Mitigation of Influence of Aquifer Thermal Energy Storage System on the Underground Environment.

Transcription

1 Mitigation of Influence of Aquifer Thermal Energy Storage System on the Underground Environment. 1 st Author : Masahiko KATSURAGI, Mutsumi YAMAYA, Satoru KURONUMA m-katsuragi@jgd.jp (Japan Groundwater Development Co., Ltd. JAPAN) 2nd Author : Hikari FUJII (Faculty of International Resource Sciences, Akita University) 3 rd Author : Yohei UCHIDA, Mayumi YOSHIOKA (National Institute of Advanced Industrial Science and Technology) 1. Introduction An Aquifer Thermal Energy Storage (ATES) system is known to effectively utilize the heat of groundwater. It is obvious that the energy of groundwater and ground source is more stable than other natural energy resources such as solar or wind. An ATES system cuts carbon dioxide emissions and reduces the heat island effect by limiting the release of waste heat from air conditions to the atmosphere. At the moment, however, the ATES system is still not widely known in Japan. From 2011, Japan Groundwater Development Co., Ltd (JGD) was adopted by the Low Carbon Technology Research and Development Program by the Ministry of Environment in Japan. In the program, we carried out a project named Mitigation of influence of Aquifer Thermal Energy Storage on the underground environment, and were committed to collecting more data and performed further studies to show the contribution of the ATES system for the prevention of the global warming. 2. Information of Test Facilities Experiment facility is located in Yamagata-City, northeastern part of Japan. The basement rock is tuff of the Cenozoic period the Neocene Miocene, and the Ryuzan mud flow lodgment of the period Pleistocene of 4 th of the Cenozoic period is distributed above it. The local average temperature from July to August and January to February was is 23.9 C and -3.5 C, respectively, during the period from 1971 to The test facility is an air-conditioning system which uses heat energy of groundwater. A air-conditioning area of the whole building is 840m2 Figure 1 shows the location of the facility, and Figures 2-1 and 2-2 show the scheme of ATES system in winter, and Table 1 lists the main equipment of this system.

2 Figure 1 : Location of the facility Figure 2 : Scheme of ATES system

3 Table 1 : Equipment List of this Facilities Item Specification Well No.1 Pump up in Winter, Injection in Summer Φ150mm 53m depth 3.7kW submersible pump Well No.2 Pump up in Summer, Injection in Winter Φ150mm 73m depth 3.7kW submersible pump Well No.3 Injection in Summer & Winter Φ150mm 54m depth 2.2kW submersible pump Heat Pump 30kw 2 Format AQ-30, 103kW Heat ability Fan Coil Unit 6000kcal/h 45 unit Circulation Pump 1.5kW kW 2 5.5kW 3 Heat Exchanger to HP HP to header Header to Fan Coil Shell & Tube Heat Exchanger 2 Format 8150 SBW Storage Tank Φ900mm L capacity In the winter operation, the groundwater which pumped up from Well No.1 is fed into the heat exchanger to collect thermal energy as shown in Figure 2-3. After receiving the thermal energy of groundwater, heat pump is used to for heating the office building. After releasing the heat energy, groundwater is inject for the Well No.2 & No.3 to make cold water zone. Well No.3 was installed as the injector of both in summer and winter operation to maximize the injection rate and to keep the size of cold water zone in a proper size. 3. Three-dimensional groundwater flow heat transportation analytic-model FEFLOW was used to evaluate the groundwater flow and heat transfer in this site. The numerical model was set up with 200m of X direction 200m of Y direction 100m of Z direction. Maximum length of the well is 85m. Wells were defined according to the actual position. Figure 4-1 shows the three dimensional view, and Figure 4-2 shows the two dimensional view of the numerical model.

