc ygroundwater (coe cient of o currepera- nts (Kaltschmitt˾ Alternating etse aal.,son a1999).l opera - tions which need a very low the use of geothermal energy is service temperature can also be a widely constant temperature oInpe rat theed in major“free he partating ” o ofr of the ground at a depth of ap- “free cooling” mode. The neces- Europe temperatures prox. 10 to 15 m. In most sary energy input then is limited European climate zones, this tounderground the electricity re quired to areop- temperature varies between 10 erate a circulation pump, be- to 15° C and remains constant caconstantuse no he at from pum p 10is n emed e tod up to a depth of approx. 50 m. to15 ra isem t he on, tem p theyeratu re range level. For buildings, this technology cabetweenn now be c o 10nsid e tore d a 15s s tat°Ce- oandf-the -art remain. During theconstant last years, Univ. Doz. Dipl.-Ing. Dr. techn. engineers have investigated Dietmar Adam, CEO of hdownow the te toch no alo gydepth can be ap of- Geotechnik Adam ZT GmbH, plied to tunnels. In comparison about 50 m. The Brunn am Gebirge/A 2 Detail of the 4 absorber loops with collection pipe with foundations of buildings, Fig. 4: „Energy Geotextile“ with absorber loops (Source: development of highly Adam, 2008)

7 106 BRANDL cages of piles, diaphragm walls or base slabs could not be used. Therefore a completely new technology had to 2 be developed. : kN/m b q Q 5 0 Q . 0 l 5 pile length ãc 5 unit weight of Cut and cover tunnel fresh concrete In section LT24 the primary side wall lining of the tunnel Hydration consists of bored piles, whereby each third pile is used as an Base pressure, Base pressure, ãc.l energy pile (Figs 44 and 45). Thus the energy plant LT24: Hadersdorf–Weidlingau comprises 59 bored piles with a diameter of 1.2 m and an average pile length of about 17.1 m. The intermittent pile wall exhibits jet-grouting col- umns between the piles. Pile excavation (by grab) was Self–weight Construction period W 1 total load Qt W W 1 dead load Qd supported by casings using rotating equipment. The energy piles are equipped with absorber pipes connected to collec- Time, t tor/distributors, which are located at a central point of the Fig. 43. Time–base pressure curve of a cast in situ concrete pile tunnel. The pipes leading from the piles to the collector/ exhibiting relevant initial contraction due to hydration distributors are placed alongside the cover of the tunnel. The connecting pipes lead into a collector/distributor room that is easily accessible on top of the cut and cover tunnel. Fig. (a) cut and cover, consisting of large-diameter bored piles, 46 shows the header block with the collector/distributor for reinforced concrete base slab and roof all collecting pipes. The manometers allow a detailed water- (b) New Austrian Tunnelling Method (NATM), with a tightness check of all absorber pipes. A manifold with a primary support of reinforced shotcrete, rockbolts and diameter of 150 mm connects the collector/distributors with anchors, and a secondary lining of reinforced concrete. heat pumps in an adjacent school in order to heat the building. Table 4 gives the relevant technical data. To optimise the energy design of the tunnel, and for Preliminary calculations yielded an extractable thermal research purposes, the following geothermal projects were power of about 150 kW in the long term. In one heating carried out. efficient, earth-coupled heat pumps (see period chapter an 3.4 energy - The amount Indirect of 214 Use MWh of can be gained. Furthermore, the benefits of this new energy concept are that (a) Energy plant:Geothermal LT24, Hadersdorf–Weidlingau Energy/Heat Pump .Systems The sec-) madeit isit economically both environmentally feasible, friendly to use the and economical: the 3 tion LT24geothermal was selected energy as a test absorbed plant, to by investigate concrete elementsreduction of of naturalurban gas and of near 34 000 surface m per year leads to a both the technical and the economic aspects. In this decrease of annual CO2 emissions of 30 t. Furthermore, section thetunnels tunnel for was heating constructed or even using cooling the cut applications. and annual For savings this purpose in operation absorber costs pipes of A10 000 will be cover method, allowing the application of already achieved, compared with the old natural gas heating system have to be fixed in bored piles, diaphragm walls or/and under the base slabs (see proven absorber techniques combined with structural of the school building. engineering.fig. 3) of cut-and-cover constructed tunnels. The In mined plant was and constructed bored tunnels as a demonstration the project in (b) Energy well: Hetzendorferstraße. Another test plant was the context of a major research initiative by the Austrian constructedabsorber in order pipes to investigate have to thebe installed performance into of the lining.government. For this Because the Vienna of this University scientific background,of the plant energy wellsTechnology that were simultaneously has developed used an for “energy lowering geotextile”is intensively (see fig. instrumented 4). A testing with plant measurement has devices. Six the groundwater level. energy piles are fitted with 18 temperature gauges at differ- (c) Energy membrane:been operating LT22, at Bierha the¨ Lainzeruslberg. Tunnel The section (Vienna/Austria)ent levels; since additionally, 2006. Anoth oneer pile new is type fitted with combined LT22 is locatedof absorber in an NATM element section, for tunneling where the proventhat is in strain–temperature development and gauges testing atare five energy levels for measuring system of attaching absorber pipes to the reinforcement strains and temperature. The aim of this measuring system is anchors (Adam, 2008).

Fig. 44. Schematic cross-section of energy plant LT24, Hadersdorf–Weidlingau. One side Fig. 5: Profile of the geothermal experimental plant Haderdorf-Weidlingau (Source: Brandl, wall of cut-and-cover tunnel used as energy wall 2006)

With the utilization of heat pumps the geothermal energy absorbed by the energy piles and textiles of near surface tunnels, temperatures up to 65° C can be generated and used for the heating or cooling of surrounding buildings (see fig. 5 – Profile of the geothermal experimental plant Haderdorf-Weidlingau).

The Use of Warm Tunnel Air Also the geothermal energy absorbed by the tunnel air can be exploited by the operation of air heat exchangers and heat pumps. The energy recovery of tunnel air

8 is reasonable in long tunnels and in metro tunnels, where temperatures are constant over the year. A pilot plant of tunnel air utilization is in operation in Grand St. Bernhard road tunnel/Suisse. The thermal output generated by the air circulating inside the tunnel is 167 MWh per year and is used for the heating of the maintenance buildings (Geothermie.ch, 2008).

The Use of Hydrothermal Energy – Geothermal Energy from Tunnel Water The temperature in the ground increases with depth. The scale of temperature increase is defined by the so-called geothermal gradient, it lies between 25 and 30° C per 1,000 meters in most of the world. Temperatures in 500 m depth are about 25-30° C on average, 35-45° C in 1,000 m. At tectonic blade boundaries, geological fault zones and volcanic areas, where the Earth’s crust is much thinner, the geothermal gradient can be substantially higher (e.g. 200°C/km at the oceanic spreading centers and along island arcs). Deep tunnels are exposed to the elevated temperatures in depth. Whereas the utilization of geothermal energy in urban and near surface tunnels requires the installation of absorber elements and energy anchors to extract the rock heat, geothermal energy in deep tunneling can be easily extracted from the warm tunnel water inflows.

As geothermal energy from tunnel water plays a central role in this master thesis, an entire chapter is dedicated to this topic.

9 3.3 Geothermal Energy from Tunnel Water in Deep Tunneling

Deep tunnels exhibit an enormous potential source of geothermal energy, based on the elevated temperatures in the depth. The rock temperatures of base tunnels in the Alps for example, with their high mass overlapping (up to 1800 m at Brenner Base Tunnel, 2500 m at Gotthard Base Tunnel), can reach 20°- 40° C or even higher. The cheapest and easiest way of tunnel heat exploitation is to make use of the heat contained in the ground water drained by the tunnel. Ground waters in the depth absorb the heat of the surrounding rocks. In deep tunneling, in most of the cases, it exhibits the same elevated temperatures as the surrounding rocks at the exit point. The ground water drained by deep tunnels is normally piped to the tunnel portals, where it is discharged into surface waters. For ecological reasons the tunnel water has to be cooled down before discharging. Therfore, it is suitable to utilize this hydrothermal energy for building heating or other purposes.

3.3.1 Tunnel Water in Deep Tunneling

Tunnel constructions below the groundwater level have the effect of draining the overlapping rock. Because of the high water pressure, technically it is possible to seal tunnels only down to a depth of 60 m below the groundwater table in an economical way. For deep tunnels, the hydrostatic pressure on the lining has to be relieved by a drainage system. Generally also drained tunnels are sealed in the sense that longitudinal drainage pipes at the tunnel face discharge the water, keeping it out from the tunnel interior (Kolymbas, 2005). Figure 6 shows a typical drainage layout of a rail tunnel. The interface drainage systems consist either of fleece, of composite geosynthetics or air-gap membranes, that are Fig. 6: Typical dewatering system of a rail tunnel (Source: placed between Kolymbas, 2005)

10 1

The geothermal potential of Swiss alpine tunnels Forecast and valorization

Jules Wilhelm1 and Ladislaus Rybach2,3

1Consulting Engineer, Chemin du Fau-blanc 26, 1009 CH-Pully, Switzerland ; e-mail : [email protected] 2Institute of Geophysics ETH Zurich, Switzerland ; 3Geowatt AG, Dohlenweg 28, CH-8050 Zurich, Switzerland ; e-mail : [email protected]

ABSTRACT A survey conducted by the Swiss Federal Office of Energy in the middle of the 90’s proved that a significant number of existing tunnels, with an estimated total heat potential of 30 MWth, is suitable to further development. Currently five sites in the Alps utilise available tunnel water for space heating and production of sanitary warm water and five more are going to do so in the next future. An additional 30 MWth of geothermal energy is estimated to be available at the portals of the two important alpine tunnels under construction, with lengths of 35 km (Lötschberg) and 57 km (Gotthard). Approximately additional 35 MWth are expected from planned tunnels during the next ten years. Thus, nearly 80 MWth will be disponible in 2012-2014. The available geothermal potential of future tunnels can be evaluated in reducing the theoretical potential by the cooling effects and the expected limitations of the water inflow rate during and after construction. Advanced computational methods and practical tools for potential assessment have been developed to give realistic values for the early planning of portal-near heating systems. Careful planning and steady cooperation betweenshotcrete tunnel and management the watertight and concrete heat consumers lining. In this area drainage, the water flows contribute to optimize the valorization of this interesting form of geothermal energy. down to longitudinal drainage pipes, which are installed at the border of the invert. INTRODUCTION Through transversal slots or cross pipes, the water gets to the dewatering pipe in Groundwater drained by deep tunnels, where thethe rockcenter temperature of the invert, can which be as leads high asto the30-40°C tunnel portals. or even more, is suitable to be used for heating of nearby buldings or agricultural developments (Fig. 1). Water intrusion (see fig. 7), also For more than 150 years, around 1200 called tunnel water tunnels with a total length in excess of 1600 km have been built in Switzerland inflow/outflow, is a common and currently a further 170 km are under problem in tunneling, it leads to construction. Temperature and inflow of tunnel water reaching the portals of some significant additional of them gave incentives many years ago to construction and operating utilize this geothermal potential locally for costs. To minimize risk, costs heating purposes. Examples of thermal utilisation of tunnel water exist for more and environmental impact of than twenty years [8]. tunneling, it is advantageous to

Fig.Figure 7: Tunnel 1 Water water inflow intrusion in a tunnel (Source: (courtesy Wilhelm Matrans) et al., choose a tunnel route through 2003) mountain ranges where little water intrusion can be expected. Hydrogeological studies and predictions are core GEOTHERMAL POTENTIAL OF SWISS TUNNELS In the framework of the programm “Energy 2000”,elements the in Federal tunnel planningoffice of. energyThey should initiated give in important answers to two questions: 1995 a study in order to determine the overall geothermal• How muchpotential water of willthe dischargeSwiss tunnels during and the drive and after finishing the tunnel galleries, including some adits [2]. As a result, 13 tunnels were selected out of more than 600 for further investigations and possible realisation.construction? The tunnels with geothermal potential • Will the tunnel construction influence surface and underground waters?

Accurate tunnel inflow estimation is especially important for the design of appropriate pumping systems and water treatment plants. Underestimations will lead to major delays in construction, overestimation to excessive, unnecessary costs (Raymer, 2003).

Physical and Chemical Characteristics of Tunnel Water

Because of the elevated rock overburden and the associated deep-seated circulation systems, tunnel water exhibits special hydro chemical and hydrological characteristics. Tunnel waters are often strongly mineralized and therefore cause other chemical reactions than surface waters. Depending on the geological and chemical-physical circumstances the water absorbs different amounts of soluble substances, especially salts, but also gases and heat on the way through the rock

11 mass. The following factors do influence the concentration of soluble substances in the tunnel water (Wetzig, 1996):

• Concentration gradient: With the increasing concentration of salt in the water the solution rate declines. Solution rates and amounts of salts not yet solved in the water are not affected. • Temperature and pressure ratio: This parameters influence the solubility especially of gases, but also salts. • PH-value: The solubility of specific substances depends on the pH-value of the water. With the absorption of substances the pH-value of the tunnel water can change on his flow path. Solved substances can therefore precipitate (e.g. lime precipitation). • Contact time with soluble substance: The longer the contact of the water with a soluble substance, the higher is the concentration of the solved amount.

The tunnel water with its physical and chemical characteristics can cause the following unfavorable impacts on the tunnel construction (Wetzig, 2009):

• Damages through solvent drive: Soft waters do exhibit high concentration gradients regarding the soluble components of the concrete, which are therefore discharged continuously. • Damages through swelling attack: Tunnel water with sulfate and/or sodium sulfate does regenerate minerals with the soluble components of cement stone or crystallizes salts. This leads to the blasting of the concrete. • Sintering/fusion: Tunnel water with high calcium- and/or magnesium- carbonate concentrations, through the progressive carbon dioxide release of the water, leads to a sintering/fusion of the flow path. • Corrosion: Water with high chloride concentrations enhances the corrosion of the reinforcement. • Gas release: The main gases soluble in mountain water are methane, carbon dioxide and hydrogen sulfide. Because of the high ventilation rates of tunnels, these in the tunnel water dissolved gases generally do not represent a hazard for the tunnel construction.

12 3.3.2 The Geothermal Potential of Tunnel Water and Discharge Conditions

The geothermal potential of tunnel water is defined by its outflow rate and temperature. These two factors depend on the geological, hydrological, geothermal and topographical conditions of the site (Wilhelm and Rybach, 2003).

The thermal potential of tunnel water Ptw can be defined as:

P = c ρ Q T tw w w tw tw with: cw thermal capacity of water (= 4,183 J/kgK at 20°C) 3 ρw mass density of water (= 1,000kg/m )

Qtw outflow rate in l/s

Ttw tunnel water temperature in °C

Accordingly the usable geothermal potential of the tunnel water can be calculated by:

P = c ρ Q Δ T tw w w tw

with: ΔT useable temperature difference (in °C) = Ttw – T0

Ttw tunnel water temperature in °C

T0 reference temperature in °C (usually 10° C or calculated as maximal temperature of the tunnel water, which allows the water to discharge it with the given flow rate in surface waters, while considering heat change limits of the surface water by environmental regulations)

Since tunnel waters of long base tunnels are generally of elevated temperature levels, discharging them directly into surface waters would significantly influence its temperature and bear negative consequences for the whole environment. This is especially true for mountain regions, where during winter months the flow rates of the rivers shrinks extremely and water temperatures drop down near the freezing point. The cooling of the tunnel water, with its constant flow rate and temperature all the year round, becomes indispensable.

The temperature of the surface water T1 after discharging the tunnel water without cooling can easily be calculated by using the simplified Richmann mixture rule for liquids with the same specific heat capacity:

13 (Q 0T 0 + QtwTtw) T 1 = (Q 0 + Qtw) with: T1 surface water temperature after tunnel water discharge in °C 3 Q0 flow rate of surface water in l/s or m /s

T0 temperature of surface water before tunnel water discharge in °C 3 Qtw flow rate of tunnel water in l/s or m /s

Ttw tunnel water temperature in °C

Because of the environmental impact, authorities usually restrict the temperature changes ΔT of the surface water by discharging the tunnel water into it. In Switzerland, discharging tunnel water into surface waters of trout regions usually allows a maximal heat increase of the surface waters by ΔT = 1.5° C. But in special cases authorities can tighten this restriction. Thus, because of its importance as spawning ground, discharging the tunnel water at the north portal of Lötschberg Base Tunnel into the Kander river, the temperature difference is limited to a maximum of ΔT = 0.5° C (Hufschmied, 2008).

The maximum temperature difference ΔTmax of the surface water is given by:

(Q 0 T 0 +QtwTtw) Δ Tmax = T1 - T 0 = - T 0 (Q 0 +Qtw)

From the ΔTmax equation the permissible discharge quantity of tunnel water Qtw max can be derived:

Δ Tmax Qtw max = Q 0 Ttw− T 0 − Δ Tmax with: Qtw max permissible discharge quantity of tunnel water, so that the surface

water temperature difference after discharge = ΔTmax

Since the outflow rate of tunnel water is constant and not reducible, the temperature of the tunnel water has to be reduced by cooling, to fulfill ΔTmax requirements. The maximal temperature of the tunnel water Ttw max for discharging it into surface waters is:

Q 0 Ttw max = T 0 + Δ Tmax(1+ ) Qtw

14 To reach the tunnel water temperature requirements for surface water discharging

(Ttw max), the following heat potential has to be extracted from the water:

P = c ρ Q (Ttw− Ttw max) tw w w tw

This heat potential of the tunnel water can be utilized for heating purposes or the like. Since tunnel water outflows and temperatures are constant all the year round, the maximal heat potential Ptw max is defined by the minimum of surface flows and temperatures in winter months. Identifying the Ptw max is necessary for the dimensioning of the required tunnel water cooling installations.

3.3.3 Tunnel Water Outflow and Temperature Prognosis in Tunneling

Geothermal Prognosis The rock heat strongly influences the working climate underground and at the same time it indicates anomalies as e.g. auriferous fault zones. Thus, geothermal prognoses in tunneling today primarily serve (Busslinger et al., 2001): • To design the ventilation and climate control plant during the construction and the operating of the tunnel • To specify the geological/ hydro geological prognosis

The temperature of the rock mass and the tunnel water outflow rate are determined by the geological, hydrological geothermal and topographical environment of the site. By advanced three-dimensional numerical modeling, detailed conditions can be prognosticated. Figure 8 shows the forecasted rock temperatures in the axis of the Gotthard Base Tunnel. The in-situ measurements during construction marked by the black dots in the figure prove the accuracy of the geothermal prediction (Wilhelm and Rybach, 2003).

The Tunnel Water Outflow Rate The hydro geological predictions and tunnel water outflow estimations are based on the geological studies that give information about water storing and piping geological formation, porosity and permeability of the rocks. The estimate of the expected tunnel water outflow is a science per se and can be obtained by

15 geomechanical classifications, through analytical formulations and the implementation of mathematical models (Scesi5 and Gattinoni, 2009).

Black line: Forecast Rock Temperature Figure 3Red Comparison Field: Field of calculatedUncertainity to measured temperatures in the Gotthard Base Tunnel [3]. BlackForecast Dots: In: -blacksitu Rock line. Temperature Field of uncertainty Measurements : red. Black dots : rock temperatures measured in the axis of the tunnel. Fig. 8: Comparison of prognosticated rock temperatures and in-situ measurements in the Gotthard Base Tunnel (Wilhelm et al., 2003) To determine the location and the excepted discharge rate of the underground water in the tunnel,These a numerical estimations, method especially based onin deepthe same tunneling, program can that exhibit for the significant temperature meanderings forecast has been fromprepared. real This tunnel three water dimensional outflow, model since theyis conceptually are partially based based on a onhydro geological geological model,assumptions the lithological and include units uncertain of the underground variables. being characterized by their hydraulic conductivity, determined through in situ investigations. As for the temperature, measurements on existingA serious tunnels, problem like the for estimatingKoralm Tunnel tunnel in waterAustria, outflow proved in thehard good rock correlation tunnels is between the calculatedpractical and rangein situ ofvalues permeability [5]. in fractured rock; it typically varies over at least six For energetic valorisation, the heating power of the tunnel water is calculated as follows : orders of magnitude. Because of this, in hard rock tunnels the main part of the total inflow comes from a small portionP [MWth] of the = C tunnel · Q · ∆ length,T whereas a small amount results from a large portion and much of the tunnel is dry (Raymer, 2003). were C is the specific heat capacity of the water (4,18 · 103 J/l · °K), Q is the water discharge (l/sec), and ∆T is the useful temperature (T – To). T is the temperature of the tunnel water,Limitations To is the temperature of Tunnel ofWater reference, Outflow i.e. the temperature of the water after heat extraction.The following factors reduce the tunnel water outflow rate (Wilhelm and Rybach, In general, the temperature of the tunnel water is the same as that of the rock. The water discharge2003). can either be calculated, as indicated before, or estimated from hydrogeologic data. The heating• Limitation power of due the tunnelto environmental water at the constraints portal is : the To sum preserve of the the partial natural powers of n sections of equal lengths. Shorter sections will be selected when the discharge is high. underground reservoir and to avoid the ebbing of springs at the earth’s The useful potentialsurface, the water drainage by the tunnel often has to be limited by grouting. To obtain theThis effective represents geothermal a significant potential cost factor at thein tunneling. portal of a future tunnel the initial geothermal potential has to be corrected by some physical and/or time dependent effects, reducing either the discharge or the temperature of the water. The water discharge could be subject to the following limitations : - limitation due to environmental constraints - reduction for the execution, by technical16 measures during tunnelling - natural decrease of the water discharge • Reduction by the implementation of the project: When crossing geologically unknown sections, advanced drilling techniques permit to detect the presence of underground water and subsequently create a watertight cylinder around the tunnel profile by grouting and ensuring the technical feasibility and the security of the tunnel construction. These measures are carried out during construction and are often not taken into account by the forecast calculations. At the Lötschberg Base Tunnel for example, by such measures the forecasted tunnel water out flow in a geological fault zone of 100-200 l/s was reduced to a few l/s in real. • Natural decrease of the water discharge: Generally the actual tunnel inflow rate changes considerably with time. So strong inflows during the tunnel construction phase decrease significantly within the first few years, reaching a new hydraulic equilibrium in the rock’s water circulation system (Rybach and Wilhelm, 1995). International Geothermal Conference, Reykjavík, Sept. 2003! Session #5!

"#$%&'#%! ()*+#,-).*%!The -.! Tunnel '#/&,#! Water )*01.23! Temperature )%.1$-).*! ,.*/)-).*%! /&')*4! .&-01.2! #-,565! 7,,.'/)*4! -.! 2$-#'! 8'.-#,-).*! '#4&1$-).*3! 2$-#'%! 2)-9! .*1:! $! 1)")-#/! $".&*-! $*/! -#"8#'$-&'#!,$*!;#!/)%8.%#/!;:!/)%,9$'4#!-.!')<#'%5!=*!#>-'#"The temperature of the tunnel water is #!,$%#%3!-9#!)*%-$11$-).*! generally the same as the one of the .0! ,..1)*4! -.2#'%! 2.&1/!surrounding ;#! *#,#%%$':5! rock (see ?9#' fig.#0.'#3! 9) and $! 8.%%);1#! can thus 4#.-9#'" be derived$1! &%#! from .0! -9#!the rock temperature .&-01.2)*4! -&**#1! 2$-#'%! )%! $*! $--'$,-)<#! .8-).*@! /#8#*/)*4! .*! 01.2! '$-#! $*/! predictions. Usually outflow rates and temperatures are calculated for tunnel -#"8#'$-&'#3!<$').&%!-:8#%!.0!)*%-$11$-).*%!$-!.'!*#$'!-9#!-&**#1!8.'-$1%!,$*!;#!%&881)#/! 2)-9!9#$-5!A%&$11:!-9#!.&-01.2!-#"sections of equal8#'$-&'#!%9.2%!*.!%#$%.*$1!<$')$-).*%5!?9&%!%&,9! length (e.g. sections of 10 m) and summed up in the end. 2$-#'%!'#8'#%#*-!$*!)*-#'#%-)*4!8.-#*-)$1!0The tunnel water temperature.'!/)'#,-!&%#3!8'.<)/#/!-9$-!,.*%&" can decrease by the natural#'%!-.!&%#! cooling of the rock mass -9#! 9#$-! $'#! %)-&$-#/! $-! .'! *#$'! -9#! 8.'-$1%5! B.*-'$':! -.! -9#! &%#! .0! ")*#! 2$-#'%! 0.'! %8$,#!9#$-)*4!#545!)*!B$*$/$!(C$**#'3!DEEF63!G#'"around the tunnel. Simulation models$*:!(H&%%" can $**3!DEEI6!.'!J.1$*/! estimate this cooling effect and predict (A%-'.*!B.*0#'#*,#3!KLLD6!29#'#!#1#,-'),$1!#*long-term tunnel water temperatures.#'4:!)%!*##/#/!-.!1)0-!-9#!2$'" When the tunnel water!2$-#'%! is used for heating 0.'"!-9#!/'.2*#/!"purpose)*#%! -.!s -9#!at the %&'0$,#3! tunnel -9 portals,#'#! )%! *.!the *##/! drainage 0.'! 8&" pipe8%! in )*! the -9#! tunnel ,$%#! should .0! be isolated to -&**#1!2$-#'%5! ! avoid heat losses. Fig. 9: Rock temperature vs temperature of inflowing water. Data from the Simplon railway tunnel (dots), and from the Gotthard highway tunnel (open circles). The black line marks equality, the best fit line through the data points has a slope of 1.01 and an intercept of –0.52°C, the regression coefficient is 0.996 (Source: Rybach and Wilhelm, 1995)

! Figure 1: Rock temperature vs temperature of inflowing water. Data from the Simplon 17 railway tunnel (dots), and from the Gotthard highway tunnel (open circles). The black line marks equality, the best fit line through the data points has a slope of 1.01 and an intercept of –0.52°C, the regression coefficient is 0.996 (from Rybach 1995).

