Development of New Ground Loop Sizing Tools for Domestic GSHP Installations in the UK

Development of new ground loop sizing tools for domestic GSHP installations in the UK

Robin Curtis1, Tom Pine1 and Chris Wickins2. 1GeoScience Ltd, Falmouth Business Park, Falmouth, Cornwall, TR11 4SZ, UK 2 Department of Energy & Climate Change, Whitehall, London, SW1A 2AW, UK [email protected]

Keywords: ground source heat pumps, ground loop 1. INTRODUCTION design

ABSTRACT For a variety of reasons, the UK has been a late adopter of ground source heat pump technology (GSHPs) (Curtis 2001). In recent years, with wider Commercially available software packages for recognition of the technology, and with incentives designing closed-loop GSHP systems, such as Earth from the "Clear Skies" microgeneration scheme, the Energy Designer (EED), Ground loop designer (GLD) EEC (Energy Efficiency Commitment) and CERT and GLHEPRO have been available in the UK for (Carbon Emissions Reduction Target) utility backed some time. However, these are rarely used by schemes, and the "Low Carbon Building Programme", domestic ground-source heat pump installers owing to the number of installations began to rise, to a level of their complexity and availability. Until recently, about 4000 per annum. In numerical terms most of installers were therefore dependent on specialist these were in the domestic sector, ranging in size from thermogeologists, manufacturers, or rules of thumb 3.5kWth in social housing installations to ~16kWth, a learned through experience or other sources. limit determined by the single phase 230VAC Consequently, when a UK field trial of domestic electrical supply that is the norm for UK housing. ground-source heat pumps showed that several systems were operating with excessively cold ground In 2008, the Energy Saving Trust, together with loops within four years of being installed, the UK industry stakeholders, initiated a one year monitoring Government and the GSHP industry identified a need exercise on ~80 domestic heat pump installations, to develop conservative design tools that were simple distributed throughout the UK (EST 2010). This study to use and readily available. A paper-based design included 48 GSHP systems, and as well as monitoring methodology for closed-loop GSHP systems of less the performance of the systems, also incorporated than 45kW heating capacity has now been brought work by Open University researchers on user into service through the UK Microgeneration satisfaction and experience. Some of the data in this Certification Scheme's Microgeneration Installer monitoring exercise has subsequently been reworked, Standard for heat pumps MIS3005 (MCS 2012). The and an updated report has been published by the sizing methods for boreholes, horizontal loops and Department of Energy & Climate Change (DECC) Slinkies encompasses the diverse geologies, and full (DECC 2012). The exercise had two major outcomes: extent of both ambient and ground temperatures encountered throughout the UK, over a range of i) it suggested that many UK domestic heat pump domestic load factors. Supplementary guidance has systems included in this monitoring study, were not also been provided on the hydraulic design of these performing as well as would be expected, closed-loop systems. This paper describes the underlying philosophy behind the new design tools and and how the multi-dimensional task of sizing a ground ii) that there were serious shortcoming in the selling, loop was reduced to 3-dimensional set of tables that design, installation and operation of these systems. It UK ground source heat pump installers could begin was decided to extend the monitoring programme for using with minimal training. With domestic GSHPs an additional year, with remedial measures being designed to these guidelines, or better, the intention is undertaken on a number of the installations in an that future installations will meet the performance attempt to see if their performance could be improved. requirements of both the UK's Renewable Heat The monitoring was concluded in 2012, and a final Incentive (RHI) scheme and the EU RES directive for report on the overall monitoring experience will be renewable energy from heat pumps. published later this year (ie 2013).

