Study On Control Strategies For Cooling Tower Of Hybrid Ground-source Heat Pump System For Office Building

Ground source heat pump (GSHP) system is a kind of highly efficient and energy-saving air-conditioning system, and has good prospects for development. In typicalcooling-dominated cities such as Wuhan, the cooling load is much lager than heating load,and the summer cooling time is longer than the winter heating period. The use of generalGSHP system will result in the problem of soil heat accumulation.The hybrid groundsource heat pump (HGSHP) system, including the GSHP and cooling tower (CT) as thesupplemental heat rejecters, is thus used to solve the problem of thermal imbalance in soil.In practical project applications, soil heat accumulation remains a burden because ofthe design of the system, the site construction and the resilience of soil. Therefore, it isnecessary to optimize the HGSHP system. The optimization of control strategy for CT isan important way to improve the efficiency and alleviate soil heat accumulation of system.In this paper, an office building was selected for study. The HGSHP model wasconstructed by TRNSYS, and different control stragegies for CT were simulated. Theauthor compared the temperature difference control with another control strategy on thebasis of temperature difference control, which operating CT in series with ground heatexchanger (GHE) at night to cool the soil. And on the basis of the above two kinds ofcontrol strategies, the author put forward some kind of temperature difference controlstrategy for CT at night, that is, when the value of temperature difference between the hotside and cold side of plate heat exchanger below a certain value, the CT and water pumpswere turn off to prevent heat transfer from CT to the soil.Simulation results show that the problem of soil heat accumulation can be alleviated,but the operation time of CT determines the system energy saving or not; when adoptdsome kind of temperature difference control strategy for CT at night, the problem of soilheat accumulation can be further alleviated, the system saves more energy, and theoperating cost is the lowest.