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AIR CONDITIONING SYSTEM WITH GROUNDWATER HEAT PUMP
BY AQUIFER THERMAL ENERGY STORAGE (ATES)
Masahiko KATSURAGI, EXECUTIVE DIRECTOR
Yoshito HORINO, MANAGER OF PLANNING DEPT
Kiichi NUMAZAWA, MANAGER OF DESIGN DEPT
JAPAN GROUND WATER DEVELOPMENT CO., LTD, YAMAGATA CITY, YAMAGATA PREF,
JAPAN
Abstract：The air-conditioning system with groundwater heat pump using the aquifer thermal
energy storage (ATES) is still quite rare domestically in Japan. Japan Groundwater
Development., Co Ltd (JGD) started utilizing this system in 1983. It creates less heat
emissions, which is believed to be one of the major causes of the heat island effect than
conventional systems.
However, we realized that we do not have sufficient data to prove this system is actually
environmental load reducing. Therefore we have decided to reevaluate its environmental
load and impact by monitoring groundwater consumption, groundwater temperature and
amount of electrical energy.
Five wells were situated, three for studying the influence to the ground and groundwater, the
other two with the temperature sensor and the water level indicator for the background
information. From these results, we have reevaluated the change in ground temperature
caused by inter annual operation of this system.
Key Words : heat island, air-conditioning system, groundwater, heat pump, ATES
1
INTRODUCTION
The historical background which led to the birth of the heat pump air-conditioning system
using ATES in Japan were as follows;
1) Government’s change in its energy policy from its heavy dependence on petroleum to
more conservative energy efficient systems after the oil crisis in 1970s.
2) Environmental problems such as the drawdown and the land subsidence caused by the
excessive pumping of groundwater for manufacture use and snow melting system in cold
region.
To prevent these environmental problems, we started research on artificial recharge for
aquifer and came to understand its great potential for heat storage tank. Moreover, JGD has
developed snow melting system without sprinkling water which became basic concept for this
ATES system. The system started operating in 1983, but by then oil price came down and
conventional air-conditioning system had achieved great improvement, the ATES system
was scarcely noticed in Japan. Recently, however, global warming and the heat island
phenomenon in urban areas have become a pressing problem and we are urged into building
more low carbon society. Our technology is now drawing attention increasingly. We would like
to demonstrate how much ATES system would be effective to prevent global warming and
heat island phenomenon
2
FACILITIES OVERVIEW
2.1 System overview
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This is an air-conditioning system which uses heat energy of groundwater (Fig 1).
In winter, groundwater is pumped from new south well, and fed into a heat pump to transfer its
heat energy to produce hot water to use heating the office building. After then it is led
through the pipes under the parking zone to melt snow, and finally injected back into aquifer
through north well to form a cold water zone. In summer, however, groundwater is pumped
from north well and fed to the heat pump to produce cold water, then like winter time operation,
it is led through the pipes under the parking zone to collect solar energy this time. The
heated groundwater is then injected at the new south well to form the warm water zone.
Thus, this system utilizes the groundwater heat energy all year round.
Storage tank
Summer: Cold water
Winter : Hot water
Office building
P
P
Summer: Cooling
Winter : Heating
Fan Coil×50unit
HP Control
sensor
Parking zone
Water Flow
2nd piping
1st piping (summer)
Summer: Solar Collector
1st piping (winter)
Sharing Plumbing
P
Pump
F
Flow meter
Winter : Snow Melting
F
F
Temperature
measurement point
Drain
Heat Pump
North Well
F
New South Well
Impermeable Layer
P
Ditch
Aquifer
Cold Water zone
P
Warm Water zone
Impermeable Layer
FIgure 1 System overview
2.2 Equipment composition
Well
Item
North well
New South
Well
Heat pump
Fan Coil Unit
Circulation pump
Table 1 : Main equipments of these facilities
Specification
φ350mm×104m depth
7.5kW Submersible pump
φ150mm×85m depth
7.5kW Submersible pump
30KW
Compressor output
0.105kW×47
0.045kW×3
2.2kW×1
CRH-40G Format
Heat pump to storage tank
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Remarks
Building in
1970
Building in
2009
Manufactured
1982
Total 50 units
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- 3 1.5kW×1
Piping in pavement
2.3
800ｍ2
Construction area
Storage tank to Fan coil
unit
Piping
SGP-15A
Operation setting
The set value of these facilities are as follows; (Table 2)
Table 2 : Observation period and operation setting
Summer operation
Winter operation
Observation period
10th August to 30th Sept
2nd December to 31st January
6:20～19:00
6:10～20:00
Heat pump
(13℃：ON、7℃：OFF）
(39℃：ON、44℃：OFF)
24 hour
Submersible pump
6:20～19:00
Secondary circulation pump
Control by timer（3:45～21:10）
in 4th floor (2 units)
Fan Coil unit
Manual：Turn in（3 steps：Low・Med・High / Turn off
Quantity of pumping
100 L/min from North well
180 L/min from South well
100 L/min to North well
Quantity of injection
100 L/min to south well
(Rest of 80 L/min were released)
Quantity of water for
200 L/min
secondary circulation
2.4
Well arrangement
These facilities are located in the southern part of Yamagata basin. Sukawa river flows 1km
east side of here. The basement rock is tuff of Cenozoic period Neocene Miocene, and
Ryuzan mud flow lodgment of the period pleistocene of 4th of the Cenozoic period distributed.