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In the UK, the evolution of incentive schemes for i) an emitter design guide, microgeneration systems (ie domestic solar thermal, solar PV, micro-wind, small biomass and heat pumps) (http://www.gshp.org.uk/pdf/MIS_3005_Heat_Emitter has been carried out in parallel with the development _Guide.pdf) of UK national "standards" for the selling, design, ii) ground loop sizing charts, installation and operation of these systems. The government has wanted to ensure that in providing (http://www.gshp.org.uk/pdf/MIS_3005_Ground_loop fiscal support for these technologies, domestic _sizing_tables.pdf) customers will receive properly designed and installed, effective systems that will meet the required iii) hydraulic pressure loss design charts. renewable energy and/or carbon targets. These standards have been developed under the (http://www.microgenerationcertification.org/images/ Microgeneration Certification Scheme (MCS). See: GSHP_Hydraulics_Design_Guide_v1.0.pdf)

(http://www.microgenerationcertification.org/mcs- This paper specifically addresses the development of standards/mcs-standards) items ii) and iii) which are of relevance to domestic closed loop GSHP systems. Because the UK government is keen to promote a rapid acceleration in the installation of heat pumps in (All of the MCS documentation, for the various the UK as part of its 2030 and 2050 decarbonisation microgeneration technologies can be found at: targets, DECC decided that the shortcomings shown http://www.microgenerationcertification.org/mcs- up in the EST monitoring study needed to be rapidly standards/mcs-standards) addressed. A DECC technical working party, drawn from the UK heat pump industry, was established in February 2011 whose objective was to revise or expand any parts of the MCS process that applied to 2. GROUND LOOP SIZING heat pumps, with a view to improving domestic heat pump performance, and the user experience. 2.1 Previous practice The major areas that were identified for consideration In the absence of any UK guidance documents or for all heat pumps were: standards, installers of domestically sized closed loop i) the assessment of building energy loads - both in GSHPs systems used several approaches to designing terms of worst day heat loss, and in annual energy ground arrays: consumption (of particular importance for GSHPs). 1) In some cases, design software such as the US ii) the selection and sizing of appropriate heat emitter based GLHEPRO from the International Ground systems for use with heat pumps Source Heat Pump Association (IGSHPA), and the European based EED (Earth Energy Designer) has and specifically for GSHPs been used by the more knowledgeable designers. In more recent years the US based GLD software from iii) the sizing of ground loop arrays Gaia Geothermal has been adopted in the UK. Whilst GLHEPRO and EED are reasonably low cost, they iv) the design of the hydraulic performance of closed may be beyond the reach of small companies, but loop ground arrays - to minimise parasitic pumping more importantly they are too complex for them to energy. use, at least without a significant investment in The working party needed to work rapidly and was training. In the case of GLHEPRO the heat pump only in existence for a period of six months. It libraries do not include data on European heat pumps, managed to achieve a significant amount of although this can be added. Gaia Software have begun development work in terms of revised MCS guidance to include data on a significant number of European and design documentation. Interested readers will find heat pumps into GLD. EED does not provide a heat the revised versions of the GSHP related MCS pump model, but relies on the designer inserting a documents on the UK Ground Source Heat Pump required SPF. Association's web site: 2) In a few rare cases, designers have made use of (http://www.gshp.org.uk/pdf/MIS_3005_Heat_Pump_ CLGS, the US based domestic design software from Systems.pdf) IGSHPA. This package can be used for small borehole based, U-tube systems and for North American style As well as revised guidance provided in the heat pump 2, 4, 6 pipe-per-trench horizontal systems. The design document MIS 3005, three other documents disadvantage is that it uses Imperial units, requires bin have been generated: style temperature data (°F!) which is not commonly available in the UK, and does not include data on European heat pumps.

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3) VDI 4640 (VDI 2001) is either used directly, or has The ground loop sizing tables would be the additional been adopted and adapted by a number of European design item that is required for GSHP design, above heat pump manufacturers and incorporated into their and beyond design principles required for air source own technical design manuals, eg Viessmann, heat pumps. The methodology now laid down in Dimplex, Stiebel Eltron. MIS3005 is:

