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Water for Energy: Ground Water Geothermal Heat Pumps
Copyright yright © IFAC. IFAC , Water Watt:r and Related Land Resource Systems C
clCI!eland, eland. Ohio 1980
ENERGY: GROUND WATER FOR E ERGY: GROU D WATER GEOTHERMAL HEAT PUMPS D. Bacon Research Fac£l£ty, Facility, National Water Well Assoc'iat£on, Association, 500 West Wilson BnOdge Bridge Road, Ohio 43085, USA Worthington, Oh£o
Abstract. A ground-water geothermal heat pump is a unitary space conditioning device that operates in either the heating or cooling mode. The heat pump utilizes ground water as an energy source in the heating mode, and as an energy sink in the cooling mode. Hydrogeologic, institutional, and environmental concerns regarding the heat pump's geographic applicability are discussed. High-density heat pump usage in suburban areas and intelendsitself grated suburban and commercial developments lends itself to the use of lowtemperature aquifer thermal energy storage. Keywords. Low-temperature geothermal, heat pump, ground water, aquifer thermal energy storage. INTRODUCTION
option by many manufacturers.
Figure 1 depicts a spectrum of geothermal reservoir temperatures and associated uses. Ground water is located at the lower end of this spectrum, indicating its use as an energy source for space heating when used in conjunction with a heat pump. The minimum water temperature that can be used with existing technology is approximately 40° F (4.4° C). One form of the second law of thermodynamics states that energy cannot flow from a lowtemperature source to a higher-temperature sink. In order to transfer energy from a heat ilt 65° F source of 40° F (4.4°C)to a heat sink at (18.3° C) (the return air temperature in a heated space), work must be exerted on the system. This work is accomplished by using a working fluid (R-22 or R-12) in a refrigeration loop. Thus, three components are required to operate a ground-water geotherma1 geothermal heat pump: 1) a heat source at sin 2) 2) a he heat sinkk 3) a refrigeration loop HEAT PUMP SYSTEM AND OPERATION Figure 2 illustrates three basic components. The ground water is the heat source and heat sink in the heating and cooling modes, respectively. The refrigeration loop consists of a closed loop containing a water-to-refrigerant heat exchanger, an air-to-refrigerant heat exchanger, a compressor; comp resso r , and an expansion valve. va 1ve. Figure 3 shows the components of the heat pump operating operati ng in the heating mode. mode . The refrigeration loop shown here contains a domestic hotwater heat exchanger, which is offered as an 179
Ground water, the heat source, is drawn into the water-to-refrigerant heat exchanger, where energy is absorbed by the refrigerant. The temperature change across the heat exchanger varies with flow rate, but usually ranges from 7 FO to 15 FO (3.9 Co to 8.3 CO). CO). The refrigerant is discharged from the compressor in a superheated state. Energy is rejected to the domestic hot water, which is circulated from the storage tank by a small, thermally activated pump. Further desuperheating and vapor condensation takes place in the refrigerant-to-air heat exchanger. Thermal energy is rejected to the return air (the heat sink) and delivered to the conditioned space by a centrifugal fan. For a typical residential unit, the heat absorption rate at the evaporator is 31,900 BTU/hr, and the rate of energy rejection at the condenser is 44,300 BTU/hr. The difference (12,400 BTU/hr) represents the ideal power input to the unit. The heating efficiency of the heat pump is expressed as the ratio of the heat rejection rate to the power input required to accomplish the heat rejection. rejection . Thus, for this example, the efficiency, expressed as the coefficient of performance (COP) is: = 44,300 BTU/hr = = 3 6 COP = 12,400 BTU/hr ·.
This figure does not include parasitic power inputs such as b1ower owance or we 11 pump blower a11 allowance well input. Overall system COP values for most currently manufactured units range from 2.5 to 3.5. 3.5 .
