Research On Combined Operation Modes Of Solar-Ground Coupled Source Heat Pump

In northern China, after long-term operations of traditional ground source heat pump (GSHP), the heating coefficient of performance (COP) of heat pump decline annually because of the decrease of soil temperature gradually year-by-year. For solving the problems, one of available options is to apply Solar-ground coupled source heat pump (SGCHP) system. Solar energy is added to the new system as one of low level heat source, the other is geothermal energy.For carrying out numerical simulation of the performance of a SGCHP system,4mathematical models for4units in the system were established respectively. A typical civil building model located in Xi’an was established as research object. The annual hourly building cooling load and heating load and some hourly meteorological parameters as basic data of system design and simulation were calculated based on DeST software.The combined operation modes and their corresponding characteristics of SGCHP system are significant for its application, thus it was discussed in this paper. There are3combined modes:(1) the coupling of solar collectors and GHEs were connected in series.(2) The coupling of solar collectors and GHEs were connected in parallel.(3) The coupling of solar collectors and storage water tank were connected in series for solar heat storage, GSHP system operated independently for space heating during the day. The coupling of GHEs and storage water tank were connected in series for space heating during the night.By developed several dynamic simulation programs to simulate3combined operation modes, operating characteristics of SGCHP system in a heating season were calculated. The calculated results show that mode1operated with highest energy efficiency, the average coefficient of heating performance (COP) was3.4879, the average energy saving-rate was9.832%compared with GSHP system. In addition, the operating characteristics in mode2is very close to model1when e=0.75(e is defined as the ratio of flow rate in GHEs to the total flow rate in heat pump). Although mode3was not the best mode in normal operating condition, but its particularly suitable for a building which heating load at night is much larger than at day.At last, After optimizing by comparing the average COP of heat pump and average efficiency of solar collectors in mode1, the optimal whole drilling depth of GHEs could been determined either by the size of88×37m.