Study On Operation Strategy Of Composite GSHP System With Cooling Tower In Office Building

Ground source heat pump(GSHP) system, chartered with energy conservation and environmental protection, uses soil as cool/heat source, and exchanges heat with soil through the circular flow of heat transferring medium in the underground closed loop. However, in the operation phase of GSHP, heating will accumulate in the soil when the GSHP system absorbs more heat from the soil than releases to. This phenomenon would have adverse effect on the preference of the GSHP system. Thus, cooling tower is always introduced as assisted source to help heat dissipation in engineering. The composite GSHP system with cooling tower can remarkably improve the operating performance of traditional GSHP system and solve the problem of heat accumulation in soil.Currently, the composite GSHP system with cooling tower is inefficient when applied to office building. To address the problem, this study analyzes the operating characteristic of heat pump unit(refrigerating unit), the cooling tower and buried tube heat exchanger, by using heat transfer mathematical model with lumped parameter method. Meanwhile, this study programed with VB6.0 to simulate energy consumption of the composite GSHP and its effect on soil temperature. Compared with the existing business software, this program has the advantage of simple calculation and useful calculation results which can meet the demand in engineering demand.This study presents a case study on an office building in Tianjin, and simulates the load for the whole year using eQUEST. The peak cooling load of the building is 301 kW, while the peak heating load is 209 kW. With traditional GSHP, the heat released to soil is 210531.6 kWh in summer, while the heat absorbed form the soil is 114643.3 kWh in winter, and the ratio is 1:0.54. Thus, the cooling tower is needed in order to ensure the heat balance of the soil. According to the load characteristic of the building, this study provides four types of connection, including parallel connection, series connection, independent connection and novel hybrid connection. We select the corresponding equipment and program to simulate each connection type. The results indicate that: the temperature control and the temperature difference control under parallel connection and hybrid connection have the minimum effect on soil temperature. and preferential operation of heat pump unit under hybrid connection has the minimum energy consumption. Thus, the optimal operation strategy in this case is the preferential operation of heat pump unit under hybrid connection. This particular strategy can save 6.6% of energy compared with the normal composite GSHP system with cooling tower. In conclusion, the composite system of hybrid connection between cooling tower and buried tube heat exchanger contributes to heat balance of the soil and energy conversation of office building. The computing method of operation strategy of this novel system can be popularized to other office buildings and can provide reference for the application of the composite GSHP system with cooling tower.