D. Bacon
180
Fo r the cooling mode operation shown in Fig. 4, For the t he unit operates as a water-cooled air conditioner. di ti one r. The reversing valve routes the refrigerant f ri ge rant in the opposite direction. The heat sou rce is the warm, moist, return air from the source conditioned condi tioned space. The refrigerant absorbs energy through the refrigerant-to-air heat exchanger and ;s is then routed to the compressor. Superheated vapor discharged from the compressor loses some of its energy to the domestic hot-water hot -water heat exchanger. Further desuperheating i ng and condensation take place at the water-torefr igerant heat exchanger. Energy rejection refrigerant to the ground water (the heat sink) increases emperature by 10 Fo to 30 Fo (5.6 Co to t he ttemperature the 16.7 16. 7 Co) Co ) depending on the heat pump used. One advantage of a heat pump which operates in the cooling mode is that hot water for domestic use can be produced as a low-cost by-product of the system. Energy that is normally rejected to t he ground water, and therefore wasted, is used the to heat water for domestic use. use . FACTORS AFFECTING THE APPLICABILITY OF GROUND-WATER GEOTHERMAL HEAT PUMPS Hydrogeo1ogic Hydrogeologic Factors A number of hydrogeo10gic hydrogeologic factors regarding site-specific installations must be considered. Mini mum entering water temperatures vary from Minimum 40° 40° F to 60° F (4.4° C to 15.6° C) depending on the heat pump design. Figure 5 shows approximate well water temperatures measured at depths between 50 and 150 feet (15 to 45 m). Thus, some units are excluded from use in northern areas where ground-water temperatures are less minimum . t han the recommended minimum. than
W at er quality can affect the life expectancy of Water the water-to-refrigerant heat exchanger. Most manufacturers man ufactu rers offer a copper heat exchanger as standard .standa rd equipment equi pment and an optional opti ona 1 copper-nickel copper-ni ckel alloy (No. 706) that should be used in areas where where corrosion problems are anticipated. Common mon ground-water constituents do not appear to have ha ve adverse effects on heat exchangers. exchangers . Most problems encountered in units operating today have ha ve resulted from faulty equipment choice or installation. in stallation. However, certain dissolved gases can create corrosion problems with heat exchangers. Dissolved oxygen can, under some circumstance?, circumstance~, serve as a depolarizing agent, leaving the metal me tal surface open to attack by other aggressive si ve constituents. Carbon dioxide can accelerate ra te the corrosion co rrosion process by the formation of carbonic acid. The copper-nickel heat exchanger chan ger is i s more resistant to attack from these gases, ga ses, but does sbow appreciable corrosion rates ra tes with high concentrations. Dissolved hydrogen sulfide has been found to be particularly aggressive agg ressive to both the copper and coppernickel ni ckel heat exchangers. The gas apparently prevents protective films from forming on the metal me ta 1 surface.
Institutional Factors Most states do not require a special permit to use ground water as an energy source. Where permits are required, they are usually identical to'those to those needed for domestic wells. However, many states have legislation regarding the injection of water underground. This ranges from strict prohibition to laws in which waivers can be obtained for heat pump installations. Some states have no legislative regulations regarding discharge.
Disposal to a surface water body is theoretically regulated by the NPDES (National Pollution Discharge Elimination System) at the federal level. However, this system is usually not equipped to consider domestic use. Thus, a permit is usually not required. Specific local laws such as wetlands wet1ands regulation and the prohibition of wells in urban areas must also be considered in site installations. Environmental Concerns Environmental consequences of heat pump usage are of concern only in those areas where high-density utilization is anticipated. Isolated installations are not expected to substantially affect the environment. In high-density usage situations, the environmental concerns mainly depend on whether the heat pump water is used consumptively or nonconsumptively. consumptively . The consumptive use of ground water involves withdrawal and subsequent remote disposal of spent heat pump effluent. This includes r i vers, discharge to nearby streams, ditches, rivers, and reservoirs. This nonreplacement nonrep1acement method could alter local hydraulic gradients. Near coastline areas, this may induce salt-water intrusion which would degrade deg r ade potable water supplies. Consumptive use can also aggravate subsidence problems in areas where overpumpage has already caused a loss of subsurface hydrostatic pressure. Nonconsumptive use or injecting heat pump discharge water into local aquifers circumvents the problems of consumptive use. Hydrologic conditions are maintained so that the only alteration alterat ion is in ground-water temperature. perature . Alteration of temperature is not considered to be of sufficient magnitude to cause precipitation or solution of existing phases. If two different aquifers are used for supply and recharge, care must be taken to ensure that the ground waters are chemichemically compatible. Precipitation of mineral mine ral salts can result in the clogging of aquifer pore spaces and subsequent loss of recharge capacity. capacity . In addition, if the supply aquifer is contaminated, the contaminated contaminated water must not be injected into a potable aquifer.
