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Groundwater Cooling Systems PDF

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Groundwater cooling systems CIBSE TM45: 2008 Engineering a sustainable built environment The Chartered Institution of Building Services Engineers 222 Balham High Road, London SW12 9BS The rights of publication or translation are reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means without the prior permission of the Institution. © February 2008 The Chartered Institution of Building Services Engineers London Registered charity number 278104 ISBN: 978-1-903287-89-7 This document is based on the best knowledge available at the time of publication. However no responsibility of any kind for any injury, death, loss, damage or delay however caused resulting from the use of these recommendations can be accepted by the Chartered Institution of Building Services Engineers, the authors or others involved in its publication. In adopting these recommendations for use each adopter by doing so agrees to accept full responsibility for any personal injury, death, loss, damage or delay arising out of or in connection with their use by or on behalf of such adopter irrespective of the cause or reason therefore and agrees to defend, indemnify and hold harmless the Chartered Institution of Building Services Engineers, the authors and others involved in their publication from any and all liability arising out of or in connection with such use as aforesaid and irrespective of any negligence on the part of those indemnified. Typeset by CIBSEPublications Printed in Great Britain by Hobbs the Printers Ltd., Totton, Hampshire SO40 3WX Cover illustration: Portcullis House, London (Hopkins Architects) (photograph: Anthony Weller/VIEW) Note from the publisher This publication is primarily intended to provide guidance to those responsible for the design, installation, commissioning, operation and maintenance of building services. It is not intended to be exhaustive or definitive and it will be necessary for users of the guidance given to exercise their own professional judgement when deciding whether to abide by or depart from it. Printed on 100%recycled paper comprising at least 80%post-consumer waste Contents 1 Introduction 1 1.1 Abbreviations 1 2 Groundwater 1 2.1 How groundwater occurs 1 2.2 Properties of aquifers 2 2.3 Chemistry of aquifers 3 2.4 Aquifers and groundwater levels in the UK 3 3 Using groundwater as a cooling resource 4 3.1 Initial design considerations 4 3.2 Detailed design considerations 7 4 Comparison between groundwater and vapour compression 12 cooling 5 Conclusions 13 References 13 Appendix A1: Environment Agency forms for application for consent 14 Appendix A2: Glossary of terms 23 Appendix A3: Useful websites and sources of information 24 Appendix A4: Groundwater systems installed in the London area 27 Foreword This publication has been developed and written as a result of a Carbon Trust funded collaborative research project, undertaken in partnership with London Underground Limited and supported by the Chartered Institution of Building Services Engineers. The project enabled the research team to demonstrate the use of a ground coupled cooling system in Victoria tube station, on the London Underground. This is a topic of growing interest, as the demand for cooling of public facilities is growing, but there is also a strong policy drive to avoid the installation of carbon intensive cooling systems. The project undertaken by London South Bank University has explored the application of ground coupled cooling in a novel environment. The authors have reviewed both the literature and the theoretical basis for ground coupled cooling. They have also reviewed the technology of existing systems, focussing on the design objectives, component and system performance, parameter measurement, control strategy and relative achievement of system aims. The information produced provides a basis for the application of ground coupled cooling systems, including the extraction of cooling from the existing groundwater abstraction, where, for example, pumping is needed to reduce the groundwater level, eliminating the need for energy intensive cooling systems. The authors and the Institution acknowledge the support and input of the Carbon Trust and of London Underground Limited. The authors wish to note that London South Bank University’s involvement with groundwater cooling based systems has been on a conceptual basis only and London Underground Limited and its consultants are responsible for the detailed design, delivery and operation of these systems. Hywel Davies CIBSETechnical Director Principal authors Felix Ampofo (London South Bank University) Graeme Maidment (London South Bank University) John Missenden (London South Bank University) Contributors John Bates (London Underground Limited) Hywel Davies (Chartered Institution of Building Services Engineers) Mark Morton (Environment Agency) Acknowledgements David Hughes Rosemary Rawlings The Institution acknowledges the support of London Underground Limited and the Carbon Trust in the preparation of this publication. Crown