Ground Source Heat Pumps (GSHPs) A Guideline Report
Ground Source Heat Pumps (GSHPs) A Guideline Report Authors Mr. Bartomeu Casals; International Geothermal Consultant Ms. Maria Anzizu; Engineer TTA Ms. Marilena Lazopoulou; Engineer TTA
Reviewers Dr. Hassan Harajli; Project Manager, EU funded UNDP – CEDRO IV Ms. Carla Nassab; Project Engineer, EU funded UNDP – CEDRO IV
Copyright © UNDP / CEDRO – 2017 All rights reserved for the Ministry of Energy and Water, the EU delegation to Lebanon and the UNDP. Reproduction is authorized provided the source is acknowledged and provided reproduction is not sold.
Acknowledgments The United Nations Development Programme (UNDP) would like to thank the European Union for the grant that established and enabled the work of CEDRO 4. CEDRO would also like to thank all its partners including the Ministry of Energy and Water, the Council of Development and Reconstruction, the Lebanese Center for Energy Conservation (LCEC), and all other institutions that closely work with this project. Forward
The EU is committed to an overall vision for a credible and responsive engagement in the world that aims to tackle the roots of poverty and promote sustainable development. Last year, we launched the EU Global Strategy that sets out this vision through a range of policies. The Sustainable Development Goals form a cross-cutting dimension of all the work to implement our Global Strategy. In Lebanon, the EU has put an emphasis on sustainable development in several of the sectors of its cooperation. We have laid out an array of financial support and technical assistance tools to promote, amongst others, the sustainable and transparent management of energy and natural resources.
It is in this spirit that the EU is supporting the UNDP-CEDRO IV project. This project has so far achieved several milestones and set up many pioneering initiatives encourage the switch towards renewable energy and energy efficiency. One of the initiatives of this EU-funded project is the 1.08 MW Ground Source Heat Pump (GSHP) system at the MEDRAR Medical Center in the South of Lebanon. This initiative provides the medical facility with its needs for hot water, heating and cooling through an innovative technology that sources under-ground heat. This is a pilot initiative that will inspire future investors, beneficiaries and contractors, and will immediately contribute to the Lebanese government’s 2020 target for ground source heat sources. It also reaffirms the EU’s continuous support to the roadmap towards a sustainable energy sector and a greener Lebanon.
Ambassador Christina Lassen Head of the Delegation of the European Union to Lebanon Forward
Following the adoption of the “Policy Paper for the Electricity Sector” in 2010 by the Lebanese Government, the Ministry of Energy and Water has drafted and adopted national action plans for both for Energy Efficiency (NEEAP) and Renewable Energy (NREAP). The Government has been committed ever since to lead the way and provide guidance in achieving Lebanon’s national target of 12% renewable energy by 2020.
This commitment has been translated into the implementation of the first 1 MW PV plant, the BRSS, followed by the 1MW PV plant at the Zahrani oil installation site, then the tendering of the 200 MW wind farms and the recent tender of 180 MW of solar photovoltaic plants. These initiatives are also mirrored in the sustainable energy stream with the recent funds added to the NEEREA financing mechanism of the Central bank of Lebanon (BDL).
It is through the long standing cooperation between the Ministry of Energy and Water and the international partners such as the United Nations Development Programme (UNDP) and the European Union (EU) that Lebanon is steadily moving towards a greener and sustainable energy sector. Thanks to the pilot projects implemented by the UNDP CEDRO project, the country is gathering pace and momentum towards achieving a more sustainable energy system.
This cooperation is demonstrated in a pioneering implementation, the 1.08 MW Ground Source Heat Pump implementation at the MEDRAR Medical Center in Choukine, South of Lebanon. This landmark project, co-funded by the Government of Lebanon through the Ministry of Energy and Water, will allow the medical facility to reduce its energy consumption for water heating and space conditioning throughout the year. The system, through the heat exchange with the underground will extract the hot air from the space and replace it with cool air during the summer and vice versa during winter. This project is the first of many to come that will feed into the Government’s set goal of 6 GWh of energy production from geothermal by 2020.
The present publication will serve as a guideline for possible future implementations based on the learnt experience form the MEDRAR project. This publication must be seen as a first and important step in developing our geothermal potential. I call on research academics to go more in-depth on the geothermal potential outlined in this report. I call on entrepreneurs to begin testing the ground and investing in geothermal resources. In turn, the Ministry of Energy and Water will ensure that the government assists in promoting and supporting the use of this renewable energy source.
César Abi Khalil Minister of Energy and Water Forward
This guideline report on ground source heat pumps is based on the actual experience gained from the design and construction of one of the largest projects of this kind in the Middle East. It is a prime example of the innovative work in the field of sustainable energy undertaken by the CEDRO at the MEDRAR Medical Center (MMC), a community health care facility in South Lebanon. The project was co-financed by the Government of Lebanon, the European Union and the Kingdom of the Netherlands.
These types of renewable energy systems use energy extracted from the earth or geothermal layers beneath the ground to heat and cool buildings. The implemented system is composed of approximately 180 vertical boreholes, each reaching 100 meters deep which will be used to circulate a special fluid that transfers energy from the depth of the earth to the building. In summer, cooling is boosted by storing the building’s heat in the ground, while in winter, heating is enhanced by extracting heat from the ground to the building. The system will also be delivering hot water to the hospital.
This type of renewable energy equipment saves on the hospital’s electricity and energy bills so that the savings can be invested in helping more people from the community. Estimated savings on heating alone from such a technology can go up to USD 140,000 a year. It also provides an environmentally-sound and clean source of energy for the facility; the system has 72% lower emissions than conventional electric heating would using conventional equipment.
The UNDP strongly believes that this project serves as both a demonstration and a market stimulator, especially for facilities with extensive need for space conditioning throughout the year. Similar facilities that could make us of such a system are resorts, hotels and hospitals to name a few.
The UNDP will continue to support the Ministry of Energy and Water in investigating and piloting new renewable energy technologies in the Lebanese context in order to reach the national climate change targets for 2030 and beyond.
Philippe Lazzarini UNDP Resident Representative Table of Contents List of Figures iii List of Tables iv Table of Acronyms v Glossary vi 1 Executive summary 1 1.1. Introduction to the geothermal concept 1 1.2. General principles on GSHPs using very low temperature geothermal energy 1 1.3. GSHP execution steps 3 1.4. Ground characterization 4 1.5. GSHP design 4 1.6 Technical specifications and standards 6 1.7 Construction and installation procedures 7 1.8 Operation and maintenance 8 1.9 Potential in Lebanon 9 2.0 Executive conclusion 10 2 Introduction to the geothermal concept 11 2.1 Definitions of geothermal energy 11 2.2 Types of geothermal energy 12 3 General principles on GSHPs using very low temperature geothermal energy 15 3.1 GSHP: How does it Work? 15 3.2 Heat pump 15 3.3 Ground heat exchanger systems 23 4 GSHP execution steps 29 4.1 Project’s conceptual design 29 5 Ground characterization 32 5.1 Ground investigation 32 6 GSHP design 35 6.1 Load assessment and GSHP Integration (sanitary hot water, heating and cooling) 35 6.2 Main components of a GSHP 37 6.3 Sizing 37 7 Technical specifications and standards 43 7.1 Component-specific specifications and characteristics 43 7.2 Regulatory framework 47 8 Construction and installation procedures 49 8.1 Planning requirements 49 8.2 Heat exchanger construction 49 8.3 System commissioning 56
i 9 Operation and maintenance 57 9.1 Measurement and monitoring 57 9.2 Protection and security 57 9.3 Maintenance requirements 58 10 Potential in Lebanon 59 10.1 Lebanese energy context 59 10.2 Climate and surface temperature (potential for the resource) 60 10.3 Geological and Temperature context 61 10.4 Main barriers and risks 62 11 Conclusions 63 12 References 65 13 Annex 1 66 14 Annex 2 67
ii List of Figures Figure 1. Ground source schematics 2 Figure 2. Steps to be followed for the construction of a GSHP 4 Figure 3. Drilling systems depending on the ground 7 Figure 4. Geologic layers of the Earth 11 Figure 5. Typical subsurface temperature evolution versus depth 13 Figure 6. Applications of geothermal energy depending on source temperature 20 Figure 7. If we consider the stability of underground temperature, why not live underground? 14 Figure 8. Carnot cycle 14 Figure 9. Geothermal scheme and cooling circuit 16 Figure 10. Expansion valve 17 Figure 11. Heat pump pressure / enthalpy diagram 17 Figure 12. Performance of a heat pump depending on the difference of temperatures 18 Figure 13. Sample ground source heat pumps 19 Figure 14. Working limits of a geothermal heat pump 20 Figure 15. Scheme for the water reversion of the cycle 20 Figure 16. Reversion cycle over the refrigerant gas circuit 21 Figure 17. Heat recovery in the reversion cycle over the refrigerant gas circuit 22 Figure 18. Construction of horizontal heat exchanger 23 Figure 19. Horizontal heat exchanger layout 24 Figure 20. Beirut seawater surface temperature variation 25 Figure 21. Slinky arrangement on wet medium 25 Figure 22. Horizontal distribution floodable medium 26 Figure 23. Set of Geothermal probe, 100 meters’ length, single U 26 Figure 24. Geothermal heat exchanger in loop 27 Figure 25. Steps to be followed for the construction of a GSHP 28 Figure 26. Sample of TRT test equipment 29 Figure 27. TRT test equipment circuit 33 Figure 28. Main components in a GSHP 34 Figure 29. Indoor recommended temperatures are the ones to be used for the designing of the heating and cooling load 37 Figure 30. Sample of distribution manifolds 38 Figure 31. Drilling systems depending on the ground 45 Figure 32. Hammer head and drilling bits 49 Figure 33. Rotary percussion drilling process 50 Figure 34. Bottom hammer and drilling bits 51 Figure 35. Direct mud circulation drilling process 51 Figure 36. End of probe weight, Y connection and spacers 52 Figure 37. Pipes connected with the Y connection at the output of the borehole 53 Figure 38. Grouting material injection 54 Figure 39: Energy mix per resource towards 12% of RE in 2020 60
iii List of Tables Table 1. Reference hot water demand depending on the facility 36 Table 2. Reference ground thermal capacity for horizontal heat exchangers 39 Table 3. Recommended piping diameters 40 Table 4. Ground thermal capacity for vertical exchangers 40 Table 5. Heat-transfer fluid characteristics 44 Table 6. Standards for heat pumps 46 Table 7. Example of heat pump commissioning checklist 56 Table 8. Hydraulic circuit check points 58 Table 9: Target Energy mix for 2020 59 Table 10. Temperature conditions in Lebanon 61 Table 11. Results of the TRT performed at the Medrar Medical Center 61
iv Table of Acronyms SHW Sanitary hot water BMS Building Management System COP Coefficient of Performance SCOP Seasonal Coefficient of Performance GSHP Ground Source Heat Pump HVAC Heating, Ventilating and Air Conditioning NP Nominal Pressure TRT Thermal Response Test EER Energy Efficiency Ratio PSV Pressure Safety Valve EU European Union Delegation to Lebanon CEDRO Country Energy Efficiency and Renewable Energy Demonstration Project for the Recovery of Lebanon UNDP United Nations Development Programme KW Kilowatt PE Polyethylene ASTM American Society of Testing and Material IGSHPA International Ground Source Heat Pump Association DVGW Deutscher Verein des Gas- und Wasserfaches; which is the German Association for Gas and Water CPU Central Processing Unit AC Alternating Current ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers KWh Kilowatt - hour EGEC European Geothermal Energy Council LSM Line Source Model CSM Cylinder Source Model CTE Spanish Technical Building Code UV Ultra Violet LCEC Lebanese Center for Energy Conservation LIBNOR Lebanese Standards Institution GEF Global Environmental Facility EEG Energy Efficiency Group MMC Medrar Medical Center MEW Ministry of Energy and Water BDL Banque Du Liban – Central Bank NEEREA National Energy Efficiency and Renewable Energy Action VAT Value Added Tax NEEAP National Energy Efficiency Action Plan NREAP National Renewable Energy Action Plan
v Glossary
Ground heat exchange field The narrow shaft bored vertically in the ground, where a geothermal probe is placed to get heat Borehole exchange between the probe and the ground. The Grouting is the fluid form of the thermal cement used to fill the gap between the walls of the Grouting borehole and the geothermal probe located inside. Geothermal probe Heat transfer tubes inserted in the borehole for the exploitation of geothermal heat. Heat source The area or media from which heat is removed. Manifolds Wide and pipe, into which smaller pipes or channels lead. Antifreeze Additive, which lowers the freezing point of a water-based liquid. The series of heat exchange pipes containing the antifreeze solution, buried horizontally in the earth or in Ground loop wet medium. Thermal energy production room Device designed to move thermal energy by absorbing heat from a cold fluid and releasing it to a warmer Ground source heat one. They use an electrical powered compressor to accomplish the work of transferring energy from cold pump to warm mediums. Buffer tank Thermal energy storage tank used on the cold or hot user side. Component which transfers heat energy from one medium to another one avoiding the fluid mixing and Heat exchanger pressure transfer of two hydraulic circuits The heat absorbing mechanism in a heat pump. Refrigerant changes phase from a liquid to a gas in this Evaporator exchanger, absorbing heat energy from the surrounding media in the process. The heat rejecting mechanism in a heat pump. Refrigeration heat exchanger where the refrigerant gives Condenser up its heat during condensation from a vapor to a liquid. COP / EER Heating / cooling capacity divided by electrical energy consumed. Liquid, which absorbs and releases heat energy by changing phase from a liquid to a gas and vice versa in Refrigerant response to the influence of a refrigerant compressor. Device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing Valve one or various passageways. Two ways valves have two operating positions either shut (closed), fully open for maximum flow, or Two-way valve sometimes partially open to any degree in between. Valves with three ports and can permit connection of one inlet to either or both outlets or connection of Three-way valve the two outlets Type of valve used to quickly release fluid from equipment to avoid over pressurization and potential Pressure safety process safety incidents. PSVs are activated automatically when pressure exceeds prescribed pressure valves (PSV) limits to return equipment pressure to a safe operating level Energy meters Device that measures the amount of energy flowing on a circuit, either electrical or thermal energy Recirculation pump Device that moves the fluid from one part of the hydraulic system to another one.
vi 1 Executive summary The EU-funded CEDRO 4 program has been (and is) implementing several innovative renewable energy systems, among which is a large ground source heat pump (GSHP) project for a Medical Facility in the South of Lebanon. To ensure that GSHP technology’s potential in highly utilized facilities are realized in Lebanon, this document provides a guideline on Ground Source Heat Pumps, aiming to be used as a practical manual for designers and installers of geothermal power plants.
1.1 Introduction to the geothermal concept Geothermal energy is the energy stored in the form of heat beneath the surface of solid earth and is considered a renewable energy source. The concept of a geothermal resource is so broad that it includes a range from the heat in the upper layers of the ground to the heat stored in rocks located in the deep subsurface. The technology available today for the exploitation of geothermal energy allows us to find and capture geothermal resources lying in depths of up to five kilometers and temperatures not exceeding 400°C. The temperature varies significantly in the first meters, reaches a stabilization point (at 10 to 15 meters) and then increases with a slightly positive gradient of about 2 - 3 degrees for every 100 meters. There are two main applications for GSHP: electricity production and direct uses of heat and selection for either application depends on the needs and local conditions. This report focuses on very low temperature geothermal energy, which uses the resources that are in the most superficial part, between the soil surface and at depths less than 200 meters. The average subsurface temperature may be found between 15ºC to 20ºC in countries like Lebanon, depending on average year around ambient temperatures.
1.2 General principles on GSHPs using very low temperature geothermal energy A typical GSHP system can be used equally effectively for heating, cooling or sanitary hot water services and consists of three main components: • Ground heat exchanger: Hydraulic circuit for extraction or injection of heat from/to the subsurface. • Heat pump: Extracts heat from the ground heat exchanger to the distribution grid or vice versa. • Distribution network: Transfers the heat from the heat pump to the building or vice versa.
1 Distribution network
Heat pump
Heat exchanger
Figure 1. Ground source schematics (source: NIBE AB, 2016)
1.2.1 Heat pump The heat pump is the device responsible for raising the temperature of the energy stored as heat from 5-22 ºC to 35-65 ºC, mainly for applications in residential HVAC systems. The heat pump consists of four items, one for each stage of the Carnot cycle and the refrigerant gas is responsible for transferring energy between the two spaces, referring to Figure 1: • Compressor (1 2): The refrigerant gas is compressed to a higher pressure. • Condenser (2 3): The refrigerant gas starts to change from gas to liquid conducting a condensation process transferring energy to the fluid used in the HVAC system. • Expansion valve (3 4): The refrigerant (fully liquid) goes through the expansion valve reducing its pressure and temperature. • Evaporator (4 1): The refrigerant enters in liquid phase and as it goes through, it reaches the evaporation temperature and changes its state from liquid to gas to start the process again. The performance of a heat pump is defined as the ratio of energy (heat) delivered to the electricity used. This relationship is known as coefficient of performance (COP) and, depending on the working conditions, the values can range between 2 and 5.
2 1.2.1.1 The ground source heat pump GSHP are designed to work in a water-to-water or water-to-air configuration. The water of the closed circuit (geothermal collector) is mixed with antifreeze glycol or methanol type. The power of these heat pumps can range from 3.3 kW to 150 kW or above. Manufacturers also offer the possibility of grouping pumps in cascades to reach power outputs of 500 kW, 1 MW or even higher. Manufacturers also offer reversible heat pumps that can act as heating or cooling equipment by using an integrated or external valve system to change the direction of the water flows.