Water for Energy: Ground Water Geothermal Heat Pumps
181
Some positive environmental impacts are expected in areas of high-density use. Due to ground water heat pump's high operating efficiencies, total energy input in these areas would be low compared to similar areas utilizing conventional space-conditioning equipment. Heat rejection to the atmosphere would be correspondingly low because there is no on-site fuel combustion. COMMUNITY APPLICATIONS Schaetzle and Brett (1979) described the design concept of a Heat Pump Centered Integrated COll111unity Energy System (ICES). In this system Community (Fig. 6), a common well or well field supplies water to a number of heat pumps. The chilled water resulting from heat extraction in the heating mode can be discharged to a storage aquifer for use in the cooling season. Likewise, rejected condenser heat can be stored in the aquifer for use during the heating season. In this design, wasteful heat rejection to the atmosphere is eliminated, and increased efficiencies and lower operating costs are anticipated. Further research is needed to determine the engineering feasibility and economics of utilizing aquifer thermal energy storage in conjunction with ground-water geothermal heat pumps.
REFERENCES Schaetzle, W.J., W.J., C.E. C. E. Brett (1979). Heat Pump Centered Integrated Community Energy Systems; Systems Development.
40
4.4
RO 80
26.7 16.7
110 120
48.9 48. 9
160
100 200
240
180 280
310 320
360
400
440
480
510 520
(O F) (OF)
71.1 71. 1
93.3
116 11 6
138
160
182 181
204 204
227 127
240 14"
271 2'1
(or:) !O[)
I I
I_ _ _ _ I
~1 ~I Heat by , !.1eat :Heat Ii PUMPS I P' MPS
I1
Fig. Fi g. 1.
Wf:lLRS -_ G WRLRS
Electri E1e ct r i c Powe r Using Us ing Binary Bin ar y Cycle Cycle
Space Heat i ng by " "s",pa'7 c e'02 He7'atTi "'".9,.e.byL,-,-_ Dirrect ect Heat Exchange Excha nge Di
Electric El ect r ic Dawprl Powe r ! (Ji rect) I r eet)
II ndustri ndust r i al Cl 1 ---;P<::: r o"';ce:"-Os.,.,si=ng,----Process; ng
Geothet""':ld1 rese r voi r temperatures temper a t ures and dnd associated Geathe~a1 reservair assoc; ated uses.
D. Bacon
182
SUpply AIr ____ Supply to Air to .-r-
Ground Water Geothermal Heat Pump
Conditioned Space
Cold Water Supply Supplv
Well
Well SCreen Sc reen
Aquifer (sandstone) (Sandstone)
Submersible
Pump
Woter OomesUc Hot Water Domestic to OomesHc Hot Water 10 1 Domestic Storage Storoge Wafer C~d&r Domestic Water 2 Colder
3 Water OUtlet to Discharge Well Pressur. 'rom Pressure 4 Water Inlet from
Tank
g. 2. Fi Fig.
tern components . Sys System Werm Suppty Air to CondttIOned
t
A._ j
sc-:e
(..:a::::---=~·~I~
,~~~'
I
[cx p-
c "
D.H.W. D.H.w. Storage
I ~~ ]
:'
\.
~r~~~~~~~~~~=~ I::: Fig. 3.
.
':
. ". .
"_'n -=- CoIoIo":-=-_~
Out
rrode operation. Heating mode
Co6d Suppty AIf to ConditIOned Spece
t
~--~J AIf Hendler
Retngerent Air h~ "-'nv-.nt .....t ......, eachenger EYeporetOf E"AIPOf'atOf 1
1
I !
I' '../
~COId" _ J_.........."'I" :... W.., ======:
D.H.W. Storage
~====== ======= =
Fig. 4.
Cooling Coo ling mode operation.
Cold WMIIr In Out Out Werm
183
Water for Energy: Ground Water Geothermal Heat Pumps
T~mpcra~ . Ground W.t~r akr T~mpcratu.re. In Wd b Jtan&in& RaneUtlr fro from SO' to 1SO' 1 SO' in i n Depth in ~11.
_____ _ _ f O___ -------FO----
__ t. &1'ft4 --lak....-ed
,,,.. ' Fig. 5.
Ground water temperatures tempe ratures in the continental U.S. at ranging m), depths rangi ng from 50 to 150 ft. (15.2 to 45.7 m).
Individual Heat Pump System
Water
~Water
AccumuAat~
Accumulat~
< ; - - - - - - - Static StatIC Water Level Level -------;> ------~
~CoId oE- CoId VlJeII Well
Pump
Hot VlJeU PumP-7
Aquifer
Fig. 6.