copyright material is reproduced with the permission of the Controller of HMSO and the Queen’s Printer for Scotland under licence number C02W0002935. Editors Ken Butcher Helen Carwardine CIBSE Technical Director Hywel Davies CIBSE Director of Information Jacqueline Balian 1 Groundwater cooling systems 1 Introduction Appendix A1 presents the necessary forms for requesting a licence from the Environment Agency for water abstrac- tion. Further appendices provide a glossary of terms, a list Maintaining a comfortable temperature inside a building of useful websites and contacts, and acomparison of can require a significant amount of energy. Separate groundwater systems installed in London. heating and cooling systems are often used to maintain the desired air temperature, and the energy required to oper- ate these systems generally comes from electricity, fossil 1.1 Abbreviations fuels or biomass. Considering that a large proportion of the sun’s energy is absorbed by the earth, another option is CAMS Catchment abstraction management to use this abundant energy to heat and cool a building. strategies GSHP Ground source heat pump The ground temperature shows seasonal fluctuations to depths of about 15 m, where the temperature is approx- mAOD Metres above ordnance datum imately equal to the mean annual air temperature, which in the UK is 8–11 °C(1). Below this the ground temperature NRV Non-return valve increases at, on average, 2.6 °C per 100 m due to heat PWL Pumping water level flowing from the interior of the earth. Mean temperatures at 100 m depth in the UK vary between about 7 and SUC Standard unit charge 15°C(1,2). Hence, in winter, the ground temperature is SWL Static water level higher than the air temperature, whilst in summer it is lower than the air temperature. These temperature differences result in thermal energy potential that can be harnessed to help heat or cool a building. Another thermal 2 Groundwater characteristic of the ground is that a few metres of surface soil insulate the earth and groundwater below, minimising the amplitude of the variation in soil temperature in 2.1 How groundwater occurs comparison with the temperature of the air above the ground. When rain falls to the ground, the water does not stop moving. Some of it flows along the surface in streams or Groundwater naturally occurs as part of the water cycle lakes, some of it is used by plants, some evaporates and and, as it flows through the ground, its temperature tends returns to the atmosphere, and some sinks into the ground to that of the ground. In the UK, groundwater is at a to become ‘groundwater’. uniform temperature of about 12 °C outside of cities, whereas in central London, groundwater temperatures of Groundwater is often thought of as an underground river around 14 °C are reported. Deeper groundwater resources or lake. Only in caves or within lava flows does ground- (up to 300 m) are slightly warmer (14–16 °C). In addition water occur this way. Instead, groundwater is water that is to the earth, the groundwater below the surface also found underground in cracks and spaces in soil, sand and provides a source of energy that can be used for heating rocks, see Figure 1(3). The area where water fills these and cooling a building. spaces is called the saturated zone. The top of this zone is called the water table. The water table may be only a metre In general, this document can be used as guidance for (or less) below the ground’s surface or it may be hundreds building services engineers interested in installing of metres down. The water table may rise or fall groundwater cooling systems. It presents an overview of depending on many factors. For example, heavy rains or the major issues affecting the exploitation of groundwater melting snow may cause the water table to rise, or an cooling systems. extended period of dry weather may cause the water table to fall. Groundwater is stored in, and moves slowly Section 2 of this publication gives an introduction about through, layers of soil, sand and rock called aquifers. groundwater as a resource, how it occurs, its properties and groundwater levels in the UK. Section 3 then presents Aquifers typically consist of gravel, sand, sandstone, or the design process of using groundwater as a cooling fractured rock, like limestone and chalk. These materials resource by considering initial viability, necessary are permeable because they have large connected spaces consents and licences, and test boreholes before looking at that allow water to flow through. Water in aquifers is the detailed design considerations for elements of the brought to the surface naturally through a spring or can be groundwater cooling system. Section 4 compares a discharged into lakes and streams. This water can also be groundwater cooling system with a vapour compression extracted through a well drilled into the aquifer, see cooling system. Figure 2(4). The water in the well can be brought to the 1 Groundwater cooling systems 1 Introduction Appendix A1 presents the necessary forms for requesting a licence from the Environment Agency for water abstrac- tion. Further appendices provide a