1.2.1.2 Ground source heat pump configuration: two or four pipes Two pipes configuration is defined when there are only two pipes that are connected with the distribution network emanating from the thermal power plant, having warm water during winter and cold water during summer. Four pipes configuration, is a system where two pipes will have always cold water, and the other two pipes will have always hot water. With this configuration two water tanks (hot and cold) are required to cover the simultaneity of heating and cooling demand.
1.2.2 Ground heat exchanger systems The ground heat exchanger systems are classified into two main groups: • Horizontal heat exchangers (buried or in a wet environment): the network of a buried heat exchange pipe is installed in shallow horizontal trenches or excavations at certain levels underground. The thermal regeneration is basically done from solar radiation and rainwater. Therefore, no construction can be made on top of these exchangers, nor can they be placed under waterproof surfaces. • Vertical heat exchangers (closed circuit, open circuit or thermal foundations): these systems are installed vertically in the subsurface to exchange heat. Knowledge of geology and hydrology of the land allows one to know the ground characteristics and to choose the right system in each case. Foundation piles, such as heat exchangers (Energy piles), is also an option: The entire heat exchange system is located under the building itself, obtaining a considerable saving of resources and space, given the fact that the heat exchangers are included in the building construction project and are developed at the same time.
1.2.2.1 Geothermal probe The geothermal probe is the tube inserted into the borehole. The refrigerant liquid circulates inside the probe to absorb and/or expel the heat from/to the heat pump. The most commonly used geothermal probe is a polyethylene pipe.
1.3 GSHP execution steps When planning the conceptual design, the selected solution should be compared to other available solutions in the market to ensure it is the optimum adapted to the real necessities of the project. When going for the GSHP, Figure 2 shows the steps that need to be followed when constructing the plant.
3 Pre dimensioning
Field work / Hydrogeological analysis
Preliminary Draft
Yes Yes No Viable? Re dimensioning? No Detailed design Archive
Construction / Assembling
Commissioning
Functioning Monitoring
Figure 2. Steps to be followed for the construction of a GSHP (source: source: TTA, 2016)
1.4 Ground characterization When a project is being planned, one of the most important considerations is the availability of the resource in the proposed area of project implementation and the final needs. When the project becomes a real possibility, and always when the design reaches values equal to or higher than 30 kW (thermal), it is necessary to perform a TRT with the objective to measure the capacity of the subsurface as generator or absorber of thermal energy. The TRT consists of the following: • Pilot borehole: opening a borehole of the same characteristics as the future boreholes. • Undisturbed ground Tº: is the mean temperature at half the active borehole depth. • TRT: Injection of thermal energy into the ground and data collection for assessment. • Data analysis: Calculation of thermal resistance (R_b) and thermal conductivity (λ).
1.5 GSHP design The design of a GSHP system must consider its technical and economic viability.
1.5.1 Load assessment and GSHP Integration The power of the heat pump should be sufficient to cover the targeted thermal demand. It is very important not to oversize the installation to avoid long amortization periods. It should be noted that in a system with a geothermal heat pump and a closed circuit, the cost of the ground heat exchanger could be half the total investment.
4 1.5.2 Sizing The basic data for sizing a geothermal installation with the ground heat exchanger combined with a heat pump is the following: • Heat demand and performance of the heat pump (to define the power of the evaporator). • Water flow must circulate through the heat pump during normal operation. • Specific heat capacity of the land.
1.5.1.1 Heat pump and buffer tank The heat pump should be sized in such a way to operate the minimum number of hours per year and recover the investment within a reasonable period. Usually, partial sizing is done where the heat pump partially covers peak power but practically covers all the energy demand over a year: • Single mode: The heat pump is the only energy source covering 100% of the annual thermal energy demand. • Parallel dual mode: Supporting electric resistance starts when the demand cannot be covered by the heat pump. The heat pump and the resistance are working in parallel to provide the necessary thermal energy for the household. • Alternative dual mode: The heat pump is disconnected when it reaches a predefined level of thermal energy demand and an alternative system is connected. • Partially parallel dual mode: The heat pump and the alternative system are working in parallel to cover a specific amount of demand. If the demand increases, the heat pump is disconnected and only the alternative system is left operating. Oversizing the heat pump and, consequently, the geothermal field, would lead to high costs that would be difficult to recover.
1.5.1.1.1 Buffer tanks Buffer tanks are intended to increase the total water volume in the distribution hydraulic circuit. They are very useful when the heat pump is of the on/off type and the total power is generated without taking into consideration the thermal demand of a specific period.
1.5.1.2 Ground heat exchanger • Horizontal heat exchanger: It is necessary to know the heating and cooling power and the regime operation of the heat pump to define the required capacity. The heat exchanger surface is to be calculated (m2) based on the specific heat capacity of the land and required capacity, previously calculated. Once the collecting area is known (m2 of pipe), the length is to be defined, based on the final diameters of the pipes. • Vertical heat exchanger: It is necessary to know the heating and cooling power and the regime operation of the heat pump to define the capacity required. The specific heat capacity (between 40 and 100 meters deep) depends on the ground thermal conductivity and the annual operating hours. Knowing the power and type of ground, one can determine the length of the probe and the number of probes.
5 1.6 Technical specifications and standards 1.6.1 Heat exchanger field
1.6.1.1 Boreholes The ground heat exchanger field consists of many boreholes. Usually the boreholes for vertical GSHP applications are 100 meters deep and have a 127 mm (5’’) diameter.
1.6.1.2 Geothermal probe They are recommended to be manufactured from a polyethylene PE100 extrusion grade material and RC (Resistance to crack) with a minimum cell classification of PE345434C per ASTM D-3350 and fully comply with the IGSHPA standard 1C “Ground Heat Exchanger Materials.”
1.6.1.3 Concrete (grouting) injection The grouting material must have a minimum thermal conductivity of 2 W/mK, must be chemical hazard free and must meet the requirements placed on groundwater measuring point sealing as stipulated in the DVGW code of practice W121:2003-07.
1.6.1.4 Circulating fluid characteristics The heat-transfer fluid in an exchange subsystem is a mixture of water and propylene glycol, usually with a 30% concentration of the total fluid volume.
1.6.1.5 Manifolds The manifolds should be equipped with flow meters, ball valves made of brass, bronze and stainless steel.
1.6.2 Heat pumps The COP must be certified under the EN 14511 standard and shall be fully functional with the selected design (2 pipes/4- pipes). They should include, at least: One or more compressors per heat pump; Condenser and evaporator per each compressor; Expansion valve; One or more circulation pumps (one per compressor); Circulation pump; Electronic control system, CPU-based and Color displays and monitoring. A first brand heat pump manufacturer must offer a minimum of two years’ warranty for the whole product range.
1.6.3 Energy meters (thermal and AC meters) The thermal energy meters should be static meters with an ultrasonic flow sensor. The measurement accuracy shall be equal to or better than Class 2. The protection class shall be a minimum IP67 with the environmental protection per EN 1434 class C; shall be compatible with the monitoring system and be able to withstand the working conditions.
1.6.4 Regulatory framework There are many standards, recommendations and technical papers that are edited by private organizations (e.g. ASHRAE), the European Commission (i.e. EN norms) and also well-reputed professional associations like VDI (German). These provide very useful references to be followed when a GSHP goes under a design process.
6 1.7 Construction and installation procedures The construction works at the selected site should start when the shop drawings are completed, a concise environmental statement specifying waste disposal arrangements during installation is finalized, a description of the proposed performance testing procedure and a letter certifying the requirements on warranties, spare parts and standards are prepared and approved.
1.7.1 Heat exchanger construction
1.7.1.1 Drilling Horizontal heat exchangers do not require special machinery for their construction. However, special attention should be paid when constructing the vertical closed loop heat exchanger. The most common systems are listed in Figure 3.
Vertical bore hole drilling
Stable ground (rock, compact clay) Unstable ground (clay, sand, gravel)
Air percussion drilling Rotary mud drilling
Rotary percussion Reverse circulation Direct circulation
Figure 3. Drilling systems depending on the ground (source: TTA, 2016)
1.7.1.1.1 Drilling on stable ground Rotary percussion drilling is performed with the fragmentation of the rock by the impact caused by a hammer, which is transmitted to the drilling tool, and which is at the same time in contact with the rock. There are two types: • A rotary percussion top hammer: It is generally used for small boreholes on hard ground. The lengths do not exceed 30 meters due to significant energy losses that occur in the transmission of the shock wave and bars deviations. • Rotary percussion with bottom hammer is generally used for hard rocks at depths of up 250 - 300m, in this case placed between the hammer rod and drilling tool.
1.7.1.1.2 Drilling unstable land In unstable lands, rotary drilling with direct circulation is performed by inserting a cutting tool, which is supported from the top using threaded steel pipes and is responsible for transmitting the rotational movement and force from the surface.
7 1.7.1.2 Geothermal probe insertion To ensure that the geothermal probe does not create thermal shorts, pipe spacers are to be used, located approximately every five meters. In order to ensure the correct introduction of the probe, the probe must be completed with a 25-kilogram weight fixed on the probe bottom.
1.7.1.2.1 Probe testing before insertion of probe into the borehole The probes should be tested filling with water at a pressure of 6.0 bar for 30 minutes, checking that the pressure does not drop more than 0.6 bar. Once the test is done, the probes shall be left sealed, pressurized, and introduced into the borehole filled with water.
1.7.1.2.2 Grouting pipe After the insertion of geothermal probe into the borehole, it must be filled with appropriate grouting material. The injection of such material must be done using a DN25 polyethylene pipe, inserted together with the geothermal probe.
1.7.1.3 Grouting The material is to be installed from the bottom to the top of the borehole. If any settling occurs during the initial 24-hour period after installation, additional material can be added to ensure that grouting material remains at surface level.
1.7.1.4 Geothermal probes pressure and tightness test Once the probes are introduced into the borehole, the following steps shall be performed. • Cleaning: The inside of the geothermal probe shall be cleaned with pressurized water to remove any particles that may have appeared during the installation, and to purge the pipes. • Pressure and tightness test: A pressure and tightness test at each borehole shall be done, according to the EN 805:2000 standard, at a minimum 1.5 times the nominal working pressure, and not less than 6 bar.
1.7.2 Components assembling (production room) All the components’ assembling jobs should be carried out according to local regulations related to thermal installations, including safety procedures. The VDI 2050 standard gives a useful outline with respect to the requirements for the technical equipment rooms.
1.8 Operation and maintenance It is recommended that the data logger has a Display Unit showing the following: • Device for real time visualization and download of stored data. • Display of: Daily, weekly, monthly, yearly and accumulated since the commissioning of the GSHP; Thermal energy produced (kWh); Electricity consumed (kWh); COP; Temperature at measuring points (ºC); Flow (m3/h); ambient (outdoor) temperature (ºC); Installation reference number. • Customization of an interface for large format TV screen.
8 After operating for one year, it is recommended to assess the project by using technical data downloaded from the data logger as well as user questionnaires. In case deviations from the scheduled performance are recorded, it is recommended to carry out an operation test of the GSHP plant to detect the cause of the deviations. The VDI 6041 standard can be used as a reference for technical monitoring and facility management.
1.8.1 Protection and security The following items are to be installed for security: • Expansion vessels: To reduce pressure in certain points of the circuit that can be affected by temperature variations and its consequent over pressure. • Pressure safety valves, adjusted to the maximum working pressure at any part of the hydraulic circuit exposed to over pressures. • Air venting devices at all high points of the piping circuit. • Differential switches and circuit breakers: To protect the electric installation.
1.8.1.1 Labeling All piping circuits should be labeled with the flow direction (arrows) and legends that allow identifying the respective functions overall hydraulic circuit. Legends are preferred to be per the GSHP design. A drawing or sign is recommended to provide warning about safety hazards, e.g. smoking, water contact, etc. as well as emergency shutdown procedures.
1.8.2 Maintenance requirements A GSHP system requires a discrete preventive maintenance, considering that the heat pump works following similar technical principles as a domestic fridge. To reach continuous and efficient day-to-day work, the hydraulic circuit, including the ground heat exchange, should be periodically checked.
1.9 Potential in Lebanon
1.9.1 Lebanese energy context Referring to the 2010 electricity balance baseline adopted by the government in drafting both the NEEAP and the NREAP, EDL electricity generation presented a 3,845 GWh gap that is covered, mostly, by private diesel operated generators. Furthermore, the Government set target for its energy mix by 2020 includes approximately 12% of electricity generation from renewable energy sources, amongst which 6 GWh (nearly 1%) from geothermal energy (LCEC, 2016). A financial incentive through the NEEREA loan has been set-up for such implementations and the guidelines for the preparation of the technical proposals has been developed by the LCEC and is included in Annex 2 of this report. The present report discusses shallow geothermal energy requiring less drilling depths, a technology that has still not been investigated in-depth in the case of Lebanon.
1.9.2 Climate and surface temperature (potential for the resource) Lebanon has Mediterranean temperature conditions. Therefore, the average subsurface temperature may be between 15ºC to 20ºC in Lebanon, depending on average year around ambient temperatures.
9 1.9.3 Geological context Geological and hydro geological conditions of the area where the GSHP plant will be implemented should be considered as the basis of the ground heat exchanger field design. Given Lebanon’s inexperience, the ground composition assessment, as well as the TRT, should be done when a project is about to be implemented to evaluate the ground thermal properties. Given the ground composition identified in Lebanon, limestone, marl, etc. an average specific heat extraction potential of 20 to 85 W/m2 depending on the area and operating hours is found.
1.9.4 Main barriers and risks
1.9.4.1 Technological barriers Given Lebanon’s short experience, the main technological barriers identified are the technology barriers. The main barrier is related to the drilling technology.
1.9.4.2 Legal barriers There are several permits that are required for geothermal plant construction, which should be further assessed and included in the Lebanese context (Vicent Badoux, 2014), such as the exploitation permit of underground resources when hydrocarbons and other extractables are targeted; construction permit for the GSHP plant; application for an environmental impact assessment and land ownership - land ownership or approvals from the land owners is necessary. Obtaining the mentioned permits may delay the implementation of the GSHP.
2.0 Executive conclusion Ground source heat pump applications are widespread in North America and Europe with rather limited applications in the Arab regions. With the current technology market status, heat pumps are considered the most energy efficient with savings reaching at least 35% when compared to the conventional counter-parts oil or gas fired boilers. This report focused on shallow ground sourced heat pumps which require very low temperature (T < 30˚ C) typically found in the upper level of the earth in depths not exceeding 200 meters. The low temperatures available at these depths are ideal for direct heating (cooling and hot water) use through heat pumps. Given the little available experience and knowledge in the GSHP construction in Lebanon, prior to any implementation a thermal response test (TRT) test is advisable in order to gather ground thermal properties. The report details the full technical specifications, action plans or steps required, and the overall benefits of ground source heat pump applications for Lebanon.
10 2 Introduction to the geothermal concept
2.1 Definitions of geothermal energy The term geothermal energy is used to concretely explain the effects and / or source of heat emanating from the interior of the Earth. Geothermal is a word of Greek origin, derived from the words “ge” meaning earth and “thermos” which means heat (heat from the ground). It is worth noting that the term geothermal energy is used interchangeably to refer to the science that studies the internal thermal phenomena of the planet, as well as all the industrial processes that attempt to exploit this heat to produce useful electricity or heat. In its broadest sense, geothermal energy is the energy (in the form of heat) transmitted from the inner layers of the Earth to the outermost part of its crust. In Directive 2009/28/EC (European Parliament), it is defined as the “energy stored in form of heat beneath the surface of solid earth” and is considered as a renewable energy source. This matches the definition in the Brussels Declaration 2009 of the European Geothermal Energy Council (EGEC), which states that geothermal energy is the energy stored in form of heat beneath the surface of the Earth. It is a source of sustainable, renewable, abundant energy, which provides heat and electricity 24 hours a day throughout the year. This heat rising from inside the Earth is the result of geodynamic heat flow among the different layers of the Earth with various characteristics. To understand this physical phenomenon, the characteristics of the subsurface layers should be looked into, according to their chemical composition (crust, mantle and core) and physical properties (lithosphere, asthenosphere, mesosphere and core), as shown in Figure 4.
Figure 4. Geologic layers of the Earth (source: Wikipedia, 2016)
11 The layers are defined depending on their composition as follows: • Core: The composition of the core is an alloy of iron, nickel, oxygen, silicon and sulphur in minor amounts, found at an estimated temperature of around 6,000°C. • Mantle: It is a solid layer extended to a depth of 2,900 km. It is estimated that the maximum temperature reached in the mantle is about 3,500°C in the zone closer to the core, decreasing to 600°C in the zone closer to the crust. • Crust: Generally, it can be subdivided between continental and oceanic. The oceanic crust is about 7 km thick and is composed by dark igneous rocks called basalts. The continental crust has a thickness of 35 to 40 km, but can reach up to 70 km. Unlike the oceanic crust, the composition of the continental crust is more heterogeneous; the upper level is composed of granitic rock, while deeper levels are more like basalt. It represents only 2% of the volume of the Earth.