Co ponen soof the he Hedt eat Pump ICES uS'ng er therlTldl henna 1 Components using aqu; aquifer energy Sstorage. orage. A er Schae zl e and Bre After Schaetzle Brett (1979).
clCI!eland, eland. Ohio 1980
ENERGY: GROUND WATER FOR E ERGY: GROU D WATER GEOTHERMAL HEAT PUMPS D. Bacon Research Fac£l£ty, Facility, National Water Well Assoc'iat£on, Association, 500 West Wilson BnOdge Bridge Road, Ohio 43085, USA Worthington, Oh£o
Abstract. A ground-water geothermal heat pump is a unitary space conditioning device that operates in either the heating or cooling mode. The heat pump utilizes ground water as an energy source in the heating mode, and as an energy sink in the cooling mode. Hydrogeologic, institutional, and environmental concerns regarding the heat pump's geographic applicability are discussed. High-density heat pump usage in suburban areas and intelendsitself grated suburban and commercial developments lends itself to the use of lowtemperature aquifer thermal energy storage. Keywords. Low-temperature geothermal, heat pump, ground water, aquifer thermal energy storage. INTRODUCTION
option by many manufacturers.
Figure 1 depicts a spectrum of geothermal reservoir temperatures and associated uses. Ground water is located at the lower end of this spectrum, indicating its use as an energy source for space heating when used in conjunction with a heat pump. The minimum water temperature that can be used with existing technology is approximately 40° F (4.4° C). One form of the second law of thermodynamics states that energy cannot flow from a lowtemperature source to a higher-temperature sink. In order to transfer energy from a heat ilt 65° F source of 40° F (4.4°C)to a heat sink at (18.3° C) (the return air temperature in a heated space), work must be exerted on the system. This work is accomplished by using a working fluid (R-22 or R-12) in a refrigeration loop. Thus, three components are required to operate a ground-water geotherma1 geothermal heat pump: 1) a heat source at sin 2) 2) a he heat sinkk 3) a refrigeration loop HEAT PUMP SYSTEM AND OPERATION Figure 2 illustrates three basic components. The ground water is the heat source and heat sink in the heating and cooling modes, respectively. The refrigeration loop consists of a closed loop containing a water-to-refrigerant heat exchanger, an air-to-refrigerant heat exchanger, a compressor; comp resso r , and an expansion valve. va 1ve. Figure 3 shows the components of the heat pump operating operati ng in the heating mode. mode . The refrigeration loop shown here contains a domestic hotwater heat exchanger, which is offered as an 179
Ground water, the heat source, is drawn into the water-to-refrigerant heat exchanger, where energy is absorbed by the refrigerant. The temperature change across the heat exchanger varies with flow rate, but usually ranges from 7 FO to 15 FO (3.9 Co to 8.3 CO). CO). The refrigerant is discharged from the compressor in a superheated state. Energy is rejected to the domestic hot water, which is circulated from the storage tank by a small, thermally activated pump. Further desuperheating and vapor condensation takes place in the refrigerant-to-air heat exchanger. Thermal energy is rejected to the return air (the heat sink) and delivered to the conditioned space by a centrifugal fan. For a typical residential unit, the heat absorption rate at the evaporator is 31,900 BTU/hr, and the rate of energy rejection at the condenser is 44,300 BTU/hr. The difference (12,400 BTU/hr) represents the ideal power input to the unit. The heating efficiency of the heat pump is expressed as the ratio of the heat rejection rate to the power input required to accomplish the heat rejection. rejection . Thus, for this example, the efficiency, expressed as the coefficient of performance (COP) is: = 44,300 BTU/hr = = 3 6 COP = 12,400 BTU/hr ·.
This figure does not include parasitic power inputs such as b1ower owance or we 11 pump blower a11 allowance well input. Overall system COP values for most currently manufactured units range from 2.5 to 3.5. 3.5 .
