Dynamic Characteristics Of Ground Source Heat Pump System Aided By Cooling Tower Under Different Control Modes

Ground source heat pump has a very good development at home and abroad dueto its higher energy efficiency caused by stable soil temperature and low grade thermalenergy. Ground source heat pump system aided by cooling tower comes out forunbalanced load in the hot summer and cold winter area. Some research was taken onthe system performance under different control modes.Based on the weather parameters of typical meteorological year in Shanghai, theall-year hourly load and the outdoor meteorological parameters of thea three-storied office building were analyzed by DeST. Based on the mass and theenergy conservation principles and the lumped parameter method, a set of dynamicmathematical model was established for a ground source heat pump system aided bycooling tower designed by GLD. For the control strategy of pre-setting29℃as themaximal value for the inlet cooling water temperature of the GSHPS, Comparison ofthe simulation results using dynamic mathematical model with those obtained bysimulations using TRNSYS indicates both are in good agreement.Taking COP of the whole system and annual soil temperature variations as theobjective functions，system operational states were simulated by using the dynamicmathematical model developed in different control strategies. Results showed that thecontrol mode of setting the highest cooling water temperature of the source sideentrance can effectively eliminate the peak load. The control mode of setting the temperature difference of cooling water temperature of the source side entrance andwet bulb temperature can make full use of the cooling tower. The control mode ofoperating cooling tower at night or during the transition season can send out more heatbut increase the pump power consumption. The parallel system is easier to adjust theheating proportion between the cooling tower and the ground heat exchanges, which ismore conducive to the heat balance of the soil. In control strategies of different controlmodes listed in this paper, the control strategy of setting the temperature difference tobe2℃to control the operation of cooling tower coupled with2-hour intermittentoperation of the ground heat exchanges is the best solution，which system averageCOP is2.857and the soil imbalance rate is1.19. It can both provide high COP of thesystem and ensure the heat balance of the soil.