2.2 Types of geothermal energy Geothermal energy is the heat stored in rocks, soil and groundwater, whatever their temperature, depth and origin is, but not the heat content in surface, continental or marine water. The heat contained in rocks and soil is too diffused to be directly extracted in an economical way; thus, it is necessary to have a fluid, usually water, to transport heat to the surface through boreholes, deep geothermal heat exchangers, or via heat exchangers buried in the shallow subsurface. Once on the surface and depending on its heat content, the heat can be harnessed to produce electricity, or it can be used in heat exchangers or heat pumps. The concept of a geothermal resource is so broad that it includes the range from the heat in the upper layers of the ground to the heat stored in rocks located in the deep subsurface to depths exceeding 1,000 meters that can be reached with techniques of oil drilling. The technology available today for the exploitation of geothermal energy allows finding and capturing geothermal resources lying to depths of up to 5 km and temperatures not exceeding 400°C. The different types of geothermal resources are listed below, according to their level of temperature: • High temperature sources (T > 150 °C): They are mainly found in areas with high geothermal gradients, situated at variable depths (usually between 1,500 and 3,000 meters). They consist of dry steam (in rare cases) or a mixture of water and steam, which is mainly used for electricity production. • Average temperature resources (90 °C < T < 150 °C): They are in areas with a high geothermal gradient at depths below 2,000 meters and in sedimentary basins at depths between 3,000 and 4,000 meters. Resources of such temperatures, in the form of water, are suitable for production of electricity using binary cycles. They can also be used for thermal applications in urban centralized heating systems (district heating) and in industrial processes. • Low temperature resources (30 °C < T < 90 °C): They are usually located in areas with a normal geothermal gradient at depths between 1,500 and 2,500 meters or even at 1,000 meters in areas with a higher geothermal gradient. This low temperature resource is used in heating and / or air conditioning and in various industrial processes. Geothermal fluids are rarely used directly and usually require heat exchangers and/or heat pumps. Such investment is profitable only when the demand occurs close to the production point and underground pipelines and distribution stations are not required. • Very low temperature resources (T < 30 °C): The temperatures of these resources tend to approach the annual average of the area where captured. They correspond to the thermal energy stored in the groundwater and in the shallow subsurface, usually less than 200 meters. In the latter case, renewable energy can be captured very efficiently when the subsurface is thermally stable given the seasonal fluctuations of the environment, resulting from the heat transfer towards the outermost areas of the cortex. This heat transfer permits constant ground temperature throughout the year at depths of 10-15 meters. This resource is used for direct heat applications with or without heat pumps.
12 During the design of a heat exchanger, the temperature is stabilized as one goes deeper into the ground. The undisturbed temperature varies significantly in the first top meters, reaches a stabilization point (10 to 15 meters) and then increases with a slightly positive gradient of about 2 - 3 degrees for each 100 meters, as seen in the graph below (Figure 5):
Figure 5. Typical subsurface temperature evolution versus depth, (source: Tellus Ignis S.L., 2016)
When analyzing the different types of geothermal resources (high, medium, low and very low temperature), it is observed that the application of each resource depends on the technologies available for the project. However, there are two main types of applications: • Electricity production: For high temperature, geothermal resources, the water vapor can be directly transformed into electrical energy; medium temperature resources can generate electricity but always through a geothermal fluid and with external energy support. • Direct use of heat: Requires some of the medium and low temperature resources, as well as very low temperatures that will be using the heat pump. The technologies applied in each case vary and depend on the type of resource that is intended to be used, the technical and economic feasibility of the solution and the possibilities of direct energy use (within the scope of zero km energy[2]). An overview on the Applications of geothermal energy depending on the source temperature is shown in Figure 6.
[2] Zero km energy refers to the production of energy as close as possible to the point of consumption, in order to avoid losses of the distribution grid. 13 Geothermal Energy Applications
Heating with heat pumps - Climate Under oor heating Leisure centres - Pool Spa therapy - Termalism Preheating (water-air) Hot water District heating Growing mushrooms Greanhouse heating for oor Greanhouse heating for air Preheating (water-air) Drying of agricultural products, wood, sh Canneries Preheating (water-air) Thaw Washed wool and dyes Drying of industrial products Production of electricity in binary cycle plants Cooling for absorption Extraction of chemical substances Distillation freshwater Recovering metals Electricity production Evaporation concentrated solutions Manufacture of paper paste Refrigeration for ammonia absorption
10 °C 30 °C 90 °C 150 °C
Very low Low temperature Medium temperature Hight temperature temperature
Figure 6. Applications of geothermal energy depending on source temperature (Source: ADEME, 2016)
Figure 7. If we consider the stability of underground temperature, why not live underground? (Author: Marta Casals ©)
14 3 General principles on GSHPs using very low temperature geothermal energy
3.1 GSHP: How does it Work? The underground can be used as a heat source, cold source and thermal reservoir. It is well suited for many applications in the low-temperature range due to the available large volume and the constant temperature level (VDI 4640, Part 1, Preliminary note). The geothermal resources of very low temperature can be potentially used in any application that requires thermal power for central heating, cooling or sanitary hot water, using a ground heat exchanger. As mentioned earlier, geothermal resources of very low temperature are located in the crust of the earth in the most superficial part, between the soil surface and at depths less than 200 meters. There, the average temperature of the ground is usually 5-6 °C in higher latitudes such as in countries like Sweden or Norway and close to 20-22 °C in lower latitude countries like Lebanon. Direct use of energy for heating is not feasible at these levels of ground temperatures. Therefore, an external device is needed to exploit the energy stored in the crust at a low temperature and raise it to necessary values for useful applications such as sanitary hot water or air conditioning through air or water systems. A typical GSHP system can be used equally effectively for heating, cooling or sanitary hot water services and consists of three main components: • Ground heat exchanger: Circuit for extraction or injection of heat into the subsurface. • Heat pump: Extracts heat from the ground heat exchanger to the distribution grid or vice versa. • Distribution network: Transfers the heat from the heat pump to the building for heating and sanitary hot water, and from the building to the heat pump during cooling applications. The distribution is out of the scope of this guideline similarly with other thermal energy generation systems using hydraulic circuits to heat or cool a space. However, it is always recommended to use low temperature heat distribution systems (like radiant floor or over dimensioned radiators) in order to reach the maximum energy efficiency.
3.2 Heat pump The heat pump is the device responsible for raising the temperature of the energy stored as heat from 5-22 ºC to 35-65 ºC, mainly for applications in residential Heating, Ventilating and Air Conditioning (HVAC) systems. The operation of the heat pump is based on the Carnot cycle: It transfers heat from a low temperature (heat source) to a high temperature (useful heat spaces). To perform this task, the heat pump requires an external source of energy that is usually the electricity driving a compressor.
15 The Carnot cycle consists of four stages, two isothermal stages at constant temperature and two adiabatic stages thermally isolated. The process is cyclical and continuous, while low-temperature energy is extracted and delivered to high temperature energy. The component responsible for transferring energy between the two spaces is a refrigerant gas with a low boiling point. The performance of a device that follows the Carnot cycle depends on the temperatures of the two working areas and the distance between them; the closer they are, the higher the performance is. The heat pump consists of four items, one for each stage of the Carnot cycle, namely the compressor, condenser, expansion valve and evaporator (Figure 8).
Figure 8. Carnot cycle (source: TTA)
To better understand the processes carried out in the heat pump’s circuit of refrigerant gas, the analysis should start with the explanation of the evaporation and condensation of liquid, related to its absolute pressure, which are directly proportional. Another very important process involved in the heat pump operation is the changes of state of a fluid without varying its temperature and the energy used during those changes, which is called latent heat. Therefore, the energy transfer is higher during the fluid’s changes of state; the heat pump uses this property for energy transfers.
3.2.1 Sequence of states of the refrigerant gas in a heat pump The following steps are the states of the refrigerant in a heat pump: Compressor (1 2 in Figure 9). The refrigerant enters in the form of gas into the compressor, which works by compressing it to a higher pressure. During this process the energy supplied by the compressor results in an increase of the gas temperature and pressure, producing a superheated gas. Condenser (2 3 in Figure 9). The superheated gas enters the condenser where the heat exchange takes place with the high temperature source, water or air. The refrigerant gas transfers energy decreasing its temperature to the condensation temperature. The refrigerant gas starts to change from gas to liquid conducting a condensation process transferring energy to the fluid used in the HVAC system.
16 Expansion valve (3 4 in Figure 9). At the output of the condenser, the refrigerant is in its fully liquid phase and totally condensed. The refrigerant goes through an expansion valve to reduce its pressure and temperature. Evaporator (4 1 in Figure 9). The refrigerant enters into a liquid phase at a low temperature in the evaporator, and as it goes through, it reaches the evaporation temperature. The refrigerant changes its state from liquid to gas by absorbing the energy from the low temperature source. Once the refrigerant has entirely evaporated, it enters at low pressure in the compressor to start the process again.
Figure 9. Geothermal scheme and cooling circuit (source: NIBE AB, 2016)
The expansion valve is responsible for ensuring that the liquid entering the evaporator is completely evaporated into gas and liquid does not enter the compressor stage. It has an input port for high pressure and output port for low pressure, a bulb associated with the outlet of the evaporator before the compressor’s input and a set point for overheating, usually an internal screw with a spring (Figure 10).
Figure 10. Expansion valve (source: Emerson climate, 2016)
17 The bulb is filled with the refrigerant gas and transmits a force for the opening of the valve in the positive direction of the refrigerant gas flow. The amount of refrigerant gas only depends on the balance of the three forces involved and the only way to vary the flow is acting through the screw. If the expansion valve is almost closed, the amount of refrigerant flowing into the evaporator will be small and the temperature in the output will increase. The bulb detects this temperature increase, which leads to an increase in the valve opening pressure, thus, more refrigerant will enter the evaporator, decreasing the temperature at the output until it reaches the equilibrium. The pressure bulb is the element of control, which transmits the thermal conditions of the evaporator output and interacts with the valve that regulates the flow of refrigerant. For each type of power compressor and refrigerant gas, a specific expansion valve will be used.
3.2.2 Performance of the heat pump Analyzing the refrigeration cycle of the gas in the operation of the heat pump in a pressure-enthalpy diagram, the electrical energy used by the compressor depends on the operating characteristics of the heat pump during a given time. Both the evaporation pressure and the condensation depend on the ambient temperature and this oscillation will affect the energy used by the compressor. The higher the difference in temperatures between the evaporation and condensation, the more energy required (Figure 11).
condensation
2 1
5 6 expansion compression
3 4 evaporation
A
B
Figure 11. Heat pump pressure / enthalpy diagram (source: Refrigeration Engineer, 2016)
The performance of a heat pump can be defined as the ratio of energy delivered in heat by the condenser to the electricity used by the compressor. This relationship is known as Coefficient of Performance (COP)
(Energy delivered ( kWh)) Coefficient ofPer formance (COP) = (Energy consumed ( kWh))
18 Depending on the working conditions of the heat pump, the values of the COP can range between 2 and 5. Low temperature systems (20 - 40°C) such as under floor heating are the most efficient. High temperature systems such as radiators are less efficient because they work at a higher temperature (COP 3 approximately). Figure 12, below, shows how for the same return temperature in the evaporator, the COP increases when the supply temperature in the condenser is lower. The most efficient working point of a heat pump is found where it condenses with low-temperature systems and where it evaporates at a not so low-temperature. GHP are a clear example: the evaporator works connected to a geothermal system that maintains a more or less constant evaporation temperature throughout the year, reaching a high COP. The influence of the ambient temperature does not affect the performance of the heat pump. When the evaporator works by absorbing heat from the ambient air (i.e. air-to-air, air-to-water heat pumps), the ambient temperature will be affected by the variations and will therefore experience a reduction in efficiency.
Figure 12. Performance of a heat pump depending on the difference of temperatures (source: NIBE AB, 2016)
Although the value of COP shows the performance of a heat pump at a certain input and output temperatures, the manufacturers of heat pumps are also obliged to give the value of SCOP (seasonal COP) that is more than the average COP value throughout the yearly period of work. This value is calculated per the EN14825 standard and gives us a better idea of the behavior of the heat pump either for a heating or cooling process.
3.2.3 Heat pumps classification A possible classification of different heat pumps can be done based on the different types of heat sources (HPA, 2016): Air-water heat pumps: Extracts heat from outside air and transfers it to a water circuit to supply thermal energy to sanitary hot water tanks, radiators, fan coils, etc. Air-air heat pumps: Extracts heat from outside air and transfers it to inside air. Water-water heat pumps (ground source heat pump): Extracts heat from ground or water and transfers it to a water circuit to supply thermal energy to sanitary hot water tanks, radiators, fan coils, etc. Water-air heat pumps (ground source heat pump): Extracts heat from ground or water and transfers it to inside air.
19 3.2.4 The ground source heat pump (GSHP) The ground source heat pump is designed to work in water-to-water or water-to-air configuration. The GSHP works connected to a piping system buried in a closed water circuit known as an underground geothermal collector. The water of the closed circuit is mixed with antifreeze glycol or methanol type which keeps the freezing point of the solution at around -15°C. These types of machines can work with evaporating temperatures of up to -10°C. The great advantage of geothermal installations is that the heat pump works with very stable evaporation temperatures during the whole heat production process, obtaining very high SCOP values when compared to other types of heat pumps such as those that use air for energy extraction. The power of these heat pumps can range from 3.3 kW to 150 kW or above. Manufacturers also offer the possibility of mounting pumps in cascades to reach power outputs of 500 kW, 1 MW or even higher. Some samples of existing heat pumps are shown in Figure 9, while Annex 1 indicates sources of information on multiple brands for GSHPs. Figure 13 shows a GSHP sample. Temperatures can reach up to 65°C and are therefore able to satisfy the needs of air conditioning
Figure 13. Sample ground source heat pumps (Source: NIBE, CIAT and Alpha Innotec, 2016)
Traditionally, these types of heat pumps have been used in cold weather areas such as North or Central Europe for sanitary hot water and heating. Figure 14 shows the working limits of a geothermal heat pump. On the X-axis, the water temperature in the input of the evaporator is shown and the Y-axis corresponds to the temperature of the condenser. In this case, it is observed that the maximum condensation temperature is 65°C from an evaporator input temperature of -8°C.
Figure 14. Working limits of a geothermal heat pump (Source: NIBE AB, 2016)
20 The GSHP system includes one heat pump with power output rated to cover the heating and/or cooling needs. When higher power outputs are requested, there is the possibility to use several heat pumps connected in cascade to reach the desired power output capacity. In this case, the heat pumps configuration is done using the Master – Slave method: The “Master” pump is set with the working mode and the selected temperature that should be reached. Based on the programmed parameters, the “Master” Pump selects the number of compressors in operation required every moment (i.e. for itself and also for the “Slaves”). The “Master” also controls the main circulation pumps and each “Slave” controls its own condenser or evaporator water circuit recirculation pumps. Because geothermal heat pumps have started to be used in lower latitudes, it is now necessary to incorporate cooling production to meet the needs with the same heat pump without having to duplicate systems (i.e. increasing the cost). To efficiently satisfy the heating and cooling needs using the same geothermal heat pump, manufacturers offer reversible heat pumps that can act as heating or cooling equipment. The most common methods available are: • To carry out the reversion of the cycle at the hydraulic level through external valves; or • To carry out the reversion of the cycle at refrigerant level using a 4-way valve. Like any technical solution, each one has its advantages and disadvantages, which are described below:
3.2.4.1 Reversion cycle on hydraulic circuit This solution is done using 3-way valves to change the direction of the water flows from/to the evaporator and condenser. When the heat pump is operating in heating mode, the evaporator is connected to the ground collector and the geothermal heat pump extracts the heat from the ground, and the condenser is connected to the distribution circuit to heat it. When the heat pump operates in cooling mode, the evaporator is connected to the distribution circuit to remove heat and send it to the geothermal collector though the condenser.
1. Heating medium supply 2. Heating medium return 3. Brine in 4. Brine out 5. Docking in (HM from heat pump) 6. Docking out (HM to heat pump) 7. Docking in (Brine from heat pump) 8. Docking out (Brine to heat pump)
Figure 15. Scheme for the water reversion of the cycle (source: TTA)
This reversion cycle (Figure 15) is interesting when the facility has the need for heat recovery in summer, for example, to maintain the temperature of a swimming pool or if the sanitary hot water production demands are high. The waste heat from the facility is not dissipated in boreholes and can be used for such applications. Another application that can be achieved is passive cooling.
21 During periods with an overall low heat refrigeration demand, the possibility of using a floor or wall cooling system with water temperature of about 15-18°C may be enough to satisfy the demand and to keep a space with a comfortable temperature. If the subsoil where the bore holes are at a constant temperature, are equal to or less than 15°C, it will allow the water and antifreeze mixture to circulate through the geothermal ground heat exchanger to maintain an adequate temperature to be sent to the distribution circuit through a circulation pump without using the compressor and thereby saving electric power consumption. This configuration allows reducing the ambient temperature of an area with low energy consumption, but with the drawback that the evaporator circuit antifreeze is mixed with the whole hydraulic circuit. There is the possibility of putting a heat exchanger between the heat pump and the distribution circuit to prevent the antifreeze being mixed with the distribution channels but it increases the price of installation and decreases the whole system’s energy efficiency.
3.2.4.2 Reversion cycle over the refrigerant gas circuit This solution is based on the installation of a 4-way valve in the compressor output, which has the function of diverting the refrigerant gas to one side during the heat and to the other during cold production. In this configuration, there is no evaporator or condenser but depending on the mode of operation it can run as condenser or as evaporator. Such type of applications are known as internally reversible geothermal heat pumps (Figure 16).