! =*! -9#! 0.11.2)*43! -9#! -&**#1! 2$-#'! %)-&$-).*! )*! C2)-M#'1$*/! 2)11! ;#! .&-1)*#/3! &-)1)M$-).*!#>$"81#%!2)11!;#!/#%,');#/3!$*/!-9#!8.-#*-)$1!.0!/##8!$*/!1.*4!-&**#1%!)*! ,.*%-'&,-).*! 2)11! ;#! /)%,&%%#/5! =*! -9#! ,.*,1&/)*4! '#"$'N%! -9#! 8'#'#O&)%)-#%! .0!$! 4#.-9#'"$1!&%#!.0!-&**#1!2$-#'%!2)11!;#!$//'#%%#/5! 2 Tunnels in Switzerland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

S05 Paper051 Page 18

3.4 The Indirect Use of Geothermal Energy – Heat Pump Systems

Before describing the different possibilities for exploiting the tunnel water heat, it is necessary to focus on technical aspects regarding geothermal heating and cooling systems. The geothermal energy can roughly be divided into two categories: a) the near- surface geothermal energy down to a few 100 m; and b) the deep geothermal energy from a few 100 m down to several 1000 m. Depending on the heat content, geothermal energy resources are classified as low enthalpy (with temperatures <100° C), medium enthalpy (100-180° C) and high enthalpy (temperatures above 180-200° C) (Brown and Garnish, 2004). With the exception of tectonic blade boundaries, geological fault zones and volcanic areas, the near-surface geothermal energy is generally of low enthalpy temperature level. Medium and high enthalpy temperatures can only be found in the deep geothermics. Obviously the numerous technical systems for exploiting geothermal energy differ from each other with the different temperature levels. Whereas medium and high enthalpy systems can be applied for electricity generation, low enthalpy systems can only be used for heating and cooling purposes. The fact, that the energy consumption of a Central European household for heating and cooling reaches 50% of total consumption and more, underlines the importance of near-surface geothermal energy exploitation for a sustainable energy system. As the geothermal energy in tunneling is of low temperatures (<40° C), only systems for the low enthalpy energy utilization are described below.

As in deep geothermal energy the heat in near-surface geothermal energy can be utilized directly or indirectly (in terms of without or with technical systems for temperature transformation). The famous Lindal Chart (see fig. 10) shows the different applications for geothermal energy according to the temperature of the heat source.

18

Fig. 10: The Lindal Diagramm with different applications for geothermal energy according to the temperature of the heat source

Temperatures near surface and temperatures of tunnel water are in most cases too low for direct heating or to high for direct cooling. So called heat pumps or refrigeration machines have to be installed for temperature transformation. Temperature transformation and heat exchanger systems for indirect geothermal heat exploitation generally consist of 3 loops/circuits (see fig. 11):

• the primary or heat source loop (respectively the heat sink in cooling mode), which absorbs the heat energy in the near-surface ground (respectively in cooling mode heat is absorbed by the lower ground temperature); • the heat pump loop (respectively the refrigeration machine loop), where temperatures are transformed into a higher or lower level by the utilization of heat pumps/ refrigeration machines and additional energy (electrical power or fuels);

19 • the secondary or heat use/sink loop (respectively the cooling loop in cooling mode), which consists of the exploited heat (coolness in cooling system) in a heat circuit (air condition system). ENERGY FOUNDATIONS AND OTHER THERMO-ACTIVE GROUND STRUCTURES 85 External power (electricity)

1 4

4 4 3 Energy flux 4 (from the ground)

Primary Secondary circuit circuit

Connecting lines Manifolds

P P

Header block: Heat pump collector (for heating) distributor (for cooling)

Absorber pipes (5 ground heat exchangers) incorporated in energy foundations (e.g. energy piles)

Fig.Fig. 11 9.: Schematic Scheme of adiagram geothermal of indirect energy geothermal plant with energyheat exploitation piles and anwith energy 3 loops flux/circuits for COP, the 4 of the heat pump. COP coefficient of performance defining the heat pump efficiency primary loop (heat source loop – energy piles, diaphragm walls etc.), the heat pump loop

(refrigerant in the heat pump) and the secondaryhydraulic loop (heat gradients sink). Additionally are favourable. the energy Dry soil makes deeper Primary Electrical power Secondary circuit flow with a heat pump with COP=4circuit is shown (Source:piles Brandl, and a 200 larger6) area of the heat exchanger necessary. Heat source Depending on soil properties and the installation depth of Compressor Heating 2 Refrigerant medium Refrigerant medium circuit the absorbers, 1 kW heating needs roughly between 20 m 0°C 135°C 2 23°C/3·65 bar 162°C/13·2 bar water (saturated soil) and 50 m (dry sand) of the surface of concrete structures in contact with soil or groundwater. Heat from 25% 3.4.1compression Heat Source Loop of Indirect GeothermalThere Energy is no limitation Use to the depth of piles or diaphragm walls as far as the installation of energy absorber systems is concerned. The energy potential increases with depth: hence Evaporator Heat from heat 100% Condenser source 75% deeper foundations are advantageous. The economically Basically near-surface geothermic utilizes theminimum heat stored length in ofthe piles, ground barrettes respectively or diaphragm wall panels rock andExpansion its pore valve’s content, e.g. groundwateris. about In the 6 m.last few years, also the air at The production of electric current from energy founda- 24°C Refrigerant medium Refrigerant medium 2the8°C/3·65 ground bar surface133°C/13·2 and bar inside130°C constructions tionsbelow and surface other has thermo-active gained in importance ground structures is theoreti- cally possible but not effective. This is similar to biomasses as a heat source. Fig. 10. Scheme of a compression heat pump with temperatures as base materials: they exhibit a high efficiency for heating (85%) but an extremely low efficiency for producing electric and pressures forT thehe refrigerantmethods to medium exploit R290 this (asnear example). surface heat can roughly be classified in: a) open Heat exchange occurs from primary circuit to refrigerant current (25%). This would be an inexpedient application of medium in the evaporatorsystems and and b) from closed refrigerant systems medium. In open to systemsenvironmental the heat technologies,source itself circulates whereas combined in heat and secondary circuit in the condenser power plants reduce CO2 production significantly. The com- the primary loop, whereas in closed system heatbustion carriers of wood absorb is CO the2-neutral heat of and the replaces heat fossil resources. In Vienna the largest biomass-operated power station in the since the year 2000sources heating and (and transport cooling) it to of the buildings heat pump has loopworld. is operating. Waste incineration for heating purposes dominated. It is estimated that these heat pumps save more also saves fossil fuels, especially in connection with district than 250 000 t of fuel oil per year. heating. Furthermore, combinations of geothermal and solar Experience has shown that these geothermal cooling/ heating and cooling have proved suitable to contribute heating systems from energy foundations and other thermo- effectively to environmental protection. The economically active ground structures may save up to two-thirds of con- optimal solution depends on numerous local conditions (e.g. ventional heating costs. Moreover, they represent an effective twin circuits and/or photovoltaically operated heat pumps). contribution to environmental protection by providing clean 20 and self-renewable energy. If only heating or only cooling is performed, high- HEAT TRANSFER IN THE GROUND permeability ground and groundwater with a high hydraulic General gradient are of advantage. However, the most economical Soil is a multiple phase system with a complex heat and environmentally friendly is a seasonal operation with an transfer mechanism involving energy balance throughout the year, hence heating in winter (i.e. heat extraction from the ground) and cooling in summer (a) conduction (i.e. heat sinking/recharging into the ground). In this case (b) radiation low-permeability ground and groundwater with only low (c) convection Open System The utilization of ground water and tunnel water typically represent an open system application. The ground water with elevated temperatures is pumped to the heat pump loop and assumes the role of the heat carrier. After extracting the heat from the water and cooling it down, it is piped back into the ground where it absorbs the heat of the rocks (Kaltschmitt, 2006). In deep tunneling, the water drained by the tunnel system and collected in pipe systems, flows in most cases by natural descent to the tunnel portals, where the heat is used directly or extracted indirectly with heat pump systems. After cooling, the water is pumped into surface water near the tunnel portals. In tunnel water utilization it is necessary to control and adjust inlet temperatures, since they can influence the surface water temperatures leading to substantial ecological impacts. Generally, the usages of the geothermal energy in ambient air are open systems, since in most cases the air itself represents the heat carrier and circulates in the heat source loop.

Closed Systems In closed systems for near-surface geothermal energy exploitation, heat carriers are used to absorb the heat of the heat sources and to carrier it to the heat pump system. For this, a heat absorber pipe or a system of more heat absorbers is installed vertically or horizontally into the ground. Horizontal systems are buried in a depth of only a few meters and have the disadvantage of a large floor space (see fig. 12). Vertical systems, so called geothermal probes, are rammed or drilled vertical into the ground and can reach depths of 250 m (see fig. 13).

Fig. 12: Horizontal closed absorber system Fig. 13: Vertical closed absorber system (Source:www.mcquay.com/ (Source: www.mcquay.com/ McQuay/ McQuay/DesignSolutions/GeothermalPage2) DesignSolutions/GeothermalPage2)

21 is the integration of the geothermal work into the quired intensive discussions, since existing regula- main construction contract. Thereby, the geothermal tions do not provide guidelines for the role of works are contracted similarly to highly-specialized absorbers in load-bearing components. Special ques- specialInside foundationthe absorber engineering pipes heat measures, carrier suchs, generally as tions, water for example-frostprotection the effect -ofmixtures, ground freezing are on freezing and compensation grouting, for which there the mechanical resistance of the plastic tubes also arecirculating, also only few absorbi qualifiedng specialthe heat enterprises. in the ground andhad tobringing be studied. it over ground to the heat A special problem in the tender is the arrange- pumps. The heat transfer between heat source and heat carrier in closed systems ment of the failure risk. Even with optimum works 4.5 Implementation and site supervision qualityoccurs it throughis impossible thermal to avoid conduction, failures of some heat ab- carriers are not in direct contact with rocks sorber loops completely. However, it is in the hand The construction of the geothermal facility and the ofand the pore executing contents company (Kaltschmitt, to minimize 2006)such failures. main construction works are closely interlinked. The by careful work. Geothermal facilities are relatively partially very cramped site conditions also have to insensitive in relation to failures. With reduced ab- be considered. The reinforcement cages must be sorberApart volumefrom the the operatingvertical andtemperature horizontal in the systems ab- equipped, there with also absorbers exist other either systemsin the reinforcement not sorber system sinks or rises slightly and therefore factory or on other free areas outside of the construc- theex clusively efficiency decreases, designed lowering for heat the absorption. value of the Intion construction site due to space, for restrictions. example, massive unit for the owner. For the tender of the Viennese The building process of the shaft and station con- metro,concrete tender elements conditions were in direct developed, contact which with pro- soilstruction can be was part as follows: of the primary loop in tectgeothermal the interests systems of the client, adopting do not the impose role unac-of heat exchangerx Producings. the perimeter walls from the ceptable loads on the contractor and at the same time ground surface and installation of the ab- areIn compatible this “massive with the absorber work contract system regulations.” absorber pipessorbers. are Bored installed piles and in di constructionaphragm walls were inserted into the ground. The reinforcement Basicallyelements a certainlike diaphragm failure rate walls, (3% of bored the total piles, ab- bottom slabs, or tunnel parts. With heat sorber length) is accepted as systems-inherent. For cages had to be constructed in sections due to highercarriers failure circulating rates, the ins contractoride the has absorber to substitute systems, largethe large earth depths-coupled of the structurescomponents. can This also or must accept a payment reduction. However he has required joints of the absorbers. Since the con- tobe guarantee activated that thermallya certain limit and (12% used failure) for is heating not andnection cooling points purposes for the absorber (Brandl loops et are al. ,gener- exceeded.2010). ally situated underneath the base slab of the pits, pressure control of the absorber loops would 4.4 Detail design Not only deep foundations, but also flat foundationshave been can possible be used only as after an uncoveringenergy the In the detail design, specific considerations were connection points again. Therefore, certain made,absorber. which Butcomponents since deof theep stationsfoundations could be, in ac- most casescages, wereare not equipped exposed with to testing seasonal pipes that tuallyvariations equipped in with soil absorbers, temperature where ,the they manifolds are especiallywere connectedappropriate to the andsurface efficient and could for be sub- can be situated and how pipe layout is most effi- jected to pressure testing immediately after con- cient.geothermal On this energy basis a detailed systems energetic (Markievic simulationz, 2004 ). creting. was performed, in which the actual heating and cool- ing demand during a year and the effects on the temperatures of the absorber system were obtained. ENERGY FOUNDATIONS AND OTHER THERMO-ACTIVE GROUND STRUCTURES 83

absorber pipes

connection point

Fig. 5. Absorber pipes attached to the reinforcement cage of a Figure 7: Top of diaphragm wall with testing tubes anddiaphragm wall (see Fig. 53) manometer.

Fig. 3. Absorber pipes fitted to the reinforcement cage of a FigureFig. 14: 6: Reinforcement cage cage for diaphragm for diaphragm wall equipped wall Fig.large-diameter 15: Reinforcement bored energy pile. cage The connecting for bored ends are withequipped absorbers. with absorbers (Source: Brandl, 2006) pileprotected Theequipped by reinforcing a tube atwith the pileabsorbers cages head had to(Source: be connected by Brandl,welding 2006) at the section overlaps for the electrical In these simulations the degree of utilization of through connection. Protection of the plastic ab- other energy carriers such as district heating, natural sorbers in this area could be accomplished by gas or electricity was decided. The arrangement of welding protection mats. Pressure tests were the absorber pipes in the reinforcement of the con- generally performed during the reinforcement structional components (piles, diaphragm walls) re- cage check - in the course of site supervision -

Fig. 6. Installation of absorber pipes (filled with heat-carrier fluid) on the subconcrete of a piled raft foundation

22 Connected to this primary circuit is the secondary circuit within the building where the thermal energy is distributed. Until recently prefabricated driven piles of reinforced con- crete with integrated heat exchanger (absorber pipes) repre- sented the majority of energy piles. But the percentage of (large-diameter) bored piles has been steadily increasing since the year 2000. Pile excavation may be supported by casing or fluid. Continuous flight auger piling and plunging of the heat exchanger with the reinforcement cage into wet pile concrete may affect the final integrity of the plastic absorber pipes. The risk of absorber pipe damage can be lowered by a stiff reinforcement cage—that is, by welding the helical reinforcement to the vertical reinforcement bars. Merely connecting with wires would allow excessive defor- mations of the reinforcement cage during lifting and insert- ing into the pile concrete. Consequently, the rotary bored technique or excavation by grab should be preferred for energy piles, and even in this case a relatively stiff reinfor- Fig. 4. Reinforcement with attached absorber pipes inserted cement cage is recommended. within casing of an auger pile; ready for casting concrete An increasingly used alternative to driven piles of prefab- ricated reinforced concrete is ductile cast iron piles with ometer are fixed. This allows the pipe circuit to be pres- integrated heat exchangers. Contrary to grey cast iron with surised to (normally) 8 bar for integrity check and to resist lamellar graphite, ductile cast iron contains spherical gra- the head of the wet concrete without collapsing. This phite. It therefore exhibits higher stresses at failure and a pressure is typically maintained until after the foundation ductile behaviour. The piles consist of 5 m long standard concrete is a few days old, and is again applied before the elements that can easily be assembled to longer sections entire primary circuit is definitely closed. during the driving procedure. The tubes are filled under Figure 6 gives a partial view of the laying system of pressure with concrete. Shaft grouting to increase friction is absorber pipes on the subconcrete of a piled raft foundation. also possible. Since 1985 more than 1 million metres of 3.4.2 The Heat Pump

Generally geothermal heat from near surface sources is too low for direct application and the temperature has to be raised with heat pumps to a higher level. Heat pumps thereby represent the centerpiece of indirect geothermal heat exploitation systems. Without auxiliary equipment, heat flow can only occur from high temperatures to low temperatures. For the utilization of low enthalpy heat, the flow direction has to be inverted. Heat has to be absorbed at lower temperatures from the ground and emitted at higher level for space and water heating (Kaltschmitt, 2006). With the utilization of technical systems and the input of higher value, tractive energy, heat pumps can absorb heat at a certain level of temperature (cold side) and emit it in the form of thermal energy at higher temperatures values. The higher the temperature raise requested, the higher is the amount of tractive energy needed. Depending on the type of tractive energy used and the resulting operating principle, there are two main types of heat pumps: compression heat pumps and absorption/adsorption heat pumps. Whereas compression heat pumps utilize mechanical energy as tractive energy, absorption/adsorption heat pumps make use of heat energy.

3.4.2.1 Compression Heat Pumps In almost all near-surface geothermal energy systems, compression heat pumps are used for heat transformation. Compression heat pumps are characterized by a closed refrigerant circuit, where a steam process is taking place. It mainly consists of four steps: evaporation, compression, condensation, and expansion. With this process the temperature of a lower level (heat source, evaporator) can be raised to a higher level (heating water, condenser)(see fig. 16). The mechanical drive for the compressor takes place by electrical or combustion engines (Markievicz, 2004). Where combustion engines are used for the compressor drive, the heat of engine cooling can be coupled into the heating process, increasing the energy efficiency of the whole system. Transporting heat from a lower level to a higher one, heat pumps apart from heating purposes can also be used for cooling by switching the components. A ground- coupled heat pump can therefore also extract heat from a building and emit it into the ground. The double utilization of a heat pump for heating in the winter and

23 ENERGY FOUNDATIONS AND OTHER THERMO-ACTIVE GROUND STRUCTURES 85 External power (electricity)

1 4

4 4 3 Energy flux 4 (from the ground)

Primary Secondary circuit circuit

Connecting lines Manifolds

P P

Header block: Heat pump collector (for heating) distributor (for cooling) cooling in the summer is especially favorable for the economy of a geothermal system (Markievicz, 2004). Absorber pipes (5 ground heat exchangers) Regarding the steps of the steam process occurringincorporated in the in energyrefrigerant foundations circuit, (e.g. heat energy piles) pumps consists mainly Fig.of four 9. system Scheme components of a geothermal: the e energyvaporator, plant the with compressor energy piles and an energy flux for COP with its drive, the condenser4, of and the the heat expansion pump. COPvalve. coefficient of performance defining the heat pump efficiency

Primary hydraulic gradients are favourable. Dry soil makes deeper Electrical power Secondary circuit circuit piles and a larger area of the heat exchanger necessary. Heat source Depending on soil properties and the installation depth of Compressor Heating 2 Refrigerant medium Refrigerant medium circuit the absorbers, 1 kW heating needs roughly between 20 m 0°C 135°C 2 23°C/3·65 bar 162°C/13·2 bar water (saturated soil) and 50 m (dry sand) of the surface of concrete structures in contact with soil or groundwater. Heat from 25% There is no limitation to the depth of piles or diaphragm compression walls as far as the installation of energy absorber systems is concerned. The energy potential increases with depth: hence Evaporator Heat from heat 100% Condenser source 75% deeper foundations are advantageous. The economically minimum length of piles, barrettes or diaphragm wall panels Expansion valve is about 6 m. The production of electric current from energy founda- 24°C Refrigerant medium Refrigerant medium 28°C/3·65 bar 133°C/13·2 bar 130°C tions and other thermo-active ground structures is theoreti- cally possible but not effective. This is similar to biomasses

as base materials: they exhibit a high efficiency for heating Fig.Fig. 16 10.: Scheme Scheme of of a compression a compression heat heat pump pump with with temperatures temperatures and pressures for the and pressures for the refrigerant medium R290 (as example). (85%) but an extremely low efficiency for producing electric refrigerantHeat exchange medium R290 occurs (as from example). primary Heat exchangecircuit to occurs refrigerant from primarycurrent circuit (25%).to This would be an inexpedient application of refrigerantmedium medium in the in evaporatorthe evaporator and and fromfrom refrigerant refrigerant medium medium to secondary to circuitenvironmental in the technologies, whereas combined heat and secondary circuit in the condenser power plants reduce CO2 production significantly. The com- condenser (Source: Brandl, 2006) bustion of wood is CO2-neutral and replaces fossil resources. In Vienna the largest biomass-operated power station in the since the year 2000 heating (and cooling) of buildings has world is operating. Waste incineration for heating purposes dominated. It is estimated that these heat pumps save more also saves fossil fuels, especially in connection with district than 250 000 t of fuel oil per year. heating. Furthermore, combinations of geothermal and solar The ExperienceEvaporator has shown that these geothermal cooling/ heating and cooling have proved suitable to contribute In heatingthe evaporator systems the from working energy fluid foundationscirculating in andthe heat other pump thermo- loop evaporateseffectively at to environmental protection. The economically active ground structures may save up to two-thirds of con- optimal solution depends on numerous local conditions (e.g. lowventional pressure heating and low costs.temperatures Moreover, with theythe supply represent of heat. an effectiveThe heat is providedtwin circuits by and/or photovoltaically operated heat pumps). thecontribution heat carrier in to the environmental primary loop, protectionand in the case by providingof cooling, cleanby the heat carrier in and self-renewable energy. the secondaryIf only heatingloop. When or the only working cooling fluid evaporates is performed, directly high- at the heatHEAT source TRANSFER IN THE GROUND permeability ground and groundwater with a high hydraulic absorbing its heat, i.e. without heat carrier utilization, we are talking aboutGeneral heat gradient are of advantage. However, the most economical Soil is a multiple phase system with a complex heat pumpsand environmentallywith direct evaporation friendly (Kaltschmitt is a seasonal, 2006) operation. with an transfer mechanism involving energy balance throughout the year, hence heating in winter During(i.e. heatthe evaporation extraction process from the the ground) temperature and coolingof the working in summer fluid keeps( aconstant,) conduction the(i.e. transferred heat sinking/recharging heat is the so-called into the“heat ground). of evaporation”. In this case Before ( andb) radiation after low-permeability ground and groundwater with only low (c) convection evaporation the temperature of the working fluid raises. Emitting the heat to the working fluid in the heat pump loop, the temperature in the primary loop decreases constantly (Markievicz, 2004). Figure 17 shows the heat transfer process, marking up the temperature development of the primary and heat pump loop and the delivered energy.

24

Fig. 17: Heat exchange in the evaporator (schematic). The temperature in the primary loop decreases (release of energy Q), while the temperature in the working fluid increases (absorption of energy Q). During the evaporating process the temperature of the working fluid remains constant (Source: Markievicz, 2004)

The Compressor After evaporation the compressor of a heat pump sucks in the gaseous working fluid and pressurizes it. Through the compression process, the vapor temperature increases. Depending on the method for affixing the compressor’s drive motor they are categorized as follows (Kaltschmitt, 2006): • Hermetical sealed (hermetic) compressors: Compressor and motor are installed in an encapsulated body within the pressurized gas. The driving power goes up to a few kW. • Semi hermetic compressors: The motor is flanged at the compressor. They have, as the hermetic compressor, a common shaft. The driving power ranges from 4 to 150 kW. • Open compressors: The drive motor is installed outside of the compressor. Motor and compressor are connected with a shaft and a clutch. This type of compressors is used for large heat pumps, the driving occurs by electrical or combustion engines.