4) Other manufacturers (primarily Scandinavian) 1) Determine the worst day heat loss of the property, provide in-house design tools for their installers. and the annual load factor (or full load equivalent run hours). This has to be done using a room-by-room Whilst codes such as EED, GLHEPRO and GLD are heat loss sizing calculation based on EN12831 extremely flexible, they are dependent on the correct input data from the designer, and the number of 2) Select the heat emitter system using the Heat variables to be considered is far more complex than Emitter Guide (specifically developed as part of this the designer of small domestic systems is generally working party). This guide has been developed to familiar or comfortable with. cover underfloor heating, radiators and convector radiator heat emitters and is designed to assist an The issue of concern around VDI 4640 and design installer in explaining to a potential customer the tools provided by European manufacturers was improvement in operating efficiency (SPF) that can be whether these had been designed for use in UK achieved by using lower temperature emitter systems. conditions of geology, climate and building design. The chart provides the designer with the expected Specific issues associated with VDI 4640 are the use space heating SPF of the system. of double U-tubes in boreholes, a practice which is not common in the UK for small domestic systems, the 3) Select a heat pump that can meet 100% of the total variability in the allowed minimum Entering Water worst day heat loss of the property (in kW) for 99% of Temperature, (EWT) (ie to 10°C below the the hours in an average year. (Note that it is now a equilibrium ground temperature), and queries over the requirement, under the MCS standard, that mono- design depth for horizontal systems, and the energetic domestic heat pumps have to be sized to associated annual temperature swing. meet the worst day heat loss of a property. This is to prevent significant increases in electrical demand at times of cold weather, and to achieve reasonable SPFs and running costs. Only bivalent systems that use non- 2.2 Underlying philosophy electrical heat sources can employ heat pumps sized to less than 100% of worst day heat loss. )

It was decided that a sizing methodology would be 4) From the desired SPF in the heat emitter guide, and developed that encompassed borehole and trench the thermal power of the selected heat pump, the based closed loop GSHPs, up to 45kW (heating/hot designer can compute the required heat extraction rate water only), under all UK geological and climatic required from the ground for a GSHP system. conditions. Thus the objective was to generate charts (at least The system would be paper based, and would produce initially) for single U-tube borehole systems, a conservative design. The approach being that if an horizontal systems and Slinky systems, that provide installer rigorously followed the procedure, they the permitted ground extraction rates from which a would be assured of a GSHP system that would designer can compute the size of a ground loop array deliver a satisfactory SPF. Designers with more (ie total borehole length, total horizontal loop length, sophisticated knowledge or with access to, and an or total length of Slinky pipe and trench.) understanding of, ground loop sizing software, would in principal be able to achieve less conservative (and For all systems, the minimum ground loop entering possibly lower cost) systems. Thus the objective was water temperature to the heat pump from the ground to provide an "open source", non-proprietary, freely- (EWT) is required to be not less than 0°C after 20 available design tool that would allow any installer to years of operation. design a GSHP system up to 45kW that would deliver a satisfactory performance, anywhere in the United This was adopted to ensure that good, long term SPF's Kingdom. There is complete independence from any are achieved by GSHPs, and to ensure that installers computer operating system, computer hardware, cannot gain significant competitive advantage by software or software versions, which isolates the MCS designing (lower cost) systems with shorter ground delivery organisation from any future software or arrays that operate at significantly lower EWTs. hardware "upgrade" issues. The major variables that have to be addressed are: In principle the methodology would be suitable for software or at least spread-sheet style adaptation. It is i) Thermal conductivity also possible that the approach adopted here could be ii) Ground "rest" or "equilibrium" temperature replicated to other "national" climates and geologies, both within the EU and beyond.