Outside 3 3 Inside Outside 3 3 Inside 4 4 2 2 4 4 2 2 Heat Heat Heat Heat
5 5 5 5 1 1 1 1
1. Compressor 2. Exchanger (Condenser/Evaporator) 3. Expansion valve 4. Exchanger (Condenser/Evaporator) 5. 4 ways valve
Figure 16. Reversion cycle over the refrigerant gas circuit (source: Tellusignis, 2016)
This configuration does not allow the simultaneous production of hot and cold water at the same time. The heat pump must stop the cold-water production and switch to the heating cycle in case there is sanitary hot water demand. Therefore, passive cooling is not possible. This solution is less complex and therefore cheaper and the antifreeze does not mix with the distribution cycle. There is the possibility to use a condenser connected to the compressor output and before the 4-way valve, which would allow the recovery of heat for covering partially or totally the sanitary hot water needs (Figure 17).
22 2 4
1. Compressor 2. Sanitary hot water 3. 4 ways valve 1 3 5 4. Indoor unit 5. Expansion valve 6. Outdoor unit
6
Figure 17. Heat recovery in the reversion cycle over the refrigerant gas circuit (source: TTA, 2016)
Technology linked to the compressor manufacturer’s evolution is advancing rapidly. Nowadays, manufacturers offer heat pumps with compressor systems that can work with variable speed technology (also named inverter), to adapt the generated power to the variations in the thermal demands and allowing higher energy performance.
3.2.5 Ground source heat pump configuration: two or four pipes? As mentioned earlier, the ground source heat pump can be used as a heating or cooling thermal energy generator, depending on the evaporator and condenser configuration. When the GSHP system is designed to cover the heating demand during winter, and /or cooling demand during summer, two pipes configuration can be used: a “two pipes” configuration is defined when there are only two pipes that are connected with the distribution grid emanating from the thermal power plant, having warm water during winter and cold water during summer. With this configuration, during winter, the heat pump condenser is connected to the distribution grid and the evaporator to the ground heat exchanger, and vice versa during the summer period. What happens when there is a heat and cool thermal energy demand at the same time? In this case, the two pipes configuration will not be able to cover this simultaneity of heating and cooling demand. But if the heat pump condenser is connected to a buffer tank, called a “hot tank,” and at the same time the heat pump evaporator is connected to another buffer tank, “cool tank,” we will have a four pipes configuration, where two pipes will have always cold water, and the other two pipes will have always hot water. This configuration gives premium energy efficiency, since it can generate double the quantity of thermal energy with similar energy consumption to the two pipes system.
3.3 Ground heat exchanger systems While analyzing the investment to build a GSHP, one will find that the cost of the construction of the ground heat exchanger may represent approximately 50% of the total investment, and in some cases this cost can undermine the viability of the project, especially in markets such as Lebanon, where, currently, there is still no adequate infrastructure of experienced companies using this technology that can provide professional services and prices in line with other more mature markets, such as Europe or the United States, where this technology has been used for many years.
23 Therefore, at the time of projecting a GSHP system, the first point that must be considered in choosing the most appropriate ground heat exchange system is knowing the power of the evaporator and the condenser of the heat pump proposed, which define the energy that needs to be extracted or injected into the ground. The most favorable ground heat exchanger solution is selected during the execution of the project and will depend on the type, needs, and available space and housing situation of the projected building. The final use of the land should be considered, so that it does not affect the operation of the geothermal system. The ground heat exchanger systems are classified into two main groups: • Horizontal heat exchangers (buried or in a wet environment) • Vertical heat exchangers (closed circuit, open circuit or thermal foundations) Knowledge of geology and hydrology of the land allows us to know their characteristics and to choose the right system in each case.
3.3.1 Horizontal ground heat exchangers Horizontal ground heat exchangers consist of a network of buried heat exchange pipes, installed in shallow horizontal trenches or excavations at certain levels underground (Figure 18).
Figure 18. Construction of horizontal heat exchanger (Source: Geotics Innova S.L)
The thermal regeneration of this type of exchangers is basically done from solar radiation and rainwater since they have a very small geothermal circuit. Therefore, construction cannot be made on top of these exchangers, nor can they be placed under waterproof surfaces. For polyethylene pipes installations, both laying trench and laying surface can be used. In both installations, one should try to avoid laying pipes on a gravel base because air bags reduce conductivity. For this reason, a thin material should be poured around the pipe to ensure moisture absorption.
24 The exchangers are made by pipe loops, dimensioned to prevent overpassing the pressure losses required by the heat pump manufacturer. Figure 19 shows the different ways to extend the heat exchange pipes.
Figure 19. Horizontal heat exchanger layout (source: TTA)
3.3.1.1 Horizontal exchangers in wet conditions This type of exchanger requires a large volume of accumulated water, like lakes or ponds. It is also possible to use them in smaller volumes, but there is the need for a constant renewal of water to avoid thermal saturation. They are a variety of exchangers with horizontal closed circuits, which instead of being buried underground are submerged in water or flooded clay. This solution is interesting from an investment and performance point of view. Without the need for long lengths of buried pipes, very good thermal performance can be achieved due to the presence of water, which has a large heat transfer capacity. The temperature of the area where the energy is taken from is influenced by seasonal variations while it happens with horizontal systems. When sizing, the minimum and maximum temperatures are to be considered. These types of exchangers have their application in large accumulations of water where the heap pump system will practically not alter its temperature during operation. Another suitable source of thermal energy is seawater, capable of delivering an almost infinite renewable thermal energy due to its large mass and temperature regeneration thanks to its constant exposure to sunlight. To properly evaluate the ability to remove or transfer heat to a seawater circuit we must consider the seasonal sea temperature at the water collection point. Figure 20 shows the average monthly sea temperatures in Beirut over the year. Temperature 30 29 January 18,5 °C 28 February 17,5 °C 27 March 17,5 °C 26 25 April 18,5 °C 24 May 21,3 °C 23 June 24,9 °C 22 20 July 27,5 °C 19 August 28,5 °C 18 September 28,1 °C 17 16 October 26 °C 15 November 22,6 °C July May June April December 20,1 °C March August October January February Novemver December September
Figure 20. Beirut seawater surface temperature variation (source: Sea Temperature, 2016)
25 Average, seawater temperature goes from 17.5°C up to 28.5°C during a year basis period. With these values, it is possible to consider using seawater flow connected to a ground source heat pump. Another application of this type of exchangers may be the large rafts of slurry. They are usually arranged in circular coils of about 100 meters’ length. The two ends of the coil are connected to the collector with weights to help it become immersed in the slurry. The Slinky pipe arrangement can also be used (Figure 21).
Figure 21. Slinky arrangement on wet medium (Source: Gurri S.L)
This system works as a closed-circuit loop, with lower level of maintenance required when compared to open systems (Figure 22). Closed circuit loop is filled with thermal fluid (water and antifreeze) that circulates inside the pipes without connection to any other external hydraulic circuit, avoiding the need of filters and its periodical maintenance.
Figure 22. Horizontal distribution floodable medium (Source: Tecnoserveis S.L)
The disposition in floodable zones is the same as the horizontal exchangers. Energy extraction capacity is very similar to the VDI4640 indicating saturated water (i.e. about 40-50W / m2 land).
26 3.3.2 Vertical heat exchangers Closed vertical exchangers are by far the most used exchanger in shallow geothermal energy since they can be used in almost every field, require little space and can cover a wide power range to cover both heating and cooling requirements. Basically, these systems are installed vertically in the subsurface to exchange heat. Available energy in the ground that we take advantage of, combined with a heat pump, raises or lowers the temperature of the fluid to a usable range for heating, cooling and sanitary hot water. Advantages They need very little horizontal space compared to other systems; they are valid for all types of grounds. Moreover, they are applicable in both residential and industrial projects. They allow both active and passive cooling and heating and sanitary hot water. Disadvantages The disadvantage of a vertical heat exchanger is the requirement of specific machinery for the boreholes perforation, as well as the high cost compared to other market systems.
3.3.3 Geothermal probe The geothermal probe is the tube inserted into the borehole. The refrigerant liquid circulates inside the probe to absorb and/or expel the heat from/to the heat pump. The most commonly used geothermal probe is a polyethylene pipe (Figure 23 provides an example). The basic configuration is two pipes with a bottom placed U-bend. To ensure the tightness and proper operation of the geothermal probe, it’s recommended to use probes from a qualified manufacturer that guarantees the quality and lifetime of the probe, because the cost of a geothermal probe, compared to the cost of drilling, should not jeopardize the construction of a vertical geothermal collector. As presented in section 7.3.2.24, depending on the results of the thermal response test (TRT) and the depth of drilling, in addition to the ground composition, the number of probes and its diameter are defined.
Figure 23. Set of Geothermal probe, 100 meters’ length, single U (source: Haka Gerodur, 2016)
27 3.3.4 Other heat sources: Foundation piles as heat exchangers (Energy piles) The utilization of stable ground temperatures from foundation structures may be an option to have a heat exchange field, when the structures need to be built anyway due bad soil conditions[3].In this case, the pile foundation itself acts as a probe. The entire heat exchange system is located under the building itself, saving considerable resources and space, given the fact that the heat exchangers are included in the building construction project and are, consequently, developed at the same time. At depths between 10 and 20 meters, the ground temperature usually remains thermally stable and far from the seasonality of the first meters. Therefore, it is possible to take advantage of the excavation that takes place in most buildings. As indicated in the standard VDI 4640, “the design of the ‘energy pile’ systems can be achieved analogue to the methods used for borehole heat exchangers. However, the temperature in the pile must never be allowed to reach the frost limit which must be taken into account in the calculations.” With respect to the dimensioning of energy piles to cover the thermal power need of the building, it is also stated in VDI 4640 that “a house with 10 kW heating requirements and 1,500 heat pump operating hours requires e.g. 20 to 26 piles, each 12 meters long.” For economic reasons, the number of piles is the only cost imposed in the calculation of the structure, since the costs related to any additional pile would not be justified in the dimensioning. Heating or cooling power totals should be covered in this case through thermal production complementary systems. Installation of heat exchange pipes can be made with different variants, loops or in U-shape. Loops With respect to loops, the pipes are extended inside the frame forming loops to cover the interior area of the pile (Figure 24). The hydraulic connection of supply and return is performed on top of the pile. This type of lying has the advantage due to its simplicity of assembly.
Figure 24. Geothermal heat exchanger in loop (source: Haka Gerodur, 2016)
U-shape The pipes extend in U shape inside the pile. The coupling in each of the circuits is carried equally on top of the pile. This form of heating distribution exchange pipes presents benefits related to air removal (venting) of all circuits.
[3] The soil conditions (charge capacity, stability) determine when foundation piles or other type of basement structures are to be applied. When foundation piles are required, one can consider using them as heat exchangers. 28 4 GSHP execution steps
4.1 Project’s conceptual design When planning the conceptual design, the selected solution should be compared to other available solutions in the market to ensure it is optimally adapted to the real necessities of the project. Section 4, “General principles on GSHPs using very low temperature geothermal energy,” shows that the performance of a GSHP is higher than other systems currently available due to the constant temperature of the subsurface that can serve as a heat source through a geothermal heat pump. However, in certain cases the complexity of the project execution can be evaluated during the initial design of the project through a feasibility study. Figure 25 shows the steps that need to be followed when constructing a ground source heat pump. These steps are described in the next sub-section.
Pre dimensioning
Field work / Hydrogeological analysis
Preliminary Draft
Yes Yes No Viable? Re dimensioning? No Detailed design Archive
Construction / Assembling
Commissioning
Functioning Monitoring
Figure 25. Steps to be followed for the construction of a GSHP (source: source: TTA, 2016)
29 4.1.1 Load profile assessment The GSHP interacts with the heating and cooling systems at the facilities, therefore it is of high relevance to understand the load profile to identify the oil/electricity consumption that can be offset by the GSHP. The first step is to perform the preliminary demand analysis for heating, cooling and domestic hot water (loads, demand and temperatures). Further information is provided in section 7.1.
4.1.2 Field work / Hydro geological analysis Geological and hydro geological conditions of the area of plant implementation should be considered as the basis of the ground heat exchanger field design. When the geological situation is unclear, it is highly recommended to perform the ground Thermal Response Test (TRT). The TRT should be the first step in order to define the correct value of heat extraction / injection of thermal energy into the ground without saturation during the year. The TRT enables us to optimally size the GSHP. Refer to point 6.1.4 for more details.
4.1.3 Preliminary sizing The Preliminary sizing outlook aims to describe the different parts that integrate the system, the technical characteristics of the drilling work, the space where the heating pumps and corresponding equipment will be located and the point where the hot and cold water distribution is to be connected to satisfy the complete (or partial) thermal needs. The preliminary draft is meant to define the following: • Demand covered. • Preliminary sizing of the system (number and depth of wells) and floor space to be occupied to determine if there is enough free space to build the geothermal exchange field. • Preliminary budget for project execution.
• Assessment of energy savings and CO2 emissions’ reductions. • Amortization period of the investment compared to a conventional system. • Required permissions for drilling vertical boreholes or wells for open system, per regulations. If the outcome of the preliminary draft concludes that the system is not feasible, either technically or economically, the designer can adjust the points that affect the feasibility of the project, or declare it as non-viable.
4.1.4 Detailed Design During this step, the detailed design (detailed engineering) is completed, and should cover the following aspects: • Detailed diagram including all the components of the system • Bill of materials and their technical specifications • Drawings of the different components • Technical description of the system and the modes of operation • Control strategy definition • Technical standards to be considered during construction
30 4.1.5 Construction / Assembling To construct an integrated system, the most important fact is the smooth coordination of the different tasks for optimum results, as well as following the requirements set in the standards in force.
4.1.6 Installation and commissioning Before commissioning the overall system performance, it is advisable to test each part separately and check if all components comply with established technical standards.
4.1.7 Monitoring, Operation and Maintenance (M&O&M) The main heat pump’s manufacturers’ offer a build-in communication system that, via MODBUS port or Ethernet, offers the possibility of fully monitored GSHP systems. Therefore, together with metering devices that can measure energy generated and energy consumed, information about the COP (reached by the whole system, including the heat pumps but also the ground heat exchanger) can be measured. It is compulsory that maintenance procedures are planned and executed in a professional way, to ensure the functionality of the system and also to achieve the objective of energy efficiency stated on the GSHP design.
31 5 Ground characterization
5.1 Ground investigation When a project for the exploitation of geothermal energy at a very low ground temperature is being planned, one of the most important considerations is the availability of the resource in the proposed area of project implementation. Depending on the objective of the project, there can be various scenarios (the main applications of ground source heat pump applications) and for each of these the following should be defined: • The generation of warm water in winter and cold water in summer. • The generation of warm water during the year, no generation of cold water. • The generation of cold water during the year, no generation of warm water.
5.1.1 Generation of warm water in winter and cold water in summer The first scenario results in a balanced usage of the subsurface since, during winter, the thermal energy can be extracted from the Earth, whereas during summer, thermal energy can be injected into the Earth. The imbalance between the effective hours of extraction and injection of thermal energy determines the dimension of the heat exchanger whether this is horizontal, vertical in closed circuit or vertical in open circuit.
5.1.2 Generation of warm water during the year, no generation of cold water The second scenario is applied in zones in cold climates that require heating most of the year. This scenario presents a certain imbalance of heat exchange since during most the year, thermal energy will be extracted from the Earth and there will be no injection of heat. In this case, there is another factor to be considered: The steady ground temperature will be, in general, lower than in the first scenario since the average temperature in climate zones that require heating during larger periods of the year will be lower than in the first scenario. This consideration would not be valid in the case where the exploited zone would be affected by a thermal anomaly underground, which is the case of low or medium temperature geothermal energy.
32 5.1.3 Generation of cold water during the year, no generation of warm water The third scenario corresponds to the case like the second scenario, since during most the year, thermal energy would be injected into the ground without periods of extraction of thermal energy.
5.1.4 Thermal Response Test The proper design of a complete GSHP system requires knowledge of the particular thermal properties of the ground where the project will be located. At an initial point of the project, like a pre-study, available local information like ground thermal data or geological maps may be enough, but when the project becomes a real possibility, and always when the design goes to values equal to or higher than 30 kW (thermal), it is necessary to perform a TRT with the objective to measure the capacity of the subsurface as generator or absorber of thermal energy (Figure 26 illustrates an example.).
Figure 26. Sample of TRT test equipment (source: Geotics Innova S.L.)
The objective is to adjust the depth of the project’s borehole to the energy extracted by the heat pump per the characteristics of the ground. To achieve this objective, it is necessary to determine the borehole thermal resistance and the thermal conductivity of the ground. This test can be performed prior to the realization of the works in a borehole done for this purpose and which can subsequently form part of the geothermal collection field. The test consists of the following: • Pilot borehole: Opening a borehole of the same characteristics as the future boreholes of the project, such as depth, diameter of geothermal probe and filling material. Once the borehole is done, it should be untouched for a reasonable time to allow the cement to harden. • Undisturbed ground temperature: Is the mean temperature at half the active borehole depth? It can be determined by circulating the thermal fluid by the geothermal probe without heating for 20-30 minutes. Measuring the mean thermal fluid temperature corresponds to the undisturbed ground temperature.