There are several construction types of compressors. The most commonly used types are (Kaltschmitt, 2006):

25 • Reciprocating piston compressors: The pressure boosting takes place by the positive displacement principle. The volume of closed compressor chambers is reduced with crankshaft driven pistons, creating higher pressures (see fig. 18). As hermetic compressors, they are constructed with a driving power up to 25 kW, as semi-hermetic compressors up to 90 kW and as open compressors for higher power. This type of compressor is used for low and for high power plants, consisting of 1 to 16 cylinders.

Fig. 18: Compression action of a piston compressor cylinder (Source: www.tpub.com/.../doe/h1018v2/css/h1018v2_85.htm)

• Scroll compressors: The compression of the refrigerant takes place by two interleaving scrolls/disks, a stationary and an orbiting scroll (see fig. 19). The refrigerant, sucked through inlet ports at the perimeter of the scroll, is transferred to the center of the scroll by the orbiting action. As the volume

of the sealed spaces in between the scrolls Fig. 19: Compression action function of a scroll compressor (Source: decreases towards the www.aircompeq.com/sos.html) center, the refrigerant gets

26 compressed and discharged at the center of the upper scroll. Compared to other compressor types, scroll compressors are quiet and smooth operating. They have the highest efficiency ratio of all compressors.

• Screw compressors: A pair of meshing helical rotors rotates (a male with lobes and a female with gullies), alternately exposing and closing off interlobe spaces. At the intake end, the refrigerant is sucked into the open interlobe space, trapped inside and forced along the length of the rotors. Since the interlobe space decreases from the intake towards the output end, the refrigerant is compressed.

Compared to other compressors, Fig. 20: Compressing action of a screw compressor (Source: screw compressors have a long life www.jagweb.com/aj6eng/superc cycle, since they consist of few harging_article.htm) moving parts.

• Turbo/ Centrifugal compressors: Turbo/ Centrifugal compressors consist of one or more impeller wheels (arranged in series) inside round chambers (volute cases). The refrigerant is sucked into the rotating impeller wheels through large circular intakes. The impeller wheels pressurize the refrigerant, exerting centrifugal drive on it and forcing it against the sides of the volute. The volute dimension, and the number and the width of the impeller wheels, determine the

centrifugal compressor’s Fig. 21: Centrifugal compressor (Source: output. Centrifugal www.fscc-online.com/.../passing_gas.htm) compressors are desirable for

27 their simple design, the low abrasion, the continuous power control and the low space requirement for high outputs.

Reciprocating piston and scroll compressors dominate in heat pumps with low performance, usually used for the exploitation of geothermal energy of the ambient air and the near surface geothermal energy. In most cases they are hermetically sealed and have an electric motor. Heat pumps with high performances typically make use of semi-hermetic or open screw and turbo compressors to pressurize the working fluid.

The Condenser and the Expansion Valve In the condenser the refrigerant condenses at high pressure and high temperature. The heat carrier of to the secondary/heat loop absorbs the heat of the condensation process. The expansion valve lowers the condenser pressure and temperature of the refrigerant to the levels for the evaporating process. At the same time the valve regulates the mass flow of the refrigerant in the heat pump loop. There exist different kinds of expansion valves, including thermostatic and electronic ones, and capillary tubes (Kaltschmitt, 2006). After the expansion valve the refrigerant turns back into the evaporator and the heat pump loop starts again.

The Refrigerant In the past primarily chlorofluorocarbons (CFC) and hydrochloro-fluorocarbons (HCFC) have been used as refrigerants (R12, R22, R502) for compression heat pumps. Since these gases significantly contribute to the ozone depletion when released, nowadays they are prohibited for new heat pumps. Because of the numerous requirements, it was complex to find substitutes for the previous refrigerants. Refrigerants with chlorine and fluorine have high stratospheric ozone depletion potential; the ones with many hydrogen atoms are inflammable and therefore dangerous. The most used refrigerants today are apart of halogen- and chlorine-free working fluids as propane (R290), propene (R1270) and ammonia (R717), the two HFC- (fluorinated hydrocarbons) mixtures R407C and R410A (Kaltschmitt, 2006).

28 For large heat pumps mainly the refrigerant R134a is used. R134 requires large compressors implying high costs. The advantage of this refrigerant is that high temperatures can be achieved easily. Figure 22 shows the properties of the refrigerant, figure 23 the thermodynamic cycle of R134 with the relation between pressure and enthalpy

(Bonin, 2009). Fig. 22: Properties of refrigerants (Source: Kaltschmitt, 2007)

Fig. 23: Thermodynamic cycle of R134a (Source: Bonin, 2009)

29 Single Stage vs. Multi Stage Heat Pumps Whereas single stage heat pumps have only one setting, multi stage heat pumps have two or more speeds with the benefit, that they can adapt the heat supply to the actual heat demand.

3.4.2.2 Absorption Heat Pumps

Whereas compression heat pumps utilize mechanical compressors to pressurize the refrigerant, absorption heat pumps operate with “thermal compressors”. The compression of the refrigerant is achieved thermally by a second circuit, the solution circuit (see fig. 24). The solution circuit itself consists of an absorber, a solution pump, a generator, and an expansion valve. In the absorber the gaseous refrigerant/working fluid coming from the evaporator is absorbed by the so-called absorbent, forming the enriched solution.

The absorbent is a liquid Fig. 24: The principle of absorption heat pumps solvent, in which the working (Source: www.heatpumpcentre.org/... /Sidor/default.aspx fluid shows a high dissolving power. Typical working pairs (working fluid/ absorbent) are water (H2O)/ lithium bromide (LiBr) and ammonia (NH3)/ water (H2O). The absorption process is characterized with the release of heat, which can be utilized. From the absorber the enriched solution is pumped by the solution pump under pressure rise into the generator, where the working fluid is boiled off by an external heat supply. The heat supply is generated by burning gas or oil, or in the ideal case by the utilization of industrial waste heat. After the generator the gaseous working fluid, as in compression heat pumps, is condensed in the condenser, while the absorbent (the depleted solution) is returned back to the absorber through the expansion valve. Compared to compressing heat pumps, absorption heat pumps generate useful heat not only in the condenser, but also in the absorber. To run the absorption circle

30 high temperature heat in the generator and electricity for the solution pump have to be supplied. The electricity consumption of the solution pump in comparison to the absorption heat pump is much lower than the one of compression heat pumps, since a liquid medium needs much less energy for a pressure rise than a gaseous one. Apart from the so-called absorber, absorption heat pumps consist, like compression heat pumps, of an evaporator, condenser and expansion valve with the same function.

3.4.2.3 The Performance of Heat Pumps

According to the first law of thermodynamics the energy balance of a heat pump is (Kaltschmitt et al., 2007): . . Q Evap. + PDrive = Q Cond. . with Q Evap. = the heat flow to the evaporator

PDrive = the compressor drive power . Q Cond. = the heat flow to the evaporator

The performance and the efficiency of an energy system is generally defined as the ratio of output to input energy, which by definition is always less than one. Unlike conventional energy systems, heat pump systems do not take into account the heat input of the heat source in efficiency calculation, since they make use of existing heat, which alternatively remains unused. This leads to efficiency ratios greater than one for heat pump systems (Kaltschmitt et al., 2006). Since there exists a great number of performance ratios for heat pumps, only the most important ones are represented in the following sections.

Coefficient of Performance (COP) – (in german: Leistungszahl ε) The steady-state performance of an electric driven compression heat pump at a given set of temperature conditions is defined as the ratio of the heat delivered by the heat pump to the electricity consumed by the compressor. This performance ratio is called the coefficient of performance (COP):

31 delivered heat power (kW) COPheating = supplied electrical driving power (kW)

A COP equalling 4, for example, means that the heat pump produces heat power four times of the needed electrical power. Thus, from 4 units of heat output, 3 originate from the heat source and 1 from the electrical driving power. The COP primarily depends on the temperature of the heat source and the utilization heat needed. The larger the temperature difference, the higher the temperature lift the heat pump has to provide. With increasing temperature lifts, the coefficient of performance of heat pumps decreases substantially. The best COPs are achieved when the temperature of the heat source compared to the utilization heat is high and vice versa (for example, ground water as heat source and low temperature heating systems like underfloor- and panelheating as heat utilization system (BOKU, n.d.). In praxis the COP of electrical heat pumps typically ranges from 2.5 up to 5 in the ideal case.

Seasonal Performance Factor (SPF) – (in german: Jahresarbeitszahl β) The performance of an electrical heat pump over the season is called the seasonal performance factor (SPF). It is defined as the ratio of the delivered heat and the supplied electrical energy over the considered season:

delivered heat energy (kWh) SPFheating = supplied electrical driving energy (kWh)

The seasonal performance factor by definition describes the efficiency of the whole heat pump system. It takes into account the energy consumption of additional heat pump components, as for example recirculation pumps, the variable heating accounts and the different heat source and sink temperatures over the year. The seasonal performance factor is consequently more significant to explain the efficiency of a heat pump system than the COP. The SPF is always lower than the COP. Regarding the European Heat Pump Association (EHPA) the following benchmarks for SPFs of heat pumps can be assumed (Bonin, 2009):

Water/ Water Heat Pump: 4.5

32 Direct Evaporator Heat Pump: 4.2 Brine/ Water Heat Pump: 4.0 Air/ Water Heat Pump: 3.5 A SPF of 4.5, for example, means that a heat pump system with one kW of electricity delivered 4.5 kW of heat at annual average.

Primary Energy Ratio (PER) – (in german: Heizzahl ζ) The steady-state performance of engine and thermally-driven heat pumps at a given set of temperature conditions is defined as the ratio of the heat delivered by the heat pump to the primary energy supplied. It is called the primary energy ratio (PER):

delivered heat power (kW) PERheating = power supplied by primary energy (kW)

The COP of electrical heat pumps is not directly comparable with the PER of thermal driven heat pumps, because it does not take into account the degree of efficiency of the electricity generation. Thus, for calculating the PER for electrical heat pumps, the COP has to be multiplied by the efficiency of electricity generation. The overall efficiency of electricity generation is the mean of all electricity producing power plants (hydro, nuclear, coal, gas, oil power plants etc.) including losses, it lies between 30 % and 35 %. Because of this low efficiency in electricity production, the PER of engine and thermal-driven heat pumps (0.8 to 2.0 for engine heat pumps; 1.0 to 1.8 for absorption heat pumps) is generally higher than the ones of electrical heat pumps (0.75 to 1.5) (IEA Heat Pump Centre, n.d.).

Respectively to the seasonal performance factor, the seasonal performance of engine and thermal-driven heat pumps can be described as the ratio of the delivered heat and the supplied primary energy over the season. Taking into account the electrical power generation efficiency, the seasonal performance factor of electrical heat pumps can be compared with the ones of the engine and thermal heat pumps.

33

Ideal (Carnot) versus Real Heat Pump Cycle The Carnot Cycle defines the ideal thermo dynamic process of a heat pump. Based on the second law of thermodynamics, the ideal coefficient of performance of a heat pump is given by:

TH Ideal COPCarnot Cycle = TH - TC

with: TH = the higher temperature at the condenser (in Kelvin) T = the lower temperature at the evaporator (in Kelvin) C

The equation shows that the efficiency of heat pumps increases with decreasing !"#$%&'()*"#+'#%temperature lift. Since the Carnot,,,-."#$/0'()*"#+'#-12 Cycle does %not take into account energy losses 3'2(45**'6%78(4'9"49'#/%"#:%!86*'*'12#5.% ! due to friction and heat losses, it is technical unrealizable and the ideal COP only a ;-<% !"#$%&"'("$)#"%*+#,-"**$%.$(,/$+010!%'/#'..$ 65#! A#%#5$B!theoretical #%C90($D! :E((! value. 8#%! FE%(-$7"%-)#BB! (5/0$! G#%C5%:15/0$! C#%8#(+%9%heat pumps is 0.30 to 0.5 for small electric heat pumps and 0.5 to 0.7 for large ones ! @5(AB'!#5(#C!69%4#,A#%$%B2#%C!)'%!DA#%05$)'(2!%#CE% ! ! =% ! (p) – specific enthalpy (h) diagram. TheL! enthalpy I#%J1,CC52#%! H of a gas or vapor is their total ! ! ! M! @NEB(C5-(CO#($51! = energy content;?% the specific enthalpy is! the enthalpy referring to the mass (h= H/m@% ! / ! ! ! with m=mass) with the unit joule per kilogram! (J/kg). ! ! ! ! 2% ! ! M#%!G#%#5(QE/0$#!"%-)#BB!RFE%(-$SB/0#%!I#%21#5/0BJ%-)#BBT!G#%19'Q$!8E((!C5#!Q-12$U!PB%C$#11'(2!54!1-2E707P5B2%B44G! ! ! ! ! ! 1-2!J! ! 1-2!E! ! ! ! ! ! ! ! &-(8#(BE$5-(!Condensation ! ! ! t $!V!:-(B$E($!= constant ;F J ! <% ! >A HLJE(B5-(!Expansion ! ! &-4J%#BB5-(!Compression 0!V!:-(B$E($!h = constant ! ! sB!V!:-(B$E($! = constant ! ! JO! ! EW! ! E% EvaporationI#%8E4JQ'(2! G @A% ! ?A% ?% @ ! $!V!:-(B$E($! t = constant ! ! ! ! ! ! ! ! '0 '0C '0! '0! O !0! 0! '0/! ! SupercoolingF($#%:,01'(2! SuperheatingDA#%05$)'(2! ! ! P'%/0!8#(!@5(CB$)!8#C!69%4#,A#%$%B2#%C!:B((!A#5!$0#-%#$5C/0!8#%!21#5/0#(!I#%85/0$#%1#5C7 "#$#%!&'()*+,%-*./0'1'(2#(*3#0%45$$#1*6"7!'(8! &91$#$#/0(5:!;;<8-/! ! .#5$#!7=7>7?@7! $'(2!C-Q-01!85#!I#%J1,CC52#%1#5C$'(2!Q5#!B'/0!85#!I#%8B4EJ#%1#5C$'(2!#%0R0$!Q#%8#(

"#$#%!&'()*+,%-*./0'1'(2#(*3#0%45$$#1*6"7!'(8!&91$#$#/0(5:!;;<8-/! ! .#5$#!7=7>7?=7! !

34

Figure 25 shows the ideal thermodynamic cycle (Carnot cycle) of a heat pump with (Markiewicz, 2004):

1-2: isoentropic (constant entropy) compression by the compressor up to maximum final compression temperature with superheating of the refrigerant; no thermal output. 2-2’: isobaric (constant pressure) cooling down to the condensation temperature in the condenser; the superheat enthalpy (h2-2’) is transferred to the medium that has to be heated; the refrigerant remains gaseous.

2’-3: isobaric condensation in the condenser; the condensation enthalpy (h2’-3) is transferred to the medium that has to be heated; during the phase transition the temperature remains constant. 3-4: Alleviation to the saturated steam area in an expansion device; constant enthalpy; the refrigerant is cooled down and alleviated to evaporation pressure. 4-1: isobaric evaporation in the evaporator; absorption of evaporation enthalpy

(h2-2’) out of the medium that has to be cooled, during the phase transition the temperature remains constant.

The real thermodynamic cycle of a heat pump is represented in figure 26, in comparison with the ideal thermodynamic cycle it exhibits the following differences (Markiewicz, 2004):

• The compression in the real thermodynamic cycle is not isentropic (without heat losses). Because of internal friction of the refrigerant and heat losses in the compressor more work has to be applied for reaching the same end pressure. Thus the compression process in the cycle will take place along the line 1’ -2’. • To avoid the aspiration of liquid refrigerant by the compressor, it is necessary that the superheating of the refrigerant takes place before compression (1-1’). • The refrigerant can be undercooled by heat exchangers (3-3’), absorbing more evaporation heat in the condenser. Because the driving power more or less remains the same, the coefficient of performance improves slightly.

35 Efficiency of Heat Pumps for Space Heating The energy consumption of the building sector averages about 40% of the total final energy consumed in the IEA (International Energy Agency) member countries. 75% of this is used to produce comfort heat in the sense of space heating and domestic hot water (IEA, 2006). According to this data, it can be assumed that between 20% and 30% of the total energy consumption is used for the production of space heat with temperatures in the range of 18°C to 28° C. A comparison of the efficiency of the primary energy input of different heating methods (see fig. 27) shows that heat pumps with low energy heating systems represent energetically the most efficient way for space heating supply. Heating with electricity is very inefficient, because of the high amounts of waste heat and the resulting low efficiency in electricity generation. For 100% of effective energy, 278% (!) of primary energy has to be supplied. However the combustion of oil and gas for space heating exhibits relatively high values of efficiency (εtot=0,86 and εtot=0,92), electrical driven heat pumps, including the losses in electricity production, show even a higher one (εtot=1,19).

Fig. 27: Energy efficiency respectively the primary energy input of different heating methods (Source: ASUE, 2002)

36

3.4.3 The Heat Sink

The heat sink consists of a heat loop, which absorbs the heat of the condensation process in the heat pump and transports it with a heat transfer medium (water or air) to devices that transmit the heat to the ambient air and the domestic hot water. Since the COP of heat pumps is best when temperature differences are small, low temperature levels in the heat loop are advantageous. Low energy heating systems as underfloor- and panel heating, using shallow geothermal energy lead to very high efficiency ratios.

Usually screw plate heat exchangers (see fig. 28) are used for the heat transfer from the geothermal fluid to the heating system or the heating water circuit. They guarantee an efficient and cost-effective heat exchange because of the following benefits: low temperature difference transfer of up to 1 K between the media, high heat transmission coefficients, low building volume and mass, sufficient pressure resistance for common geothermal pressure of up to 16 bar, low water contents to be processed or disposed of in case of damage or service, and easy maintenance of the plate surface thanks to easy disassembly. Mainly the heat exchangers are made of titanium, since it is Fig. 28: Screw plate heat exchanger (Source: highly resistant to corrosive geothermal www.genemco.com) fluids (Kaltschmitt, 2007).

Monovalent vs. Bivalent Heat Pump Systems In heating systems with heat pumps distinctions are made if the heat pump is the only heat source or if there are alternatives. In monovalent heat pump systems the heat pump is the only heat source, whereas in bivalent systems heat pumps are supplemented with other heating equipment, which can operate in parallel or as an alternative.

37 Space Cooling with Heat Pumps Heat pumps can also be used for cooling in the summer by reversing the heat pump’s function with a four-way valve in the refrigerant circle. Heat from inside the buildings can be absorbed and delivered to the ambient. The utilization of heat pumps for heating and cooling can significantly improve the economic efficiency of the whole system. Earth-coupled heat pump systems where ground temperatures are not above 10°C, can also be used directly for cooling buildings in the summer, without heat pump operation. The heat in the building is generally absorbed by a separate cooling circle and transported in the earth coupled with absorbers in the cool ground (Sanner, n.d.).

Single House vs. District Heating Systems Because of the limited output of shallow geothermal energy utilization most of the installations are for single houses, the technique for single house applications is well developed and standardized. Since single house applications in the utilization of the huge potential of the tunnel water of BBT are not part of this master thesis, they are not described in detail at this point. Where the potential of shallow energy sources is quite high and easy extractable (e.g. tunnel water, hot reservoirs or hot springs at earth’s surface), district-heating systems can be an economical solution for the supply of high low-temperature demand, as needed in urban areas for space heating and domestic water.

3.5 District Heating Systems „The fundamental idea of District Heating and Cooling is simple but powerful: connect multiple thermal energy users through a piping network to environmentally optimum energy sources, such as combined heat and power (CHP), industrial waste heat and renewable energy sources such as biomass, geothermal and natural sources of heating and cooling. The ability to assemble and connect thermal loads enables these environmentally optimum sources to be used in a cost-effective way“ (IEA DHC/CHP, 2002).

A typical district heating system can roughly be divided into (Hakansson, 1973): • production, central power plant • distribution, preinsulated pipes • consumption, substation

38 3.5.1 Heat Production/ Distribution/ Consumption

Production In the district heat production, a distinction is made between heat plants and cogeneration plants (also called combined heat and power plants CHP). Whereas heat plants only produce heat by the combustion of fossil fuels, biomass etc., cogeneration heat plants generate electricity and make use of waste heat. Cogeneration plants can reach energy efficiencies of 70% to 80%, whereas heat plants reach only 20% to 35% (Matthöfer, 1977). Cogeneration plants are therefore from an ecological point of view and by producing electricity also from an economical view more valuable than simple heat plants. The heat and cogeneration plants can be powered by fossil fuels (oil, gas), nuclear power, biomass, biogas, waste, waste heat from industry and last but not least geothermal energy. Large district heating systems often consist of a combination of multiple power plants with different energy sources. Sometimes district heating systems are equipped with large heat storage tanks to compensate time differences between heat supply and demand and to cover peak-period demand for heat.

Distribution The distribution system of a district heating system consists of a network of insulated pipes connecting the heat production plants with the heat consumers by one, two, three, or four lines. Usually the pipelines are water operated in the sense that water is used as the medium for heat transportation. In industrial applications, because of higher temperature needs, also vapor is used as transport medium. The predominant pipe system is the two-line system, with a feed and a return line. The feed line brings the heat in the form of heated water to the consumers, where the heat of the water usually is extracted by heat exchangers. The return line returns the cooled water back to the heat plant, where it is heated again.

Figure 29 shows different network types of district heating systems: radial, ringed and meshed networks (Kaltschmitt, 2007). Ringed networks compared to radial ones are more expensive due to their greater length and the required larger nominal diameter of the pipelines. Ringed networks are especially advantageous for the incorporation of several heating plants. High supply reliability and very good extensibility of the ringed network should compensate higher costs. Nevertheless, because of the high investment costs,

39 ringed networks are suitable only for large to very large district heating systems. Radial networks, because of the reduced pipeline length, are cheaper and appropriate for small- and medium-sized distribution networks. Radial networks are the typical type for geothermal energy utilization (Kaltschmitt, 2007).

Fig. 29: Main distribution networks of heatings systems (Source: Kaltschmitt, 2007)

Heat consumers (i.e. houses) can be connected to the district heating grid individually, or houses can be connected among each other. Individual connections provide high flexibility and are preferred in partly developed areas. In densely built- up areas routing from house to house is in general more economical. In grouped houses only one is connected to the district heating network, whereas the others are connected to this one (see fig. 30). Generally a mix of both transmission routings is applied (Kaltschmitt, 2007).

Fig. 30: Transmission routings of district heating (Source: Kaltschmitt, 2007)

In most of the cases the pipes of the district heating distribution systems are installed underground within ducts or directly within the ground (ductless line). Compared to pipes in ducts, ductless lines need only a little space and can be installed in short periods at lower costs. In systems below 20 MW thermal capacity, direct earth laid pipelines generally prevail (Kaltschmitt, 2007).

40 Lines aboveground are uncommon. Apart from the visual impact, they occupy precious space (especially in densely populated areas) and have to be provided with expansion loops and special anchors to allow pipe movements (Bloomquist et al., 2002). The main requirements of district lines are the resistance against environmental impacts to guarantee a long operating life and the insulation to prevent heat losses. Especially for ductless lines, because of moisture in the soil, corrosion resistance is very important. Steel medium pipes with foam insulation and external waterproofed polyethylene jacket prevail in district heating line construction, but also plastic medium pipes are in use. Sub-lines and house connections are in general made by flexible metal or plastic medium tubes (Kaltschmitt, 2007). If distribution systems are of great length, they have to be equipped with booster stations in addition of the circulation pumps. To avoid unnoticed losses on district heating lines and expensive leak detection during operation, leak detection systems can also be installed.

Consumption Finally the heat transported in the distribution network has to be transferred to the heating system of the houses by so-called substations. Distinction is been made between direct and indirect substations. In direct substations the heating water from the district heating system Fig. 31: Simplified indirect substation (Source: flows through the whole www.swep.net) heating system installed in the house, temperatures are regulated by adding cool water. Indirect substations consist of heat exchangers between the district heating and the houses heat distribution system. The indirect substation systems require higher investment costs, but they have the advantage of independency of systems regarding functioning, pressure conditions and water properties. Most substations are indirect ones, figure 31 shows a simplified system.

41 Usually energy meters at the substations measure in-flow/out-flow temperatures and flow rates, so that houses can be easily billed for their heat consumption. Remote monitoring of energy meters helps to optimize district system operation and eliminates personnel needed for meter reading (Bloomquist et al., 2002).