Highest stratum is the alluvium in 4th period Holocene.
Horizontal arrangement of wells are as follows; (Fig 2)
Location
５ｋｍ
Figure 2 : Horizontal arrangement of wells and topographical map
3
Observation record
Summer operation started at 9 AM, August 10, 2009 and lasted until September 30.
Groundwater was pumped up from the north well and injected at the south well. After a
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month of intermission, the winter operation began November 2. This time, groundwater was
pumped up from the new south well and injected at the north well. Operation records of this
demonstration are as follows; (Fig 3 and Fig 4)
3.1 Temperature record in the piping
60
【Temperature in piping(Summer)】
Temp（℃）
45
Pumping water
Entrance piping in parking zone
Exit of secondary HP
Entrance of secondary HP
Injecting water
30
13℃:ON
15
7℃:OFF
0
Summer operation（8/10～9/31）
Before operation
-15
2009/8/7
2009/8/14
2009/8/21
2009/8/28
2009/9/4
2009/9/11
2009/9/18
2009/9/25
Figure 3 : Records of summer operation
60
【Temperature in piping(Winter)】
44℃:OFF
Temp（℃）
45
30
39℃:ON
15
0
Entrance of piping in parking zone
Entrance of secondary HP
Pumping water
Winter operation（11/2～）
Exit of secondary HP
Injecting water
-15
2009/11/2
2009/11/17
2009/12/2
2009/12/17
2010/1/1
2010/1/16
2010/1/31
Figure 4 : Records of winter operation
As you can see at Fig 3 and Fig 4, the No.2 heat pump which was used for the office building
air-conditioning system operated keeping the setting temperature without a problem in both
summer and winter.
The groundwater used in the No.1 heat pump (heat source), exchanged heat energy at the
office, then it ran through heat radiation pipe under the pavement to collect solar heat in
summer time. The heated water was injected into the aquifer at the new south well.
All through the summer operation, the water temperature before it was piped to heat radiation
pipe was almost constantly 33℃, however, when it was injected at the well its temperature
was considerably high several times, possibly due to intense summer heat.
The stored heat was utilized during the winter operation. The water was pumped up from the
new south well and heat energy was used to warm up the office building and to melt snow.
Nonetheless, the temperature change in the north well (injection well) was confirmed.
The office heating and snow melting demanded greater heat load that it was stored over the
summer.
Temperature of the new south well showed 18℃ when the winter operation started but it
declined to 15℃ at the end of following January.
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Temperature 0f pumping water from NSW（℃）
- 5 20
19
18
17
16
15
14
09/11/2
09/11/17
09/12/2
09/12/17
10/1/1
10/1/16
10/1/31
Figure 5 : Temperature of new south well (2008, winter)
3.2
Fluctuation in the office and ambient temperature
60
【Temperature in storage tank&outside】
Strage tank
Outside
Inside
Temp（℃）
45
30
15
0
Before operation
Summer operation（8/10～9/31）
-15
2009/8/7
2009/8/14
2009/8/21
2009/8/28
2009/9/4
2009/9/11
2009/9/18
2009/9/25
Figure 6 : Records of summer operation
60
【Temperature in storage tank&outside】
Strage tank
Outside
Inside
Temp（℃）
45
30
15
0
Winter operation（11/2～）
-15
2009/11/2
2009/11/17
2009/12/2
2009/12/17
2010/1/1
2010/1/16
2010/1/31
Figure 7 : Records of winter operation
The ambient temperature stayed within average during both operation periods.
