Research On Design And Operation Strategies Optimization Of The Hybrid Ground Source Heat Pump System With Cooling Tower

Ground source heat pump has already developed greatly at home and abroad inrecent years as a kind of energy saving and environmental friendlyair-conditioner technology. But the operational performance may get worse and worsedue to the unbalance of the heat rejection into the soil in summer and the heat extractionfrom the soil in winter when traditional ground source heat pump systems are used. Thiswill bring about the obvious increase or decrease in soil temperature.. Therefore, ahybrid ground source heat pump system coupled with cooling tower were designed foran office building in the climate zone of hot summer and cold winter.,The operationalstrategies are optimized to solve the unbalance problem of soil heat absorptionand release to obtain a better energy saving effect.An office building in Shanghai was token as research prototype. The whole yearhourly cooling and heating load of the air conditioning system were computed under thetypical weather data of Shanghai. And with the program GLD2012was used to studythe impact of the rock-soil thermal properties, backfill material and the distance of twoburied branch tubes on soil temperature increases when the ground source heat pumpsystem operations for several years. Then A hybrid ground source heat pump systemwith cooling tower was designed for this building.The hybrid ground source heat pump system simulation model was developed byusing the software TRNSYS. The operational strategies of temperature differencecontrol, the highest temperature set control and the operational time of cooling towercontrol were applied to the hybrid system to reveal how the operational conditions and the soil temperature change are, respectively. The results show that the whole yearoperational efficiencies are the highest when the temperature difference is set to be4℃,among the four cases when the temperature difference is set to be2℃,4℃,6℃and8℃,respectively. And the whole year operation efficiencies are the highest when the valuethe highest inlet temperature of the heat pump unit is set to be25℃among the threecases when the set temperature are25℃、30℃and35℃, respectively, The operationaltime is from8:00h to18:00h in the daytime during cooling season, and the whole yearaverage operation efficiency is2.18. Compared these three operation strategiescomprehensively, the whole year operation efficiency is the highest when theoperational strategy of setting the temperature difference to be4℃is applied, Theyearly average system COP can reach2.92. And the temperature of the soil has notincreased obviously and the soil maintains good thermal balance after the hybrid systemoperates under this operational strategy for five years.