The Ecology and Economy of District Heating Systems The energy efficiency of heat generation with centralized plants (especially with cogeneration plants) generally is much higher than with individual plants. Moreover, polluting emissions are minimized with central plants, since they are constantly controlled and typically have flue gas cleaning systems. From an ecological point of view district heating systems powered by renewable energy resources exhibit great sustainability (Aringhieri and Malucelli, 2003). Because of the high thermal output of central heating plants and the elevated costs for grid installations, district heating systems require huge initial investments. District heating systems are long-term investments. They require detailed feasibility studies, with the analysis of the potential heat demand and the valuation of the penetration. Densely populated areas and industries with a constant heat demand over the whole year are good premises for an efficient district heating system. The higher and constant the heat demands, the better is the economic feasibility of a district heating. An important factor that influences the economy of a district heating system during operation is the temperature difference between feed and return line. The higher the difference, the more heat energy is transferred to consumers. Efficient heat transportation means less heat loss because of lower volume flow rates and electricity savings due to less pumping. Especially when there are more energy sources, district heating systems represent complex systems with many factors influencing efficiency. Remote and computerized monitoring systems can optimize the district heating operation significantly and increase efficiency and economy. Planning district heating systems requires detailed preliminary studies about potential heat demand and feasible connection rates to evaluate and guarantee their economy.

42 3.5.2 Geothermal District Heating

In the last decade, district-heating systems supplied by geothermal energy gained more and more importance and several projects have been realized. When temperatures of the geothermal energy source are high enough, the district-heating system can be operated by direct heat exchange. Generally geothermal heating plants are operated in base load. The heat from the geothermal energy source is constant over time. Temperatures in the district heating system cannot be varied; increasing the flow rate can therefore only cover higher heat demands. Thermal storage equipment can help to meet peak demand. Empirically the required increase of geothermal flow can reach 50% to meet peak demands, which in turn requires a substantial over-sizing of the whole transmission and distribution piping network of 40 to 60%. Since peak demand typically occurs only 3 to 5% of the time, economically it makes sense to cover peak loads by higher temperatures and constant flow rate, integrating fossil fuel or biomass boilers and heat pumps for increasing temperature input into the system (Bloomquist, 2003). Figure 32 shows typical operating principles of geothermal heating stations with heat exchangers, peak load boilers, heat pumps, and an example of an incorporated combined heat and power (CHP) station. The combinations of the different systems provide base and peak load in a cost-efficient way.

Fig. 32: Operating principles of geothermal heating stations (Source: Kaltschmitt, 2007)

43

If the temperatures of the geothermal energy source are of low enthalpy and thereby too low for direct exchange, heat pumps have to be integrated. In geothermal district-heating systems a distinction can be made between central heat pump and peripheral heat pump systems. In central heat pump systems, centralized heat pumps provide for the temperature elevation of the heat transport medium, which circulates in the district-heating grid at high temperatures. In peripheral systems, the transport medium in the grid circulates at low temperature, the individual heat consumers provide their own heat pump for the temperature elevation. Because of the low temperature of the grid fluid, these systems are also called low-temperature district heating. There is no general rule as to when to use which system. For small district-heating systems with limited heat demand it can be economically more feasible to choose peripheral heat pump systems. A peripheral heat pump district heating system, which uses tunnel water as heat source, is described in chapter 3.7.1.

“Geothermal heating stations are designed according to site-specific requirements. Due to the multitude of existing impacting factors (such as the characteristics of the geological resources, the geothermal fluid characteristics, the demand and the consumer behaviour, the (existing) heating network parameters, regionally influenced prices of fossil or renewable energy carriers, the organizational structure of the plant operator) general statements can only serve as reference values” (Kaltschmitt, 2007).

3.5.3 Combined Heat and Power and Heat Pump Systems for Residential Use

Because of the economical and ecological advantages of combined heat and power district-heating systems (CHP) mentioned above, they prevail in the realization of new urban power supply systems. At the same time, heat pumps (HP) are gaining strong acceptance for residential heating due to their reliability, fuel economy and lower CO2 output. By combining CHPs and HPs it is possible to benefit from the individual advantages of both systems. With HP-CHP systems heat can be produced in a more ecological way than with a traditional boiler. As figure 33 illustrates, by combining a heat pump to a CHP system, only 67 units of primary

44 energy are needed to cover 100 units of heat requested, resulting in an efficiency of 149%. Since a natural gas boiler system without heat pump requires about 110 units of primary energy to supply 100 units of heat (see also fig. 27), the HP-CHP system with the lower primary energy requirement can reduce the production of CO2 by about!"#$%&'()*)'+)$&'$,')*-. 40% (Conti et al., 2007 (&*$/$%0)/'$,'12*&'3)'"). 456$780. 499:

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1$+C".D 1$$:#

Fig. 33: Energy flow of!"#$%&'(')'*+&%#,'-./0'1"2#%23 a CHP - HP system (Source: /-'2'456745'8,89&3 Conti et al., 2007)

;&*)&1)*<$8=2'-$#)/"$="&*/-)$"&$=8>>0. #)/"$?8*2'-$>)/@$#&8*=<$"#)$AB$ Figure+&80?$C)$?2=+&'')+")?$/'?$=8*>08=$)0)+"*2+2".$+&80?$C)$=&0?$"&$"#)$')"D&*@E 34 represents the overall efficiency of a HP-CHP system, depending on the heatF#)$&1)*/00$)+&'&3.$&($"#)$>*&+)==$+/'$"#8=$C)$)'#/'+)?E$ pump’s Seasonal Performance Factor (SPF). It shows that also heat pumps with low SPF lead to a higher efficiency of the overall system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

Fig. 34: The overall efficiency of a CHP-HP system depending on the heat pump's seasonal performance factor (Source: Zogg, 2001)

45

The designing and the dimensioning of a HP-CHP system are complex, since it depends on many impact factors. In determining the size of each element from an economical point of view heating costs, at the same time from an ecological point of view, CO2 emissions should be minimized (Conti et al., 2007).

3.6 Utilization Possibilities of Tunnel Water Heat

The geothermal heat contained in the tunnel water of deep tunnels can be used for different heating and cooling applications. They range from self-exploitation in the tunnel operation to third-party utilization by private and public buildings. Since the geothermal energy of tunnel water in most of the cases is lower than 25°C, heat pumps are necessary for heating purposes. The direct use of tunnel water is more or less limited to agricultural applications and fish breeding (see fig. 10 - Lindal Diagram). Low enthalpy, the cost factor of the distribution piping, as well as heat losses due to long transportation make it indispensable to exploit the heat of the tunnel water near the tunnel portals. To guarantee the efficiency and cost effectiveness of tunnel water heat exploitation systems, comprehensive geothermal planning is necessary, which takes into account all the site-specific circumstances influencing the project. Oberhauser and Adam (2006) in the article “Optimierungspotenziale der Erdwärmenutzung an Verkehrsinfrastrukturprojekten” distinguish between three possibilities of tunnel water heat utilization from the view of the tunnel operator: a) self-exploiting (utilization in the tunnel infrastructure system); b) measures to increase safety (frost inhibitor of station platforms, stairs, access roads, bridges); and c) third-party utilization (sale of the energy). With the self-exploitation of the heat energy, tunnel infrastructures, such as station and office buildings, can be heated and cooled in an energy-self-sufficient way. During winter safety measures can be adopted by heating station platforms, stairs, access roads, or bridges with tunnel water to keep them ice-free. The most interesting utilization of the tunnel water is the utilization of the heat by third parties. By selling the heat to residential and commercial buildings near the tunnel portal, the tunnel operator becomes a producer and distributor of environmentally friendly geothermal energy (Oberhauser and Adam, 2006).

46 The following table shows different utilization possibilities of the geothermal heat energy of tunnel water.

Tab. 2: Geothermal utilization forms of tunnel water and its temperature levels (Source: Different internet sites)

Temperature in °C Utilization Form Utilization Time from to all-season (limited Building heating with conventional demand in summer, flat-panel radiators and domestic 50 75 because of domestic hot hot water water only) Building heating with floor and panel heating (low temperature winter only 30 55 heating) all-season (limited Conventional district heating (high demand in summer, 60 130 temperatures) because of domestic hot water only)

Low temperature district heating winter only 35 60

only winter (also in summer, if it is used for Cold district heating up to 40 domestic hot water production by heat pump) Process heat for commerce and all-season 30 > 100 industry Agriculture (open-field soil winter only; partially all- irrigation/heating and greenhouse 30 75 season heating) Animal husbandry (animal breeding) and aquaculture (fish all-season 10 30 breeding)

3.6.1 Heating of Buildings (Conventional vs. Low Temperature Heating)

Conventional heating systems generally require much higher temperatures in the flow lines than is supplied by the tunnel water. The high temperature necessity comes from the heat transfer by conventional flat-panel radiators inside the buildings, which require temperatures from 50° C up to 75° C. If the heat for conventional systems is provided by a district heating network, because of losses in heat transmission, temperatures have to be even higher. This leads to the high temperatures of district heating systems from 60° C up to 130° C.

47 Low temperature heating systems are characterized by underfloor- and panelheatings inside the buildings, which require much lower temperatures than conventional systems. Flow temperatures of low temperature heating are between 30° C and 55° C, heating temperatures of low energy houses are even lower. Buildings with low temperature heating can be also supplied by low temperature district heating networks with temperatures from 35°C to 60°C.

For both heating forms it is necessary to install heat pumps, since generally tunnel water temperatures are lower than the temperatures required. In the utilization of the geothermal heat of tunnel water for building heating, heat pumps can be installed centrally in power plant stations or locally in the individual buildings. When centralized, the lift of the tunnel water temperature to the temperature required for heating occurs by large heat pumps. The heated medium afterwards is delivered to the single buildings by conventional or low temperature district heating systems. In decentralized heat pump systems, the individual buildings are supplied by so called cold district heating networks with the tunnel water. The temperature lift occurs by small heat pumps in the buildings themselves. As mentioned already in the chapter on heat pump performance, energy efficiency substantially decreases with increasing temperature lifts. Therefore, the most efficient form of tunnel water utilization is the one for low temperature heating in individual houses, low district and cold district heating systems. In planning a geothermal system for exploiting tunnel water heat for heating buildings, no general rules can be set up. Every project has to be planned individually, taking into account the specific heat supply/demand and all site-specific circumstances. In the following section the benefits and drawbacks of the geothermal heat utilization of tunnel water for heating buildings are summarized:

Benefits: 1) The heat of the tunnel water is used in a target-specific way and not wasted.

2) The heat of the tunnel water can substitute for fossil fuels and lower CO2 emissions. 3) The heat of the tunnel water can increase efficiency and reduce electricity consumption of heat pumps, when geothermal energy sources with lower temperatures, such as ground water, are replaced.

48 Drawbacks: 1) The heat demand is seasonal and limited to winter months. 2) High investments for heat pumps are necessary. 3) To fulfill environmental regulations regarding discharging the tunnel water into surface water, separate cooling systems for the summer are required. The cooling systems imply additional investment costs. 4) Because of low temperatures of tunnel water and losses with long pipes, heat consumers located near the tunnel portal are required too guarantee efficient utilization. 5) To guarantee the economy of high investments, the heat demand has to reach a certain amount.

3.6.2 Process Heat for Commerce and Industry

Most of commerce and industry companies need process heat at high temperature levels for their productive activity. But there also exist some with lower temperature requirements, for example for tempering purposes (especially in the food industry). When temperature level needs are higher than the tunnel water temperatures, the installation of heat pumps is required. As for building heating, the tunnel water heat can also be used for heating production halls.

Benefits and drawbacks of tunnel water heat exploitation for commerce and industry applications are as follows:

Benefits: 1) The heat of the tunnel water is used in a target-specific way and not wasted.

2) The heat of the tunnel water can substitute for fossil fuels and lower CO2 emissions. 3) With appropriate commerce and industry applications, high heat demand and consumption is guaranteed over the whole year.

Drawbacks: 1) Appropriate commercial and industrial heat consumers located near the tunnel portal are needed. If not existent, a systematic commerce and industry settlement has to take place.

49 2) When temperature needs are higher than the tunnel water temperature, high investments for heat pumps are necessary. 3) Additional investments for cooling systems are required, if the commercial and industrial heat demand does not reach the tunnel water cooling target needed to fulfill environmental regulations.

3.6.3 Process Heat for Agriculture

Another target-specific application of tunnel water heat is its utilization for agricultural purposes in open-field agriculture and greenhouse heating systems. Open-field agriculture applications are rare; they consist of soil irrigation and/or heating. By contrast, greenhouse heating by thermal water is widely used in many countries and technically well developed, also in large scale. There are different systems for geothermal greenhouse heating. The most common ones are the forced circulation of air in heat exchangers, hot-water pipes/ducts located in/on the floor and finned units along the walls and under benches. By the exploitation of thermal water, greenhouse operation costs can be reduced considerably. Greenhouse heating for the production of vegetables, flowers, house-plants, and tree seedlings can account up to 35% of the product costs (Dickson and Fanelli, 2005). Greenhouses with special heating systems (close-by plants heating, energy screens, substrate heating or the like) and plants with low heat requirement (e.g. strawberries) can be heated directly with the geothermal energy of tunnel water. However, when higher temperatures are required, as for high pipe heaters and exotic plants, for the tunnel water heat exploitation the installation of heat pumps is necessary.

Benefits and drawbacks of tunnel water heat utilization for agricultural purposes are:

Benefits: 1) The heat of the tunnel water is used in a target-specific way and not wasted.

2) The heat of the tunnel water can substitute for fossil fuels and lower CO2 emissions. 3) With appropriate agricultural applications, high heat demand and consumption is guaranteed over the whole year.

50 4) In special cases heat can be used directly with heat exchangers, without heat pumps and additional energy.

Drawbacks: 1) Appropriate agricultural heat consumers located near the tunnel portal are needed. If not existent, a systematic greenhouse agriculture settlement has to take place. 2) When temperature needs are higher than the tunnel water temperature, high investments for heat pumps are necessary. 3) Additional investments for cooling systems for emergency cooling in case of operating failures can be required. Additional cooling systems are also necessary, when the agricultural heat demand does not reach the tunnel water cooling target needed to fulfill environmental regulations.

3.6.4 Process Heat for Animal Husbandry and Aquaculture

As well as in vegetable and plant cultivation, ideal environmental temperatures significantly promote the breeding of farm animals and aquatic species in quality and quantity. Since the heat energy required of animal breeding is about 50% of that of greenhouses, adopting the so called cascade utilization, geothermal waters can profitably be used in a combination of animal husbandry and geothermal greenhouses. Because of a worldwide increase in demand for fish, shrimp, caviar, lobster, etc., aquaculture (the controlled breeding of aquatic forms of life) is gaining more and more importance. The impact of the optimal breeding temperature for aquatic species on growth is much higher than for land species. By maintaining ideal temperature artificially, exotic species can be bred, production can be improved and, in some cases, the reproductive cycle can be doubled (Dickson and Fanelli, 2005). Temperatures for aquaculture reach from 10°C up to 30°C, depending of the aquatic species bred. For tunnel water of deep tunnels, aquacultures for sturgeon with temperature requirements around 20°C are very well suited to exploit the tunnel water heat. Sturgeon breeding provided by the heat of tunnel water was realized in Frutigen/Switzerland in 2008.

51 If the tunnel water’s temperature is high enough for the specific aquaculture requirements, the aquaculture’s circulation water can be simple heated by heat exchangers.

Benefits and drawbacks of tunnel water heat exploitation for animal husbandry and aquaculture are as follows:

Benefits: 1) The heat of the tunnel water is used in a target-specific way and not wasted.

2) The heat of the tunnel water can substitute for fossil fuels and lower CO2 emissions. 3) With appropriate animal husbandry and aquaculture applications, high heat demand and consumption is guaranteed over the whole year. 4) Heat can be used directly with heat exchangers, without heat pumps and additional energy.

Drawbacks: 1) Appropriate animal husbandry and aquaculture heat consumers nearby the tunnel portal are needed. If not existent, a systematic settlement has to take place. 2) When temperature needs are higher than the tunnel water temperature, high investments for heat pumps are necessary. 3) Additional investments for cooling systems for emergency cooling in case of operating failures can be required. Additional cooling systems are also necessary, when the heat demand does not reach the tunnel water cooling target needed to fulfill environmental regulations.

52 3.6.5 Suitability of Tunnel Heat Utilization for Different Utilization Forms and Heat Sources

Table 3 shows the different tunnel heat sources and their characteristics. Thus, conclusions can be drawn on their suitability for different heat utilization forms (see table 4).

Tab. 3: Different tunnel heat sources and their characteristics

Availability Investments Investments for Heat necessary for Temperature Where Quantity Extraction Heat Utilization Tunnel water pipe, heat 10° to 35 °C Generally exchangers for Deep long Low (constant over Tunnel Water large heat direct use, water tunnels investments the year) capabilities to water heat (Rybach, 2006) pumps for indirect use Air heat Metro and long exchangers for tunnels, where Limited heat Low direct use, air to Tunnel Air temperatures up to 15° C capability investments air/water heat are constant pumps for over the year indirect use Absorber pipe system, heat Absorber Pipe High exchangers for 8° to 20° C (in Systems Near surface Limited heat investments direct use, summer) (Geotextile, tunnels capability for absorber brine/water to (Brandl et al., Energy pipe systems water heat 2010) Anchors etc.) pumps for indirect use

As table 4 shows, tunnel water heat is suitable for almost all utilization forms with certain limits. Generally tunnel water heat utilization is limited by: a) high investments for the tunnel water pipe; b) the costs for heat pumps; and c) the limited performance of heat pumps with high temperature lifts. Tunnel water heat utilization is most suitable for commercial and industrial process heat, agricultural and animal husbandry purposes with large heat demands at low temperatures. Because of the limited heat capability of tunnel air and absorber pipe systems, they are more suitable for single heating applications than for district heating systems.

53 Tab. 4: Suitability of tunnel heat utilization for different utilization forms and tunnel heat sources Suitability of Tunnel Heat Utilization for Different Tunnel Heat Sources Utilization Form Absorber Pipe Systems Tunnel Water Tunnel Air (Geotextile, Energy Anchor etc.) Limited use through: Limited use through: Building heating High costs of tunnel Limited use through: High costs for absorber with conventional water pipe installations, High costs of HPs, pipe installations and flat-panel radiators and HPs, limited limited performance of HPs, limited performance and domestic hot performance of HPs HPs because of high of HPs because of high water because of high temperature needs. temperature needs. temperature needs. Limited use through: Limited use through: Limited use through: Building heating High costs of tunnel High Costs for absorber High costs for HPs if with floor and water pipe installations, pipe installations and necessary, limited panel heating (low and HPs if necessary, HPs if necessary, performance of HPs if temperature limited performance of limited performance of high temperatures are heating) HPs if high temperatures HPs if high temperatures needed. are needed. are needed. Unsuitable through: Limited use through: Unsuitable through: High c osts for absorber High costs for tunnel Conventional Limited heat capability, pipe installations, limited water pipe installations, district heating high costs of HPs, heat capability, high costs and HPs, limited (high limited performance of for HPs, limited performance of HPs temperatures) HPs because of high performance of HPs because of high temperature needs. because of high temperature needs. temperature needs. Limited use through: High costs of tunnel water pipe installations, Low temperature and HPs if necessary, district heating limited performance of HPs if high temperatures are needed. Very limited use Very limited use through: Limited use through: through: Limited heat Costs for absorber pipe High costs for tunnel capability, high costs of installations, limited heat water pipe installations, HPs if necessary, capability, high costs for Cold district and for decentralized limited performance of HPs, if necessary, limited heating HPs if necessary, limited HPs if high performance of HPs if performance of HPs if temperatures are high temperatures are high temperatures are needed. needed. needed. Limited use if: Process heat for Long tunnel water pipe commerce and installations and high industry temperature heat with a necessary use of HPs. Agriculture (open- Limited use if: Limited use through: field soil Long tunnel water pipe Limited use through: High investment costs for irrigation/heating installations and high Limited heat capability, absorber pipe and greenhouse temperature heat with a high costs of HPs if installations, limited heat heating) necessary use of HPs. necessary, limited capability, high costs for performance of HPs if Animal husbandry Limited use only if long HPs, limited performance high temperatures are (animal breeding) tunnel water pipe of HPs if high needed. and aquaculture installations are temperatures are needed. (fish breeding) necessary.

54 3.7 Operating Examples of Tunnel Water Heat Utilization

3.7.1 Tunnel Water Heat Utilization in Switzerland

A large part of Switzerland is located in the Alps chain. It has over 700 road and 76 railwayGeothermie tunnels and it is the pioneerTunnelwärmenutzung and leading country in tunnel water heat utilization. Table 5 shows 15 selected main Suisse tunnels. The geothermal potential of these tunnels is estimated to be around 30 MW, with outflow rates from 360 to 24,000 liters/ minute and temperatures from 12° C to 24° C (Rybach, 2006). trittsort (Bild 1); die anfäng- Tabelle: Geothermisches Potenzial und gegenwärtige thermische Nutzung von Bahn- und Straßentunneln in der lich z. T. starke Schüttung geht Tab.Schw ei5z :n a Geothermalch [2, 4] potential and current thermal utilization of rail and road tunnels in im Laufe der Zeit weitgehend SwitzerlandTable: Geotherm (Source:al Potential aRybach,nd current 2006)thermal Utilisation of Rail and Road Tunnels in Switzerland according to zurück und erreicht konstan- [2, 4] te Werte (= Beharrungszu- Wärme- Wasser- Heutige Nutzung stand). leistung Aus uss temperatur Heiz-/Kühlenergie Kanton Tunneltyp Heat Tunnel Out ow Water Present Canton Tunnel Type Capacity Thermische Leistung [l/min] temperature [MWh/Jahr] Use2 Für eine energetische Nut- [° C] [MWh/year] [kW] zung der Tunnelwässer sind Ascona TI Straße/Road 360 12 150 die thermische Leistungska- pazität und die Ausfl usstem- Furka1 VS Eisenbahn/Rail 5400 16 3758 1700/– peratur beim Portal maßge- Sondierstollen Frutigen BE 800 17 612 bend. Die thermische Leis- Expl. heading tung P (z. B. in Megawatt Gotthard1 TI Straße/Road (A2) 7200 15 4510 660/1440 thermisch; MWt) berechnet Grenchenberg SO Eisenbahn/Rail 18 000 10 11 693 sich nach (Südportal/South portal)

1 P = c x Q x !T, Hauenstein SO Eisenbahn/Rail 2500 19 2262 2100/– (Basistunnel/Base Tunnel) wo c die Wärmekapazität von Isla Bella GR Straße/Road 800 15 501 Wasser, Q die Ausfl uss-Schüt- Lötschberg VS Eisenbahn/Rail 731 12 305

1 tung (Liter/s) und !T (=T–T0) Mappo-Morettina TI Straße/Road (A13) 983 16 684 120/200 das nutzbare Temperaturge- Pilotstollen Mauvoisin VS 600 20 584 fälle in °C bedeuten. T ist die Pilot heading Wassertemperatur und T0 die Sondierstollen Polmengo TI 600 20 584 Referenztemperatur (meist 10 °C). Expl. heading Bei einem Tunnelprojekt Sondierstollen Rawyl VS 1200 24 1503 wird deshalb schon in der Expl. heading Projektierungsphase abge- Ricken1 SG Eisenbahn/Rail 1200 12 501 250/– klärt, welche thermischen Leistungen und Ausfl usstem- Simplon (Portal Brig) VS Eisenbahn/Rail 1380 13 672 peraturen zu erwarten sind. Vereina GR Eisenbahn/Rail 2100 17 1608 Dazu sind Prognoseberech- Total [kW] 29 927 nungen notwendig. Für die 1 bestehende geothermische Nutzungsanlagen/existing geothermal utilisation facilities Prognose werden numerische 2 L eistung berechnet am Tunnelportal, ohne Wärmepumpe, bei einer Abkühlung auf 6 °C Simulationsmodelle (fi nite Ele- Capacity calculated at the tunnel portal without heat pump, given cooling down to 6° C mente, dreidimensional, insta- Only a small amount of this geothermal potential is utilized, table 6 lists realized tionär) eingesetzt; dabei sind projectswerden. Hierüberwith their bestehen yearly heatd uoutput.ced in th e course of time and ture in °C. T is the water temper- insbesondere die hydrauli- Gewässerschutz-Vorschriften attains constant values (state of ature and T0 the reference tem- schen und thermischen Rand- und -Grenzwerte: So darf z. B. stability). perature (usually 10° C). bedingungen wesentlich. Eine ein Fluss – beim niedrigsten As a consequence, in the solche Prognose wurde u. a. Wasserstand – nicht mehr als case of a tunnel project it is usu- für das Koralm-Projekt in um 1,5 °C (=!Treg) erwärmt Thermal Capacity ally established during the plan- Österreich durchgeführt [3]. werden. Die maximale, noch The thermal capacity and ning phase which thermal ca-

Das Temperaturniveau der einleitbare Schüttung Qmax lässt the exit temperature at the por- pacities and out ow tempera- Tunnelwasserausfl üsse ist meist sich wie folgt berechnen: tal are determining for the ex- tures are to be expected. Ana- zu niedrig für eine direkte ploitation of the tunnel water in lytical calculations are required

Nutzung (z. B. mittels eines Qmax = energy terms. Th55e t hermal ca- for this purpose. Numerical sim-

Fernwärmenetzes); in den !Treg x Qrmin/(Tp – Trmin – !Treg). pacity P (e.g. in Megawatt ther- ulation models ( nite elements, meisten Fällen kommen Wär- mal; MW) is worked out in ac- three-dimensional, non-station- mepumpen zum Einsatz. Qmax ist die noch zulässige cordance with ary) are employed for the prog- Einleitschüttung, Q die Mi- nosis; in this connection the hy- rmin P = c x Q x T Umweltaspekte nimalschüttung des nächstlie- draulic and thermal general

Werden die ausfl ießenden genden Flusses, Trmin dessen With c representing the ther- conditions are especially essen-

Tunnelwässer energetisch minimale Temperatur und Tp mal capacity of water, Q the out- tial. Such a prognosis was for in- nicht genutzt, müssen sie in die Temperatur des Tunnel- ow delivery (l/s) and T (= T – T0) stance undertaken for the Oberfl ächenwässer eingeleitet wassers am Portal. the useful decrease in tempera- Koralm Project in Austria [3]. Einige Zahlen Jede der Anlagen ist einzigartig. Sie sind entsprechend der vor- handenen geothermischen Ener gie und des Wärmebedarfs, aber In der Schweiz stehen heute sechs Anlagen in Betrieb, mit wel- auch im Bezug auf die Umwelt, geplant und rea lisiert worden. chen Tunnelwärme genutzt wird. Sie befinden sich an den Aus- Die kleinen Anlagen ermöglichen es, einzelne Gebäude zu be- gängen des Gott hard strassen-, des Furka-, des Mappo-Moret ti- heizen, während mit grösseren Anla gen hunderte von Haushal- na-, des Hauenstein-, des Ricken- und zuletzt des Grossen St. ten mit Energie beliefert werden können. Bernhardtunnels. Bei letztgenanntem wird nicht das Draina ge- Die bestehenden Anlagen nutzen meist nur einen Bruchteil des wasser, sondern die Abluft des Stollens genutzt. Meist erfolgt geo thermischen Potenzials, das an den Tunnelportalen zur Verfü- eine Erhöhung des Temperaturniveaus auf der Verbraucherseite gung steht. Zur De ckung eines steigenden Energiebedarfs besteht mittels Wär me pumpe. hier noch ein grosses Ausbau poten zial.