3 EGC 2013 Curtis et al. iii) Required annual energy delivery, eg load factor / 2.4 Horizontal / trenched systems Full Load Equivalent run hours. The permitted heat extraction values for horizontal systems were more difficult to generate because there After investigating relationships between the variables are additional parameters and design considerations in this multi-dimensional space, it was decided that it compared to boreholes. As well as ground was possible to produce tables for a given annual load equilibrium temperature, data is required on the factor, that relate the permitted ground heat extraction annual temperature swing. In addition the designer rate to the mean ground temperature, and the ground could vary the depth and spacing of the pipework. In thermal conductivity. order to keep the number of tables to a practical Given the significant impact that the annual thermal minimum, the variance in these parameters was energy requirement has on the size of ground loops, an investigated. initial exercise looked at the potential impact of Whilst there is no underlying physical relationship, a different load profiles in the UK environment. Load review of data from the UK Meteorological Office profiles for three UK locations, Plymouth, London and suggested that there was at least an approximate Aberdeen were generated, for heating only and for linear correlation between annual average temperature heating and hot water generation. It was found that the (and hence ground equilibrium temperature) and the variation in the shape of these annual load profiles, for annual temperature swing (Appendix, Figure A1). It domestic heating GSHPs, was relatively minor, was therefore decided to eliminate annual temperature compared to the much larger impact of the total annual swing as a variable, but to take account of it over the energy requirement. In all of the work that followed, a range of ground equilibrium temperatures adopted for common annual load profile was adopted for a set of the UK tables. The linear relationship shown in Figure annual full load equivalent run hours (FLEQs) of A1 produces conservative designs in most cases. 1200, 1800, 2400, 3000 and 3600 hours. An investigation was also carried out into the optimal depth placement for horizontal pipework. There was 2.3 Boreholes concern that calculation methods developed for the US, Canada or Scandinavia could have adopted Determining the permitted extraction rates for allowances for snow cover in the winter. This borehole based systems was more straightforward than encourages the use of shallower depths to take for the horizontal options. advantage of solar input in the summer, whilst being 2.3.1 Borehole fixed parameters: insulated by snow cover in the winter. This does not apply to the UK as the period and extent of any snow HDPE single U-tube 32mm OD, SDR11 with a cover is generally very limited. The series of graphs thermal conductivity of 0.420W/mK. 52mm pipe shown in Figure A2 in the Appendix illustrates the centre-to-centre shank spacing. complex variation in predicted extraction rates for a range of thermal conductivities, at different depths, for 130mm diameter boreholes. Thermal resistance of differing swing temperatures. After investigating the borehole/grout/U-tube completion 0.1 mK/W optimal placement depth based on thermal performance, primarily driven by a combination of 6m minimum spacing, boreholes in a line. ground equilibrium temperature and annual temperature swing, it was found that practical 25% mono-ethylene glycol heat transfer fluid. Re > considerations vis-a-vis depths of other services (eg 2500 in active elements of ground loop array. water electricity, cable, telephone etc), protection from 2.3.2 Borehole variable parameters: other shallow ground excavations, frost protection and Health and Safety requirements, indicated a depth of Mean ground temperature: 6.0°C to 15.0°C 0.8 - 1.2m for developing the horizontal tables. This is an example where a designer with access to more Ground conductivity: 1.5 - 4.5 W/m/K, sophisticated modelling software, and knowledge of the local temperature swing, may be able to come up Load factors: 1200, 1800, 2400, 3000, 3600 full load with a more optimal (possibly lower cost) solution. equivalent (FLEQ) run hours. Investigations were also made into the variation in The borehole values were computed with these extraction rate, either as a W/m value or a W/m2 value, parameters using GLHEPRO, and EED. A selection of with horizontal pipe spacing. This exercise revealed the results were cross checked with results both from issues relating to the computation of the "effective GLD, and from VDI 4640 (albeit with a correction area" to be used for a W/m2 calculation, and is why factor for double U-tubes vs single U-tubes). The the Tables give a W/m of pipe length value for values derived from the code runs were then horizontal pipes, for a specified pipe separation, rather transformed into the sizing tables using an than a W/m2 value. Figure 1 is an example, generated extrapolation algorithm developed in MATLAB. An during this study, of the variation in extracted W/m or example of a completed Borehole Heat Extraction W/m2 values for a range of pipe separations, at Table is shown in the Appendix, Figure A3. different thermal conductivity values.

