Groundwater Cooling Systems

37 Pages·2009·2.898 MB·English

by  Ampofo, Felix, Maidment, Graeme, Missenden, John

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
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© February 2008 The Chartered Institution of Building
Services Engineers London
Registered charity number 278104
ISBN: 978-1-903287-89-7
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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.
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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