Übersicht zu geothermischen Anlagen an Tunnelportalen der Schweiz Tsowieab. 6 :zu Overview den neuen of Alptransit-Basistunnels operating and planned geothermal plants for tunnel water utilization in Switzerland (Source: SVG, n.d.)

Tunnel Typ Kt. Max. Ausfluss Wassertem- Nutzung der Geothermie Wärmeleistung am Tunnelportal peratur am (MWh/Jahr) (l/sek.) Portal (°C) Furka Eisenbahn VS 90 16 177 Wohnungen, Sporthalle 1700 Gotthard Strasse (A2) TI 110 15 Wärmen und Kühlen des Autobahnwerkhofs 860 (Winter) 1440 (Sommer) Hauenstein Eisenbahn SO 42 19 150 Wohnungen 2100 Mappo-Morettina Strasse TI 16 16 Sport- und Erholungszentrum 180 Ricken Eisenbahn SG 12 12 Mehrzweckhalle von Kaltbrunn 249 Grand-St-Bernard Strasse VS – – 8 (Luft) Bürogebäude der Wartungszentrale 167

Projekte im Bau oder in Untersuchung an den Ausgängen der Alptransit-Basistunnel Lötschberg Eisenbahn BE Nord: 150–200 18–22 Tropenhaus, Störzucht, Wärmenetz in Frutigen (im Bau) projektierte Leistung: VS Süd: 80–200 15–17 3–5 MWth Gotthard Eisenbahn UR Nord: 60–110 19–25 Gewächshäuser, Fischzucht, Thermalzentrum, Wärmenetz – – TI Süd: 80–440 30–35

Switzerland, Gotthard Highway Tunnel The installation for theFörderstelle utilization Geothermie of tunnel water heat atWeitere the Gotthard Information highway tunnel is the oldest one andZentral- in operation und Nord-Schweiz since 1979. The outflowDachorganisation rate at Geothermiethe south portal is Dr. Mark Eberhard www.geothermie.ch 110 l/s with a temperatureEberhard &of Partner 17° AGC. A heat pump supplies a highway service center Schachenallee 29 Fördergemeinschaft Wärmepumpen with 1.9 MW heatingCH power,-5000 Aarau cooling the water down bySchweiz 2.3° (FWS) C. The energy output of T 062 823 27 07 www.fws.ch the system is 860 MWhF 062 823for 27 heating06 (winter) and 1,440 MWh for cooling (summer). By modernization [email protected] increasing the cooling of the tunnel water the system could provide an additionalOst-Schweiz 4 MW (SVG, n.d.). Dr. Roland Wyss GmbH Zürcherstrasse 105 Switzerland, Furka CHRailway-8500 Frauenfeld Tunnel Impressum T 052 721 79 00 8/08 The tunnel water heatF 052 utilization 721 79 01 system at the Furka railwayHerausgeber: tunnel GEOTHERMIE.CH, is an example Frauenfeld of [email protected] Redaktion: CREGE, Neuchâtel a cold district heating system with decentralized heat pumps. The water with a outflow rate of 90 l/s with 16°C is piped to the single houses of the nearby village of Oberwald, where individual heat pumps lift the temperature for heating purposes and cool down the tunnel water. The installed heat capacity of the system is 960

Schweizerischen Vereinigung für Geothermie SVG kW, 177 apartmentsSociété and Suisse pour a la Géothermie sports SSG hall are supplied with 1.700 MWh/year. The Swiss Geothermal Society SGS system has been in operation since 1991 (SVG, n.d.).

Switzerland, Ricken Railway Tunnel The multipurpose building, gymnastic hall, civil shelter center, and kindergarten of Kaltbrunn/Switzerland at the south portal of the Ricken railway tunnel have been heated by tunnel water using a heat pump since 1998. The outflow rate of the tunnel

56 water is 12 l/s with a temperature of 12° C. The heating capacity of the system is 156 kW, the yearly supplied heat energy is 249 MWh (SVG, n.d.).

Switzerland, Mappo-Morettina Highway Tunnel The outflow rate of tunnel water at the northern portal of the Mappo-Morettina highway tunnel is 16 l/s with a temperature of 16°C. The sport and recreation center right at the tunnel portal are heated by the tunnel water since 1999. The yearly supplied heat energy is around 180 MWh, the seasonal performance coefficient of the system during the heating season 2000/2001, including the heat pump, was SPC=4.0 (Rybach et al., 2003).

Switzerland, Hauenstein Railway Tunnel Since 1999 150 apartments of Trimbach/Switzerland have been heated and supplied with domestic hot water by the tunnel water of the Hauenstein railway tunnel. The outflow rate at the south portal is 42 l/s with a temperature of 19° C. The heating system has a capacity of 1.0 MW and consists of a heat pump for the tunnel water and two oil burners for peak load times. The yearly produced heat energy is 2,100 MWh, the seasonal performance coefficient of the overall system is 4.0 (Rybach et al., 2003).

The presented tunnels above and their heat utilization systems have been in operation over several years. The operating experiences with these installations are satisfactory to good. They demonstrate the technical feasibility of the tunnel water heat exploitation; only minor technical improvements became necessary. The almost constant outflow rate and temperature of the tunnel water over the years confirms that the geothermal heat of tunnel water represents a reliable and sustainable energy source (Rybach et al., 2003).

3.7.2 Tunnel Water Heat Utilization Projects at Lötschberg and Gotthard Railway Base Tunnel

More actual and innovative concepts are the tunnel water heat utilization systems and projects of the alpine railway base tunnels Lötschberg and Gotthard. The geothermal potential of both (Lötschberg tunnel with a length of 35 km and a max. rock overburden of 2.0 km; Gotthard tunnel with 57 km and rock overburden up to

57 2.4 km) is considerable (see table 7). For both tunnels heat exploitation projects near the tunnel portals have been set up. The Lötschberg base tunnel has been in operation since 2007 and thermal exploitation systems have already been realized. The Gotthard base tunnel is still in construction, the heat utilization concepts in planning phase. Since the Brenner Base Tunnel with his length and his rock overburden can be compared with the two Suisse alpine base railway tunnels of Lötschberg and especially Gotthard, the tunnel water heat utilization projects of both tunnels are examined in more detail.

Lötschberg Base Railway Tunnel The Lötschberg Base Railway Tunnel is a 34.57 km long railway tunnel crossing the Bernese Alps. It is an important part of the NEAT (Neue Eisenbahn- Alpentransversale) railway project, which is tasked with improving the railway transit traffic in the north-south direction and with shifting traffic from road to rail. The tunnel runs between Frutigen, Berne (north portal) and Raron, Valais (south portal). In the end stage it will consist of two tubes, one for each direction. For financial motives the whole project is divided in three realization phases. In December 2007 phase one of the project (i.e. the complete east tube and 75% of the west tube) have been finished and the tunnel started operating. As mentioned already, because of the length of the tunnel and the high rock overburden, the expected tunnel water outflow and its temperature is considerable. After the first construction phase the tunnel water outflow rates are 150 liters per second with 18° to 22° C at the north portal, and 80 to 181 l/s with 20° to 25 C° at the south portal. Cooling down the water by 10° C the heat potential at the north portal corresponds to 6 MW, the one at the south portal 3.3 MW to 7.6 MW (Koedel, 2007).

Gotthard Base Railway Tunnel Also the 57 km long Gotthard Base Railway Tunnel is part of the NEAT project. It is still in construction and will start operation in 2016. The tunnel, consisting of one tube for each direction, connects Erstfeld, Uri in the north with Bodio, Ticino in the south. The tunnel is characterized by high rock overburdens up to 2.4 km and elevated tunnel water temperatures. The expected temperature of the tunnel water at the north portal is 30° C to 34° C with a flow rate of 60 to 555 liters per second, the one

58 at the south portal is 30° to 35° C with 80 to 460 l/s. The heat potential of the tunnel water is 2.7 MW to 23 MW in the north and 3.3 MW to 19 MW in the south, by cooling it down for 10° C (Koedel, 2007).

Utilization of the Tunnel Water Heat at Lötschberg and Gotthard Base Tunnel For both base tunnels, feasibility studies were made to determine existing heat demand of villages at the tunnel portals, to analyze how to integrate the tunnel water heat in existing heating systems and last but not least, to identify new, innovative utilization possibilities. The criteria of the studies in determining the tunnel water heat utilization possibilities are as follows (Koedel, 2007): • The route of the tunnel water pipe after the tunnel portal • Direct utilization possibilities (greenhouses, aquacultures, water parks, street heating) • Indirect utilization possibilities with heat pump (bivalent operation, redundancy, temperature of heat source, conventional/low temperature heating, temperature lift and energy efficiency) • Existing heat supply and district heat stations • Alternative heat sources in the planning area (e.g. waste heat) • Development structure and heat density • Grouping of public buildings • New building and area planning

The results of the studies for the heat utilization possibilities are summarized in table 7.

With detailed heat inquiries and derived calculations of profitability, potential areas and so called local heat islands (Wärmeinseln - district heating networks) for space heating by tunnel water heat had been defined. The number of heat islands ranges from 3 at the north portal of the Lötschberg Tunnel with a yearly heat demand of 8,100 MWh, up to 7 at the north portal of the Gotthard Tunnel with a calculated heat demand of 23,700 MWh/year (Koedel, 2008).

59 !"#$%&'()*+)(,-.)/-0)(('1#.//'% -----2%3*'%3'(-45%-6$%&'7'%/8%,)(,-.)/-0)(('1#.//'%

 !"#$%&'()&**"$+%,,"#-."/0&*1(%2(34#0%$  5/#"60*&07&*1(891$/:;< Tab. 7: Tunnel!"#$%&'()&*+,-.%/012)2*3),-453*63$73#,-87#*))%'2%(93':; water heat estimations, potentials and its utilization possibilities of Lötschberg and Gotthard Base Tunnel (Source: Koedel, 2007)  =&07&*1(/*(>?#8"@&8@"*%*$%1" LÖTSCHBERG BASE !<(=*$%'7%-43)$%:3':,->%+3'+*'9,-?%@A%#*73#-B0#@%53%$$%,-C%3DE4$7&*3,GOTTHARD BASE TUNNEL TUNNEL ?%@A%#*73#23&-3'+-C3793':):#*+; North Portal South Portal North Portal South Portal  A",0";"*B"(>?#8"C"#,4#1&*1"*(&*B(D"/77"*0#%$"*Frutigen Raron Erstfeld Bodio

 >"/0"#"(>?#8"E&"$$"*(/*(3$%*&*1,74*"<(F7GAG(H2+?#8"I Tunnel Water Temperature 19 - 20°C 20 - 25°C 30 - 34°C 30 - 35°C  A"2%&&*1,,0#&60&#(J(>?#8"B/:;0" Tunnel WaterK#&@@/"#&*1(9''"*0$/:;"#(K"2?&B" Outflow Rate 150 l/s 80 - 181 l/s 60 - 555 l/s 80 - 460 l/s Heat Potential with  ="&2%&@#4L"60"(&*B(M4*"*@$%*&*12.7 - 23 MW 3.3 - 19 MW 6 MW 3.3 - 7.6 MW ΔT=10°C

Number of Local Heat Islands (District Heating 3 3 - 4 7 5 - 6 Networks) Aquaculture, Tropic House, Mushroom Low Temperature Projects Greenhouses Flower Center, Aquaculture Breeding Greenhouses

Heat Demand District 8,100 MWh/a 10,400 MWh/a 23,700 MWh/a 11,180 MWh/a Heating 4.1 MW 5.4 MW 12.1 MW 8.1 MW

Apart. Equivalents(à 5 KW) 1,000 apart. 1,350 apart. 2,900 apart. 1,970 apart.

!"#$%&'()*+)(,-.)/-0)(('1#.//'% The principle of the tunnel water utilization for heating purposes and the local heat 9%3(+3:/;<'&.-6$%&'()*+)(,-45%-='3++#';>' islands of Lötschberg and Gotthard Base Tunnel is shown in figure 35.

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Fig. 35: The principle of the tunnel water utilization for heating purposes of Lötschberg and Gotthard Base Tunnel (Source: Dups, 2004)

60

4 Apart from the direct heating applications for greenhouses, aquaculture etc. (direkte Nutzung), single houses and district heating networks with heat pumps will make use of the tunnel water heat (Wärmequelle/Heat Source). The district heat stations, in addition to the heat pumps, are equipped with thermal storage systems and fossil fuel boilers. The boilers are needed to reach temperatures above 70° C for conventional heating systems, to cover heat peak loads and to guarantee supply during failures in the geothermal heat system. The utilization of the tunnel water heat by heat pumps lowers its temperature by 10° to 15° C, permitting it to be piped afterwards into flowing waters (Fliessgewässer). The supply temperature of the heat station delivered to the distribution network (Wärmeverteilung) is 80° to 85° C in the winter, lowered to 70° C in the summer to avoid losses. In designing the distribution networks, existing large heating boiler plants have to be taken into account and possibly integrated in the system. According to the feasibility studies, in some cases also the realization of cold district heating should be taken into account (Dups, 2004).

Economics calculations of the Lötschberg and Gotthard Tunnel water heat utilization defined heat generation costs of 8.6 to 13.6 Rp/kWh. The heat generation costs are highly sensitive to the electricity price for the electricity consumed by the heat pumps and the number of consumers, i.e. the amount of heat consumed.

Usually the level of the tunnel water’s temperature is equal for all heat users in the heating network (parallel utilization). When temperature level requirements are different, a serial utilization of the tunnel water heat should be taken into consideration. The serial utilization of heat for different applications with decreasing heat level requirements is called the cascade use of heat.

The Cascade Use of Heat – Tropic House Frutigen An innovative realized project for the utilization of the tunnel water heat and at the same time an example for a cascade use of heat is the Tropic House Frutigen at the north portal of the Lötschberg Base Tunnel. The Tropic House Frutigen makes use of the Lötschberg tunnel water heat to cultivate tropical fruits in greenhouses and to breed sturgeon and produce caviar in aquacultures. The house is open to the public and contains a restaurant and a museum. Figure 36 shows the cascade use of the tunnel water heat in the winter. A heat pump extracts heat from the tunnel water and lifts the temperature level to the

61 !"#$%&'()*+)(,-.)/-0)(('1#.//'% ------230456%7-5)*+)(,/86(+'9*-:%)*;,'(

7.%812'/&3)0$ 95$(+$/$#:; !"##$%&'(($)%$*+"#, $%&'(&)*&+ #+,-./0'&1 -$.+/$)0*$12'/&3)0$

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requirements of the greenhouse with a tropical climate, where tropical plants are cultivated and Tilapia fish is breed. Afterwards the cooled tunnel water is used for the breeding of Sturgeons and Rainbow Trout in outdoor basins with water temperatures!"#$%&'()*+)(,-.)/-0)(('1#.//'% typical for a Mediterranean/moderate climate (12° C to 15° C). Finally the tunnel water cools down in an equalizing reservoir, from where it is piped into the Kander river.230456%7-<%6='8*-0%69'(>.)/-:%)*;,'(

Fig. 36: Cascade use of tunnel water heat at Tropic House Frutigen (Source: Koedel, 2007;  Erich+Berger AG and Seecon GmbH)

Other Projects The huge heat potential of the tunnel water at the base tunnels’ portals and the success of the Tropical House Frutigen, led to the planning of similar and thermal bath projects. In Bodio at the south portal of the Gotthard Base Tunnel for example it is planned to create a thermal bath centre. The yearly heat demand is calculated to be around 1,230 MWh which will be supplied as follows: tunnel water direct heating (11%), 6 indirect tunnel water heating with heat pump (56%), recovery from ventilation (22%), recovery from water (6%), auxiliary heating (5%) (Pahud et al., 2004).

62 Another planned innovative project of tunnel water heat utilization in Erstfeld at the Gotthard north portal is “Basis 57 nachhaltige Wassernutzung” (see www.basis57.ch). The goals of basis 57 are to exploit the heat by cascade use for biological fish breeding and the production of biomass.

Conclusion The studies on the Lötschberg and Gotthard Base Tunnel show, that the utilization of the tunnel water heat is feasible and economical. Also from an ecological point of view it makes sense to exploit the heat, because tons of fossil fuels can be substituted, CO2 emissions reduced. The studies illustrate, moreover, that by supplying the heat demand around the tunnel portals, only a small part of the geothermal potential of the tunnel waters will be utilized.

63 4. GEOTHERMAL HEAT POTENTIAL OF THE BBT’S TUNNEL WATER AT THE SOUTH PORTAL AND ITS UTILIZATION POSSIBILITIES

4.1 Analysis of the Geothermal Energy Potential of BBT’s Tunnel Water

4.1.1 Conceptual Hydrogeological Model of the BBT Project

The hydrogeological conceptual model of the BBT project consists of the following elements (Perello et al., 2007): • Permeability characterization and distribution • Flow system characterization • Infiltration and recharge analysis

Fig. 37: Flow diagram illustrating the conceptual process for hydrogeological interpretation of the BBT project (Source: Perello et al., 2007)

Permeability Characterization Aquifer zones with two different types of permeability, the fracture-induced permeability and the chemical dissolution-enhanced permeability (also called karstic permeability), are expected to cause water inflows in the BBT project. Both types of permeability can superimpose and coexist, but since all rocks crossed by the BBT are cohesive metamorphic ones, they are characterized by fracture-induced

64 permeability. Fracture-induced permeability occurs in brittle fault zones and where fractured blocks are separated by brittle fault zones. Permeability will vary according to the different tectonic evolution of geological units. Karstic permeability will only in some cases superimpose the fracture induced one. It occurs in rocks, which consists of water-soluble minerals like carbonates and evaporitic minerals (Perello et al., 2007). Information about permeability is obtained by designing a reference geological model, by core log analysis and borehole testing. The reference geological model is a 3D picture of an area that will be crossed by the planned tunnel and includes the data provided by core log analysis. It represents the rock bodies with different mineralogical properties, different fracturing and faulting intensity and is indispensable for hydrogeological characterization. The core log analysis for hydrogeology concentrates on specific aspects, as evidence of fracture corrosion, presence of brecciation phenomena induced by rock mass dissolution, etc., which gives a picture of the water circulation. More than 40 boreholes with a length up to 1350m give a detailed picture of rock permeability along the tunnel route. To obtain more information about permeability, in almost all drillholes borehole permeability tests at different depth have been made. Because of different problems, like the short duration of pressure impulse, the limited rock volume tested, faults and chemical dissolution zones etc., the validity of the test results was limited and had to be evaluated by a careful process of further analysis. Data obtained by the reference geological model, the core log analysis and borehole testings lead to a classification of the rock mass to be excavated by the BBT project in different hydrogeological complexes with homogeneous hydrogeological behavior, i.e. rock mass units with a single permeability type and a relatively narrow permeability range (Perello et al., 2007).

Flow System Characterization A flow system is defined as the ground water circulation between different hydrogeological complexes and rock types. Tunnels crossing the flow systems, because of the drainage effect, can substantially influence and modify flow paths. The flow system characterization in the BBT project was made due to hydrogeochemical analysis, borehole logging and the analysis of monitoring data. The hydrogeochemical analysis is represented by the monitoring of almost 700 outflows along the BBT route over 3 to 5 years for their ion composition and the chemical analysis of borehole water samples, which gave a picture of the water

65 circulation underground and at the tunnel depth. Another important part for the flow system characterization in depth was the borehole logging, since indications about the water flow can be obtained by measuring electrical conductivity and temperatures in the borehole. Monitoring the data of hydrogeochemical analysis, borehole logging, springs outflow rates, rainfall data and comparing all this time series, led to the design of a detailed and dynamic ground water flow system in the area of the BBT route (Perello et al., 2007).

Infiltration and Recharge Analysis The long term and steady state tunnel inflows are strongly influenced by the recharge area width. Infiltration and surface runoff of the BBT project have been evaluated by a geographic information system (GIS).

4.1.2 Forecast of BBT’s Tunnel Water Flow Rates and Temperatures

The BBT project consists of multiple tubes (main tunnels, exploratory tunnel, access tunnels, multifunction tunnels); therefore, water inflow forecasts are quite complex and linked to uncertainties. Nevertheless the attempt has been made to give a picture about water inflows over the whole construction period. The first step was to evaluate the transient state inflow (during construction period) and the steady state inflow of the exploratory tunnel. In a second step transient and steady inflows of the two main tunnels have been estimated (Perello et al., 2007).

Transient State Inflow For estimating the transient state inflow of the first tunnel to be excavated the following analytical formula has been used:

2!Kld Q = z " 2L% ln $ r ' # 0 & ! Q (m3/s) = amount of water inflow K (m/s) = hydraulic conductivity l (m) = length of aquifer crossed by tunnel r0 (m) = tunnel radius

66 dZ (m) = distance between tunnel and water table surface L (m) = correction factor related to the possible inclined geometry of the aquifer

The inflow is usually, as for the BBT Project, calculated over 10 meters of tunnel.

Steady State Inflow The heterogeneous complex geological conditions with folding and faulting make it impossible to forecast with certain accurateness the amount of water table decline due to tunnel drainage and the resulting steady inflow. Using analytical model calculations will lead to unrealistic results. Steady state inflow estimations for the BBT are therefore “based on a water ingress back-analysis in already excavated tunnels with analogue or comparable topographical and geological conditions” (Perello et al., 2007).