The office temperature was set to 26℃ in summer and 23℃ in winter when we could
experience way over 30℃ or below 0℃ outside.
3.3 Water level fluctuation
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The natural water level stays approximately 125m above sea level around this area. The
observation well #1 (near the north well) indicated no definite change of water level after the
operation.
However, at the #2 well (near the new south well) , water level dropped, even though water
was injected at the new south well in summer time. Yet no further change became evident
during the winter operation, though water was pumped up from the same well this time.
From these facts, the changes were suspected to occur due to seasonal variations in natural
water level and less likely to be caused by the operation itself.
128
Elevation（m）
【Records of water level】
126
Water level of
Observation Well#1
124
Water level of
Observation Well#2
122
Water level of Back
ground Observation Well
120
Summer operation ←
→ Winter operation
118
2009/8/5
2009/8/25
2009/9/14
2009/10/4 2009/10/24 2009/11/13 2009/12/3 2009/12/23 2010/1/12
2010/2/1
Figure 8 : Graph of the water level from the observation well (Daily average)
4
4.1
The evaluation of these facilities based from observation results
Reduction of the exhaust heat emissions into the atmosphere
Amount of the groundwater pumped up and injected into aquifer were stayed approximately
same over the operation periods.
We have pumped up 4,131 ㎡ and injected exactly same amount during the summer
operation.
From the daily study of pumping discharge and injection volume, and temperature change in
piping, the heat budget (shown in Fig 10) and quantity of heat energy transfer to the ground
from the new south well (shown in Fig 11) were derived.
Between August and September, the quantity of heat exchange (the exhaust heat) of heat
pump for air-conditioning was 71GJ and the solar heat to collected at parking zone was 82GJ
which would make 153GJ total, was injected into the aquifer,
Since summer time operation lasted only 2 month, we believed we could make twice as much
of energy saving if we had operated 4 month, between June and September.
In another word, our facilities can reduced approximately 300GJ of artificial exhaust heat
emitted into the atmosphere.
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35,000
3
200
15,000
150
100
5,000
50
0
50
5,000
（m/d）
100
150
15,000
Pumping in summer
Injecting in summer
200
Multiple pumping in summer
250
25,000
Multiple injecting in summer
300
350
09/8/10
09/8/24
09/9/7
35,000
09/9/21
3
25,000
250
Multiple injecting wate（
r m）
3
（m/d）
300
3
Figure 9 : Amount of pumping and injecting during summer operation
8
Heat exchange quantity of HP
Heat quantity of parking zone
All heat capacity
7
Heat Capacity(Daily) [GJ/d]
Pumping fromNewSouth well
Pumping fromNorth well
350
Multiple pumping wate（
r m）
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6
5
4
3
2
1
0
09/8/10
09/8/17
09/8/24
09/8/31
09/9/7
09/9/14
09/9/21
Figure 10 : Daily heat budget of summer operation (New south well)
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Total heat quantity in summer（Injecting heat quantity）
153GJ
Multiple heat capacity(GJ)
160
120
Multiple heat exchange quantity of HP
71GJ
Total heat quantity of parking
zone
82GJ
80
40
0
09/8/10
09/8/17
09/8/24
09/8/31
09/9/7
09/9/14
09/9/21
09/9/28
Figure 11 : Amount of heat injection into ground during summer operation (New south well)
4.2
The energy saving
COP of the facilities is listed in table 3 and daily results in Fig 12 and 13.
As will be noted from these, COP of heat pump for cooling is less than 3, and heating is less
than 4. However, early reports from Katsuragi(1996) and Hiyama(1992), showed that it was
4.3 for winter heating. Considering the fact that facilities are 25 years old, the decline in
number is most probably due to aging. By using the latest heat pump, COP for air conditioning
will mark more than 5 will be expected.