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Figure 1: Horizontal loops: variation in predicted A comparison was made of horizontal and vertical heat extraction rates with separation Slinkies, pitch, and trench separation. Modelling of distance, for a range of thermal Slinky geometry is not straightforward, and all of the conductivities. work carried out here was done within the confines of the analytical modelling employed in CLGS. 50 Temperature swing = 13.5oC However, there are some interesting mind exercises Depth = 0.75m 40 that can be undertaken when exploring the extremes of

30 pitch. At a pitch of zero, the installation simply W/m2 20 becomes a coil, or roll of pipe in the ground. In this 2.5W/m/K configuration there are obviously extreme cases of 10 1.4W/m/K pipe overlap, with only the two extreme (ie outer) 0.3W/m/K 0 coils actually being in contact with the ground. At the 2.5W/m/K other extreme, ie as pitch tends to infinity, there is 20 minimal pipe cross over and practically all pipe is in 1.4W/m/K contact with the ground. Comparisons were made with W/m 10 analogous horizontal pipe layouts in order to develop

0.3W/m/K consistency between the Slinky and horizontal loop

0 sizing values. In this case the extraction tables are 0 200 400 600 800 1000 1200 1400 Pipe separation (mm) quoted as W/m of trench length for a specified pitch and loop diameter. The horizontal pipe extraction values were generated Once again, designers with access to more using the IGSHPA CLGS code, with cross checks sophisticated modelling software may be able to arrive being made against VDI 4640 in the parameter space at ground loop arrays based on different Slinky where the latter overlays the work described here. geometric parameters. The more difficult exercise was in the generation of Having explored the factors affecting the design of values for Slinkies. The only code that the authors are these <45kW heating only, closed loop GSHP ground aware of that treats Slinkies is GLD. They are not arrays, the sizing tables were generated for single-U covered by VDI 4640. Upon investigation, it appears boreholes, horizontal loops, and Slinkies, that the method used in GLD is based on the technique described in the IGSHPA Slinky Installation guide 2.4.1 Horizontal and Slinky fixed parameters: (IGSHPA 1995) which employs a modified form of the algorithms used in CLGS for horizontal pipework. 25% mono-ethylene glycol heat transfer fluid. Re > 2500 in active elements of ground loop array. After an exploratory study, it was concluded that it was possible to represent a Slinky in the CLGS code Horizontal pipe: 25mm OD MDPE SDR11, horizontal as four equally spaced pipes with a separation of d/3 pipe spacing at least 0.75m, pipe depth 0.8 - 1.2m between pipe centres, where d is the diameter of single Slinky loop (Figures 2a and 2b). Slinkies: 32mm OD MDPE SDR11. Trench spacing at least 3m. Mean slinky depth 0.8 - 1.2m. Pipe length to Figure 2a: Slinky geometry trench length ratio at least R > 4. (For 900mm diameter = 1250mm pitch)

2.4.2 Horizontal and /Slinky variable parameters:

Mean ground temperature 6.0°C to 12.0°C

Ground conductivity: 0.4 - 2.4 W/m/K

Load factors; 1200, 1800, 2400, 3000, 3600 full load equivalent (FLEQ) run hours. d p (pitch) Examples of completed Horizontal Loop and Slinky Figure 2b: Equivalent horizontal loop geometry Heat Extraction Tables are shown in the Appendix, Figures A3 and A4.

3. Hydraulics design

Having prepared the ground loop heat extraction tables, it was recognised that an additional topic that needed to be addressed was in the hydraulic design of closed loop GSHP ground arrays. Systems were being encountered where the parasitic pumping energy of 5 EGC 2013 Curtis et al. the ground loop pump was significant, and badly Figure 4: Main flow chart from the Hydraulic affecting the SPF of the installation. For many Design Guide. designers this appears to be a neglected component of the design. Figure 3 shows the impact on the SPF of a heat pump with increasing power of the ground loop circulating pump as a fraction of the heat pump compressor power.

Figure 3: Impact of ground loop circulation power on overall SPF of a GSHP system