4 Figure 3-1.Three dimensional model Figure 3-2. Two dimensional model For the purpose of estimating the groundwater flow velocity and thermal conductivity, we carried out a history matching of the initial ground temperature. Figures 3-1 and 3-2 compare the measured and calculated vertical temperature profiles in Well-A and Well-B, respectively. Groundwater velocity of 20m/year gave the best matching of the temperature profiles. Table 2 shows the groundwater velocity and the rock properties obtained through the history matching. Tabel 2 : Groundwater velocity and other parameters Layer Coefficient-of-permeability (m/s) Thermal conductivity (W/m K) Groundwater Velocity Gravel Clay m/year Tuff

5 Figure 5-1 Figure 5-2 History matching of History matching of observation well A observation well B FEFLOW was used to simulate the extent of the heat storage zone for 1 year and 10 years operations to investigate the suitable recharge method that forms an appropriate heat storage zone. Conditions of the operation are shown in Tables 3-1 & 3-2. Table 3-1 : Conditions of the operation Summer operation Winter operation Calculation period 10 years Operation period 7/1~9/30 11/1~3/31 Pumping operation 6:20~19:00 24 hours Recharged water temperature 20 C 10 C Table 3-2 : Pumping and recharge rates Well No.2 Well No.1 Well No.3 Pump in summer & recharge in winter Pump in winter & recharge in summer Recharge in summer & winter Summer +300m3 /day -228m3 /day -76m3 /day Winter -228m3 /day +576m3 /day +288m3 /day Note: + shows the pumping rate, and - shoes the recharge rate

6 Temperature of groundwater in this aquifer is confirmed 15 C. In summer, the temperature of the recharge water was set as 20 C, which is higher than the groundwater temperature by 5 C considering the heat disposal to the groundwater. In winter, the temperature of the recharge water was set as10 C, which is lower than the groundwater temperature by 5 C to the heat extraction by the heat pump. Figure 5 shoes the area of temperature influence during the 10 years calculation. After summer operations, the warm water zone (temperature is 20 C), which is shown in red is confirmed. After winter operations, cold water zone (temperature is 10 C) arises, which is shown the blue. Comparing the heat storage zone between 1 st year to 10 years, because of the influence of the groundwater flow, heat storage zone was expanding to the northern area. Although the warm water zone which was formed by the summer operation disappeared before the end of winter operation, the cold water zone which was formed in the winter operations was maintained after end of summer operations. Figure 4 : Simulation of the temperature influence after seasonal operation

7 Because the winter operation is longer than the summer operation by 2 month, the cold heat injected in winter is larger in quantity than warm heat injected in summer. Hence, we have to find out the way of controlling the size of the cold water plume formed in winter. According to the simulation mentioned above, the daily operation time was set as 24 hours in the winter. Because it is possible to decrease the operation time of the heating system at night significantly in the actual operation. The operation time was set to 12 hours. Figure 6 compares the temperature distribution of groundwater in 12 hours operation case and 24 hours operation case at the end of 10 years operation. Heating operation : 12 hours/day Heating operation : 24 hours/day Figure 5 : Comparison of the temperature distribution at the end of winter operation for 10 years The simulation shows that the water temperature of 12 hours operation is 0.5 C higher than the case of 24 hours operation in January, when the heating load is at its peak. Comparing the evaluation of influence of cold water zone of the 10 th year, the area of influence of 12 hours operation time is 5 meters shorter than 24 hours operation. Since Yamagata-City is a cold area in Japan, the 0.5 C rising of pumped water temperature in the winter result the increasing efficiency of whole system operation. 4. Conclusion We could predict that cold water zone will be bigger than warm water zone in the future, because of warming season is longer than cooling season in Yamagata-City, and numerical simulation support to figure out our expectation.

8 We can conclude from the above result that the efficiency of the aquifer thermal energy storage system was improved by shortening the operation time from 24 hours per day to 12 hours per day and it is possible to restrain the expand of cold water zone. REFERENCES Masahiko KATSURAGI, Yoshito HORINO, Kiichi NUMAZAWA (2011) : Air Conditioning System with Groundwater Heat Pump by Aquifer Thermal Energy Storage (ATES), 2011 IEA HEAT PUMP CONFERENCE, TOKYO, 1-12

9