33 • TRT: Injection of thermal energy into the ground through the geothermal probe and data collection. • Data analysis: Calculation of the borehole thermal resistance (R_b) and ground thermal conductivity (λ). There are two analytical techniques used to analyze the measured variables, both based on Fourier’s law of heat conduction: Linear source (LSM) (Hellström, 1991) and Cylinder Source (CSM) (Jaeger, 1956) The LSM is the most widely used, valid for one dimensional heat transfer like radial heat flow. To evaluate a thermal response test with multi-dimensional heat transfer process, like, for instance, an area with significant ground water flow, the CSM method should be used. The TRT is done with a machine that is formed by an electric boiler that generates the thermal energy injected into the probe. A set of measurement devices registers the evolution of the temperatures in the input and output of the probe, the flow rate that circulates and the energy that is injected. Figure 27 illustrates the basic elements of a TRT machine.
Figure 27. TRT test equipment circuit (source: TTA)
34 6 GSHP design
The design of a GSHP system must consider every one of the steps to define the project as well as consider the system’s technical and economic viability. The minimum requirements to take into account are: • Thermal load of the space to heat/cool. • Annual balance between needs for heating, sanitary hot water and cooling. • Dimensioning of ground heat exchanger, depending on the balance of heat extraction and injection in an annual cycle. • Ensuring the necessary area to build the heat exchange field and compliance with local regulations. • Sizing the GSHP, depending on the power required to cover the thermal load space to heat / cool and annual operating hours foreseen. • Distribution system for heating and cooling that offers the highest energy efficiency. • Control and monitoring system that enables the follow-up of the operation of GSHP and energy efficiency obtained by the ground heat exchanger, heat pump & distribution system.
6.1 Load assessment and GSHP Integration (sanitary hot water, heating and cooling) The power of the heat pump to be installed should be sufficient to cover the targeted thermal demand, based on the following parameters: • Thermal loads of the space to heat/cool • Need of heating • Need of cooling • Need of both heating and cooling • Demand of sanitary hot water It is very important not to oversize the installation during the design of the geothermal system to avoid long amortization periods and a non-feasible project from an economic perspective. It should be considered that in a system with a geothermal heat pump and a closed circuit, the cost of the ground heat exchanger could be half the total investment. Another important factor to be taken into account is that the sizing of the geothermal heat exchanger should be based on the thermal energy demand, since heating or cooling affects, in reverse mode, the subsurface temperature stability (heating process extracts and cooling process injects energy to ground).
35 6.1.1 Sanitary Hot water For a correct assessment of needs in sanitary hot water, the following parameters should be taken into account: • Necessary volume in liters per day • Water temperature coming from network • Temperature of the water for the end-user As a reference, the list in Table 1 includes the demand of sanitary hot water per person, as indicated in the Technical Building Code (CTE) of Spain.
Table 1. Reference hot water demand depending on the facility (source: CTE, Spain) Reference demand per person Facility (liters/day) Household 28 Hospitals and clinics 55 Ambulatory and health centers 41 5-star hotels 69 4-star hotels 55 3-star hotels 41 2-star hotels 34 Camping 21 Prison 28 Changing rooms/community showers 21 Military quarters 28 Factories 21 Gyms 21 Restaurants 8 Cafeterias 1
The European standard EN 15316-3-1: 2008 Sanitary hot water systems, characterization of needs (tapping requirements), establishes the calculation method for the sizing of the thermal power to be considered during load assessment of a heat pump in order to cover the demand of hot sanitary water.
6.1.2 Heating and cooling The thermal loads of the space to be heated or cooled will give us the information about the size of the heat pump power output. In summary, the thermal load should be defined considering different partial loads that affects the space: • Solar radiation through glasses / windows • Internal thermal load transmission through outside walls and ceilings • Thermal load transmitted by outside air infiltration • Sensitive load added by internal contributions (lights, electrical equipment…)
36 6.2 Main components of a GSHP A sample of the main components involved in a GSHP is presented in Figure 28 and described in the following sub-sections.
Figure 28. Main components in a GSHP (source: Tellus Ignis S.L.)
• Ground heat exchanger • Ground source heat pump • Buffer tank (cold / hot water) • Sanitary water tank • Heat / cool distribution grid
6.3 Sizing As previously indicated in point 6.1, correct sizing of heat pump systems is extremely important since it works more efficiently and gives the user the shortest payback period than under- or oversized ones. When a heat pump system is undersized, it will work overtime to get the desired indoor temperature with the consequence of it being costly to run and it having a decreased efficiency; while an oversized heat pump system will be more expensive to install, compared to the appropriately sized equipment.
37 The basic data for sizing a geothermal installation with the ground heat exchanger combined with a heat pump is the following: • Design heating (or cooling) load and performance of the heat pump (in order to define the thermal power of the heat pump). • Water flow must circulate through both condenser and evaporator at recommended manufacturer values. • Specific heat capacity of the land. To calculate the design heating or/and cooling load, indoor temperatures should be considered and maintained during the season. Owing to variations in humidity and likely clothing, recommendations for summer and winter may vary; a suggested typical range for summer could be between 23ºC to 25.5 ºC, while for winter between 20ºC to 23.5ºC.
Figure 29. Indoor recommended temperatures are the ones to be used for the designing of the heating and cooling load (Source: Cernunnos, 2016)
6.3.1 Heat pump and buffer tank The heat pump should be sized in such a way to operate the minimum number of hours per year and recover the investment within a reasonable period. This is feasible only when there is reliable data of thermal loads available. In some countries, mainly in cold climate latitudes where there is only or mostly heating demand and sanitary hot water, there is a tendency to size geothermal installations where they do not reach 100% of the design-heating load. Generally, a heat pump sized to meet 60% of the design-heating load is likely to meet 85 to 95% of the annual heating energy requirement. The remaining 5% to 15% of the thermal energy demand over the year can be covered by another system of thermal energy production, such as a backup boiler or an electric boiler.
38 6.3.1.1 Buffer tanks Buffer tanks are intended to increase the total water volume in the distribution hydraulic circuit. They are useful when the heat pump is of the on/off type and the total power is generated without taking into consideration the thermal demand over a specific period. In this case, a low water volume in the distribution circuit will consequently have a start/stop process for the heat pump compressor and that will affect the lifetime of such a device. As a general rule, a compressor should not start more than three times per hour. The dimensioning of buffer tanks for on/off heat pumps is done based on 15 to 25 liters capacity per kW of heat pump power output at nominal working conditions. It is recommended to use inverter heat pumps (variable frequency of compressor) - buffer tanks can be reduced or avoided - in case the heat pump control unit adjusts the heat pump power output as a function of thermal demand.
6.3.2 Ground heat exchanger The sizing of these geothermal exchangers is described in Part 2 of the German standard VDI 4640 and summarized below.
6.3.2.1 Horizontal heat exchanger To size the ground heat exchange system, it is necessary to previously know the technical characteristics of the chosen heat pump, and assign a COP depending on the annual temperatures, the heating and cooling power calculated and the regime operation. Thus, one can calculate the power of the evaporator as follows: (Heating Power (COP-1)) Power of the evaporator = COP Table 2 shows that the specific heat capacity of the land on the surface depends on its conductivity and annual operating hours.
Table 2. Reference ground thermal capacity for horizontal heat exchangers (source: VDI 4640)
Specific extraction output Underground for 1,800 h for 2,400 h Dry, non-cohesive soils 10 W/m2 8 W/m2 Cohesive soils, damp 20 - 30 W/m2 16 - 24 W/m2 Water satured sand/gravel 40 W/m2 32 W/m2
Based on heating hours and once the power of the evaporator and the subsoil thermal capacity is known, the geothermal exchange area required is calculated in the following way: (Capacity of the evaporator (W)) Heat exchanger surface( m2) = (Thermal capacity extraction terrain (W/m2 )) The second step is defining the type and length of pipe that must be used to build the exchanger. Per the VDI-4640 standard, separation between pipes with a range of 0.50m to 0.80m should be maintained. The length shall be determined as follows: • Pipe length (m): Surface of ground heat exchanger (m2) • Separation between pipes (m)
39 The choice of the pipes’ dimensions depends on the thermal capacity that the subsoil is able to provide. As we can see in the following table (Table 3), the higher the heat capacity is, the greater the flow required for a temperature differential between the flow and return, therefore the piping must be bigger. Table 3. Recommended piping diameters (source: VDI 4640) Underground ø Recommended Dry, non-cohesive soils 20 mm Cohesive soils, damp 25 mm Water satured sand/gravel 32 mm
The geothermal exchanger temperature alters the subsurface, therefore the pipes should be extended to a sufficient distance from trees, shrubs and plants. The German VDI 4640 indicates that in the implementation of a horizontal geothermal exchanger, the pipes should be buried at 1.2m - 1.5m deep.
6.3.2.2 Vertical heat exchanger It should be noted that in large heating installations, with heat pumps above 30 kW, precise calculations are required. The first step should be finding out the needs of the building; simulation programs that may be used to obtain the heating or cooling demand, such as CYPECAD MEP [4], VE for Engineers [5], Trane Trace [6] or Carrier HAP [7]. When sizing the heat exchange system, if the geological situation is unclear, a TRT should be performed. To learn more about TRTs, please refer to Section 6.1.4 in this guideline report. To size the vertical heat exchanger per VDI 4640, the first step is assigning a heat pump that can carry the required performance (i.e. COP) and the power heating output and operating mode. Calculating the power of the evaporator can be done: (Heating Power (COP-1)) Power of evaporator = COP Table 4 shows how the specific heat capacity (between 40 and 100 meters deep) depends on the ground thermal conductivity and the annual operating hours. Table 4. Ground thermal capacity for vertical exchangers (source: VDI 4640, Part 2) Underground Specific heat extraction for 1,800 h for 2,400 h General guideline values Poor underground (dry sediment)(λ<1.5 W/(m.K)) 10 W/m2 8 W/m2 Normal rocky underground and saturated sediment (λ=1.5-3.0 W/ (m.K)) 20 - 30 W/m2 16 - 24 W/m2 Consolidated rock with high thermal conductivity (λ<3.0 W/ (m.K)) 40 W/m2 32 W/m2
[4] www.cype.es [5] www.iesve.com [6] www.trane.com [7] www.carrier.com 40 Underground Specific heat extraction for 1,800 h for 2,400 h Individual rocks Gravel, sand, dry <25 W/m <20 W/m Gravel, sand, satured water 65-80 W/m 55-65 W/m For strong groundwater flow in gravel and sand, for individual systems 80-100 W/m 80-100 W/m Clay, loam, damp 35-50 W/m 30-40 W/m Limestone (massif) 55-70 W/m 45-60 W/m Sandstone 65-80 W/m 55-65 W/m Siliceous magmatite (e.g. granite) 65-85 W/m 55-70 W/m Basic magmatite (e.g. basalt) 40-65 W/m 35-65 W/m Gneiss 70-85 W/m 60-70 W/m
Knowing the hours under heating mode, and having the evaporator power and type of ground, one can determine the length of the geothermal probe as follows: Power of evaporator Length of probe = Ground thermal capacity extraction (W/m) Once the total length of geothermal probe has been calculated, the number of geothermal probes can be determined as follows: Length of probe (m) Number of probe = Length of borehole (m) Per VDI 4640, the minimum distance between each borehole should be at least 5 meters for boreholes of 40 to 50 meters deep and 6 meters in boreholes of 50 to 100 meters deep.
6.3.2.3 Number of probes to be inserted in boreholes: one or two? In grounds with low thermal conductivity (less than 2 W/(m K)), it is advisable to use a single U geothermal probe, either with a 32 or 40 mm (DN32 or DN40) diameter, depending on the exchange rate and calculated pressure drop. With higher thermal conductivity (more than 2 W/(m K)) the use of two geothermal probes in the same borehole can be considered in order to have a wider heat exchange surface with the ground and in turn increase the extraction or injection power per borehole. In this case, twice the power of heat exchange will not be obtained, but an increase of around 20% could be achieved. With this configuration, the two geothermal probes should be connected in parallel, using a Y connection (see Figure 36 and Figure 37).
6.3.3 Plates heat exchanger The insertion of a plate heat exchanger between the heat pump and the hydraulic distribution system (i.e. to radiators or to fan coils) is required when mixing the fluid that circulates through the boreholes with the fluid that will be used as heat or cool transfer to the distribution circuit is not considered. This solution is very useful when non-reversible heat pumps are used, and they are designed to provide heating and cooling, via an external circuit reversion (see sub-section 3.2.5.1). In this case, the evaporator side contains water with an anti-freeze solution, while the condenser side is only filled with water. Mixing both circuits during the seasonal shift from winter to summer or vice versa, will result in a lower concentration of anti-freeze solution on the boreholes’ side with the associate periodical maintenance works to keep the correct freezing point on the evaporator.
41 6.3.4 Condensers and evaporators piping circuits The pipes for the evaporating circuits should be high density polyethylene PE100 [8] in the main section and branches to the equipment. The pipes for the condensing circuits should be of polypropylene PP-R in the main section and output of the equipment. These pipes are recommended to be isolated with polyurethane foam according to local regulations, but the isolation is recommended to be of at least 30 - 40 mm. The pipes will be fastened using metal clamps, the symphonic type, to avoid thermal bridges between the pipes and the ambient, and will be fastened to the wall or to supporting structures. Vibrations from pipes to supporting structures or walls should be avoided using appropriate anti-vibration fasteners.
6.3.5 Recirculation pumps Some heat pump manufacturers include the evaporator and condenser recirculation pumps. In this case, the manufacturer has already done the sizing of those units, and the only job left for the installer is to adjust the circulation pump speed to reach the correct temperature difference between in/out circuits of evaporator and condenser circuits. In case the recirculation pumps are not included, the installer must carefully follow the instructions in the Installer’s Manual related to the type and sizing of the recirculation pumps to reach the correct flow values in both, condenser and evaporator.
6.3.6 Other devices The hydraulic circuit that links the ground source heat pumps to the recirculation pumps, plates’ heat exchangers and the buffer tanks should include all the auxiliary elements required to ensure the proper operation of the thermal power plant: • Air venting devices in the selected points, based on the distribution of the pipes which connect the equipment, could be susceptible to retain air pockets that may render fluids circulation difficult. The most critical points are usually the highest points of the hydraulic circuit where air pockets could be retained. • Mesh filters, which avoid the entrance of rare particles into the evaporators, condensers and heat exchangers, with the consequent obstruction risk. • Thermometers and ball gauges for the visualization of the temperatures in the production process and the pressure of the different hydraulic circuits. • Closed expansion vessels with the capacity to absorb the total volume variations of the hydraulic circuit, located at evaporator and condenser sides, following the standard EN13831. • Three-way valves.
[8] For more information about regulatory framework, please refer to DIN 8075 42 7 Technical specifications and standards
7.1 Component-specific specifications and characteristics
7.1.1 Heat exchanger field
7.1.1.1 Boreholes The ground heat exchanger field consists of many boreholes to function for the total project’s thermal power. Usually the boreholes for such GSHP applications are 100 meters deep and have a 127 mm (5’’) diameter.
7.1.1.2 Geothermal probe The geothermal probes installed in the boreholes should be of thermal welding polyethylene PE 100-RC (Resistance to crack) of the latest generation. They are recommended to be manufactured from a polyethylene PE100 extrusion grade material with a minimum cell classification of PE345434C per ASTM D-3350 and fully comply with the IGSHPA standard 1C “Ground Heat Exchanger Materials” (IGSHPA). Other accepted polyethylene probes may be the ones manufactured per the DIN 8074 (dimensions, wall thickness and mass) and DIN 8075 (pipe resistance, test and inspection methods), the ones that have a SKZ (Süddeutsches Kunststoffzentrum – Germany) approval per the HR 3.26 system, with a lifetime exceeding 100 years at 20ºC. The geothermal probe is to be factory assembled and pressure tested at 100 psi. The type of geothermal probe usually specified is of single U, most commonly used are of DN40 and DN32 size. Another aspect considered when specifying probes is the nominal pressure (NP), or the pressure that pipes can support with water at 20ºC, measured in bars. Examples of NP values are 2.5, 4, 6 and 10. An NP16 is adequate for a geothermal probe when boreholes are 100 - 120 meters deep.
7.1.1.3 Concrete (grouting) injection The grouting material must have a minimum thermal conductivity of 2 W/mK, must be chemical hazard free and must meet the requirements placed on groundwater measuring point sealing as stipulated in the DVGW code of practice W121:2003-07 (DVGW).
43 The grouting material shall have a density that allows easy injection from the borehole’s lower part. A separate DN25 polyethylene pipe must be used to inject the grouting.
7.1.1.4 Recirculation of the heat exchange unit The recirculation pumps in the GSHPs should ensure that the system operates under the required design operating flow and pressure of the complete hydraulic circuit between the GSHP and the heat exchange field. When the GSHP system includes more than one heat pump (Master / Slave configuration), recirculation pumps with variable speed are highly recommended to provide the possibility to adjust the flow according to the power output steps under operation.
7.1.1.5 Safety devices for the ground heat exchanger circuit The ground heat exchanger field circuit must be protected against volume and pressure variations with appropriate expansion vessel(s) installed in the technical production room, together with pressure safety valves. The pressure safety valves shall drive the conduction of the fluid until the drainage system in the thermal energy production room.
7.1.1.6 Ground heat exchanger piping circuit (ground loop) The ground loop that interconnects the ground heat exchanger field with the thermal energy production room should be high- density polyethylene PE100 and PN10. The internal diameter of the pipe should be calculated to maintain the fluid’s velocity within concrete ranges.