glossary of terms, a list Maintaining a comfortable temperature inside a building of useful websites and contacts, and acomparison of can require a significant amount of energy. Separate groundwater systems installed in London. heating and cooling systems are often used to maintain the desired air temperature, and the energy required to oper- ate these systems generally comes from electricity, fossil 1.1 Abbreviations fuels or biomass. Considering that a large proportion of the sun’s energy is absorbed by the earth, another option is CAMS Catchment abstraction management to use this abundant energy to heat and cool a building. strategies GSHP Ground source heat pump The ground temperature shows seasonal fluctuations to depths of about 15 m, where the temperature is approx- mAOD Metres above ordnance datum imately equal to the mean annual air temperature, which in the UK is 8–11 °C(1). Below this the ground temperature NRV Non-return valve increases at, on average, 2.6 °C per 100 m due to heat PWL Pumping water level flowing from the interior of the earth. Mean temperatures at 100 m depth in the UK vary between about 7 and SUC Standard unit charge 15°C(1,2). Hence, in winter, the ground temperature is SWL Static water level higher than the air temperature, whilst in summer it is lower than the air temperature. These temperature differences result in thermal energy potential that can be harnessed to help heat or cool a building. Another thermal 2 Groundwater characteristic of the ground is that a few metres of surface soil insulate the earth and groundwater below, minimising the amplitude of the variation in soil temperature in 2.1 How groundwater occurs comparison with the temperature of the air above the ground. When rain falls to the ground, the water does not stop moving. Some of it flows along the surface in streams or Groundwater naturally occurs as part of the water cycle lakes, some of it is used by plants, some evaporates and and, as it flows through the ground, its temperature tends returns to the atmosphere, and some sinks into the ground to that of the ground. In the UK, groundwater is at a to become ‘groundwater’. uniform temperature of about 12 °C outside of cities, whereas in central London, groundwater temperatures of Groundwater is often thought of as an underground river around 14 °C are reported. Deeper groundwater resources or lake. Only in caves or within lava flows does ground- (up to 300 m) are slightly warmer (14–16 °C). In addition water occur this way. Instead, groundwater is water that is to the earth, the groundwater below the surface also found underground in cracks and spaces in soil, sand and provides a source of energy that can be used for heating rocks, see Figure 1(3). The area where water fills these and cooling a building. spaces is called the saturated zone. The top of this zone is called the water table. The water table may be only a metre In general, this document can be used as guidance for (or less) below the ground’s surface or it may be hundreds building services engineers interested in installing of metres down. The water table may rise or fall groundwater cooling systems. It presents an overview of depending on many factors. For example, heavy rains or the major issues affecting the exploitation of groundwater melting snow may cause the water table to rise, or an cooling systems. extended period of dry weather may cause the water table to fall. Groundwater is stored in, and moves slowly Section 2 of this publication gives an introduction about through, layers of soil, sand and rock called aquifers. groundwater as a resource, how it occurs, its properties and groundwater levels in the UK. Section 3 then presents Aquifers typically consist of gravel, sand, sandstone, or the design process of using groundwater as a cooling fractured rock, like limestone and chalk. These materials resource by considering initial viability, necessary are permeable because they have large connected spaces consents and licences, and test boreholes before looking at that allow water to flow through. Water in aquifers is the detailed design considerations for elements of the brought to the surface naturally through a spring or can be groundwater cooling system. Section 4 compares a discharged into lakes and streams. This water can also be groundwater cooling system with a vapour compression extracted through a well drilled into the aquifer, see cooling system. Figure 2(4). The water in the well can be brought to the 2 Groundwater cooling systems Figure 1 How ground water occurs in rocks(3)(reproduced by permission of the United States Geological Survey) Land surface Unsaturated zone Water table Surface water Saturated zone Ground water Creviced rock Gravel Air Air Water (not ground water) held by molecular attraction surrounds surfaces of rock particles Approximate level of the watertable All openings below water table full of ground water Water-table Artesian 2.2 Properties of aquifers well well Land surface The three important properties of an aquifer are its: Unsaturated zone Unconfined Capillary fringe e — porosity (the volume of water it holds or stores) aquifier