Effect of ground loop circulation pump on SPF

% reduction in SPF Reduced SPF

3.50 0.00%

3.45 -1.00%

3.40 -2.00%

3.35 -3.00%

3.30 -4.00% SPF SPF 3.25 -5.00%

3.20 -6.00%

3.15 -7.00% Reduction in COP (%) (%) COP in Reduction 3.10 -8.00%

3.05 -9.00%

3.00 -10.00% 1 2 3 4 5 6 7 8 9 10 Pump power as % of compressor power

To address this, it was decided, using the same reasoning as was applied to the Heat Extraction Tables, to develop a paper based sizing procedure for the hydraulic design of closed loop GSHP systems up to 45kWth. The guidance document combines an iterative flowchart based design process, with paper charts Conclusions giving head loss vs flow rates for commonly used Following the deliberations of the DECC working pipework that make up the various ground loop group and after review and approval from the MCS elements. The underlying requirement is to achieve a committees, the MCS Microgeneration Installer for minimum head loss across the entire ground loop heat pumps, MIS2005 was revised and reissued in array, whilst maintaining turbulent flow (Re>2500) in September 2011. A series of awareness days and the thermally active elements of the array. The training sessions were carried out to make existing overarching flow chart is shown in Figure 4, which heat pump installers aware of the significant changes points at two further flow charts, one for the thermally that have been incorporated into the new guide. active components and one for the header components. An example of a head loss chart is shown It is hoped that the implementation of these new in the Appendix, Figure A6. The design guide guidance document will result in an overall (available at: www.microgenerationcertification.org improvement in the performance of newly installed /images/GSHP_Hydraulics_Design_Guide_v1.0.pdf) domestic heat pumps systems in the UK. DECC is has been developed for three heat transfer fluids, viz currently running a large-scale heat pump monitoring monoethylene glycol to freeze protection levels of - exercise based on experience gained during the EST 10°C and -15°C, and mono propylene glycol to a monitoring project. The objective is to demonstrate freeze protection level of -10°C. The charts provide whether heat pump installations are now capable of pressure drop values for active elements constructed meeting the target requirements of both DECC and the from 25mm, 32mm and 40mm OD, SDR11 and EU RES directive in terms of delivering low carbon SDR17, and for header pipework in 25mm, 32mm renewable heat at a reasonable running cost to users. 40mm, 63mm and 90mm SDR11 and SDR17. These This will also provide information that the encompass practically all of the pipework sizes used Government can use to evaluate the anticipated value in domestic systems up to 45kWth. for money of the domestic Renewable Heat Incentive (RHI) for heat pumps

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In generating the GSHP heat extraction tables described here, it is believed that a robust basis has been put in place for evaluating how ground loops can Acknowledgements be sized for the climatic and geological conditions that arise throughout the whole of the UK. It will now be possible to test sizing methodology and software from The authors would like to acknowledge the assistance various other sources to check that that they also cover provided by other members of the DECC technical all conditions of relevance to the UK. It is suggested sub-group that was established to revise the MCS that the methodology adopted here could be replicated domestic heat pump design and installation to other countries within the EU, and beyond. documents.

The entire set of new design documents (ie MIS 3005 and related) have now been in use for over a year. A number of comments and queries have been received, but so far no major flaws have been reported. It is anticipated that any comments will be taken into account, and some of the basic design requirements may be reviewed. For example, there is a possible case to be made that a minimum EWT of 0°C could be relaxed for GSHP systems with low load-side temperatures. It is also possible that the various heat extraction and hydraulic tables will be expanded to cover other pipework layouts and geometries.

Given the requirement for EU-wide training and certification for GSHP installers as called for in the EU RES directive, There may be useful lessons to be incorporated from this exercise into schemes such as GEOTRAINET and EUHP Cert.

REFERENCES

Curtis, R.H.: Earth Energy in the UK. International Geothermal Days "Germany2001",International Summer School, Bad Urach Germany, (2001). Dunbabin, P. and Wickins, C.: Detailed analysis from the first phase of the Energy Savings Trust's heat pump field trial. (May 2012). Available at: www.decc.gov.uk/assets/decc/11/meeting-energy- demand/microgeneration/5045-heat-pump-field- trials.pdf Energy Saving Trust (EST): Getting warmer: a field trial of heat pumps, (Sept 2010) International Ground source Heat Pump Association (IGSHPA): Closed-Loop Geothermal Systems Slinky Installation guide. ISBN 0-929974-04-2, (1995) Microgeneration Certification Scheme (MCS): Microgeneration Installation Standard: MIS 3005 Requirements for Contractors Undertaking the Supply Design Set-to-Work Commissioning and Handover of Microgeneration Heat Pumps, Issue 3.1a, (2012). Verein Deutscher Ingenieure (VDI): VDI 4640 Part 2 Thermal Use of the Underground: Ground source heat pump systems, Düsseldorf, (2001)

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APPENDIX Figure A1: Collection of UK locations showing mean annual air temperature, and annual temperature swing.

