Study On Design Optimization Of Hybrid Geothermal Heat Pump Systems With Seasonal Storage Of Solar Energy

In severe cold areas, the heating load of buildings is always much larger than its coolingload. If only ground source heat pump system is used, the amount of heat extraction from thesoil in winter may be greater than the heat release into the soil during summer. Thus, theunderground soil temperature will decrease year by year and the temperatue can not fullyrecover in transition seasons. The operational performance of the ground source heat heatpump will become worse and worse. The solar-ground coupled heat pump system (SGCHP)can collect the solar energy during non-heating seasons and inject the heat collected into thesoil through borehole heat exchangers. And the heat is extracted from the soil by the heatpump for space heating of the buildings during heating seasons, Seasonal soil thermal storagenot only can help to transfer the abundant solar energy resources in the non-heating season towinter, but also can make the soil temperature fully recovered to ensure the efficiency of theheat pump system. If the hybrid system can be designed reasonably, then it can enlarge therange of use of solar energy as renewable resources and bring remarkable energy savingeffect.Therefore, at first, the solar radiation data were collected from the “TypicalMeteorological Database Handbook for Buildings” and the calculating method of the amountof solar radiation which can be obtained by the solar collector with different installationangles in different regions. And the best installation angles of the solar collector weresuggested for different regions. Then, the basic design theory of solar heating system wereintroduced.And then，the hourly air conditioning and heating load of an office building with the areaof3500m2in YuLin was calculated by using the professional load calculation software DEST. Investigations were conducted by the using the software GLD Premier2012on the soiltemperature variation characteristics after several years operation of the system to satisfy thethe hourly cooling and heating load of the building. The influences of the main designparameters of the borehole heat exchanger, such as the horizontal spacing of borehole, theconductivity of the backfill materials and the thermal physical properties of the soil, on itsheat transfer performance were analysed. The influences of these parameters after differentyears operation were also illustrated.In addition,3D dynamic numerical method were used to simulate the heat removal andstorage process of the borehole heat exchanger in the soil. The heat storage performances ofthe ground heat exchanger were analysed. The heat storage of the multi-borehole weresimulated as well. The influence of the horizontal spacing of the boreholes, the inlet watertemperature of the borehole heat exchangers and the time length of thermal charging onthermal storage performance were discussed. focusing on the difference of the soiltemperature field. A large amount of data were obtained to reveal the soil temperature fieldcharacteristic when borehole heat exchangers reject and absorb heat from the soil. And theheat accumulated in the soil during summer and the heat extracted from the soil during winterwere calculated. The results indicated that the heat release rate of soil is92.8％，the averagesoil temperature rises is0.54K which is desirable in the engineering application.This indicates that seasonal storage of solar energy through borehole heat exchangersinto the soil makes geothermal heat pump systems used in cold area possible. The results canbe referred when designing hybrid geothermal heat pump systems coupled with seasonalsolar energy storage.