Study On Control Strategies For Ground Source Heat Pump System Aided By Cooling Tower

Ground source heat pump system has been applied more and more widely at home and abroad for its characteristics of high efficiency, energy saving, and environmental friendly. But the summer building cooling load is generally greater than the winter heating load in the hot summer and cold winter climate region. Thus, hybrid ground source heat pump systems aided by cooling tower as supplemental heat rejection equipment are often adopted to keep soil heat balance. Appropriate cooling tower on/off control strategy is the key to soil heat balance and energy consumption reduction. The existing control strategies can not provide sufficient guidance forthe optimization of control and operation of the ground source heat pump system under different soil conditions. Therefore, we focused on the performance of hybrid ground-source heat pump systems under different control strategies, to explore a better control strategy and reveal its applicability.Firstly, the whole-year hourly heating and cooling loads of an office building in Shanghai were calculated by DeST. Then, the ground loop was designed for the hybrid ground source heat pump system by GLD2012. And then, a model of the hybrid ground source heat pump system was established on TRNSYS platform. 13 operating points of the highest temperature control strategy and of the temperature difference control strategy were implanted and ten- year operations were simulated, respectively. Based on simulation results, analyses, a new synthetic control strategy was proposed, combining the temperature difference control on the inlet fluid temperature of the heat pump and the highest temperature control with the outlet fluid temperature of the heat pump. 30 operating points of the new comprehensive control strategy were implemented and simulation results were analyzed. The optimal control points of three control strategies mentioned above were obtained, respectively, based on two assessment indicators of soil heat balance and energy consumption. Comparing the energy consumption as the three optimal control points for the three control strategies in the cases of the same final soil temperature achieved, it is found that the total systems energy consumption under comprehensive control strategy was 407448 kW·h, 4621 kW·h less than the consumption under temperature difference control strategy and 8359 kW·h less than the consumption under highest temperature control strategy.In order to discuss the applicability of the optimal control po ints of hybrid ground-source heat pump systems in the same area but with different soil conditions, the systems design and control strategy for the same building under condition of light clay(water content 15%) and dense sand(water content 15%) were studied as well. The applicability of the optimal control points of three control strategies combined with differences of soil thermal properties was analyzed...