ur s — specific yield (the volume of water it yields, when Water es table pr it drains naturally or is pumped) n a — permeability (the rate that water flows through it). Confining esi Saturated layer Art zone Not all the stored water represented by the porosity can be abstracted for water supply. Part, referred to as the specific Artesian or retention, is retained in the aquifer against the force of confined gravity. The proportion that can drain freely represents aquifier the specific yield and this is the water that can be abstracted from a well or borehole or which eventually Figure 2 Typical aquifer(4) drains from the aquifer at springs. Typical values for the specific yield of sandstone vary between 10 and 30% of the surface by a pump. Shallow wells may go dry if the water total rock volume(5). In most limestones, it amounts to table falls below the bottom of the well. Some wells, called only 1 or 2%. The specific yield approaches the porosity in artesian wells, do not need a pump because of natural aquifers that drain readily, for example coarse sands and pressures that force the water up and out of the well. The gravels, see Figure 3(5). capillary fringe (or capillary zone) extends from the water table, due to capillary action of the water in the ground, up Groundwater flows very slowly. Typical speeds can be to the limit of capillary rise of water. between 1 m/year and 1 m/day, although in very fractured limestones maximum rates are similar to those in rivers(5). In unconfined aquifers, the groundwater only partially The direction of groundwater flow is indicated by the fills the aquifer and the upper surface of the groundwater slope of the water table, which is called the ‘hydraulic (the water table) is free to rise or decline. The ground- gradient’. The velocity of the flow of water is proportional water is at atmospheric pressure. The height of the water table will be the same as the water level in a well constructed in that unconfined aquifer. The water table typically mimics, in a subdued way, the topography of the 60 e) land surface above, resulting in a water table with hills, m valleys, or flat areas. It is important to note that olu 50 Porosity unconfined aquifers, especially those close to the surface, y v Specific b 40 can be vulnerable to contamination from activities on the e retention land surface. ag nt 30 e c Confined aquifers may also be referred to as ‘artesian per 20 aquifers’. A confined aquifer is sandwiched between o ( confining beds (i.e. layers of impermeable materials, such ati 10 Specific as clay, which impede the movement of water into and out d r yield of the aquifer). Groundwater in these aquifers is under oi V 0 0·001 0·01 0·1 1 10 100 pressure because the confining beds prevent water rising to its natural level. However, because of the pressure, the Clay Silt Sand Gravel water level in a well will rise to a level higher than the Grain size / mm water level at the top of the aquifer. Figure 3 Properties of an aquifer(5) Groundwater 3 to the hydraulic gradient and a coefficient referred to as — clogging of the aquifer as a result of precipitation the ‘hydraulic conductivity’, which is dependent upon the of minerals within the aquifer or the transport of interconnectivity of the pore spaces. This relationship is precipitation into the aquifer. known as Darcy’s law and is given as: These problems are avoidable if consideration of the q= Ki (1) potential for geochemistry problems is considered in advance of the system design phase. Further information where q is the volume flow rate per unit cross-sectional on the mitigation of these problems is available from area (m·s–1), i is the hydraulic gradient (dimensionless) Jenne et al(8). It is also appropriate that any proposed and Kis the hydraulic conductivity (m·s–1). scheme uses the skills of a specialist hydrologist to sample the water and provide a report on the quality of the water The hydraulic conductivity of good aquifers exceeds available. Specialist hydrologists in the UK can be found 30m/day and for many gravels is 500 m/day. By way of from the Well Drillers Association (http://welldrillers. contrast, 10–5 m/day is more usual for un-weathered org.uk). clay(5). A more useful practical unit is the transmissivity. This is 2.4 Aquifers and groundwater the product of the hydraulic conductivity and the levels in the UK saturated thickness of the aquifer and represents the ability of the aquifer to transmit water through its entire Figure 4 shows the major aquifers in England and thickness. The unit used is m2/day and values for good Wales(9). The most important ones are the chalk, the aquifers exceed 2000 m2/day(5). Details on the properties of sandstone and the limestone. The ground properties will specific aquifers can be found from the British Geological affect the productivity of the aquifer. Figure 5 shows the Survey(6,7). likely productivity of aquifers. Further information on the aquifers of the UK can be found in Downing(5). 