Temperature and Flow Rate Predictions The steady state inflows and its temperatures in the different tunnels and sections are represented in table 8. The overall steady tunnel water inflow at the south portal at Aicha will be 745 liters per second with temperatures between 22° C and 26 °C.

Tab. 8: Forcasted discharge rates and temperatures of the BBT’s tunnel water at the south portal in Aicha

Stabilized Tunnel Water Temperature (°C) Tunnelsection Lenght (m) Discharge Rate (l/s) min max

Service Tunnel Aicha between Portal and the Junction with the 5,400 105 18 22 Exploratory Gallery

Access Gallery Mauls 1,850 10 17 22 Base Tunnel (two tubes) and Exploratory Gallery (between 22,840 630 23 27 National Border and Junction with Service Tunnel Aicha)

Temperature of the stabilized Total Tunnel Water Discharge 745 22 26 at the Portal of Aicha

The limitations of tunnel water outflow rate and temperature predictions are described in chapter 3.3.3.

67 4.1.3 Geothermal Potential of the BBT’s Tunnel Water

As defined in chapter 3.3.2, the heat potential of water is P = c ρ Q T with cw tw w w tw tw thermal capacity of water = 4,183 J/kgK at 20°C and ρw mass density of water ≈ 1,000kg/m3. The thermal potential of the tunnel water of the Brenner Base Tunnel at different outflow and temperature conditions is presented in the following table in terms of kW. With an expected stabilized flow rate of 745 liters per second and a temperature of 22° C to 26° C, the geothermal potential is between 68 MW and 81 MW.

Tab. 9: The thermal potential in kW of the tunnel water of Brenner Base Tunnel depending on outflow rate and temperature

Outflow Rate of Tunnel Water in liters/ second at Brenner Base Tunnel 400 500 600 700 800 900 1000 Temperature in °C 15 25,098 31,373 37,647 43,922 50,196 56,471 62,745 16 26,771 33,464 40,157 46,850 53,542 60,235 66,928 17 28,444 35,556 42,667 49,778 56,889 64,000 71,111 18 30,118 37,647 45,176 52,706 60,235 67,765 75,294 19 31,791 39,739 47,686 55,634 63,582 71,529 79,477 20 33,464 41,830 50,196 58,562 66,928 75,294 83,660 21 35,137 43,922 52,706 61,490 70,274 79,059 87,843 22 36,810 46,013 55,216 64,418 73,621 82,823 92,026 23 38,484 48,105 57,725 67,346 76,967 86,588 96,209 24 40,157 50,196 60,235 70,274 80,314 90,353 100,392 25 41,830 52,288 62,745 73,203 83,660 94,118 104,575 26 43,503 54,379 65,255 76,131 87,006 97,882 108,758 27 45,176 56,471 67,765 79,059 90,353 101,647 112,941 28 46,850 58,562 70,274 81,987 93,699 105,412 117,124 29 48,523 60,654 72,784 84,915 97,046 109,176 121,307 30 50,196 62,745 75,294 87,843 100,392 112,941 125,490

To calculate the usable thermal potential, the maximal discharge amount in surface waters for a given temperature, the maximal discharge temperature for a given outflow rate of the Brenner Base Tunnel and temperatures and flow rates of the Eisack River, passing at the south portal, have been taken into account.

4.1.3.1 Flow Rates and Temperatures of Eisack River

The flow rate of the Eisack River can be derived by the size of its drainage area and the discharge intensity. The drainage area of the Eisack River at the BBT south portal is around 680 km2, discharge intensity varies with a minimum of 9.24 l/s/km2

68 in February to reach its maximum in June with 65.07 l/s/km2. The flow rate of the Eisack at the tunnel water discharge point is mainly determined by the reservoir of Franzensfeste located 500 meters before, where a considerable amount of the water is drained for electricity production. Considering the mandatory residual water of 1,360 l/s and the maximal water drain of 19,100 l/s for the reservoir of Franzensfeste, flow rates of the Eisack River at the tunnel water discharge point in Aicha are as presented in table 10. For the Eisack water’s temperature determination, measurements are made since 2003. The Eisack’s temperatures listed in table 10 are the averages of these measurements.

Tab. 10: Temperatures and flow rates of the Eisack River and the influence of tunnel water discharge without cooling Temperature of Eisack Temperatur change (ΔT) of Flow Ø Temp. River after discharge of Eisack River after Rate of of Eisack BBT tunnel water without discharge of BBT tunnel Eisack River in cooling in °C water without cooling in °C River °C in lt/s 800 lt/s 500 lt/s 500 lt/s 800 lt/s 500 lt/s 500 lt/s at 25°C at 25°C at 22°C at 25°C at 25°C at 22°C January 1.9 1,360 10.5 8.1 7.3 + 8.5 + 6.2 + 5.4 February 3.0 1,360 11.2 8.9 8.1 + 8.1 + 5.9 + 5.1 March 5.4 1,360 12.7 10.7 9.9 + 7.2 + 5.3 + 4.5 April 7.2 1,360 13.8 12.0 11.2 + 6.6 + 4.8 + 4.0 May 8.4 15,908 9.2 8.9 8.9 + 0.8 + 0.5 + 0.4 June 9.2 25,149 9.7 9.5 9.5 + 0.5 + 0.3 + 0.2 July 10.5 16,346 11.2 10.9 10.8 + 0.7 + 0.4 + 0.3 August 11.0 8,526 12.2 11.7 11.6 + 1.2 + 0.8 + 0.6 September 10.0 2,589 13.5 12.4 11.9 + 3.5 + 2.4 + 1.9 October 7.3 1,360 13.8 12.0 11.2 + 6.6 + 4.8 + 4.0 November 4.4 1,360 12.0 9.9 9.1 + 7.6 + 5.5 + 4.7 December 2.4 1,360 10.8 8.5 7.7 + 8.4 + 6.1 + 5.3

4.1.3.2 Tunnel Water Discharge Conditions/ Environmental Regulations

Since the construction of the Brenner Base Tunnel is affiliated with environmental impacts, a detailed environmental impact assessment (EIA; in german Umweltverträglichkeitsprüfung UVP) was made during the planning phase. To prevent negative environmental impacts, regulations and restrictions have been derived from this assessment. As tunnel water at elevated temperatures can substantially influence the flora and fauna of surface waters, the EIA of the Brenner Base Tunnel refers to the discharge restriction described by South Tyrolean provincial water law of 18. Juni 2002, Nr. 8, which in annex D says as follows:

69

“Bei Oberflächengewässern darf die maximale Differenz der Temperaturmittelwerte beliebiger Flussabschnitte vor und nach der Einleitestelle höchstens 3 °C betragen. An mindestens der Hälfte aller beliebigen Querschnitte darf die Differenz stromabwärts nicht mehr als 1 °C betragen. Bei künstlichen Kanälen darf der Temperaturmittelwert eines beliebigen Querschnittes stromabwärts der Einleitestelle höchstens 35 °C betragen, wobei diese Bedingung der Zustimmung der für den Kanal zuständigen Behörde untergeordnet ist. Per i corsi d’acqua la variazione massima tra le temperature medie di qualsiasi sezione del corso d’acqua a monte e a valle del punto di immissione dello scarico non deve superare i 3°C. Su almeno metà di qualsiasi sezione a valle tale variazione non deve superare 1°C. Per i canali artificiali, il massimo valore medio della temperatura dell’acqua di qualsiasi sezione del canale a valle del punto d’immissione dello scarico non deve superare i 35°C; la condizione suddetta è subordinata all’assenso del soggetto che gestisce il canale.”

As stated in the regulation the maximal temperature difference before and after the tunnel water discharge into the Eisack River should not be higher than 3° C. Since the temperature difference on more than half of random river cross section after the discharge point should not exceed 1° C, it can be assumed, that the overall tunnel water discharge should influence the Eisack River’s temperature by a maximum of +/- 1° C. Given that the tunnel water predictions are of a partial uncertainty, calculations of the geothermal potential etc. have been made for three different scenarios with different flow rates and temperatures: 800 liters/ second with 25° C, 500 liters/ second with 25° C and 500 liters/ second with 22° C. As table 10 shows, discharging the Brenner Base tunnel water into the Eisack River at the south portal in Aicha without cooling, significantly influences the temperature of the river in all 3 scenarios. Especially from September to April, when river temperatures and flow rates are low, temperature changes exceed limits prescribed by regulations. To fulfill the discharge regulations, either the discharge amount has to be lowered by discharging the tunnel water in alternative surface waters, or the temperature of the tunnel water has to be lowered by cooling it.

70 Considering the maximal allowed temperature change of the river water (+1° C), the maximal discharge amount of BBT tunnel water with given temperatures (25° C and 22° C) into the Eisack River is calculated by the methods described in chapter 3.3.2. In addition the maximal discharge temperature for the given flow rates (800 and 500 l/s) is calculated. The following table summarizes the results:

Tab. 11: Maximal dischargeable tunnel water amount and maximal discharge temperature of tunnel water into Eisack River Maximal dischargeable tunnel water Maximal discharge temperature of amount in l/s with x °C, so that Δ tunnel water in °C with x l/s, so that Δ temperature Eisack ≤ +1°C temperature Eisack ≤ +1°C 25°C 22°C 800 l/s 500 l/s January 62 71 4.6 5.7 February 65 76 5.7 6.8 March 73 87 8.1 9.2 April 81 99 9.9 10.9 May 1,022 1,266 29.3 41.3 June 1,701 2,134 41.7 60.5 July 1,208 1,553 31.9 44.2 August 654 849 22.6 29.0 September 185 235 14.2 16.2 October 81 99 10.0 11.0 November 69 82 7.1 8.1 December 63 73 5.1 6.1

To fulfill the discharge regulations of a maximal temperature change of +1° C after tunnel water discharge, regarding the different scenarios the following cooling power is required:

Tab. 12: Required cooling power for discharging the tunnel water into Eisack River at Aicha Required cooling power in kW, so that Δ temperature Eisack ≤ +1°C 800 l/s with 25°C 500 l/s with 25°C 500 l/s with 22°C January 68,215 40,499 34,219 February 64,529 38,195 31,915 March 56,464 33,154 26,874 April 50,554 29,461 23,180 May cooling not required cooling not required cooling not required June cooling not required cooling not required cooling not required July cooling not required cooling not required cooling not required August 7,985 cooling not required cooling not required September 36,065 18,476 12,195 October 50,325 29,318 23,037 November 60,094 35,424 29,143 December 66,626 39,506 33,225

71 4.1.3.3 The Usable Geothermal Energy

The necessary cooling power of the BBT tunnel water, can be seen as usable geothermal energy. But since the allowed Eisack River temperature change is also minus 1° C, with an increased cooling e.g. increased heat extraction out of the tunnel water the usable thermal power is even higher.

Tab. 13: Usable thermal potential of the BBT tunnel water at the south portal for different scenarios with maximal possible and minimal required cooling

SCENARIO 1: Tunnel Water Flow Rate: 800 l/s - Tunnel Water Temperature: 25°C Usable Thermal Potential of the Tunnel Cooling Amount of Tunnel Water with: Water in kW with: Δ°C Δ°C, so that Δ°C Δ°C Δ°C, so that Δ°C max.* T(T) = T(F) min.** max.* T(T) = T(F) min.** January 24.0 23.1 20.4 80,390 77,259 68,215 February 24.0 22.0 19.3 80,390 73,573 64,529 March 22.3 19.6 16.9 74,551 65,508 56,464 April 20.5 17.8 15.1 68,642 59,598 50,554 May 24.0 16.6 80,390 55,475 June 24.0 15.8 no cooling 80,390 52,874 no cooling July 24.0 14.5 80,390 48,660 August 24.0 14.0 2.4 80,387 47,033 7,985 September 19.2 15.0 10.8 64,445 50,255 36,065 October 20.4 17.7 15.0 68,413 59,369 50,325 November 23.3 20.6 17.9 78,182 69,138 60,094 December 24.0 22.6 19.9 80,390 75,670 66,626 SCENARIO 2: Tunnel Water Flow Rate: 500 l/s - Tunnel Water Temperature: 25°C January 24.0 23.1 19.3 50,244 48,287 40,499 February 24.0 22.0 18.2 50,244 45,983 38,195 March 23.3 19.6 15.8 48,730 40,942 33,154 April 21.5 17.8 14.1 45,036 37,249 29,461 May 24.0 16.6 50,244 34,672 June 24.0 15.8 no 50,244 33,046 no cooling July 24.0 14.5 cooling 50,244 30,413 August 24.0 14.0 50,244 29,396 September 21.2 15.0 8.8 44,343 31,409 18,476 October 21.4 17.7 14.0 44,893 37,105 29,318 November 24.0 20.6 16.9 50,244 43,211 35,424 December 24.0 22.6 18.9 50,244 47,294 39,506 SCENARIO 3: Tunnel Water Flow Rate: 500 l/s - Tunnel Water Temperature: 22°C January 21.0 20.1 16.3 43,964 42,007 34,219 February 21.0 19.0 15.2 43,964 39,703 31,915 March 20.3 16.6 12.8 42,450 34,662 26,874 April 18.5 14.8 11.1 38,756 30,968 23,180 May 21.0 13.6 43,964 28,391 June 21.0 12.8 43,964 26,766 no cooling no cooling July 21.0 11.5 43,964 24,132 August 21.0 11.0 43,964 23,115 September 18.2 12.0 5.8 38,063 25,129 12,195 October 18.4 14.7 11.0 38,613 30,825 23,037 November 21.0 17.6 13.9 43,964 36,931 29,143 December 21.0 19.6 15.9 43,964 41,013 33,225 T(T) = Temperature of Tunnel Water T(F)= Temperature of Eisack River Δ°C = T(T) before cooling - T(T) after cooling * maximal possible cooling, T(F) after Tunnel Water Discharge = T(F) before Tunnel Water Discharge - 1°C ** minimal, required cooling, T(F) after Tunnel Water Discharge = T(F) before Tunnel Water Discharge + 1°C

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The table above shows the usable thermal power of the tunnel water in kW, regarding the cooling amount in the different tunnel water scenarios. As we can see from the table, also during summer months, when no cooling of the tunnel water is necessary to accomplish the environmental restrictions, heat can be extracted. The highest usable potential that can be reached is 80 MW in winter months of scenario 1. But still in scenario 3 with the lowest tunnel water flow rate and temperature, the usable heat potential of the tunnel water sums up to 44 MW for almost the whole year, cooling the tunnel water as much as possible.

Tunnel Water Discharge in the Reservoir of Franzensfeste As the calculations show, the tunnel water has to be cooled down by a huge quantity, especially in the winter months. Thus, discharging the water directly into the Eisack River leads to high investments for the construction of cooling attachments, ponds and towers. Since the flow rate of the Eisack River is much higher before the water discharge for electricity production in Franzensfeste, the cooling requirement of the tunnel water is much lower, when discharging the water into the reservoir of Franzensfeste. Since the tunnel portal of Aicha is at a distance of around 500 meters from the reservoir and about 40 meters lower, the installation of a pump station would be necessary. It has to be evaluated how much of the altitude difference can be dealt with the inherent pressure. Pumping the tunnel water up to the reservoir of Franzensfeste implies the integration of the water in the electricity production; at the same time the tunnel water heat could be used for heating buildings in the village of Franzensfeste, located directly at the reservoir. Regarding the flow rates and temperatures of the Eisack River at the reservoir of Franzensfeste, the maximal dischargeable tunnel water amount for given temperatures, the maximal discharge temperature for given flow rates and the cooling requirements for the tunnel water are as follows:

73 Tab. 14: Maximal dischargeable tunnel water amount and maximal discharge temperature of tunnel water into Eisack River at reservoir of Franzensfeste; Required cooling power for discharging the tunnel water into Eisack River at the reservoir of Franzensfeste Maximal Maximal discharge dischargeable tunnel temperature of water amount in l/s tunnel water in °C Required cooling power in kW, so with x °C, so that Δ with x l/s, so that Δ that Δ temperature Eisack ≤ +1°C temperature Eisack ≤ temperature Eisack +1°C ≤ +1°C 800 lt/s 500 lt/s 500 lt/s 25°C 22°C 800 lt/s 500 lt/s with 25°C with 25°C with 22°C January 337 390 12.2 17.8 42,788 15,072 8,791 February 300 350 11.9 16.6 43,917 17,583 11,302 March 377 449 15,2 20.4 32,887 9,577 3,297 April 681 829 22.5 31.1 8,361 May 2,250 2,787 53.2 79.5 June 2,993 3,755 65.5 98.7 July 2,620 3,367 55.8 82.4 no cooling no cooling no cooling August 2,118 2,751 46.5 67.2 required required required September 1,549 1,971 38.1 54.4 October 1,214 1,479 33.7 48.9 November 753 889 23.8 34.9 3,855 December 419 487 14.7 21.5 34,445 7,325 1,044

Restrictions of the Geothermal Energy Utilization Also if the geothermal potential of the Brenner Base Tunnel’s water is enormous, in practice only a very small amount of this can be utilized in an economical and ecological way. This is mainly due the absence of direct heat use applications at the tunnel portal. The heat demands for higher heat levels require the installation of heat pumps for the utilization of the tunnel water heat. Heat pumps require the achievement of certain coefficient of performance (COP) levels and a guaranteed amount of yearly operation hours to generate heat at higher levels in an economical way. Since the COP decreases with increasing heat level lifts, the tunnel water heat utilization is limited.

To enlarge the tunnel water’s geothermal energy utilization, the allocation of potential heat consumers such as industries with suitable process heat needs, greenhouses, aquacultures, leisure infrastructures such as thermal baths, theme parks like tropical houses should be taken into consideration.

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4.2 Evaluation of Different Tunnel Heat Utilization Possibilities for District Heating Purposes

In designing a geothermal energy system for a deep tunnel the valorization of the geothermal potential represents only one piece of the puzzle. Equitable focus must rest on both the energy supply side, as well as, on the evaluation of the amount of thermal energy demanded by the railway tunnel and the surrounding environment. Only by taking into account the energy supply and the energy demand will it be possible to plan a feasible geothermal energy system. Technological and resulting economical efficiency are crucial factors for operating a geothermal energy system of low enthalpy.

Nearby the south portal of the Brenner Base Tunnels no industries, commerce, agricultures, aquacultures, etc. with significant process heat needs can be identified. Thus, the actual geothermal energy utilization possibilities of the tunnel water are limited to building heating purposes in nearby villages. Based on the huge geothermal potential, this pre-study is limited to the use of the tunnel water heat in district heating systems, single building applications, as heating and cooling purposes of tunnel infrastructures, are not dealt with.

The municipalities that directly adjoin the south portal of the BBT exploratory gallery are Franzensfeste, Natz/Schabs and Vahrn (see figure 38). Brixen is located farther away (6.8 km direct line), but because of its population numbers and heat demand it is very interesting for the tunnel water heat utilization. Schabs, Vahrn and Brixen have already a district heating system, the ones of Vahrn and Brixen are interconnected. For Franzensfeste a feasibility study for the construction of a district heating system has been made in 2006, but it has not been realized yet. To draw conclusions on the economical and ecological feasibility of the tunnel water heat utilization by these district heating systems, two systems, different in size, are analyzed in the following chapters: the projected relatively small district heating system of Franzensfeste (4,195 MWh/ year) and the large one of Brixen/ Vahrn (over 100,000 MWh/ year). Because of the similar size to Franzensfeste and the limited scope of this master thesis, the district heating of Schabs was not investigated. However, conclusions for the district heating of Schabs could be drawn from the results of Franzensfeste.

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Fig. 38: Municipalities around the tunnel portal of the BBT exploratory gallery at Aicha (Source: Google maps)

4.2.1 Municipality of Franzensfeste

The center of Franzensfeste is located 2.3 km northwest of the south portal of the exploratory gallery, where the tunnel water will be discharged. Its located 723 m above sea level, that’s about 50 m higher than the exploratory gallery exit. Franzensfeste has 975 inhabitants (status at 31.12.2010; Source: Wikipedia), including the two villages Mittewald and Grasstein. To date it has neither a district heating, nor a gas distribution system.

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In 2006, on behalf of the municipality of Franzensfeste, the SEL AG and the Pro Manage Service Srl made a study about Franzensfeste’s heat demand and investigated the following 4 different possibilities of future heat and electricity energy supply systems: • District heating system powered by biomass; • District heating system with combined heat and power technique powered by methane; • Centralized heating system for the municipalities buildings in the center, leaving the private buildings with their individual heating systems; • The construction of a gas distribution system to supply the buildings of Franzensfeste with their individual gas heating systems.

4.2.1.1 Prognosticated Heat Demand

The study shows, that many of the heating systems in Franzensfeste are antiquated. The average age of the systems is 14 years, 93% of the combustible used is fossil heating fuel. The old, inefficient heating systems and the increasing price for heating oil, result in a high willingness to connect to a district heating system (54% of the interviewees accounting for 84% of the total heat consumed in Franzensfeste). Even though the study showed, that a district heating system with a cogeneration plant powered by methane is desirable from an economical and an ecological point of view, the project has not yet been realized. Thus, the utilization of the geothermal energy of the tunnel water for the heating of the buildings of the center in Franzensfeste may be a good alternative to the projects examined in the study of 2006.

The following table represents the heat demand of Franzensfeste resulting from the study of 2006. To design the future power plant and to simulate the heat consumption as realistically as possible, heat consumers in Franzensfeste are divided into three groups, with different heat consumption characteristics: private buildings, the municipality building including the Kindergarten and the school building with the fire station.

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Tab. 15: Analyzed heat demand of Franzensfeste (Source: Pro-Manage Service Srl, 2006)

Municapility Building School Building Private Buildings incl. Kindergarten with Fire Station

SPACE HEATING: Thermal Demand 3,497 MWh 205 MWh 84 MWh Specific Thermal Potential 115 W/m2 95 W/m2 70 W/m2 Heated Surface 22,700 m2 2,140 m2 1,400 m2 DOMESTIC HOT WATER: Thermal Demand 381 MWh 22 MWh 6 MWh Hot Water Consumption 5,004 m3 292 m3 73 m3 Boiler Capacity 15,000 l 800 l 350 l Number of Persons 457 40 40 Consumption per Person 30 l/day 20 l/day 5 l/day Distribution Losses 30% 30% 30% Temperature of Hot Water 60°C 60°C 60°C TOTAL THERMAL DEMAND 3,878 MWh 227 MWh 90 MWh

The annual heat demand of the center of Franzensfeste is calculated to be 4,195 MWh, the required heat potential of the district heating’s power plant is 2,800 kW.

The annual load duration curve of the planned district heating is represented by the following figure.

Fig. 39: Annual load duration curve of Franzensfeste (Source: Pro-Manage Service Srl, 2006)

In addition, the study of 2006 investigated the impact of the allocation of 550 persons in Franzensfeste for the construction of the Brenner Base Tunnel. The additional annual heat demand is around 1,215 MWh, leading to a total annual heat demand of 5,040 MWh. The potential of the power plant has to be raised by 500 kW

78 resulting in a total installed potential of 3,300 kW. In the sensitivity analysis, this additional heat demand substantially increases the economical output of the district heating system, whereas at the same time it significantly minimizes risks regarding the investment costs, the future energy prices, the development of interest rates, etc. Because of the uncertainties and the timely limited heat demand, this additional heat is not taken into account in the following calculations.

4.2.1.2 Heat Supply – Heat Pump System Design

As mentioned already in the background information chapter, geothermal heating plants generally are operated in base load. This is because the heat from geothermal energy sources in most of the cases is constant over time and the cost- effectiveness increases with elevated heat pump operation hours. From the annual load duration curve of Franzensfeste a base load of around 600 kW can be identified, supplying 65% of the annual heat energy demand. The base load can be covered by three heat pumps of the Suisse heat pump manufacturer CTA, each with a heat capacity of 200 kW and COPs of 3.5 with the given tunnel water temperatures and a heating water output temperature of 75° C. There exist numerous other heat pump brands and solutions to cover this heat power, but they do not have a significant effect on the results and conclusions of this master thesis. To cover the residual heat demand and the full load hours, the heat pump system is equipped by oil boilers with a total capacity of 2,000 kW and a buffer tank. Including the heat losses due to the energy conversation and heat distribution, the produced heat is 4,802,971 kWh, the overall efficiency 0.8734 (see table 16).