16.0$ 14.7$ E Pennines East Anglia 14.0$ North-eastern 13.1$ Thames Valley NE Scotland W Scotland South-eastern E Scotland Midlands 11.6$ Severn Valley 12.0$ Southern

% North-western C)

o se ( rst ca N Ireland South-western 10.0$ Wo Borders 10.0$ Wales W Pennines swing%

ine Trendl NW Scotland 8.0$ Region Monthly mean temperature Monthly mean temperature (/oC) swing (/oC) temperarture% NE Scotland 8.48 11.1 NW Scotland 8.56 8.8 E Scotland 8.76 11.4

annual% 6.0$ Borders 9.04 10.5 W Scotland 9.08 11.6 N Ireland 9.35 11.0

Mean% North-eastern 9.42 12.4 North-western 9.43 11.5 4.0$ Midlands 9.78 12.7 Wales 9.88 10.3 E Pennines 9.98 12.7 W Pennines 10.01 12.1 East Anglia 10.13 13.2 2.0$ South-eastern 10.17 12.9 Southern 10.35 12.2 Severn Valley 10.63 12.3 South-western 11.04 10.5 Thames Valley 11.31 13.5 0.0$ 6$ 7$ 8$ 9$ 10$ 11$ 12$ Mean%annual%air%temperature%(oC)%

Figure A2: Example graphs showing variation in horizontal loop ground extraction rate with temperature swing, depth and thermal conductivity.

50 Thermal conductivity = Thermal conductivity = Thermal conductivity = Thermal conductivity = 0.3 W/m/K 1.1 W/m/K 1.8 W/m/K 2.5 W/m/K

30 2 /m ex W

2.4m

1.6m 10

0.8m

0.15m 0.4m 0 8 101214161820228 101214161820228 10121416182022 8 10121416182022 Temp Swing (oC) Temp Swing (oC) Temp Swing (oC) Temp Swing (oC)

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Figure A3: Borehole heat extraction table as published in MIS 3005 for 2400 FLEQ hours load.

Maximum power to be extracted per unit length of borehole heat exchanger (W/m) with 2400 FLEQ run hours Conditions for use: Heat extraction only (inc. hot water) 6m minimum borehole spacing. Only valid for boreholes arranged in a line; not applicable for a large number of systems in a small area Table created assuming: 130mm borehole diameter; single U-tube; 32mm OD SDR-11, PE100 pipe with thermal conductivity = 0.420W/m/K; 52mm pipe centre-pipe centre Sandstone

Sand (water-saturated) Granite shank spacing; 25% Mono Ethylene Gylcol thermal transfer fluid; Re > 2500 in the borehole active elements; thermally enhanced grout with thermal conductivity = 2.4W/m/K Assumptions result in borehole thermal resistance = 0.1 m.K/W at 12oC mean ground temp. and 2.5W/m/K average ground thermal conductivity 5.0

31 35 40 44 48 53 57 62 66 71

4.0

3.4 27 31 35 39 43 46 50 54 58 62

3.0

2.4 22 25 29 32 35 38 41 44 47 51 2.3 2.2 2.0

1.7 37

for different (W types rock / m/ K) 16 18 21 23 25 27 30 32 34

1.0 Average thermal ground conductivity (W / m/ K)

0.5 Recommended values and ranges ofthermal ranges and Recommended values conductivity 0.4

6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 o

Sand (dry) Mean ground temperature ( C) Clay/silt (dry)Clay/silt slates and shales) slates and Wales Borders Midlands Southern Claystone, siltstone (inc. siltstone (inc. Claystone, E Scotland East Anglia East Clay/silt (water-saturated) Clay/silt W Scotland E Pennines W Pennines NE Scotland NE NW Scotland NW Severn Valley Severn North-eastern North-western South-eastern South-western Thames Valley Thames Northern Ireland

Mean annual air temperature for UK regions (oC) Issue 1.0 (02/09/2011) 7

Figure A4: Horizontal loop heat extraction table as published in MIS 3005 for 2400 FLEQ hours load.