7.1.1.7 Circulating fluid characteristics The heat-transfer fluid in an exchange subsystem is a mixture of water and propylene glycol, usually with a concentration of 30% of the total fluid volume. The circuit is usually filled under a pressure of 2.5 bars at the height of the expansion vessel. Table 5 gives the physicochemical characteristics of the heat transfer fluid (propylene glycol). Table 5. Heat-transfer fluid characteristics (propylene glycol)
Concept Unit Value Concentration Vol % 30% Temperature ºC 0 Density kg/m3 1035,93 Conductivity W/(m•K) 0,423 Specific heat kJ/(kg•K) 3,801 Dynamic viscosity 105 Pa•s 707,529 Kinematic viscosity cSt 6,83 Freezing point -15ºC Formula C3H8O2 Molecular weight g/mol 76,10
44 Concept Unit Value CE number 200:338:0 Aspect Liquid Color Colorless
pH 6 - 8 (@ 100 g/l H2O, 20ºC) Boiling point ºC 188 Flash point ºC 371 Freezing point ºC -13,1 Melting point ºC -59 Density (@20º; g/cm3 1,04 (@ 20ºC) Distribution rate n-octanol/water log P(o/w) -0,92 Steam pressure hPa 0,11 (@ 20ºC)
7.1.1.8 Manifolds The manifolds have the mission to connect different geothermal probes to a bigger size pipe that is going to be connected to another bigger size manifold or directly to the heat pumps room. The manifold piping sizes should be designed according to the flow that is the correct one for a specific project. The manifolds should be equipped with flow meters, ball valves made of brass, bronze and stainless steel. Figure 30 provides an illustration of manifolds.
Figure 30. Sample of distribution manifolds (source: GWE, 2016)
7.1.2 Heat pumps One or several heat pumps can be used to satisfy the demand. The coefficient of performance (COP) of the ground source heat pumps must be certified under the EN 14511 standard and shall be fully functional with the design selected (2-pipes/4-pipes).
45 The ground source heat pumps are recommended to be from a premium international brand manufacturer, including, at least: • One or more compressors per heat pump. • Condenser and evaporator per each compressor. • Expansion valve. • One or more circulation pumps, condenser side (one per compressor). • Circulation pump, evaporator side. • Electronic control system, CPU based. • Multilingual full color displays with comprehensive dialog menus. English is compulsory to be included on the different display languages. • Control and monitoring system of all the operation parameters of the group of heat pumps, via Ethernet. The modification of the adjusting parameters must be done through an authorized user and must be password protected. Table 6. Standards for heat pumps Coefficient of performance, output EN 14511 Energy label EU Directive 2010/30/EU Noise output EN 12102 Sound pressure level EN ISO 11203
7.1.3 Buffer tanks When buffer tanks are required, Triple-Layer Tanks with an external solid-skin layer to protect the fluid inside the tanks from UV light are recommended. The tanks’ second layer, made of polyethylene foam, should provide thermal insulation and add strength to the tanks. The internal layer shall be free from colorants. Tanks for hot water are preferred to follow the guidelines stated in Eco-design [9] Directive (EU, 2013). The buffer tanks shall be designed around the thermally stratified system. The primary objective of a stratified storage design is to prevent the warmer water from transferring heat to the stored chilled water. Outlet diffusers are required and should be designed to minimize mixing, and to design the diffuser manifold for balanced flow. The diffusers should introduce water to the tank in a uniform low velocity horizontal flow where the buoyancy forces create and maintain the thermo-cycle. High velocity jet like flows will cause undesirable mixing. Tank insulation should be made of rigid fiberglass with a 92 Kg/m3 density of thickness to prevent surface condensation on insulation with a high integrity exterior vapor barrier and aluminum jacketing of 0.6 mm thick. Minimum thickness of insulation is 100 mm. The contractor should provide thermal loss calculations and provide necessary insulation to prevent condensation and heat transfer to and from the tank.
[9] The Ecodesign Directive provides consistent EU-wide rules for improving the environmental performance of products, such as household appliances, information and communication technologies or engineering. 46 7.1.4 Energy meters (thermal and AC meters) The thermal energy meters should be static meters with an ultrasonic flow sensor. The measurement accuracy shall be equal to or better than Class 2 [10].The protection class shall have a minimum IP67 with the environmental protection per EN 1434 class C; it shall be compatible with the monitoring system and be able to withstand the working conditions. When a four pipes configuration is done (see sub-section 4.2.5) there should be one thermal energy meter to measure the cold-water production, and another one to measure the hot water production. The energy AC meters should be digital three phase meters with an output pulse signal and accuracy class 1 per EN 62053- 21; electric-shock protection Class II; input: current (depending on rated power), Dimension 1-DIN module, compatible with monitor system.
7.2 Regulatory framework There are many standards, recommendations, and technical papers that are edited by private organizations (e.g. ASHRAE [11]), or the European Commission (i.e. EN [12] norms), in addition to well-reputed professional associations like VDI (German). These provide very useful references to be followed when a GSHP goes under a design process. Some of them are listed below. Sizing EN 15316-3-1:2008 Heating systems in buildings - Method for calculation of system energy requirements and system efficiencies - Part 3-1: Sanitary hot water systems, characterization of needs (tapping requirements) Geothermal heat Exchange field • EN 12211-2:2012: Plastic piping systems for water supply and for drainage and sewerage under pressure – Polyethylene (PE) – Part 2: pipes. • VDI 4640, Part 1 & 2: Thermal use of the underground. • ASTM D3350: Standard specification for polyethylene plastics pipe and fitting materials • DIN 8074: Polyethylene (PE) pipes – Dimensions. • DIN 8075: Polyethylene (PE) pipes - General quality requirements and testing. • EN 805:2000: Water supply. Requirements for systems and components outside buildings. Technical room • DVGW W121: 2003-07: Construction and expansion of ground water monitoring wells. • EN 12241:2008: Thermal insulation for building equipment and industrial installations. • RITE 2007: Regulations on thermal installations on buildings. • EN 14825: Air conditioners, liquid chilling packages and heat pumps, with electrically driven compressors, for space heating and cooling – Testing and rating at part load conditions and calculation of seasonal performance. • VDI 4640 Part 1: Thermal use of underground. Fundamentals, approvals, environmental aspects. • VDI 4640 Part 2: Thermal use of underground. Ground source heat pumps system.
[10] For a Class 2 thermal energy meters, the máximum measuring uncertainty is stated to be +/- 2% [11] American Society of Heating, Refrigerating and Air-Conditioning Engineers [12] ec.europa.eu/growth/single-market/European-standards_en 47 • VDI 2050 Requirements for technical equipment rooms. • VDI 6041 Facility management. Technical monitoring of buildings and building services References and bibliography: • Directive 2009/28/CE (U European Parliament): Promoting the use of energy from renewable energies. • Drilling Methods for Ground Source Heat Pump System Installations. ISBN 1-931862-02-8: Harvey M. Sachs - American Society of Heating, Refrigeration and Air-Conditioning Engineers, Inc. • Geothermal Heating and Cooling Design of Ground-Source Heat pump Systems. ISBN 978-1-936504-85-5: Steve Kavanaugh, Kevin Rafferty – ASHRAE.
48 8 Construction and installation procedures
8.1 Planning requirements The construction works at the selected site only start after completing the shop drawings, a concise environmental statement specifying waste disposal arrangements during installation, a description of the proposed performance testing procedure and a letter certifying the requirements on warranties, spare parts and standards are prepared and approved. All supplied units shall be accompanied by their respective datasheets that clearly indicate the specifications of the components that need to be supplied.
8.2 Heat exchanger construction
8.2.1 Drilling Horizontal heat exchangers do not require special machinery for their construction. However, special attention should be paid when constructing the vertical closed loop heat exchanger. The implementation of vertical exchangers should be done by the most appropriate drilling technology based on the type of ground. The most common systems are listed in Figure 31.
Vertical bore hole drilling
Stable ground (rock, compact clay) Unstable ground (clay, sand, gravel)
Air percussion drilling Rotary mud drilling
Rotary percussion Reverse circulation Direct circulation
Figure 31. Drilling systems depending on the ground (source: TTA)
49 In hard, compact and flat surfaces such as slate, granite, limestone, etc., systems such as rotary percussion are used. In case of unstable soils such as sand or gravel, rotary systems with direct or reverse mud circulation are used.
8.2.1.1 Drilling on stable ground The rotary percussion is the method most used in stable, usually rocky grounds. Rotary percussion drilling is performed with the fragmentation of the rock by the impact caused by a hammer, which is transmitted to the drilling tool, and which is at the same time in contact with the rock (Figure 32). The rotational movement occurs when the tool hits the rock to spread the impact on the entire bottom surface and at the same time facilitating the evacuation of detritus. A rotary percussion top hammer is generally used for small boreholes on hard ground. In this method, the hammer outside the hole communicates the movement to the drilling tool through a hollow rod with a considerably smaller diameter than the wellbore.
Perforator Push
Rotation
Pushrod
Drill Circulation flow Detritus
Figure 32. Hammer head and drilling bits (source: TTA)
The hammer can be pneumatic or hydraulic. The length of this drilling system does not exceed 30m due to significant energy losses that occur in the transmission of the shock wave and bar deviations. Rotary percussion with bottom hammer is generally used for hard rocks at depths of up 250 - 300m, in this case placed between the hammer rod and drilling tool (Figure 33). A hydraulic motor positioned outside transmits the rotary motion. Evacuating the detritus is similar to the previous case. An air compressor supplying the required compressed air, which removes the debris generated during drilling at the same time, powers the hammer. The borehole diameter is usually between 120-160mm and if the ground is completely stable, an iron or plastic pipe of about 5m is installed to keep the first drilling part stable.
50 Figure 33. Rotary percussion drilling process (source: Terraterm SL, 2016)
The bottom hammer (Figure 34) drilling system is more effective than the top hammer since the performance of the top hammer decreases at a certain depth due to the loss of energy in the linkage. Drilling speed remains constant, not decreasing with depth. Moreover, borehole remains more stable than using the top hammer, provided that the cleaning of the borehole debris is more effective. This system provides low noise in the working area. The bottom hammer requires high-performance compressors to reach significant depths and they do not serve small diameters, since the hammer is located at the bottom of the borehole.
Figure 34. Bottom hammer and drilling bits (source: Sandvik Mining and Construction, 2016)
51 8.2.1.2 Drilling unstable land In unstable lands, inserting a cutting tool performs rotary drilling with direct circulation. The cutting tool is supported from the top using threaded steel pipes and is responsible for transmitting the rotational movement and force, operating the whole mechanism from the surface. This drilling method is completed by injecting pressured mud inside the pipe (Figure 35). The function of the mud injection can be summarized by the following points: 1. Removing detritus outwards. 2. Stabilizing the non-jacketed wall of the drilling, preventing its collapse. 3. Elevated compensation pressures in aquifers. 4. Different aquifer levels protection. 5. Cooling and lubrication of drilling tools. Features of this drilling system are: • The mud and perforated material go up between the drilling and the gimlets. • Drilling diameter 140-160 mm. • Mud pump. • Not too big machinery. • Lower cost of execution compared to rotary percussion drilling.
Muds pump
Drilling machine
Container
Tri-cone roller
Figure 35. Direct mud circulation drilling process (source: Terraterm SL,2016)
52 8.2.2 Geothermal probe insertion A geothermal probe together with the grouting pipe is inserted in the borehole. The polyethylene probe manufactured from a polyethylene PE100 extrusion grade is recommended. When the geothermal probe has been installed at the bottom of the borehole, a minimum pipe length of 1.5 meters (for both the supply and return legs) shall be left above the ground level, with the pipe ends sealed. To ensure that the geothermal probe does not create thermal shorts, pipe spacers are to be used, located approximately every five meters. Geothermal probes are normally supplied by the manufacturers in rolls with the requested length, plus a safety margin in the order of 5-10% of the nominal length.
Figure 36. End of probe weight, Y connection and spacers (source: Haka Gerodur, 2016)
Figure 37. Pipes connected with the Y connection at the output of the borehole (source: Geotics Innova S.L.)
53 It is recommended that the geothermal probe include spacers to ensure that the pipes have a correct linear position once inserted into the borehole. To ensure the correct introduction of the probe, the probe must be completed with a weight fixed on the probe bottom to support the introduction of the probe into the borehole.
8.2.2.1 Probe testing procedure to be carried out before insertion of probe into the borehole The probes should be tested by filling with water at a pressure of 6.0 bar for 30 minutes, checking that the pressure does not drop more than 0.6 bar. Once the test is done, the probes shall be left sealed, pressurized, and introduced into the borehole filled with water, whereby during the grouting process no crushes result from increasing the external pressure.
8.2.2.2 Grouting pipe After the insertion of geothermal probe into the borehole, it must be filled with appropriate grouting material. The injection of such material must be done using DN25 polyethylene pipe, inserted together with the geothermal probe (Figure 38).
Concrete Injection Pipe Geothermal probe
Weight
D
Figure 38. Grouting material injection (source: Tellusignis, 2016)
8.2.3 Grouting The annular space between the borehole wall and the geothermal probe should be filled with appropriate grouting material that holds a 20% minimum solid content. It is recommended that grouting material is injected using a pressure pump and the injection pipe. The material is to be installed from the bottom to the top of the borehole. If any settling occurs during the initial 24-hour period after installation, additional material can be added to ensure that the grouting material remains at surface level. If the filling does not harden during the corresponding time, the heat that is generated during the period of hardening of the filling material could distort the test data and especially the initial temperature of the ground. The filling of the borehole with the required piping, probe and grout must be done within a very limited timeframe from the hole being drilled to avoid the risk of losing the borehole if it collapses.
54 8.2.4 Geothermal probes pressure and tightness test Once the probes are introduced into the borehole and prior to their filling, the following steps shall be performed. General guidelines to follow (please note that flow and pressures may vary depending on the total number of boreholes): 1. Cleaning: The inside of the geothermal probe shall be cleaned with pressurized water to remove any particles that may have appeared during installation, and to purge the pipes. Purging is considered correct when the outlet water is transparent, without impurities. To correctly purge test, the water velocity in the pipe shall be at least 0.6 m / s, implying a rate of 1.8 m3h for geothermal probe DN40. 2. Pressure and tightness test: A pressure and tightness test at each borehole shall be done, according to the standard EN 805:2000, at a minimum of 1.5 times the nominal working pressure, and not less than 6 bar. The pressure test shall be documented, providing a final report upon completion of the borehole works, showing at least: • Flow and pressure of the test. • Duration of the test, in minutes. • Changes in pressure recorded at the end of the test, compared to the initial pressure tightness test. After test validation, the contractor should proceed to the complete final tests (including the entire group of boreholes and all the piping until the final manifold), consisting of circulating water through all the circuit at a speed of 0.6 m/s for 15 minutes, and maintaining the facility without water circulation at 6 bar pressure for 24 hours. After this period, the pressure drop should not be higher than 0.5 bar.
8.2.5 Components assembling (production room) All the components’ assembling jobs should be carried out according to local regulations related to thermal installations, including safety procedures. RITE 2007 norm can be applied as a reference (see subsection 7.2). The VDI 2050 standard gives a useful outline with respect to the requirements for the technical equipment rooms.
8.2.6 Electrical Installation The heat pumps are to be connected to the electrical distribution supply circuit available in the facility. It should be noted that the electrical equipment requires a stable and continuous power supply network. However, voltage sags and voltage surges from the utility grid side during storms should be expected. Moreover, and specifically due to the electricity supply network characteristics of countries such as Lebanon, it should be noted that the utility grid suffers periodical blackouts and that the electricity is provided by back-up gensets with a 10-second blackout until the gensets are turned on. The electrical installation of all the components installed within the thermal energy production room shall follow the local regulations in force in Lebanon. Other regulations to follow could be standard IEC 60634 and particularly sections 4: safety, 5: selection and execution of electrical equipment and 6: Verification. In case of periodical brownouts and blackouts of the power network, a power stabilizer should be taken into consideration, at least to keep the power supply stable to all control circuits present on heat pumps and associated devices.
55 8.3 System commissioning After completing the installation, certain verification and acceptance tests shall be performed before the GSHP plant enters operation. A sample checklist for heat pump commissioning is presented in Table 7. Table 7. Example of heat pump commissioning checklist Current regulations require heat pump installation to be inspected before it is commissioned. A suitable qualified person must carry out the inspection. In addition, fill the following table with the inspection results, date and signature of inspector.
Description Notes Signature Date Evaporator side Non-return valves System flushed System vented Antifreeze Expansion vessel Particle filter Expansion valve Shut off valves Circulation pumps Condenser side Non-return valves System flushed System vented Expansion vessel Particle filter Safety valve Shut off valves Circulation pumps Electric power Fuses heat pump Fuses property Outdoor temperature sensor Indoor temperature sensor Buffer tanks sensors Sanitary water temperature sensor
56 9 Operation and maintenance
9.1 Measurement and monitoring A data logger should store current and historical data from the meters and have a data logging capacity that computes averages or at least integrates the following hourly values: • Year; Month; Day; Hour. • Flow at the measuring points selected. • Thermal energy produced. • Electricity consumed. • Power and temperature of the measuring points selected. The logger shall at least have the capacity to store two years of data. It is recommended that the data logger have a Display Unit with the following: • Device for real time visualization and downloading stored data. • Display (at least): daily, weekly, monthly, yearly and accumulated since the commissioning of the GSHP; Thermal energy produced (kWh); Electricity consumed (kWh); COP; Temperature at measuring points (ºC); flow (m3/h); ambient (outdoor) temperature (ºC); installation reference number. • Customization of an interface for large format TV screen. After operating for one year, it is recommended to assess the project by using technical data downloaded from the data logger as well as user questionnaires. In case deviations from the scheduled performance are noted, it is recommended to conduct an operation test for the GSHP plant to detect the cause of the deviations. VDI 6041 standard can be used as reference for technical monitoring and facility management.