Tab. 16: Heat supply and efficiency of a heat pump system for Franzensfeste Heating Oil Heat Pump Total Boiler Percentage of Supply 65,00% 35,00% Heat Demand in kWh 2,726,750 1,468,250 4,195,000 Requested Heat Supply 3,029,722 1,773,249 4,802,971 including Losses in kWh Efficiency incl. Distribution 0.900 0.828 0.873

79 The heat station for Franzensfeste is located about 50 m higher than the tunnel water outflow point at the exploratory gallery in Aicha. To utilize the tunnel water heat by a district heating in Franzensfeste, a pump station and a 2.7 km long pipeline have to be installed. Assuming that the heat pumps extract heat of 10 Kelvin from the tunnel water, the required tunnel flow rate is 14.33 liters per second. More energetic data and assumptions for the heat pump system utilizing the tunnel water from the BBT for a district heating in Franzensfeste are shown in table 17.

Tab. 17: Energetic data and assumptions for a heat pump system utilizing the BBT’s tunnel water heat for a district heating Franzensfeste Heat Pump (HP) Unit Heat Pump Potential 600 kW COP 3.50 Heat supplied by HP 65 % Heat supplied by HP 3,029,722 kWh Heat from Heat Source 2,164,087 kWh Heat from Electricity/ Electricity Consumption 865,635 kWh Tunnel Water Demand Cooled by x °C 10 °C Energy Content/ l/ K 4,186 Kj Yearly Water Heat Demand in kWh 2,164,087 kWh Yearly Water Demand in m3 260,559 m3 Water Demand per Second for 600kW 14.33 l/s Tunnel Water Pump Height Difference 50 m Pipeline Lenght 2,700 m Water Pump Input Power 20 kW Operation Hours 5,050 hours Yearly Electricity Consumption by Pump 100,991 kWh Heating Oil Boiler (OB) Oil Boiler Potential 2,000 kW Annual Use Efficiency 0.92 Heat Supplied by OB 35 % Heat Supplied by OB in kWh 1,773,249 kWh Energy Content of Oil 9.6 kWh/ l Heating Oil Consumption 177,325 l Heat Distribution and Network Annual Use Efficiency 0.9

4.2.1.3 Energy and Environmental Balance

Non-Renewable Primary Energy Factors The primary energy factor explains the efficiency of an energy source, carrier or a whole heating system regarding the primary energy input and the related energy output. The non-renewable (non-r.) primary energy factor is the ratio of the non-

80 renewable energy part of the primary energy input to the energy output. The non-r. primary energy factor of a district heating system can easily be calculated by the energy input of different sources, their non-r. primary energy factors and the net thermal energy output. The following tables (table 18 and 19) illustrate the primary energy factor concerning the non renewable energy part for the district heating system of Franzensfeste and the different energy sources (heat pump, gas CHP-plant, biomass heat plant).

The non-r. primary energy factor of the heat pump system utilizing the tunnel water heat depends on the origin of the electricity. Assuming the electricity to be a mix of different energy sources, the primary energy factor of electricity regarding DIN V 18599-1 and EnEV 2009 is equal to 2.6, the resulting non-r. primary energy factor for the district heating system Franzensfeste 1.06. Things look totally different when utilizing electricity exclusively from renewable energy sources to drive the heat pump. Since the non-r. primary energy factor for electricity from renewable energy sources equals zero, the one derived for the whole heat pump system is 0.46. Only the biomass heat plant with a non-r. primary energy factor of 0.25 shows a higher efficiency regarding the non-renewable energy input.

Tab. 18: Non-renewable primary energy factor of a district heating system for Franzensfeste powered by a heat pump system and the tunnel water heat Non-Renewable Primary Energy Factor of a HEAT PUMP System for Franzensfeste utilizing the Tunnel Water as Heat Source Primary Energy Primary Energy Consumed Energy Source Energy Consumed (concerning the not Factors* Ren. Energy Part) Tunnelwater Heat 2,164,087 kWh 0 0 kWh Electricity (Mix) consumed by HP 865,635 kWh 2.6 2,250,651 kWh Electricity (Mix) Tunnel Water Pump 100,991 kWh 2.6 262,576 kWh Heating Oil 1,773,249 kWh 1.1 1,950,574 kWh total 4,463,800 kWh Primary Energy Input 4,463,800 kWh * Primary Energy Factors concerning Net Energy Output 4,195,000 kWh the not Renewable Energy Part Non-R. Primary Energy Factor of the System according to DIN V 18599-1 and 1.06 with Electricity Mix (Prim. Energy Factor=2.6) EnEV 2009 Non-R. Primary Energy Factor with Electricity from Renew.Energy Sources (Prim. En. 0.46 Factor=0)

81 Tab. 19: Non-renewable primary energy factors of a district heating system for Franzensfeste powerd by a gas CHP-plant and a biomass heat plant

Non-Renewable Primary Energy Factor of a GAS CHP-Plant System for Franzensfeste

Primary Energy Primary Energy Consumed Energy Source Energy Consumed (concerning the not Factors* Ren. Energy Part) Methane 7,540,130 kWh 1.1 8,294,143 kWh

Electricity produced 2,049,848 kWh -2.6 -5,329,605 kWh total 2,964,538 kWh Primary Energy Input 2,964,538 kWh * Primary Energy Factors concerning the not Renewable Energy Part Net Thermal Energy Output 4,195,000 kWh according to DIN V 18599-1 and Non-R. Primary Energy Factor of the CHP EnEV 2009 0.71 System Non-Renewable Primary Energy Factor of a BIOMASS HEAT PLANT System for Franzensfeste Primary Energy Primary Energy Consumed Energy Source Energy Consumed (concerning the not Factors* Ren. Energy Part) Biomass (Wood Chips) 4,719,924 kWh 0.1 471,992 kWh Methane 540,800 kWh 1.1 594,880 kWh total 1,066,872 kWh Primary Energy Input 1,066,872 kWh *Primary Energy Factors concerning the not Renewable Energy Part Net Energy Output 4,195,000 kWh according to DIN V 18599-1 and Non-R. Primary Energy Factor of the System 0.25 EnEV 2009

Emissions The emissions for the different heat plants have been calculated with the emission data of the GEMIS (Global Emission Modell for Integrated Systems) Software Version 4.6 (see www.gemis.de), the results are represented in table 20. As with the non-r. primary energy factor, the emissions of a heat pump system highly depend on the electricity source. The heat pump system powered by electricity mix (EU-27) belongs to the systems with the highest emissions. When powered with electricity from hydropower, the heat pump technique represents one of the emission friendliest systems.

82 Tab. 20: Air pollutant and greenhouse gas emissions of a district heating system Franzensfeste for different heat plants Air Pollutant Emissions Greenhouse Gas Emissions in Kg/ Year in To/ Year SO - CO - 2 SO NO Dust 2 CO CH N O Equivalent 2 x Equivalent 2 4 2 HEAT PUMP pow. 2,540 1,446 1,521 131 1,005.656 972.600 0.998 0.034 by Electricity Mix HEAT PUMP pow. 1,118 674 633 57 594.020 584.339 0.219 0.016 by Hydro Pow. El. GAS CHP PLANT 960 27 1,339 7 995.123 897.960 4.076 0.012 BIOMASS HEAT 2,039 535 2,082 1,033 250.213 216.937 1.077 0.028 PLANT

Air Pollutant Emissions Greenhouse Gas Emissions Kg / Year Tons / Year 3.000 1200 2.500 1000 2.000 HEAT800 PUMP powerd by HEAT PUMP powerd by Electricity Mix (EU-27) Electricity Mix (EU-27) 1.500 600 HEAT PUMP powerd by HEAT PUMP powerd by 1.000 400 Greenhouse Gases Emissions Hydro Power Electricity Hydro Power Electricity 500 200 kg / year GAS CHP PLANT GAS CHP PLANT 0 0 1.000.000 Greenhouse Gases900.000 Emissions BIOMASS HEAT PLANT 800.000 BIOMASS HEAT PLANT kg / year SO2 NOx Dust CO2 CH4 N2O 700.000 HEAT PUMP powerd by 600.000 Electricity Mix (EU-27) 1.000.000 500.000 900.000 400.000 HEAT PUMP powerdCO2-Equivalent by 800.000 SO2-Equivalent 300.000 Hydro Power Electricity 700.000 200.000 HEAT PUMP powerd by 600.000 100.000 Electricity Mix (EU-27) GAS CHP PLANT 500.000 0 400.000 HEAT PUMP powerd by 300.000 Hydro Power Electricity BIOMASS HEAT PLANT 200.000 CO2 CH4 N2O 100.000 GAS CHP PLANT 0 CO2-Equivalent Fig. 40: Air pollutantBIOMASS HEAT and PLANT greenhouse gas emissions of a district heating system CO2 CH4 N2O Franzensfeste for different heat plants CO2-Equivalent

4.2.1.4 Investments and Economy

The following table shows the valuation of the investment costs and the derived annuities for the district heating system powered by a heat pump system described in the chapters before. The annuities have been calculated regarding the methods and lifetimes of the technical directive VDI (Verein Deutscher Ingenieure) 2067. The total investment costs are calculated to be 3,121,303 € including a provincial aid of 30%, the derived annuity is 229,251 €. The investment costs of the heat

83 distribution/ network and most of the ones of the heat station are adopted from the study from 2006, the costs for the heat pumps are from a heat pump manufacturer. For the heat generation cost calculations actual energy prices for electricity and heating oil have been taken into account (see table 22).

Tab. 21: Investment costs and annuities for a heat pump district heating system Franzensfeste

Service Investment Annuity in INVESTMENT Life in costs in € €/year Years Tunnel Water Catchment and Pump Station

Water Catchment, Pump 50,000 30 3,659 Station Building Water Pump and Installation 50,000 18 4,431 total 100,000 8,089 Lenght in Cost per Tunnel Water Pipe Meter Meter in € from Tunnel Portal to Heat 2,700 300 810,000 Station from Heat Station to Surface 300 160 48,000 Water total 858,000 40 57,811 Heat Station Heat Station Construction 250,000 50 15,976 Heat Pump incl. Installations 660,000 18 58,488 Oil Heating Burner 185,000 20 15,680 Buffer Tank 50,000 20 4,238 Central Control System 130,000 20 11,018 Hydraulic Installations 150,000 20 12,714 total 1,425,000 118,114 Heat Distribution &

Network Distribution Network 1,370,640 40 92,351 Substations 300,000 20 25,427 total 1,670,640 117,778 Project Costs (Professional Fees, Additional Costs...) 10% of Investment Costs 405,364 25 31,539 TOTAL 4,459,004 333,332 without Provincial Aid Provincial Aid in % of 30,00% 1,337,701 104,080 Investment TOTAL 3,121,303 229,251 after Provincial Aid

The economic assumptions for the annuity and the heat generation costs are as follows:

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Tab. 22: Economic assumptions for annuity and heat generation cost calculation Economic Assumptions unit Interest Rate 5 %/ year Inflation 2 %/ year Calculation Time 15 years Electricity Price (Nov. 2011) 0.14 € /kWh Heating Oil Price per l (Nov. 2011) 1.2 € /l Energy Content of Oil 9.6 kW/l Maintanance/Inspection Costs in % of Investment (without Project Costs) 2 % Insurance Costs in % of Investment (without Project Costs) 0.2 %

The following table shows the heat generation costs for the whole district heating system of Franzensfeste powered by heat pumps and the ones for the heat production by heat pumps without distribution investments and heat losses. Heat generation costs are calculated with and without financial aid, and in addition without the investment for the tunnel water pump and pipeline.

Tab. 23: Heat generation costs for a heat pump district heating system Franzensfeste

without with without Energy Study 2006 HEAT GENERATION T.- Water Unit Financial Financial Catchem., (Pro-Manage Service COSTS Aid Aid Pump and Srl, 2006) Pipe Gas CHP Biomass Plant* Plant Investment Annuities €/year 333,332 333,332 267,432 Maintanance/Inspection €/year 91,806 91,806 91,806 * modified by actual Insurance €/year 9,181 9,181 9,181 green Provincial Aid €/year -104,080 -81,719 certificate compensati Total Investment and €/year 434,318 330,238 286,699 on = Operation Costs 0.055€/ Electricity consumed by kWh €/year 137,233 137,233 137,233 HP (2006 = Electricity consumed by 0.090/kWh) €/year 16,011 16,011 16,011 T-Water Pump Heating Oil €/year 240,961 240,961 240,961 Total Energy Input €/year 394,204 394,204 394,204 Costs Total Costs €/year 828,523 724,442 680,903 371,778 404,310

Heat Sale kWh 4,195,000 4,195,000 4,195,000 4,195,000 4,195,000 Heat Generation €/kWh 0.1975 0.1727 0.1623 0.0886 0.0964 Costs Heat Generation Cost by Heat Pump without €/kWh 0.1252 0.1076 0.0933 Heat Distribution and Losses

85 The heat generation costs for a district heating with a heat pump utilizing the BBT’s tunnel water heat will be 0.1727 €/kWh including the provincial aid payments. This is substantially higher than the costs calculated for the gas CHP-plant (0.0886 €/kWh) and the biomass heat plant (0.0964 €/kWh) in the study of 2006 (see table 23). With the considerable lower heat generation costs by alternative energy sources and the average heat price of 0.092 €/ kWh for district heat consumers (see table 24), the heat pump system for a district heating of Franzensfeste utilizing the BBT’s tunnel water heat is not competitive and economically not feasible. Comparing the heat generation costs (0.1076 €/kWh) of the heat pump system without distribution investments and heat losses with alternative energy sources, it can be seen that only heating oil and liquid gas in tanks are more expensive.

Tab. 24: Comparison of heating costs for different combustibles (Source: www.centroconsumatori.it/40v26395d28081.html; Prices of 01/10/2011)

Energy Price per Combustible Price Comparison Content kWh

Heating Oil 1.275 €/l 10 kWh 0.128 € 100% Liquid Gas in Tank 2.260 €/kg 12.8 kWh 0.177 € 139% Methane 0.823 €/m3 9.8 kWh 0.084 € 66% Wood Pellets 0.252 €/kg 4.8 kWh 0.053 € 41% Wood Chips 0.148 €/kg 5.5 kWh 0.027 € 21% Firewood 0.151 €/kg 4.3 kWh 0.035 € 28% District Heating (including 0.092 €/kWh 1 kWh 0.092 € 73% basic fees)

Sensitivity Analysis Tab. 25: Heat generation costs of a heat pump The sensitivity analysis shows the system for DH Franzensfeste dependent on the influence of the energy input prices energy input prices

Heating (electricity and heating oil price) Electricity Heat Oil Price Heat Price Generation (Electr. Generation and the heat demand on the heat (Oil Price Costs Price = 14 Costs =1.2€/l) generation costs of a heat pump Cent/kWh) Cent/ kWh Cent/ kWh €/ kWh Cent/ kWh system in Franzensfeste. Results 10 16.23 0.6 14.40 are represented in table 25 and 12 16.75 0.8 15.35 14 17.27 1.0 16.31 figure 41. It can be seen that the 16 17.79 1.2 17.27 18 18.31 1.4 18.23 heat pump system is far away from 20 18.83 1.6 19.18 competitiveness, also when 22 19.36 1.8 20.14 assuming unlikely low energy prices and an unrealistic doubling of the heat demand

(neglecting required additional investments) .

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Heat Generation Costs of a Heat Pump System for a DH Franzensfeste as a function of Net Heat Demand 30

25 25,91 20,40 20 16,00 14,11 13,07 15 17,27 14,90 10 13,52 12,70

5

0

HeatGeneration Costsin Cent/kWh 0 2000 4000 6000 8000 10000 12000

Net Heat Demand in MWh

Fig. 41: Heat generation costs of a heat pump system for a district heating Franzensfeste as a function of the net heat demand

4.2.2 Municipality of Brixen/ Vahrn

The municipalities of Vahrn and Brixen are located approx. 4 and 7 kilometers south of the exploratory gallery portal in Aicha. With 4,236 inhabitants in Vahrn and 20,689 inhabitants in Brixen (at 31.12.2010 including suburbs; Source: Wikipedia) the heat demand for building heating and domestic hot water is remarkable. The preconditions for a feasible heat pump system utilizing the BBT’s tunnelwater heat are much more favorable than the ones in Franzensfeste.

4.2.2.1 Existent Heat Supply System

Both municipalities have district heating systems, which are connected with each other. The district heating system of Brixen/ Vahrn has 4 district heat stations. The heat station in Vahrn consists of a biomass CHP plant with two methane gas boilers for peak loads. The three stations in Brixen are all methane CHP plants, even equipped with gas boilers for peak loads. All stations are heat conducted, which

87 means that their power curve is defined by the heat demand curve and not by the maximization of electricity production. The district heating system Brixen/ Vahrn forms a ringed network with main and connection lines. The supply temperatures in the network are 80° C to 95° C, the return temperatures on average in between 50° C and 55° C. To avoid heat losses, supply temperatures are lowered during summer operation. The district heating system is still being extended and optimized in heat production. In the final stage of extension, the district heating system will achieve a length of over 150 kilometers, with a connected load of 90 MW in Brixen and 11 MW in Vahrn. Actually the district heating system reaches a length of 120 kilometers and serves 1,700 users (1,400 in Brixen, 300 in Vahrn) (Enertour, n.d.). The heat production of the district heating system Brixen/Vahrn in 2010 was derived from the heat production data of the single heat stations. Figure 42 shows the load curve as average per day, figure 43 the annual load duration curve of the district heating system Brixen/Vahrn. The total heat production in 2010 was 106,441,896 kWh, with a maximal thermal output of just above 40 MW.

34000 33000kWh 32000 31000 30000 29000 28000 27000 26000 25000 24000 23000 22000 21000 20000 19000 18000 17000 16000 15000 14000 13000 12000 11000 10000 9000 8000 7000 6000 5000 4000 3000 2000 1000 0

Time 01.01.10 01.02.10 01.03.10 01.04.10 01.05.10 01.06.10 01.07.10 01.08.10 01.09.10 01.10.10 01.11.10 01.12.10 Fig. 42: Load curve of the district heating Brixen/Vahrn – 2010

88 44000 43000 42000 41000 40000 39000 Annual Load Duration Curve 38000 37000 District Heating Brixen/Vahrn 2010 36000 35000 (Total Heat Production 106,441,896 kWh) 34000 33000 32000 31000 30000 29000 28000 27000 26000 25000 24000 23000 22000 kW kW 21000 20000 19000 18000 17000 16000 15000 14000 13000 12000 !"#$%&'(!))*! ! !!! ! 11000 10000 9000 8000 ;! <=#>=20(#,-.!?2@!A0$B,&#?2C!,22&#.=B>!@&#!DE#F&/?F/&2C#?//&! 7000 6000 ;! G&#'=>&B?2C!,22&#.=B>!@&#!DE#F&/?F/&! 5000 ;! 0&/=#=(&#H!2&>&2!@&#!DE#F&/?F/&!=?1C&0(&BB(&#!I(&?�-.#=2'!F,(!I,&F&20!I,F=(,-!IJ! 4000 ;! KEB(&F,((&B!?2@!LB1MBB?2C! 3000 2000 ;! N&0,C2!C&FE00!OP!+&C&BQ&#'&2!1M#!KEB(&F=0-.,2&2!R"ONH!OS:JTH!333U!! 1000 ;! ?2@!C&FE00!<#,$(.&#F!I(=2@=#@!! 0 ;! V>&#Q=-.?2C!@&0!W>B=@&20H!O,2>#,2C?2C!?2@!I&(X&20!=?1!@=0!&(#,&>2=.F&!=?1!@&#!)=0,0!Y$2!57!W#>&,(0(=C&2!!! 4001 5001 6001 7001 8001 2,-.(!&2(.=B(&2Z! hours ;! W>B=@&2H!O,2>#,2C?2C!?2@!I&(X&2!=?1!@=0!$Y&#@,-.(&#^W2(#,&>0F$($#&2! - 2010 ;! G&#'=>&B?2C!X?F![$($#!?2@!W20-.B?00!=2!@&2![$($#'B&FF&2'=0(&2! ;! G&#'=>&B?2C!X?F!0&/=#=(!=?1C&0(&BB(&2!I(&?�-.#=2'! ;! PF1MBB=CC#&C=(!1M#!I&#Y,-&=#>&,(&2! ;! *=/#$CC&!+$.##&,2,C?2C00_0(&F!1M#!@&2!G&#@=F/1&#!R0$Q&,(!$#@&#B,-.U! ;! `&#M0(&!?F!@,&!DE#F&/?F/&!X?#!)&C&.?2C!?2@!D=#(?2C!R0$Q&,(!$#@&#B,-.U! ;! [=0-.,2&2#=?F(&-.2,'!?2@!W?0#M0(?2C&2! ;! "?F/&2H!!W2B=C&2^+$.#B&,(?2C&2H3333! 4.2.2.2 Heat Pump System Design;! 0$Q,&!0EF(B,-.&0!2,-.(!=2C&1M.#(&0!a?>&.b#!! ! !"#$%&'(")*+,'*-*.%,#/*01'2(&32&(*45&*67849:*;;<=>-?@6* NN"!G=.#2!2&(($!$.2&![DI*!!A6!9*-BCDEBEEEFEE! According to the heat supply data ofR)=0,0!<#,$(.&#F!],&1&#>&@,2C?2C&2U!! the district heating Brixen/ Vahrn and the tunnel ! ! water data of the BBT at the south],&1&#X&,(!=>!D&#'!-=3!!54![$2=(&! portal, the world market leader for heat pumps of large capacity Friotherm/ Switzerland (www.friotherm. com) proposed the installation of two heat pumps type UNITOP 33C with a heat capacity of 5,269 kW each (see figure 44) for the tunnel water heat utilization. The full load COP of the heat pumps with a heating water supply temperature of 75° C is 3.368, ! ! by cooling the tunnel water ! W?10(&BB?2C0/B=2!&,2&#!E.2B,-.&2!W2B=C&!@&#!*_/&!PSA*\"!::c3! from 25° to 21°C (∆T = 4 Fig.+,-.(/#&,0$11&#(&!2$3!4556789!4835634655! 44: Heat pump design of Unitop ! 33C-6145U/ Friotherm !!!49:!

89 Kelvin). The heat pump output can be reduced to 65% with an expected COP of 3.171. More technical data are represented in figure 45. Given the heat pump data and the heat supply data of the district heating Brixen/ Vahrn of 2010, the yearly operating hours and related heat supply of the heat pumps have been calculated. The results are illustrated in table 26. Overall the two heat pumps with a produced thermal energy of almost 70,000 MWh could cover 59% of the yearly total heat supply of the district heating Brixen/ Vahrn. The calculated yearly COPs of the heat pumps are 3.334 and 3.360. Assuming that the heat pump station will be placed at the biomass heat station in Vahrn, which is located about 100 m lower than the portal of the exploratory of !"#$%&'(!))*! ! !!! ! Aicha, the tunnel water should flow by inherent pressure through a 6.1 km long insulated!"#$%&'(")*++('%(,-'.,/00123, pipeline to the heat station. ! 4-5678,99:;30<=4, ! )&(#,&;0/<2'(! ! ! 566=! ! ! ! ! 87=! ! ! ! ! >?!@AB8C?!, >! ?@#A&B<&CC&! ! *<22&CDE00&#F! ! ! ! *<22&CDE00&#F! ! >! G@C(&C&,0(<2H! ! :IJ76!'?! ! ! ! 4IK:L!'?! ! >! M,29N<0(#,(((&A/&#E(<#&2!!! 47945!OP! ! ! ! 479443K!OP! >! Q$C! U#<-'V&#C<0(! ! 63JL!;E#! ! ! ! 63JL!;E#! >! Q�-.A<(W<2H01E'($#! 636666LL!A4G9?! ! ! 636666LL!A4G9?! ! >! "E00WE.C! ! ! 4! ! ! ! ! 4! ! F!#&,2&0X!H&1,C(&#(&0!*<22&CDE00!?&,0(!Y#<2ZDE00&#!&,2&!.[.&#&!Q�-.A<(W<2H!E<1X!0$CC(&!*E/#$HH&! +$.##&,2,H<2H00\0(&A!&,2H&0&(W(!D&#Z&23!!! !! D7-@?-EA67!,4-@,, 4-6?!D4?FG?!, >! ]&,WC&,0(<2H! ! 7I48R!'?! ! ! ! :IKLK!'?! >! ]&,00DE00&#! ! 869J7!OP!! ! ! ! 869J7!OP! >! Q$C! U#<-'V&#C<0(! ! 63RK!;E#!! ! ! ! 63:7!;E#!! ! ! >! ^$! "E00WE.C! ! ! :!SA,(!_2(&#'`.C&#T! ! ! :!SA,(!_2(&#'`.C&#T! ! ! ! G?5E64-HEA4C-AFB?, >! a$($#!E2!Z&#!GC&AA&! 5I78K3:!'?! ! ! ! !"#$%&'()*+( ! >! :78,F("I,, , 9.93=, , , , , !"#$#%&, >! +&H&C;&#&,-.!!! ! 566!;,0!-E3!87=!$.2&!]Y)!S]&,00HE0b)\/E00T! >! +&H&C;&#&,-.!! ! -E3!87!;,0!K6=!A,(!]Y)! !!!!!!!!U<#-.!N;0&2'<2H!Z&#!]&,WDE00&#(&A/&#E(<#!,2!Z&#!*&,CCE0(!'E22!Z&#!+&H&C;&#&,-.! !!!!!!!!$.2&!]Y)!&#D&,(&#(!D&#Z&23!! ! ! F!&#DE#(&(&!?&#(&!! ! ! A-6!5?JEB767!, >! c&22C&,0(<2H!Z&0!a$($#0! 5I766!'?! >! d/E22<2H! ! ! 8I666!Q! >! ^#&B<&2W! ! ! 76!]W! >! d-.<(WE#(! ! ! e"7K! >! G`.C<2H0E#(! ! DE00&#H&'`.C(! !!!!!!! ! !! AJB?EE4-H?-, >! f!g!)!g!]!! ! ! JI866!g!KI566!g!KI666AA!! >! Y&D,-.(!! ! ! -E3!!K7I666'H!9!:LI666'H!