D. Bacon
180
Fo r the cooling mode operation shown in Fig. 4, For the t he unit operates as a water-cooled air conditioner. di ti one r. The reversing valve routes the refrigerant f ri ge rant in the opposite direction. The heat sou rce is the warm, moist, return air from the source conditioned condi tioned space. The refrigerant absorbs energy through the refrigerant-to-air heat exchanger and ;s is then routed to the compressor. Superheated vapor discharged from the compressor loses some of its energy to the domestic hot-water hot -water heat exchanger. Further desuperheating i ng and condensation take place at the water-torefr igerant heat exchanger. Energy rejection refrigerant to the ground water (the heat sink) increases emperature by 10 Fo to 30 Fo (5.6 Co to t he ttemperature the 16.7 16. 7 Co) Co ) depending on the heat pump used. One advantage of a heat pump which operates in the cooling mode is that hot water for domestic use can be produced as a low-cost by-product of the system. Energy that is normally rejected to t he ground water, and therefore wasted, is used the to heat water for domestic use. use . FACTORS AFFECTING THE APPLICABILITY OF GROUND-WATER GEOTHERMAL HEAT PUMPS Hydrogeo1ogic Hydrogeologic Factors A number of hydrogeo10gic hydrogeologic factors regarding site-specific installations must be considered. Mini mum entering water temperatures vary from Minimum 40° 40° F to 60° F (4.4° C to 15.6° C) depending on the heat pump design. Figure 5 shows approximate well water temperatures measured at depths between 50 and 150 feet (15 to 45 m). Thus, some units are excluded from use in northern areas where ground-water temperatures are less minimum . t han the recommended minimum. than
W at er quality can affect the life expectancy of Water the water-to-refrigerant heat exchanger. Most manufacturers man ufactu rers offer a copper heat exchanger as standard .standa rd equipment equi pment and an optional opti ona 1 copper-nickel copper-ni ckel alloy (No. 706) that should be used in areas where where corrosion problems are anticipated. Common mon ground-water constituents do not appear to have ha ve adverse effects on heat exchangers. exchangers . Most problems encountered in units operating today have ha ve resulted from faulty equipment choice or installation. in stallation. However, certain dissolved gases can create corrosion problems with heat exchangers. Dissolved oxygen can, under some circumstance?, circumstance~, serve as a depolarizing agent, leaving the metal me tal surface open to attack by other aggressive si ve constituents. Carbon dioxide can accelerate ra te the corrosion co rrosion process by the formation of carbonic acid. The copper-nickel heat exchanger chan ger is i s more resistant to attack from these gases, ga ses, but does sbow appreciable corrosion rates ra tes with high concentrations. Dissolved hydrogen sulfide has been found to be particularly aggressive agg ressive to both the copper and coppernickel ni ckel heat exchangers. The gas apparently prevents protective films from forming on the metal me ta 1 surface.
Institutional Factors Most states do not require a special permit to use ground water as an energy source. Where permits are required, they are usually identical to'those to those needed for domestic wells. However, many states have legislation regarding the injection of water underground. This ranges from strict prohibition to laws in which waivers can be obtained for heat pump installations. Some states have no legislative regulations regarding discharge.
Disposal to a surface water body is theoretically regulated by the NPDES (National Pollution Discharge Elimination System) at the federal level. However, this system is usually not equipped to consider domestic use. Thus, a permit is usually not required. Specific local laws such as wetlands wet1ands regulation and the prohibition of wells in urban areas must also be considered in site installations. Environmental Concerns Environmental consequences of heat pump usage are of concern only in those areas where high-density utilization is anticipated. Isolated installations are not expected to substantially affect the environment. In high-density usage situations, the environmental concerns mainly depend on whether the heat pump water is used consumptively or nonconsumptively. consumptively . The consumptive use of ground water involves withdrawal and subsequent remote disposal of spent heat pump effluent. This includes r i vers, discharge to nearby streams, ditches, rivers, and reservoirs. This nonreplacement nonrep1acement method could alter local hydraulic gradients. Near coastline areas, this may induce salt-water intrusion which would degrade deg r ade potable water supplies. Consumptive use can also aggravate subsidence problems in areas where overpumpage has already caused a loss of subsurface hydrostatic pressure. Nonconsumptive use or injecting heat pump discharge water into local aquifers circumvents the problems of consumptive use. Hydrologic conditions are maintained so that the only alteration alterat ion is in ground-water temperature. perature . Alteration of temperature is not considered to be of sufficient magnitude to cause precipitation or solution of existing phases. If two different aquifers are used for supply and recharge, care must be taken to ensure that the ground waters are chemichemically compatible. Precipitation of mineral mine ral salts can result in the clogging of aquifer pore spaces and subsequent loss of recharge capacity. capacity . In addition, if the supply aquifer is contaminated, the contaminated contaminated water must not be injected into a potable aquifer.