9.2 Protection and security The following items are to be installed for security: 1. Expansion vessels: to reduce pressure in certain points of the circuit that can be affected by temperature variations and its consequences over pressure.
57 2. Pressure safety valves, adjusted to the maximum working pressure at any part of the hydraulic circuit exposed to over pressures. 3. Air venting devices at all high points of the piping circuit. 4. 4Differential switches and circuit breakers: to protect the electric installation.
9.2.1 Labeling All piping circuit should be labeled with the flow direction (arrows) and legends that allow identifying the respective functions overall hydraulic circuit. Legends are preferred to be per the GSHP design. A drawing or warning sign about safety hazards, e.g. smoking, water contact, etc. as well as emergency shutdown procedures is recommended.
9.3 Maintenance requirements A GSHP system requires a discrete preventive maintenance, considering that the heat pump works following similar technical principles as a domestic fridge. To reach continuous and efficient day-to-day work, the hydraulic circuit, including the ground heat exchange, should be periodically checked. A basic guideline about the preventive maintenance could be as follows: • Periodicity Every six months, in any case before the seasonal change from heating to cooling and vice versa. • Check points The recommended checkpoints are listed in Table 8 and defined below. Table 8. Hydraulic circuit check points
Parts to be controlled Action
Particle filters on heat pumps inlet Cleaning
Anti-freeze mix at boreholes’ circuit Check freezing value according manufacturer’s instructions and refill if necessary Repair leakages and refill the circuit. In case of boreholes’ circuit, check freezing Leakages overall hydraulic circuit value and restore adding anti-freezing if necessary Pipes insulation Visual inspection. In case of damage, repair it.
Pressure safety valves Check the functioning (open at rated pressure)
Heat pumps Internal visual inspection to find possible leakages In case the heat pump offers the alarms log, retrieve all the data to analyze possible hidden bad functions. Check the working hours and number of starts for each compressor.
58 10 Potential in Lebanon
10.1 Lebanese energy context The year 2010 has been used as baseline year for both NEEAP and NREAP which identified the total electricity generation as 12,089 GWh as opposed to a 15,934 GWh electricity demand. Electricity is primarily produced by EDL’s thermal plants which provide 68% of the demand, the hydro plants (main source of Renewable energy in Lebanon) produces 6% of the demand and 3% is covered by the imports from Egypt and Syria. The remainder, constituting the deficit (23%), is covered by private diesel – run generators; these values are based on primary energy conversion - “0.21626 tow / MWh with the efficiency of both EDL and PG combined” (LCEC, 2016). Energy potential in Lebanon from renewable energy sources has been investigated in order to set the national energy mix target for years 2020 and 2030. To date, nearly 20 MW energy capacity in small – scale distributed PV projects have been installed. With UNDP managed projects such as the EU – funded CEDRO and the GEF funded DREG, and the Central Bank and LCEC efforts in rolling out soft loans, small to medium scale implementations are ongoing in various industrial and commercial sites in Lebanon, adding on to the existing capacities and contributing to the set target of 160 GWh under the realistic scenario. The streams various include: solar, wind, water, biomass and ground sources; table 9 and figure 39 here after show the targeted energy mix for 2020 based on the realistic scenario. Table 9: Target Energy mix for 2020 (source: LCEC, 2016)
Year 2010 2015 2020 MW GWh ktoe MW GWh ktoe MW GWh ktoe Wind ------200 595.7 128.7 PC, CPV ------150 240 51.8 Distributed PV ------100 160 34.6 CSP ------50 170.6 36.8 SWH 211,988 m2 137.8 12.72 413,988 m2 269.3 58.2 1,053,988 m2 685.5 148.1 Total hydro 190 836.5 181 190 836.5 181 331.5 961.9 207.8 Geothermal ------1.3 6 1.3 Bioenergy ------771.5 166.6 Total Renewable - 974.30 193.72 - 1,105.80 239.20 - 3,591.20 775.70 Energy
Total Primary - 15,934.00 3,438.50 - 22,324.10 4,822.00 - 29,578.70 6,389.00 Energy Demand Target 6.1 5.0 12.1
59 CSP5% Distributed PV4% Geothermal 0%
PV, CPV 7% Hydro 27% Wind 17%
Biomass 21% SWH 19%
Figure 39: Energy mix per resource towards 12% of RE in 2020 (source: LCEC, 2016)
Geothermal applications discussed in the present report fall under the shallow geothermal energy where smaller drilling depths are required. A publication by the World Energy Council identifies potentials in several countries along with favorable applications such as: India, Japan, Switzerland, etc… (WEC, 2013). Both Turkey and the Kingdom of Saudi Arabia (KSA) have investigated their national shallow geothermal potential. Turkey’s first shallow geothermal application dates back to 1998 in Istanbul with 15.6 kW of heating capacity (Cetin, A. and Paksoy, H., 2015). To date, Lebanon does not have any assessment for shallow geothermal potential, the only geothermal assessment available is for ‘deep’ geothermal implementations (CEDRO, 2014). The NEEREA (National Energy Efficiency and Renewable Energy Action), a joint initiative by the LCEC and the Central Bank of Lebanon through an initial fund by the EU, is a soft loan that has helped kick start the renewable energy market through the near 0% interest over a 10 year period. Guidelines were available for energy efficiency measures (such as LED lighting, boilers, etc…), solar water heaters and solar photovoltaic implementations. Guidelines for the preparation of technical proposals for ground source heat pumps implementation has been developed by the LCEC. The template can be found on LCEC’s website and/or in Annex 2.
10.2 Climate and surface temperature (potential for the resource) As mentioned earlier, geothermal resources at a very low temperature are in the crust of the earth in the most superficial part, between the soil surface and at depths less than 200 meters. There, the average subsurface temperature may be between 15ºC to 20ºC in Lebanon, depending on average year round ambient temperatures (i.e. Zone 4 or Zone 1, Table 3). Lebanon has Mediterranean climate conditions. Table 9 summarizes the temperature conditions in Lebanon.
60 Table 10. Temperature conditions in Lebanon (Source: (UNDP/GEF, 2005)
Zone 1: Zone 2: Western Zone 3: Zone 4: Zone Coastal Mid-mountain Ilnad Plateau High Mountain City Beirut Bayssour Qartaba Zahle Cedars Max. Temperature (ºC) 32.8 (Aug) 33.9 (May) 31.7 (Jun) 39.4 (Jul) 34.4 (Jul) Min. Temperature (ºC) 4.4 (Jan) 1.1 (Jan) 0.0 (Jan-Feb) -6.7 (Jan) -11.1 (Feb) Average daily max (ºC) 23.6 20.6 19.8 22.5 15.4 Average daily min (ºC) 9.7 13.7 13.2 9.8 5.6 Average daily (ºC) 23.1 20.2 19.5 20.3 14.6 Average night (ºC) 20.4 13.7 14.1 11.9 7.1
Although the average conditions around the country are adequate, they should match the on-site conditions, more specifically, the thermal properties of the ground where the project will be located.
10.3 Geological and Temperature context Geological and hydrogeological conditions of the area where the GSHP plant will be implemented should be considered as the basis of the ground heat exchanger field design. When several GSHP projects have been implemented in one region, area or country, the conditions can be extrapolated for a new project, when the power capacity is small (below 30kW). Given the little experience in Lebanon, the ground composition assessment as well as the TRT should be carried out when a project is implemented to evaluate the ground thermal properties. In Lebanon, two TRT were done by different companies in different areas: • Bejjeh; Jbeil District of Mount Lebanon Governorate, Lebanon. Performed by EEG • Medrar Medical Center; Choukine, South Lebanon. Performed by EEG and the results are shown in Table 10. Table 11. Results of the TRT performed at the Medrar Medical Center (EEG, 2015) DATA RESULTS Project Medrar Medical Complex Ground composition 40m rock Location Choukine South Lebanon Ground average specific heat (Cp) 1.6 MJ/m3•K Altitude 550m above sea level Ground T 18.5ºC Date 13-22 October 2015 Ground thermal conductivity (ℓ) 1.94 W/m•K Borehole depth H 100m Ground diffusivity (a) 1.21 x 10-6 m2/s Borehole Diameter D 170 mm Borehole equivalent resistance Rb 0.07m•K/W Injected Thermal Power P 5.2 kW (52W/m) Circulating water flow 0.82 m3/h
61 The results obtained from both TRT show similar results in terms of thermal conductivity. However, both projects are different in terms of operation strategy (2 and 4 pipes), and, therefore, their perforation field is significantly different, in terms of W•m since there are more meters of perforation in comparison to the thermal power of the GSHP at Bejjeh than the one at MMC. As indicated in previous sections, depending on the ground composition and quality, the specific extraction output changes. Given the ground composition identified in Lebanon, limestone, marl, etc. have been identified which have an average specific heat extraction potential of 20 to 85 W/m2 depending on the area and operating hours. Given the previous geological and climatologic context, GSHP of low temperature may be a suitable resource to partially satisfy the heating and cooling needs in Lebanon.
10.4 Main barriers and risks Although there are available resources and potential for GSHP use in Lebanon, there are still barriers that need to be removed for the promotion of this solution.
10.4.1 Technological barriers Given the very little experience, the main technological barriers identified are technology barriers. The main barrier is related to the drilling technology. For the reference project constructed in MMC, the proper drilling machinery was not locally available; therefore, it had to be imported. The final machinery selected did not work at optimal conditions in terms of productivity. Another technological barrier is Lebanon not having companies with enough experience in the different types of applications with GSHP and the lack of operators with specific training in this field. A training plan could be a very useful tool to create a pool of well-trained professionals who could develop this technology in Lebanon.
10.4.2 Legal barriers Currently in Lebanon, one cannot find appropriate legislation considering the lack of clarity in the energy water and environmental legislation. There are several permits that are required for the construction of a geothermal plant, which should be further assessed and included in the Lebanese context (Vicent Badoux, 2014): 1. Permit for exploitation of the underground resources when hydrocarbons and other extractables are targeted. 2. Permit for construction of the GSHP plant: In general, following the current building code. 3. Application for an Environmental Impact Assessment: Per annex 1 of the law decree number /8633/ related to the Electricity Regulatory Authority (ESA), the installation of power generation plants and energy conversion plants requires a scoping report. 4. Land ownership: Land ownership or approvals from the landowners are necessary. Obtaining the mentioned permits may delay the implementation of the GSHP.
62 11 Conclusions
GSHP applications are widespread in North America and Europe. With the current state of equivalent technologies, the heat pumps are the most efficient in terms of primary energy requirements, with savings of 30% to 35% when compared to oil-fired boilers and 20% to 35% compared to gas-fired ones. This report focused on implementation requiring very low temperature resources (T < 30ºC), commonly found in the crust of the earth, i.e. in the most superficial part lying between the soil surface and less than 200 meters depths. The average subsurface temperature at the targeted depths range between 15ºC to 20ºC in Lebanon, depending on average year-round ambient temperatures. Given that the temperature is very low, applications are for direct heating use through heat pumps. A typical GSHP system can be effectively used for heating, cooling and sanitary hot water services and consists of three main components: • Ground heat exchanger: circuit for extraction or injection of heat from and to the subsurface. Depending on the soil conditions it can be horizontal or vertical, in wet or buried condition. It can also be two or four pipes depending on the need to be covered (two pipes for heating in winter and cooling in summer or four pipes to simultaneously cover heating and cooling demands). • Special attention should be given to the sizing and construction of the ground heat exchanger as it may represent approximately 50% of the total investment. • Heat pump: Extracts heat from the ground heat exchanger to the distribution grid or vice versa. • Distribution network (out of the scope of this report): Transfers the heat from the heat pump to the building for heating and sanitary hot water, and from the building to the heat pump during cooling applications. When planning the conceptual design, the selected solution should be compared to other available solutions in the market to ensure it is the best option for the ; the key steps are: 1. Identification of needs: characterize the heating and cooling requirements around the year. 2. Ground investigation: assess ground thermal data like geological maps or perform a TRT, depending on the size of the implementation and the knowledge of the local conditions. 3. Design and sizing: it is recommended to follow Part 2 of the German standard VDI 4640 (among others) for the sizing of the geothermal heat exchanger. 4. Construction and installation: It is very important to select the proper machinery for the drilling process (especially for vertical closed loop). Inspection, testing and verifications are to be done before commissioning. 5. Operation and maintenance: the data logger shall store current and historical data from the meters and display them. Protection devices such as expansion vessels, pressure safety valves, air venting devices, differential switches and breakers should be installed for safety.
63 A GSHP system requires a discrete preventive maintenance. To reach a continuous and efficient day-to-day work, the hydraulic circuit, including the ground heat exchange, should be periodically checked. For the construction of a GSHP in Lebanon, given the little local experience, the ground composition assessment as well as the TRT is to be done when a project is to be implemented to evaluate the ground thermal properties. Although there are available resources and potential for the use of GSHP, there are still barriers that are to be removed for the promotion of this solution. Technological barriers: • The main barrier is the drilling technology. • Lack of experience and operators with specific knowledge in this field. A training plan could be a very useful tool to create a pool of well-trained professionals who could develop this technology in Lebanon. Legal barriers: Currently there is no appropriate legislation. There are permits that can be requested for the construction of a geothermal plant (should be further assessed): • Permit for exploitation of the underground resources • Permit for construction of the GSHP plant • Application for Environmental Impact Assessment • Land ownership: land ownership or approvals from the land owners are necessary
64 12 References
CTE. (n.d.). Technical Building Code paragraph H4, 4.1. Spain. DVGW, G. A. (n.d.). W121:2003-07.
EEG. (2015). Thermal Response Test (TRT) on a ground closed loop heat exchanger MEDRAR MEDICAL CENTER (MMC) Project Choukine. Beirut: UNDP CEDRO PO15116.
EU. (2013). Ecodesign Directive 814/2013/EU . European Parliament.
Hellström. (1991). Linear source (LSM).
HPA, H. P. (2016, November). Types of Heat Pumps. Retrieved from http://www.heatpumps.org.uk/TypesOfHeatPump.html
IGSHPA, I. G. (n.d.). Standard 1C “Ground Heat Exchanger Materials”.
Jaeger, C. &. (1956). Cylinder Source (CSM).
Llopis Trillo, G., & Rodrigo Angulo, V. (2008). Guia de la Energía Geotérmica. Madrid: Fundación de la Energía de la Comunidad de Madrid.
Tarbuck, E. J. (2005). Ciencias de la Tierra: Una introducción a la geología física (8ª Edición ed.). PEARSON EDUCACIÓN S.A. .
UNDP/GEF, M. (2005). Climatic Zoning for buildings in Lebanon.
VDI 4640 Part 1 (2000).
(2000). VDI 4640 Part 2.
CEDRO (2014). The National Geothermal resource Assessment of Lebanon.
Cetin, A., Paksoy, H. (19 - 25 April 2015). Shallow Geothermal Application in Turkey. Proceedings World Geothermal Congress 2015.
LCEC, 2016. The National Renewable Energy Action Plan for the Republic of Lebanon 2016 - 2020
LCEC, 2016. The Second National Energy Efficiency Action Plan for the Republic of Lebanon - NEEAP 2016 - 2020
65 ANNEX 1: 13 Heat Pump Associations Worldwide
Associations have been created in order to provide a single platform where end users or researchers could obtain information on the available ground source heat pumps and technologies. This annex provides a list of those associations along with a brief description of the services offered and their websites. EHPA: European Heat Pump Association: http://www.ehpa.org/ The European Heat Pump Association (EHPA) represents most the European heat pump industry. Its members comprise of heat pump and component manufacturers, research institutes, universities, testing labs and energy agencies. IGSHPA: International Ground Source Heat Pump association: http://www.igshpa.org/ Established in 1987, International Ground Source Heat Pump Association (IGSHPA) is a nonprofit, membership-based organization that advances Geothermal Heat pump technology on the local, state, national and international levels. IGSHPA operates as an outreach unit of the College of Engineering, Architecture and Technology (CEAT) at Oklahoma State University. IGSHPA is an association of companies, professionals and users dedicated to promoting the science, utility and use of geothermal (ground source) heating and cooling technology. Canadian GeoExchange Coalition (CGC): http://www.geo-exchange.ca/en/ Back in 1999 a study by the Natural Reousrces Canada proposed a strategy for a market development based on a new multi- stakeholders approach. This strategy materialized in the creation of the CGC in 2002 as an initiative of the Canadian Electricity Association (CEA), the industry stakeholders with the support of the Natural Resources Canad’s (NRCan) Renewable Energy Depolyment Initiative (REDI) in support of the Ground Source Heat Pump industry in Canada. Heat Pump Association (HPA): http://www.heatpumps.org.uk/ This is a trade association in the UK representing heat pump manufacturers and distributors, it is the focal point for the exchange of know-how and information, and provides legal, technical and financial support.
66 14 Annex 2: NEEREA guidelines for GSHP template
Introduction The National Energy Efficiency and Renewable Energy Action (NEEREA) is a national financing mechanism dedicated to the financing of loans in energy efficiency, renewable energy, and green buildings. NEEREA is a joint initiative between the Central Bank of Lebanon (BDL) and the Ministry of Energy and Water (MEW). NEEREA receives the technical support of the United Nations Development Programme (UNDP) through funding by the Global Environment Facility (GEF). As part of the contract signed between the BDL and the LCEC under the name “Technical Support Consultancy Services Agreement in Energy Efficiency and Renewable Energy”, the Technical Support Unit to the Central Bank of Lebanon (BDL) at LCEC is dedicated to offer BDL technical assistance to evaluate the eligibility of submitted loans under NEEREA.