Maximum power to be extracted per unit length of horizontal ground heat exchanger (W/m) with 2400 FLEQ run hours Conditions for use: Heat extraction only (inc. hot water) 0.75m minimum pipe spacing (d > 0.75m) Pipe depth between 0.8m and 1.2m Table created assuming 25mm OD SDR 11 pipe Clay/silt (water-saturated) Clay/silt Sand (water-saturated) 4.0 Table created assuming a relationship between the mean monthly temperature swing and annual mean ground temperature

3.6

3.2

2.8 (W/m/K) ity 2.4 2.4 7.6 10 12 14 16 18 20

2.0 6.9 9.0 11 13 14 16 18

1.7 1.6 6.0 7.7 9.4 11 12 14 15

1.2 for different (W types rock / m/ K) 4.7 6.0 7.4 8.7 10 11 12 Ground thermal conductiv 0.8 3.4 4.2 5.2 6.1 7.1 8.2 8.8

0.5

Recommended of and thermalranges values conductivity 0.4 0.4 2.1 2.5 3.1 3.6 4.1 4.6 5.0

6.0 7.0 8.0 9.0 10.0 11.0 12.0

Sand (dry) Mean ground temperature (oC) Clay/silt (dry) Clay/silt Wales Borders Midlands Southern E Scotland East Anglia East W Scotland E Pennines W Pennines NE Scotland NE NW Scotland North-eastern Severn Valley North-western South-eastern South-western Thames Valley Northern Ireland Mean annual air temperature for UK regions (oC) Issue 1.0 (02/09/2011) 13

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Figure A5: Slinky heat extraction table as published in MIS 3005 for 2400 FLEQ hours load.

Maximum power to be extracted per unit length of slinky ground heat exchanger trench (W/m) with 2400 FLEQ run hours Conditions for use: Heat extraction only (inc. hot water) 3m minimum trench spacing (d ≥ 3m) Mean slinky depth between 0.8m and 1.2m Table created assuming 32mm OD SDR 11 pipe Clay/silt (water-saturated) Clay/silt Sand (water-saturated) Sand 4.0 Pipe length to trench length ratio, Rpt ≥ 4. For a 900mm slinky diameter this corresponds to a maximum 1250mm slinky pitch Table created assuming a relationship between the mean monthly temperature swing and annual mean ground temperature

3.6

3.2

2.8 (W / m/ K) ity 2.4 2.4 27 34 40 47 52 57 63

2.0 24 30 36 41 46 50 55

1.7 1.6 21 26 30 35 39 43 47

1.2 for different (W types rock / m/ K) 16 20 24 28 31 35 38 Ground thermal conductiv 0.8 12 14 17 19 22 25 27

0.5

Recommended values and ranges of thermal ranges conductivity and values Recommended 0.4 0.4 7.0 8.2 9.9 11 13 14 15

6.0 7.0 8.0 9.0 10.0 11.0 12.0

Sand (dry) Mean ground temperature (oC) Clay/silt (dry)Clay/silt Wales Borders Midlands Southern E Scotland East Anglia W Scotland W E Pennines W Pennines W NE Scotland NE NW Scotland North-eastern Severn Valley North-western South-eastern South-western Thames Valley Thames Northern Ireland Northern Mean annual air temperature for UK regions (oC) Issue 1.0 (02/09/2011) 19

Figure A6: Example of Pipe pressure loss chart for header elements.

1.20 SDR11 Header Pipework ‐ Ethylene Glycol (‐10°C) 1.15

1.10

1.05

1.00

0.95

0.90

0.85

0.80

0.75 Pipe)

0.70

0.65

(kPa/m 0.60

0.55 Drop 0.50

0.45

0.40 Pressure

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4

Flow Rate (l/s)

10 EGC 2013