Table 3 : Calculation result of this facility
HP only
2.87
3.26
Summer cooling
Winter warming
COP
Heat source
2.34
2.64
Air-conditioning
2.11
2.26
4.0
COP[－]
3.5
COP of heat source
Average　2.34
COP of Heat Pump
Average　2.87
COP of air conditioning
Average　2.11
3.0
2.5
2.0
1.5
09/8/10
09/8/17
09/8/24
09/8/31
09/9/7
09/9/14
09/9/21
Figure 12 : COP in summer operation
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COP of Heat Pump
Average　3.26
COP of heat source
Average　2.64
COP of air conditioning
Average　2.26
COP[－]
3.5
3
2.5
2
1.5
09/11/1
09/11/15
09/11/29
09/12/13
09/12/27
10/1/10
10/1/24
Figure 13 : COP in winter operation
4.3
The estimated underground temperature simulation
To evaluate environmental impact on underground temperature and groundwater temperature,
FEFLOW Ver5.4 (numerical calculation software) was used.
Fig 14 and 15 show the results of the simulation calculated based on observation of maximum
influenced area of warm and cold water zone and on the assumption of extended operation of
the facilities for certain period of time.
Barely any change in temperature caused by injected summer heat energy was confirmed
with long-term operation. This is because it is pumped up in winter consumed entirely during
winter operation. Rather, quantity of the water needed in winter was greater than summer,
so that unused cold energy stayed in the north well and expanded cold water zone along the
underground water flow. A maximum influenced area with temperature change of 1℃ over
20 years were estimated about 65m.
Table 4 : Influence of temperature from injection well after operation finished (1℃)
Elapsed years
Warm Water Zone
(New South Well)
Cold Water Zone
(North Well)
1 year
10 years
20 years
12m
11m
11m
17m
47m
65m
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Maximumarea of influence （m）
100
End of summer operation(Warm water zone,New South well)
End of winter operation(Cold water zone,North well)
80
60
40
20
0
0
5
10
15
20
25
Year
Figure 14 : Influence of temperature from injection well after operation finished
Ground water flow
2.7m/y
Ground water flow
2.7m/y
11ｍ
65ｍ
Figure 15 : 20 years simulation about area of influence (temperature) for
warm water zone(left side) and cold water zone after 20 years
CONCLUSION:
The results from this case study are as follows;
1) Total of 153 GJ of heat energy was injected into the wells during summer operation.
71 GJ of which was come from the air-conditioning exhaust heat and 82 GJ was from
solar energy collected in the parking zone. This clearly shows that the system reduces
amount of heat emitted into the atmosphere and cools down the road temperature. Part
of the heat energy stored in the aquifer is presumably utilized during winter operation.
2) Our facilities were built over a decade ago thus deteriorating of heat pumps and wells are
evitable. However, COP still marks more than 2 point in both summer and winter.
3) Considering the fact that our facilities are situated in a cold region in Japan, and use of
groundwater in winter time is greater than summer time, the heat energy is lost rather than
remained in aquifer. Therefore, numerical simulation of heat transport shows the loss of
1℃, in 47m of the groundwater flow over a decade and 65m in two decades.
No other considerable environmental impact was reported.
This system has been adapted by the Japanese Ministry of Environment as one of the Cool
City Project in 2009. We would like to express our deepest appreciation for their kind
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offering of various data from the facilities.
REFERENCES
Takao YOKOYAMA・Hiromichi UMEMIYA・Hiroto ABIKO (1975) : Aquifer thermal storage with
artificial recharge. Japanese Association of Groundwater Hydrology, 17-2, 55-67
Takao YOKOYAMA・Hiromichi UMEMIYA・Tatsuo TERAOKA・Hideo WATANABE・Kohei
KATSURAGI・Keisuke KASAHARA(1980) : Seasonal thermal storage to use aquifer.
Japan Society of Mechanical Engineer (Editing B), 46-402, 322-330.
Kohei KATSURAGI・Tadashi YOSHIDA・Takayuki HIYAMA(1986) : Aquifer thermal storage
with the annual period, Groundwater, well, and pump, 28-3, 1-8
Takayuki HIYAMA(1992) : Snow Melting System using solar energy with aquifer and cold heat
storage for air conditioning. Institute of snow management and control, 1992, 178-182
10thIEA Heat Pump Conference 2011