G5?C?!4BCA-H,, Fig.>! G$A/#&00$#!A,(!hC0\0(&AX!Y&(#,&;&!<2Z!N2(#,&;0A$($#!45: Heat pump data of Unitop 33C-6145/ Friotherm >! Q&#ZEA/1&#X!A,(!,22&2!H! Q$#;&#&,(<2H!Z&0!Q&#ZEA/1�!1`#!Z&2!&V&2(<&CC&2X!0/@(&#&2X!;E<0&,(,H&2!N20-.C<00!&,2&0!*E/#$HH&b d\0(&A0! >! G$2Z&20E($#!,2!d(E2ZE#ZE<01`.#<2H!A,(!d(E.C#$.#&2! >! _2(&#'`.C&#!,2!d(E2ZE#ZE<01`.#<2H!A,(!d(E.C#$.#&2! >! +$.#C&,(<2H&2!<2Z!e20(#

Heat Pump System for the District Heating Brixen/ Vahrn with two Heat Pumps UNITOP 33C-6148U/ Friotherm (2x 5,269 kWh) Total Heat Supply Vahrn/Brixen 106,441,896 kWh Heat Supplied by Heat Pumps 62,937,522 kWh Heat Supplied by Heat Pumps in % of Total 59% Heat Pump (2x 5,269 kW) HP1 HP2 Heat supplied by HP in kWh 41,194,111 21,743,411 Full Load Hours 5,479 3,831 Partial Load Hours 2,911 350 Total Operation Hours 8,390 4.181 Yearly COP 3.334 3.360 Heat supplied by HP in % of Total 38.70% 20.43% Heat supplied by HP in kWh 41,194,111 21,743,411 Heat from Heat Source (Tunnel Water) 28,837,608 15,271,773 Heat from Electricity/ Consumed Electricity 12,356,503 6,471,638 Tunnel Water Demand Cooled by x °C 4 °C Energy Content of Water 4,186 kJ / l / K Yearly Water Heat Demand 44,109,380 kWh Yearly Water Demand 9,483,622 m3

4.2.2.3 Energy and Environmental Balance

Non-Renewable Primary Energy Factors As for the planned district heating system of Franzensfeste, also for Brixen/ Vahrn the non-renewable primary energy factor (non-r.) of the existing and the heat pump system can be calculated. Since the final heat energy, i.e. the heat energy consumed by the users, is not given, the non-r. primary energy factor here does represent the one of the heat energy supply by the heat plants and not the one of the whole district heating system.

Due to the high non-r. primary energy factor of electricity (= 2.6 for electricity mix regarding DIN V 18599-1 and EnEV 2009), the actual district heating Brixen/ Vahrn with the gas CHP-plants and its electricity output exhibits a negative non-r. primary energy factor for the heat production (-0.26; see calculations table 28) . Not taking into account the electricity production by the CHP plants, the non-r. primary energy factor heat input is equal to 0.78. Assuming that the heat pump system is equipped with gas CHP-boilers for the heat not covered by the heat

91 pumps, the non-r. primary energy factor is 0.38, respectively 0.45 calculating with electricity from renewable energy sources.

Tab. 27: Non-renewable primary energy factor of heat production for the district heating Brixen/ Vahrn with heat pump system utilizing tunnel water heat

Non-Renewable Primary Energy Factor of Heat Production for District Heating Brixen/ Vahrn with Heat Pump System and Tunnel Water Primary Energy Primary Consumed Energy Source Energy Consumed Energy (concerning the not Factors* Ren. Energy Part) Tunnel Water Heat 44,109,380 kWh 0 0 kWh Electricity (Mix) consumed by HPs 18,828,142 kWh 2.6 48,953,169 kWh Methane 43,504,374 kWh 1.1 47,854,811 kWh Electricity produced by Methane CHP** 21,752,187 kWh -2.6 -56,555,686 kWh Total Heat Production 106,441,896 kWh total 40,252,294 kWh Primary Energy Input * Primary Energy Factors concerning the not (with Electricity Mix: Non.R. Primary 40,252,294 kWh 0.38 Renewable Energy Part Energy factor = 2.6) according to DIN V Primary Energy Input 18599-1 and EnEV 2009 (with Electricity from Renewable Energy ** Assumption: Electricity 47,854,811 kWh 0.45 Sources: Non.R.-Primary Energy Factor production = 50% of Heat = 0) Production by Methane

Tab. 28: Non-renewable primary energy factor of heat production for the district heating Brixen/ Vahrn with actual heat plants

Non-Renewable Primary Energy Factor of Heat Production for District Heating Brixen/ Vahrn with actual Heat Plants Primary Energy Primary Consumed Energy Source Energy Consumed Energy (concerning the not Factors* Ren. Energy Part) Biomass 31,217,766 kWh 0 0 kWh Electricity produced by Biomass ORC 5,000,000** kWh -2.6 -13,000,000 kWh Methane 75,224,129 kWh 1.1 82,746,542 kWh Electricity produced by Methane CHP*** 37,612,065 kWh -2.6 -97,791,368 kWh Total Heat Production 106,441,896 kWh total -28,044,826 kWh * Primary Energy Factors Primary Energy Input concerning the not (with Electricity Mix: Non.R. Primary -28,044,826 kWh -0.26 Renewable Energy Part Energy factor = 2.6) according to DIN V 18599-1 and EnEV 2009 ** Data from Enertour, Primary Energy Input n.d. (with Electricity from Renewable Energy 82,746,542 kWh 0.78 *** Assumption: Electricity Sources: Non.R.-Primary Energy Factor production = 50% of Heat = 0) Production by Methane

92 Emissions As for Franzensfeste, with the emission data of the GEMIS (Global Emission Modell for Integrated Systems – www.gemis.de), emissions for the actual heat plants of the district heating Brixen/ Vahrn and the ones for a heat pump system can be calculated. Because of the electricity production by CHP-technology, the actual heat plants exhibit very low and mostly negative emission data. Due to its considerable electricity consumption, the emissions of a heat pump system mainly depend on the origin of electricity. When utilizing electricity from renewable energy sources, the heat pump system has very low emissions. Since the heat pump system is equipped with a gas CHP boiler for full load hours, some parameters are also negative.

Tab. 29: Air pollutant and greenhouse gas emissions of a district heating system Brixen/Vahrn with a heat pump system and with actual heat plants Air Pollutant Emissions Greenhouse Gas Emissions in Kg/ Year in To/ Year SO - CO - 2 SO NO Dust 2 CO CH N O Equivalent 2 x Equivalent 2 4 2 HEAT PUMP SYSTEM pow. 27,767 4,562 33,390 394 8,003.20 7,044.64 35.92 0.38 by Electricity Mix (EU 27) HEAT PUMP SYSTEM pow. 58 -10,477 16,096 -1,056 -14.74 -517.99 20.75 0.02 by Hydro Power Electr. ACTUAL HEAT -2,257 -18,580 25,125 -2,332 -1,314.69 -1,492.90 39.42 0.17 PLANTS

Air Pollutant Emissions Greenhouse Gas Emissions in Kg/ Year in Tons/ Year 40.000 9.000 HEAT PUMP SYSTEM 8.000 30.000 7.000 powerd by Electricity Mix 6.000 (EU-27) 5.000HEAT PUMP SYSTEM powerd 20.000 HEAT PUMP SYSTEM 4.000by Electricity Mix (EU-27) Air Pollutant Emissions powerd by Hydro Power 3.000HEAT PUMP SYSTEM powerd Electricity 10.000 in Kg/ Year 2.000by Hydro Power Electricity 1.000 ACTUAL HEAT PLANTS of 40.000 ACTUAL0 HEAT PLANTS of DH 0 DH Brixen/Vahrn -1.000Brixen/Vahrn 30.000 -2.000 -10.000 SO2 NOx Dust CO2 CH4 N2O HEAT PUMP SYSTEM powerd 20.000 -20.000 by Electricity Mix (EU-27) SO2-Equivalent CO2-Equivalent HEAT PUMP SYSTEM powerd 10.000 by Hydro Power Electricity ACTUAL HEAT PLANTS of DH 0 Brixen/Vahrn

-10.000 SO2 NOx Dust Fig. 46: Air pollutant and greenhouse gas emissions of the district heating system -20.000 Brixen/Vahrn SO2-Equivalentwith heat pump system and with actual heat plants

93

4.2.2.4 Investments and Economy

Given the heat supply data of the district heating system Brixen/ Vahrn and the required heat pump system design, investments are estimated (see table 30) and heat generation costs are derived. Since the district heating system has already been realized, net and distribution investments are not included in the calculations. The resulting heat generation costs therefore represent the ones of the heat pumps only. They simply can be compared with the actual heat generation costs, excluding the expenses for distribution.

Tab. 30: Investment costs and annuities for a heat pump system supplying the district heating of Brixen/ Vahrn

Service Investment Annuity in INVESTMENT Life in costs in € €/year Years

Tunnel Water Catchment

Water Catchment 300,000 30 21,951 total 300,000 21,951 Lenght in Cost per Tunnel Water Pipe Meter Meter in € from Tunnel Portal to Heat 6,100 500 3,050,000 Station from Heat Station to Surface 800 200 160,000 Water total 3,210,000 40 216,285 Heat Station Heat Station Construction 1,000,000 50 63,903 Heat Pump incl. Installations 4,000,000 18 354,474 & Central Control System total 5,000,000 418,377 Project Costs (Professional Fees, Additional Costs...) 10% of Investment Costs 851,000 25 66,212 TOTAL 9,361,000 722,825 without Provincial Aid Provincial Aid in % of 30.00% 2,808,300 218,501 Investment TOTAL 6,552,700 504,324 after Provincial Aid

94 With the economic assumptions of the calculations for the district heating system of Franzensfeste (see table 22) the following heat generation costs for the heat pump system utilizing the tunnel water heat can be defined:

Tab. 31: Heat generation costs for a heat pump system supplying the district heating of Brixen/ Vahrn

without with without HEAT GENERATION T.- Water Unit Financial Financial Catchem., COSTS (Annuities) Aid Aid Pump and Pipe Investment Annuities €/year 631,131 631,131 475,097 Maintanance/Inspection €/year 165,102 165,102 165,102 Insurance €/year 16,510 16,510 16,510 Provincial Aid €/year -187,176 -128,379 Total Investment and €/year 812,744 625,568 528,331 Operation Costs Electricity consumed by €/year 3,837,741 3,837,741 3,837,741 HP Total Energy Input €/year 3,837,741 3,837,741 3,837,741 Costs Total Costs €/year 4,650,484 4,463,308 4,366,071

Heat Production kWh 62,937,522 62,937,522 62,937,522 Heat Generation €/kWh 0.0739 0.0574 0.0691 Costs

The heat generation costs of a heat pump system for the district heating Brixen /Vahrn utilizing the tunnel water of the BBT’s south portal are 5.88 Cent/ kWh (with a electricity price of 0.14 €/ kWh) including the provincial aids. The heat generation cost does not vary much excluding the financial aid or the tunnel water catchment and pipe, because the main part of the costs is the one for the electricity consumed by the heat pumps (86% of total costs!).

Sensitivity Analysis When varying input data as investment, operation and energy input costs, it immediately turns out that the heat pump system for the district heating Brixen/ Vahrn is highly sensitive with regard to the price of electricity consumed by the heat pumps. This is because the electricity consumption amount of the heat pumps as mentioned already represents the main part of the total yearly heat generation costs. Figure 47 shows the heat generation costs of a heat pump system in relation to the electricity price. Compared to the electricity price, the variations of the heat amount supplied by the heat pumps or the investment costs do not have much effect on the final heat

95 generation cost. Diminishing the heat supply of the heat pumps by 50 % (i.e. supplying only 30 % of the district heat plants output), the heat generation costs increase by 1 Cent/ kWh. With a heat supply increasing of 25 %, costs decrease only by 0.2 Cent/ kWh. The scenario is similar with the investment costs. Increasing the costs by 2 million €, the heat generation costs rise by 0.3 Cent/ kWh. Lowering the investments by 2 million € leads to a decline of the costs by 0.3 Cent/ kWh.

Heat Generation Costs by Heat Pump System depending on Electricity Price 10 9 8,59 8 7,91 7 7,24 6,56 6 5,88 5 5,2 4,53 4 3 2 1 0 HeatGeneration Costsin Cent/kWh 10 12 14 16 18 20 22 Electricity Price in Cent/ kWh

Fig. 47: Heat generation costs of a heat pump system for the district heating Brixen/Vahrn as a function of the electricity price

96 5. SUMMARY & CONCLUSION

Geothermal Heat Potential of the Tunnel Water The geothermal heat content of the BBT’s tunnel water is enormous. At the BBT’s south portal the expected stabilized tunnel water outflow rate is approximately 745 liters per second with temperatures of 22° C to 26° C, which corresponds to a geothermal capability of 68 MW to 81 MW year-round.

Because of the elevated temperatures, the tunnel water would have a considerable influence on the flora and fauna, discharging it directly from the exploratory gallery at Aicha into the Eisack River. Temperature change of the river can reach + 8° C and more, especially during winter months, when river flow rates and temperatures are low. Thus, it is necessary to cool the tunnel water. Due to environmental regulations, the temperature change of the Eisack River is limited to +/- 1° C after tunnel water discharge. Taking into consideration the uncertainty of the tunnel water flow rate and temperature predictions, the geothermal heat content and the required cooling power has been calculated for three scenarios with different flow rates and temperatures: viz. 800 liters/ second with 25° C, 500 liters/ second with 25° C and 500 liters/ second with 22° C. Whereas for all scenarios in summer months cooling is not necessary, during winter the required cooling power can reach 68 MW. Pumping the tunnel water into the reservoir of Franzensfeste, which is located a few hundred meters northwest of the exploratory gallery’s south portal, can lower the cooling requirements. This is because flow rates of Eisack River are higher in the Franzensfeste reservoir, where a large amount of river water is discharged for electricity production. The required cooling power of the BBT’s tunnel water can be defined as usable geothermal energy for heating purposes. Since the temperature change of the Eisack River is allowed up to minus 1° C, also in summer months when no cooling is required, heat can be extracted from the tunnel water. Regarding the environmental regulations on the allowed Eisack River temperature change of +/- 1° C, the maximal usable geothermal potential of the tunnel water in the three scenarios reaches from 38 MW in spring and autumn (with 500 l/s at 22° C) up to 80 MW in winter (with 800 l/s at 25° C). From an ecological point of view it would be desirable to utilize the whole geothermal energy of the tunnel water and replace thereby fossil fuels. In practice,

97 due the absence of direct heat use applications at the tunnel portal, and technical and economical restrictions in lifting temperature levels with heat pumps, only a small amount could be used in a efficient way.

Heat Utilization Possibilities for District Heating Purposes The most extensive and efficient utilization of the tunnel water heat would be the all season direct heat use for industry, commerce and agriculture. Presently there do not exist such direct heat applications nearby the south portal of the BBT. The only comprehensive utilization possibilities of the tunnel water’s geothermal potential are planned and existing district-heating systems of nearby villages. Namely these are: • the planned district heating system for Franzensfeste, • the district heating system of Schabs, • the district heating system of Brixen/Vahrn. With an aim to draw conclusions on the economical and ecological feasibility of the tunnel water heat utilization for this district heating systems, two systems, different in size, have been analyzed: the projected relatively small district heating system of Franzensfeste with a heat demand of 4,195 MWh per year and the large one of Brixen/ Vahrn, with a yearly heat production of over 100,000 MWh. Because of the similar size to Franzensfeste and the limits of this master thesis, a study on the district heating of Schabs has not be done. Conclusions for the district heating of Schabs could be drawn from the results of Franzensfeste.

District Heating Franzensfeste Investments for a district heating for Franzensfeste with a heat pump system utilizing the BBT’s tunnel water heat are estimated to be around 4.5 million €, the resulting heat generation cost with a net heat demand of 4,195 MW is 0.1727 €/ kWh. This is substantially higher than the ones of the district heating feasibility study for Franzensfeste of 2006 with 0.0886 kWh for a gas CHP-plant and 0.0964 kWh for a biomass plant. The heat pump system for Franzensfeste with a potential of 600 kW is designed to cover the base load of heat. Total yearly heat production is calculated to be 3,029 MWh, that is 65% of total production. Even if from an ecological point of view it would be desirable, economic efficiency refuses the realization of a district heating in Franzensfeste with a heat pump system for the BBT’s tunnel water heat utilization. The diseconomy especially comes from the relatively high investments in proportion to the heat demand and the elevated electricity consumptions of the heat pumps. Due to the required high

98 temperature lifts of the heat pumps, a higher COP than 3.5 and resulting lower electricity consumption in relation to the heat production is technically not realistic. Although the heat from the tunnel water is “free of charge”, a heat pump district heating system in Franzensfeste results in elevated heat generation costs.

District Heating Brixen Integrating a heat pump system to exploit the BBT’s tunnel water heat at the south portal for the district heating Brixen/ Vahrn, implicates investments of about 9 million €. Over 3 million € are constituted by the 6.1 km long insulated tunnel water pipeline from the tunnel portal to the heat station in Vahrn. These costs may be partly absorbed by the Brenner Base Tunnel Corporation, since cooling costs could be saved with the tunnel water heat utilization. The heat pump system for the district heating consists of two large heat pumps with a heat output of 5,269 kW each. 59% of the heat demand of the district heating could be covered by the heat pumps with a yearly heat generation of almost 70,000 MWh. The COPs of the heat pumps are 3.334 and 3.360. The calculated heat generation costs of 5.88 Cent/ kWh (with an electricity price of 0.14 €/ kWh) by utilizing the BBT’s tunnel water heat with heat pumps for the district heating system Brixen/ Vahrn, seems to be very interesting and competitive with alternative energy sources. The future competitiveness highly depends on the future price development of electricity and the different energy sources. Since this master thesis represents only a rough pre-study of a heat pump system, more detailed studies should be made on the tunnel water heat utilization by heat pumps for the district heating of Brixen/ Vahrn. A lot of technical questions and details have to be clarified, such as the routing of the tunnel water pipeline, the required cooling system for the tunnel water after the heat pumps, the integration of the heat pumps in the existing heat plants, the heating water temperatures, etc. As mentioned in chapter 3.5.3, the combinations of heat pumps with CHP-plants can considerably increase the overall efficiency of heat plant systems. At the described heat pump system for the district heating Brixen/ Vahrn, the electricity produced by the CHP plant could cover the electricity demand of the heat pumps and improve energetic and economic efficiency.

99 Key Factors of Economy for a Heat Pump System to Exploit the Tunnel Water Heat for District Heating Systems From the results of this study it can be concluded, that apart of the tunnel water pipe length the two key factors for the economy of tunnel water heat utilization for district heating systems are: the amount of heat demand and the electricity price for driving the heat pumps. As table 32 shows, there is a substantial difference between the heat generation costs of the heat pump system in Franzensfeste and the one in Brixen/ Vahrn. This can be explained by the high investments implicated by the tunnel water heat utilization (tunnel water pipeline etc.) and the economies of scale with increasing heat demand. From this results it can be derived, that also for the district heating of Schabs, with an esteemed yearly heat demand of 5,000 MWh, tunnel water heat exploitation is not feasible.

Tab. 32: Comparison of heat generation costs for heat pump systems for Brixen/ Vahrn and Franzensfeste Heat without HEAT GENERATION COSTS Production by without with T.- Water (by Heat Pump without Heat Pump Financial Aid Financial Aid Catchement, Distribution) in €/ kWh per Year Pump and Pipe

Brixen/ Vahrn 62,938 MWh 0.0623 0.0588 0.0565

Franzensfeste 3,030 MWh 0.1252 0.1076 0.0933

Due to the high electricity consumptions of heat pumps in relation to their heat production, the second key factor for the economy of a heat pump system for district heating is the electricity price. In the heat generation cost calculation for the district heating of Brixen/ Vahrn the expenses for electricity represent 86 % (!) of total costs. Because of the required high temperature lift of the heat pumps for the tunnel water heat utilizations in district heating systems, COP’s higher than 3.5 are very unrealistic. Improving the COP would substantially increase the economy of a heat pump system for district heating.

Energy and Emission Balance The energy and emission balance of heat pumps in general as in this study are heavily dependent on the origin of the electricity consumed by the heat pumps. Because of the elevated primary energy consumption of global electricity production (especially fossil primary energy) and the resulting high air pollutant and

100 greenhouse gas emissions, heat pump systems do not belong to the environmental friendliest heat generation systems when fed with an international “electricity mix”. In contrast, when using exclusively electricity from renewable energy sources, heat pump systems rank among the most green and sustainable heat energy systems.

Degree of Tunnel Water Heat Utilization by District Heating With the investigated district heating systems only a small amount of the tunnel water’s geothermal potential at the south portal could be utilized. As table 33 shows, also in the scenario with the lowest geothermal output of the tunnel water, the heat surplus referring to the required cooling of the tunnel water is still over 100 MWh per year (69% of the cooling energy).

Tab 33: Degree of BBT’s tunnel water heat utilization by the district heatings at south portal

with 500 l/s at 22°C with 500 l/s at 25°C with 800 l/s at 25°C MWh/ year MWh/ year MWh/ year Tunnel Water Cooling 155,213 100.00% 191,690 100.00% 334,711 100.00% Necessity Franzensfeste 2,100 1.35% 2,100 1.10% 2,100 0.63% Schabs (with valued total heat 2,300 1.48% 2,300 1.20% 2,300 0.69% supply of 5,000 MWh/ year Brixen/ Vahrn 44,109 28.42% 44,109 23.01% 44,109 13.18%

Heat Surplus 106,704 68.75% 143,181 74.69% 286,202 85.50%

Proposals for Future Tunnel Water Heat Utilizations In addition to the investigated district heating systems at the BBT’s south portal, tunnel water heat utilization should be analyzed also for single house applications. Single house applications are only reasonable, when they are very close to the tunnel portal or the tunnel water pipeline. Also a feasibility study on a cold temperature district heating for Franzensfeste and Aicha with individual small heat pumps in the single houses may be useful. To exploit the tunnel water heat of the BBT in an economically and ecologically worthwhile way, industrial, commercial and agricultural heat consumers with considerable heat demands at low levels all over the year should be settled systematically near the tunnel portal. The preconditions for this are already given. Near the tunnel portal of the exploratory gallery there are areas for agricultural purposes as well as an existing expandable commercial area directly at the highway exit Vahrn/Brixen.

101 A special emphasis should be placed on innovative ideas and projects like sustainable agricultural and aquacultural applications as planned and already realized in Switzerland (see Chapter 3.7.2). Because of the sustainability of such projects, the utilization of the tunnel water heat gains further importance. The examples in Switzerland show, that such projects can easily become attractions and form recreation areas, so that locals as well as tourists indirectly could gain from the geothermal potential of the BBT’s tunnel water.

102 6. LITERATURE

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