2.3 Chemistry of aquifers The chemistry of aquifers often represents a significant problem in the design of groundwater systems(2,8). The primary problems related to groundwater chemistry include: — precipitation of minerals such as calcium car- bonate, and iron and manganese oxides, which result in the scaling of heat exchangers and Fissure flow clogging of wells productive Fissure flow — corrosion of piping and heat exchangers by moderate ambient and heated groundwater Intergranular flow — bio-fouling of the well intake area productive Intergranular flow moderate Limited or local Chalk Unproductive Sandstone Limestone Figure 4 Major aquifers in England and Wales(9)(Crown copyright) Figure 5 Hydrological map for the UK 4 Groundwater cooling systems Groundwater levels are also indicated by maps. A general map for England and Wales is shown in Figure 6, whereas Figure 7 shows specific contours of groundwater levels in the chalk aquifer beneath London on 1st January 2007. In Figure 7, ‘mAOD’ stands for ‘metres above ordnance datum’. Groundwater levels are important as they will impact on the pumping energy required to abstract the Height of water table water and therefore may affect the viability of the cooling above sea level (metres) system. 250 to 300 200 to 250 3 Using groundwater as a 150 to 200 cooling resource 100 to 150 50 to 100 3.1 Initial design considerations 0 to 50 –50 to 0 3.1.1 Initial viability below –50 Before a groundwater cooling system can be specified there are a number of factors to be considered: (1) Availability of suitable aquifer: groundwater cooling technology can only be applied where there are suitable aquifers. In view of this, it is advisable for a prospective groundwater cooling system owner to firstly obtain a water borehole prognosis report for his or her site from the British Geological Survey (BGS) at a cost of £310 in 2007. The report contains an evaluation of the expected geological sequence and aquifers beneath the site, potential groundwater yields, water levels and groundwater quality. The report also contains map extracts taken from the BGS Digital Geological Map of Great Britain showing various geological layers (artificial (man-made), landslip, superficial and solid (bedrock) geology) and also an index listing of borehole and water well records held in the Figure 6 Groundwater levels for England and Wales 510000 520000 530000 540000 550000 0 0 0 0 0 0 0 0 21 Hatfield Harlow 21 Groundwater level Hemel Hempstead St Albans (mAOD) –40 00 Potters Bar Epping 00 00 00 –30 0 0 2 2 Watford Borehamwood Enfield –20 Barnet –10 0 0 0 0 0 0 190 Walthamstow 190 0 Uxbridge Wembley Dagenham 10 00 Paddington Trafalgar Square 00 20 0 0 0 0 8 8 1 Ashley Gardens Westminster Greenwich 1 30 Clapham Richmond Dartford 40 00 Staines 00 00 00 50 17 Kingston upon Thames 17 Croydon 60 Weybridge Sutton 00 Epsom 00 70 Figure 7 Groundwater levels in 00 00 the aquifer beneath London(10) 6 6 1 1 (Crown copyright) 510000 520000 530000 540000 550000 4 Groundwater cooling systems Groundwater levels are also indicated by maps. A general map for England and Wales is shown in Figure 6, whereas Figure 7 shows specific contours of groundwater levels in the chalk aquifer beneath London on 1st January 2007. In Figure 7, ‘mAOD’ stands for ‘metres above ordnance datum’. Groundwater levels are important as they will impact on the pumping energy required to abstract the Height of water table water and therefore may affect the viability of the cooling above sea level (metres) system. 250 to 300 200 to 250 3 Using groundwater as a 150 to 200 cooling resource 100 to 150 50 to 100 3.1 Initial design considerations 0 to 50 –50 to 0 3.1.1 Initial viability below –50 Before a groundwater cooling system can be specified there are a number of factors to be considered: (1) Availability of suitable aquifer: groundwater cooling technology can only be applied where there are suitable aquifers. In view of this, it is advisable for a prospective groundwater cooling system owner to firstly obtain a water borehole prognosis report for his or her site from the British Geological Survey (BGS) at a cost of £310 in 2007. The report contains an evaluation of the expected geological sequence and aquifers beneath the site, potential groundwater yields, water levels and groundwater quality. The report also contains map extracts taken from the BGS Digital Geological Map of Great Britain showing various geological layers (artificial (man-made), landslip, superficial and solid (bedrock) geology) and also an index listing of borehole and water well records held in the Figure 6 Groundwater levels for England and Wales 510000 520000 530000 540000 550000 0 0 0 0 0 0 0 0 21 Hatfield Harlow 21 Groundwater level Hemel Hempstead St Albans (mAOD) –40 00 Potters Bar Epping 00 00 00 –30 0 0 2 2 Watford Borehamwood Enfield –20 Barnet –10 0 0 0 0 0 0 190 Walthamstow 190 0 Uxbridge Wembley Dagenham 10 00 Paddington Trafalgar Square 00 20 0 0 0 0 8 8 1 Ashley Gardens Westminster Greenwich 1 30 Clapham Richmond Dartford 40 00 Staines 00 00 00 50 17 Kingston upon Thames 17 Croydon 60 Weybridge Sutton 00 Epsom 00 70 Figure 7 Groundwater levels in 00 00 the aquifer beneath London(10) 6 6 1 1 (Crown copyright) 510000 520000 530000 540000 550000

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