Discussion of a combined solar thermal and ground source heat pump system operation strategy for office heating

Abstract Combined operation of solar thermal and ground source heat pump (GSHP) is widely applied in regions with unbalanced cooling and heating demands. The combined system could achieve a better performance if it is well performed. Optimal operation of the combined system is an interesting topic since different systems have their own characteristics in design, site, local resource etc. The effect of different operation strategies of the combined system to the system performance, soil temperature variation are discussed in this paper. A results discussion of a combined solar thermal and GSHP system for office heating under different operation strategies by simulation is presented firstly, and the real operation of the combined system for a building heating in Beijing, north of China, utilize solar thermal as an assistant system of HP unit is addressed then. Water temperature variation in water tank and the HP unit is plotted and discussed as well, finally, solar thermal energy directly storage into the ground, soil temperature variation in the autumn season is introduced at the end. A system simulation tool, TRNSYS, is used to model three different operation strategies of the combined system in winter season: solar thermal preheats return water in the condenser side, evaporator side of the HP unit and the combination of the two. The simulation results manifest the system would be more economically efficient if solar thermal preheats return water of condenser side of the HP unit, but the utilization of solar thermal would be maximized if it preheats the return water of the evaporator side of the HP unit. A real operation of a combined system in winter season in an office building is presented then, in which the operation data in typical days 2014/12/25 to 2014/12/26 are analysed. The data discovers that with the assistant of solar thermal, heat pump could work temporarily, with a COP of 5.2 is found in the day.

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