Important Notes 1. All sentences written in italic format in these Guidelines are for instructions purposes only. These sentences should be removed from the technical feasibility study. 2. This guide is for instructional purposes. It is designed to help potential beneficiaries and contractors in preparing comprehensive technical reports and proposals about solar water heating systems installation. 3. This guide is a mandatory requirement towards facilitating the green loan applications and ensures sufficient and proper technical and financial analysis. 4. The present report contains part of the Deliverable D4d-IV from project CEDRO IV, Guidelines on Ground Source Heat Pump 5. The Annex has been elaborated based on the reference: LCEC Guidelines on Preparing Technical Proposals for Solar Water Heating Systems (SWH) Applications 6. The authors of this report are Bartomeu Casals and Eng. Maria Anzizu from TTA. 7. For questions, clarifications, or suggestions, please contact the LCEC: 01-569101 or by email: [email protected]
Evaluation of projects requesting financing of Ground Source Heat Pumps under NEEREA will be based on these issued GSHP Guidelines. Contractors are entailed to abide by the requirements set in these guidelines and must submit the technical reports following the steps and regulations clearly identified. 67 Ground Source Heat Pumps Guideline Content Introduction Important Notes Ground Source Heat Pumps guideline Content 13.1. Introduction 13.2. Overview of Preliminary Study of GSHP Appliance 13.3. Ground Source Heat Pump System Sizing 13.3.1. Energy demand 13.3.1.1. Heating and / or Cooling loads 13.3.1.2. Hot Water Demand 13.3.1.2.1. Hot Water load 13.3.1.3. Total Demand 13.3.2. Heat Pump selection 13.3.3. Underground Heat Exchanger 13.3.4. Sizing the Storage tank (sanitary hot water) 13.3.5. Buffer tanks / heating and cooling 13.3.6. Recirculation pump Sizing 13.3.7. Summary of Ground Source Heat Pump System Components 13.4. Financial Analysis 13.5. Green House Gas Emissions Reduction 13.6. Post-Installation Measurements 13.7. Conclusion 13.8. Appendices 13.9. General Notes
68 13.1 Introduction [This section should include the objective of the proposed GSHP system installation, the financial criteria and technical/operational limitations, the conclusions on the technical study and economic evaluation of the project, annual energy savings and cost savings in a table format] A detailed summary of the proposed project is provided in this section in the table here below:
GSHP system supplier
Indoor area to be covered
Installed cost of GSHP system ($)
Estimated energy consumption heating (kWh/y)
COP according EN 14511, heating
Estimated energy consumption cooling (kWh/y)
COP (also known as EER [13]) according EN14511, cooling
Estimated energy consumption sanitary hot water (kWh/y)
COP according EN14511, sanitary hot water
Estimated Annual Energy savings (kWh/y)
Estimated Annual cost savings ($/y)
Payback period (years)
Total avoided CO2/y due to GSHP (kg)
System working days per year
Supplier’s Signature Client’s Signature
[13] EER is equivalent to the COP in cooling mode 69 13.2 Overview of Preliminary Study of GSHP Appliance [This section should include dates of preliminary study or audit and data collected from facility or building owner. A general description of the relation between the existing appliances at the facility and the GSHP system to be installed is required]
13.3 Ground Source Heat Pump System Sizing [Multiple factors play an important role in determining the GSHP system size (indoor area to be heated or cooled, sanitary hot water demand, budget, outdoor area available for underground heat exchanger, electricity power available, etc…)] [Before installing a GSHP system, the heating, cooling and sanitary hot water demands must be considered first, since the efficiency and design of a GSHP system depends on the thermal insulation of the building to be heated or cooled. Furthermore, sizing the system properly is a must to ensure that it meets the thermal energy needs of the facility] [In addition to GSHP, a number of other components are required to ensure the energy efficiency of the system, like underground heat exchanger, control system and the distribution of the thermal energy to the building, among others. The specific components required depend on the functional and operational requirements for the system. The major components for GSHP system are heat pumps, underground heat exchanger, storage tank (sanitary hot water), buffer tanks (heat, cool), pumps, control system, energy meters (electricity, thermal energy) and data logger. • Heat pumps: the unit used to drive underground thermal energy to the building. • Underground heat exchanger: boreholes, horizontal heat exchangers or any other device that could be used to extract or inject thermal energy from / to the underground. • Plates heat exchanger: heat exchanger which uses metal plates where fluids are exposed to much larger surface area. • Storage tank (sanitary hot water): storage tank is used to store the sanitary hot water for future use. It can contain the heat exchanger where heat is exchanged from the heat pump to the cold water, or it could be a tank-in-tank system) • Buffer tanks (heat, cool): store water to reduce the starting and stopping of the system, while maintaining a reserve of thermal energy that enables providing the service of heating and cooling during periods when the compressors are shutdown. • Pump: it is used to circulate water and/or heating fluid in the active GSHP system. • Control unit: takes care of the whole GSHP system. It is usually integrated in the heat pump machine. • Energy meters (electricity, thermal energy): are used to measure the energy efficiency of the whole GSHP system. To be used when the energy efficiency of the whole GSHP system is to be monitored. • Data logger: it is used to record the data measured by the energy meters. • Auxiliary Elements: such as manifolds, expansion, pressure safety, two and three-ways valves or filters and others for safety and long term sustainability. [An accurate system of the customer’s needs is the starting point for specifying, designing and installing GSHP systems. Developing and planning GSHP projects requires an understanding of the customer’s expectations from both financial and energy perspectives] [The following sub-sections must be followed, described and completed to achieve a full technical GSHP project proposal. All the tables in these sub-sections are not shown as examples, they must be filled and completed in such technical feasibility studies and should include these minimum required information and details needed to assess the GSHP systems]
70 13.3.1 Energy Demand
13.3.1.1 Heating and / or Cooling Demand [Information about heating or cooling loads that are using water as thermal fluid, specified monthly and in a round year basis (kW)] should include these minimum required information and details needed to assess the GSHP systems]
Heating and cooling demand
Month 01 02 03 04 05 06 07 08 09 10 11 12
Cooling demand (kWh/month) Heating demand (kWh/month)
13.3.1.2 Hot Water (for sanitary use) Demand [Estimate the hot water consumption] [The below table must be filled according to clearly made assumptions, specified monthly and in a round year basis]
Monthly Hot Water Demand (litres)
Average daily hot water demand (litres/day) Hot Water Average litres Number Use per person of persons 01 02 03 04 05 06 07 08 09 10 11 12
Total daily Hot Water Demand (litres/day)
[Add additional rows for additional uses as needed]
71 [The below table must be filled according to clearly made assumptions]
Location Temperature Location
Latitude
Longitude
Cold Water Temperature (°C) [Temperatures must correspond to regions for the Lebanon model energy building code]
13.3.1.2.1 Hot Water (for Sanitary use) energy demand (kWh) [Once the total daily demands have been stated, the thermal energy (kWh) to cover should be calculated and indicated] Knowing the Temperature Difference and Volume of water, the thermal power requirements can be calculated using the following formula: (ρ∙V∙c∙∆T) E_SHW = (3600•η) Where: ESHW: Energy demand hot water for sanitary use (kWh/day) ρ: Density of water (kg/liter) V: Volume of water required (liter/month) c: Specific Heat (kJ/kg•K) = 4.1784 kJ/kg•K η: Efficiency of the storage tank (%) ∆T: Temperature Difference (K)] [As an example, a house which uses 2.400 l in the month of April which heats the water 35ºC (from 10ºC to 45ºC) and a tank efficiency of 90% will require 108.32 kWh/month to cover the demand] [The monthly thermal power demand should be calculated]
Monthly Hot Water Demand (litres)
Month 01 02 03 04 05 06 07 08 09 10 11 12
Hot water for sanitary use demand (kWh/month)
72 13.3.1.3 Total Underground Energy Demand [The total demand should be calculated] [For small projects (i.e. < 12 kW) losses related to the distribution and storage are negligible. However, for projects of higher thermal power, the loss factor to the heating and cooling demand as well to the hot water demand should be added to calculate the final underground demands] [Compressor demand cool and Compressor demand heat (points 2 and 5) refers to the Power required by the compressor which is the result (cooling or heating demand / COP). As a reference a COP of 4,34 could be considered.] [Hot water demand comprises the demand for heating and the demand for hot water for sanitary uses] [Total cooling demand (point 3) is the result of the total cooling demand plus the compressors demand for cooling] [Total hot water demand (point6) is the result of the total cooling demand minus the compressors demand for hot water]
Month 01 02 03 04 05 06 07 08 09 10 11 12
Cooling demand (kWh)
Compressor demand cool (kWh)
Total cooling demand (kWh) (1+2)
Hot water demand (kWh)
Compressor demand heat (kWh)
Total hot water demand (kWh) (4-5)
Total (from/to ground) (kWh) (3+6)
[The result of the heating demand minus the cooling demand. When (+) it refers to heat extracted from the ground, when (-) it refers to heat injected into the ground.]
13.3.2 Heat Pump Selection [Once heat, cool and sanitary hot water demands are stated, appropriate heat pump should be selected) [The heat pump is responsible for extracting heat from the ground heat exchanger to the distribution grid or vice versa.] [To determine the size of the needed pump of the system, the maximum demand must be identified. When buffer tanks are available, as general rule, a compressor should not start more than three times per hour] [For direct use (without buffer tanks), the input rating of the heat pump should be same as the loads to allow for safe and efficient operation] [All features concerning the specific site and GSHP project must be detailed and provided in this sub-section; such as buffer tanks operation, remote control operation, load transfer switch, etc.] [The following table should be filled considering the heat pumps size]
73 Heat pump important information
Number of heat pumps
Heat pumps configuration (master-slaves)[14]
Number of compressors per heat pump
Rated output per heat pump (kW) (for operating conditions)
COPEN 14511 (in cooling operating conditions)
COPEN 14511 (in heating operating conditions) Rated voltage (V)
Refrigerant circuit type
Refrigerant circuit volume
13.3.3 Underground Heat Exchanger [The selection of type of heat exchanger to be used for a given project may be based on any number of factors, including the ground composition, availability of outdoor space for vertical or horizontal methodology, costs and availability] [In case a thermal response test TRT has been performed to assess the ground characteristics, the details should be included here] [To properly size an underground heat exchanger the thermal energy extraction / injection round the year and the stability of the non-disturbed ground temperature in a medium term basis (not less than 25 years) should be taken into consideration]
Underground Heat Exchanger information
Outdoor area available (m2) Bore holes: number and length (m) Horizontal exchanger: area (m2) Total thermal power of underground exchanger (W) Yearly hours of operation Energy to be extracted (kWh/y) Energy to be injected (kWh/y) Balance (extracted versus injected) (%) Underground exchanger manufacturer/contractor Expected lifetime with undisturbed underground Tº
[14] In case of projects with heat pumps working in cascade configuration (more than one heat pump installed in the same GSHP system) 74 13.3.4 Sizing the Storage tank (sanitary hot water) [The size of the storage tank is directly related to the daily and peak hot water consumption] [The average tank capacity is approximated to be 50 L/member in the Lebanese family]
13.3.5 Buffer tanks / heating and cooling [The buffer tanks are needed to reduce the number of starts of compressor’s heat pump and enlarge his lifetime. Heat pumps having variable speed (inverter type) can avoid the use of such buffer tanks] [Usually, a volume of 15 to 20 liters capacity per each KW of compressor’s capacity should be considered]
13.3.6 Recirculation pump Sizing [The pump is needed to push enough heat transfer fluid through the underground heat exchanger to the heat pump, and from the heat pump to the buffer tanks or heat/cool distribution system. The steps involved in the pump sizing are: 1. Calculate the flow that the water velocity, according heat pump manufacturer’s instructions. 2. Calculate the pressure drop and flow velocity for the plumbing system. 3. Select a pump(s) that provides, the flow, the vertical lift calculated, and can handle the pressure drop calculated. 4. Select a pump(s) of the maximum energy efficiency class]
13.3.7 Summary of Ground Source Heat Pump System Components [Use manufacturer’s specifications to fill in the GSHP system components blocks] [The specifications of all the system components should be summarized in this section through the available tables below] [All the technical data should be supported by data sheets from the manufacturers in the appendices]
13.3.7.1 Heat Pump [Heat Pump specifications and information will be summarized in the following table] Heat pump Information Manufacturer COP cool mode (also known as EER) Type/Model Type of refrigerant gas Power output heat Dimensions Power output cool Weight COP heat mode Warranty (years) Cost (USD)
[Heat Pumps COP and EER should be stated according EN 14511 norm. Energy Label according Regulation (EU) No 811/2013 should be also fulfilled.]
75 13.3.7.2 Underground Heat Exchanger [Underground Heat Exchanger specifications and information will be summarized in the following table] Underground Heat Exchanger Manufacturer/Contractor Type: Vertical or Horizontal Total thermal power Cost (USD)
13.3.7.3 Storage Tank [Storage Tank specifications and information will be summarized in the following table] Storage Tank Information Manufacturer Efficiency (%) Type Insulation Number of tanks used Heat Exchanger Yes / No Capacity (L) Cost (USD) Water Flow Mechanism
13.3.7.4 Buffer Tanks [Buffer Tanks specifications and information will be summarized in the following table] Buffer Tanks Information Manufacturer Capacity Maximum working temperature Minimum working temperature Cost (USD)
13.3.7.5 Recirculation pumps [Pumps specifications and information will be summarized in the following table] Pumps Specifications Manufacturer Type Number of pumps used Power (W) Input Voltage (V) Life time Efficiency (%) Cost (USD)
76 13.3.7.6 Additional Equipment’s [Additional equipment, if any, should be specified and detailed in this sub-section] Additional Equipment’s Specifications Manufacturer Type / Model Function Cost (USD) [Use an individual table customized according specifications for each additional equipment]
13.3.7.7 Electrical, Hydraulic & Mechanical Drawings and Connections [Electrical, Hydraulic & Mechanical Drawings and Connections must be attached to the proposal in this sub-section] [Real drawings must be clear to check the global view of installation of the real system]
13.4 Financial Analysis [The detailed financial proposal of all the products of the PV system must be provided in the below table format]
Ref. No. Item Item Description Quantity Amount Needed (USD) 1 Heat Pump 2 Underground Heat Exchanger 3 Pump(s) 4 Controller 5 Sanitary and buffer tanks 6 Flow Meter 7 Data logger 8 Accessories 9 Installation 10 VAT Total Amount of the GSHP system (USD
[Add additional rows for more detailed accessories items] [Details on system life and maintenance are to be mentioned in this section such as expectancy, yearly degradation factor, yearly maintenance cost, etc…] [In order to compare the different GSHP system options and to determine the most cost-effective system designs and to give the client a global view of the advantages and benefits of his investment in such projects, the life cycle cost analysis of the GSHP system should be provided in this section showing the total cost of ownership for this renewable action including energy cost, replacement cost and maintenance cost over the lifetime of the system]
77 [Three different parts must be studied to achieve a complete and clear financial analysis: the first one about all the parameters to take into consideration in the life cycle cost analysis, the second about the cash out-flows and the third discussing the cash in-flows] [All the information to be provided for the financial analysis must be clear, comprehensible and detailed] [The net cumulative savings will be the essential data for concluding on the profitability and the return on investment. The following tables should be used in such analysis and more detailed tables can be provided according to the contractor or consultant detailed analysis: Yearly Cost Savings Month Energy Savings (kWh) Cost Savings (USD) January February Year [Energy and Cost Savings must be detailed]
Net Cumulative Savings Year Cash Out-Flows Cash In-Flows Total Cash Flow Total Cumulative Cash Flow Year 1 Year 2 Net Present Value (NPV) IRR
13.5 Green House Gas Emissions Reduction [This section is dedicated to the environmental part of the project to be implemented. The calculation of the avoided green house gas emissions must be provided and detailed]
13.6 Post-Installation Measurements [Most important data to be noted when measurements will be done after installation of the solar water heating system is the Monthly Total Energy Saved in addition to the hot water temperature in winter and summer, etc…]
13.7 Conclusion [The conclusion of the GSHP study proposal must include the following: • Summary of recommendations, estimated annual kWh produced, estimated cost savings, projected investment cost and payback period in the table format below: Summary Table of the proposed GSHP system GSHP System Energy Savings Cost Savings Implementation Payback tCO reduced Description (kWh/year) ($/year) Cost Period 2
• ESCO’s or Solar Energy Company’s recommended action plan and implementation schedule • Statement by the client on which recommendations will be implemented and timeframe for implementation]
78 13.8 Appendices [Information of significant importance, which cannot be presented as a part of the text report (because of number of pages, quality of presentation, etc.) shall be presented as appendices] [The appendices should include: • Details of all products specifications (Collector’s Certificate of Compliance from the IRI must be provided) • Details on simulation tools employed and calculations method • Construction and physical characteristics and warranties conditions for concerned products]
13.9 General Notes [Documentation – All numbers related to the results should be supported by information showing how they were derived. This includes all energy produced; cost savings, investment and payback information] [Mathematical accuracy – All calculations in the report should be checked for mathematical accuracy] [SI units must be used in all parts of the report] [Grammar and style – The report should be written in proper prose. The language should be clear, concise and understandable]
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