## 4 An Efficient Operation Method of Aquifer Heat Storage System  
Figure 7 shows the schematic diagram of the air conditioning system according to each case and operation method in this study. Table 3 shows the rated capacity of the heat pump and heat exchanger. In this study, a schematic diagram of the air conditioning system introduced by AHU was assumed throughout the building. The heat source equipment introduced a water-cooled heat pump and aquifer heat storage system. Three heat source devices have been introduced, two for nighttime heat storage and one for daytime operation. Figure 6: AHU inlet air temperature and outside air temperature. (**a**) The indoor temperature in summer and outside air temperature. (**b**) The indoor temperature in winter and outside air temperature. Figure 7: Air conditioning system diagram in each system. (**a**) WTES system. (**b**) ATES system. (**c**) ATES system (pre-cooling/pre-heating). In this study, we assume three types of cases. Figure 7a is a WTES system, which exchanges cold/hot water sent to the secondary side by a heat exchanger and cold/hot water from the heat storage tank. Figure 7b is an ATES system that sends heat to the secondary side in the same way as in Figure 7a. In Figure 7b, only the part of the water heat storage tank in Figure 7a is replaced with the ATES system, and the other configurations are the same. Figure 7c is an ATES system, in which heat is dissipated by the AHU pre-cooling/pre-heating coil installed on the secondary side. In Figure 7c, a pre-cooling/pre-heating coil that uses cold/hot water sent from the ATES system and a cold/hot water coil that uses cold/hot water sent from the water-cooled HP are introduced in the AHU. Figure 8 shows the configuration of the AHU. Table 4 shows the cooling and heating operation cases. Case WTES is a WTES system operation, and Case ATES is an ATES system operation. C is a cooling operation, and H is a heating operation. The numbers divide the heat storage temperature. Case WTES is a case that reproduces the operation of a WTES system, and stores heat at a heat storage temperature of 7 \({}^{\circ}\)C for cooling operation and 45 \({}^{\circ}\)C for heating operation. Case ATES stores the ATES system at the same operation case as the WTES system, with the heat storage temperature at 7 \({}^{\circ}\)C for cooling operation and 45 \({}^{\circ}\)C for heating operation. CaseATES-C2 is a case in which a pre-cooling/pre-heating coil is provided in the AHU to search for a more suitable operation method for the ATES system (Figure 7c). Case ATES-C2 is divided into Case ATES-C2-7 and Case ATES-C2-14 according to the temperature level at which heat is stored. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Heat Source Equipment** & \multicolumn{2}{c}{**Rated Capacity**} & \multicolumn{2}{c}{**Number of Units**} \\ \hline \multirow{2}{*}{Water-cooled HP} & Cooling capacity [kW] & 194.2 & \multirow{2}{*}{3} \\ \cline{2-3} \cline{5-5}  & Heating capacity [kW] & 291.5 & \\ \hline Heat Exchanger 1 & Heat exchange capacity [kW] & 292.0 & 1 \\ \hline Heat Exchanger 2 & Heat exchange capacity [kW] & 210.0 & 1 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The rated capacity of the heat source equipment. Figure 8: Configuration of the AHU. (**a**) Cold/Hot water coil. (**b**) Pre-cooling/Pre-heating coil. In each case, the heat storage operation is 10 h, the heat utilization operation is 10 h, and the operation stop is 4 h. The initial temperature of the aquifer is 19.1 \({}^{\circ}\)C, and the temperature of the water storage tank is 15 \({}^{\circ}\)C. The water-cooled HP of the heat source equipment operates the outlet temperature at 7 \({}^{\circ}\)C for cooling operation and 45 \({}^{\circ}\)C for heating operation. Case studies will be conducted using BEMS data from July to September for cooling operations and from December to February for heating operations. In the simulation of heat storage operation, a one-month run-up period is provided to stabilize the actual temperature change of the heat storage layer.