Performance Of Solar-Ground Double Heat Sources Compound Heat Pump System

With its high efficiency, energy saving and environmental protection technical characteristics, the heat pump technology is one of widely used way in building heating, air conditioning. However, the single source heat pumps exist their respective prominent problems in the actual application. Such as air source heat pump, outdoor heat exchanger existing frosted, defrost problem in winter, solar energy heat pump existing intermittent and instability issues, ground source heat pump existing water greatly, pump power high in using the groundwater system and existing larger buried pipes area, larger initial investment in using soil buried tube system, these problems restrict their further development and application. At present, the compound heat source heat pump technology has become one of HVAC industry research and development trends combining a single source heat pump system characteristics.Aiming at the defects of single source heat pumps, considering widespread the solar energy and shallow geothermal energy resource and mutually making up deficiencies as heat pump source, this paper puts forward a new kind of Solar-Ground Double Heat Source Compound Heat Pump System aiming at the northern climatic characteristics. Through the self-developed design shell-casing pipe three medium compound heat exchanger, it realizes two kinds of renewable energy (solar energy and shallow geothermal energy) synchronous or alternate utilization, and improves year-round operation reliability, stability and economy of heat pump system.In this paper, work principle, working mode, the compound characteristics and other key issues of SGCHP are first analysed. On this basis, the experiment platform of SGCHP is designed and constructed. The heating performance of different work modes including the single ground-source, the single solar-source and the effective compound working mode is tested in various experimental conditions. The system performance is obtained and operation strategy is put forward in various work modes.Experimental results showed that with the decrease of geothermal energy water flow in shell side and the increase of solar water flow and temperature in inner tube side, the heating capacity and COP of heat pump in the double heat sources effective compound heating work mode are greater than under the rated conditions in the single ground-source work mode. Therefore, this SGCHP reduces the groundwater circulation and improves the heating capacity and operating efficiency of system through the solar energy heat source effectively complement.According to the experimental results, the reasonable operation strategy is put forward in different working conditions. When the heat storage tank temperature is above 20℃, the single solar-source mode is adopted; When the heat storage tank temperature is between 15 to 20℃, the double heat sources mode is adopted; When the heat storage tank temperature is below 15℃, the single ground-source mode is adopted.