Water for Energy: Ground Water Geothermal Heat Pumps
181
Some positive environmental impacts are expected in areas of high-density use. Due to ground water heat pump's high operating efficiencies, total energy input in these areas would be low compared to similar areas utilizing conventional space-conditioning equipment. Heat rejection to the atmosphere would be correspondingly low because there is no on-site fuel combustion. COMMUNITY APPLICATIONS Schaetzle and Brett (1979) described the design concept of a Heat Pump Centered Integrated COll111unity Energy System (ICES). In this system Community (Fig. 6), a common well or well field supplies water to a number of heat pumps. The chilled water resulting from heat extraction in the heating mode can be discharged to a storage aquifer for use in the cooling season. Likewise, rejected condenser heat can be stored in the aquifer for use during the heating season. In this design, wasteful heat rejection to the atmosphere is eliminated, and increased efficiencies and lower operating costs are anticipated. Further research is needed to determine the engineering feasibility and economics of utilizing aquifer thermal energy storage in conjunction with ground-water geothermal heat pumps.
REFERENCES Schaetzle, W.J., W.J., C.E. C. E. Brett (1979). Heat Pump Centered Integrated Community Energy Systems; Systems Development.
40
4.4
RO 80
26.7 16.7
110 120
48.9 48. 9
160
100 200
240
180 280
310 320
360
400
440
480
510 520
(O F) (OF)
71.1 71. 1
93.3
116 11 6
138
160
182 181
204 204
227 127
240 14"
271 2'1
(or:) !O[)
I I
I_ _ _ _ I
~1 ~I Heat by , !.1eat :Heat Ii PUMPS I P' MPS
I1
Fig. Fi g. 1.
Wf:lLRS -_ G WRLRS
Electri E1e ct r i c Powe r Using Us ing Binary Bin ar y Cycle Cycle
Space Heat i ng by " "s",pa'7 c e'02 He7'atTi "'".9,.e.byL,-,-_ Dirrect ect Heat Exchange Excha nge Di
Electric El ect r ic Dawprl Powe r ! (Ji rect) I r eet)
II ndustri ndust r i al Cl 1 ---;P<::: r o"';ce:"-Os.,.,si=ng,----Process; ng
Geothet""':ld1 rese r voi r temperatures temper a t ures and dnd associated Geathe~a1 reservair assoc; ated uses.
D. Bacon
182
SUpply AIr ____ Supply to Air to .-r-
Ground Water Geothermal Heat Pump
Conditioned Space
Cold Water Supply Supplv
Well
Well SCreen Sc reen
Aquifer (sandstone) (Sandstone)
Submersible
Pump
Woter OomesUc Hot Water Domestic to OomesHc Hot Water 10 1 Domestic Storage Storoge Wafer C~d&r Domestic Water 2 Colder
3 Water OUtlet to Discharge Well Pressur. 'rom Pressure 4 Water Inlet from
Tank
g. 2. Fi Fig.
tern components . Sys System Werm Suppty Air to CondttIOned
t
A._ j
sc-:e
(..:a::::---=~·~I~
,~~~'
I
[cx p-
c "
D.H.W. D.H.w. Storage
I ~~ ]
:'
\.
~r~~~~~~~~~~=~ I::: Fig. 3.
.
':
. ". .
"_'n -=- CoIoIo":-=-_~
Out
rrode operation. Heating mode
Co6d Suppty AIf to ConditIOned Spece
t
~--~J AIf Hendler
Retngerent Air h~ "-'nv-.nt .....t ......, eachenger EYeporetOf E"AIPOf'atOf 1
1
I !
I' '../
~COId" _ J_.........."'I" :... W.., ======:
D.H.W. Storage
~====== ======= =
Fig. 4.
Cooling Coo ling mode operation.
Cold WMIIr In Out Out Werm
183
Water for Energy: Ground Water Geothermal Heat Pumps
T~mpcra~ . Ground W.t~r akr T~mpcratu.re. In Wd b Jtan&in& RaneUtlr fro from SO' to 1SO' 1 SO' in i n Depth in ~11.
_____ _ _ f O___ -------FO----
__ t. &1'ft4 --lak....-ed
,,,.. ' Fig. 5.
Ground water temperatures tempe ratures in the continental U.S. at ranging m), depths rangi ng from 50 to 150 ft. (15.2 to 45.7 m).
Individual Heat Pump System
Water
~Water
AccumuAat~
Accumulat~
< ; - - - - - - - Static StatIC Water Level Level -------;> ------~
~CoId oE- CoId VlJeII Well
Pump
Hot VlJeU PumP-7
Aquifer
Fig. 6.
Co ponen soof the he Hedt eat Pump ICES uS'ng er therlTldl henna 1 Components using aqu; aquifer energy Sstorage. orage. A er Schae zl e and Bre After Schaetzle Brett (1979).