Research On Characteristics Of A Solar-air Source Heat Pump System

With the energy shortage and ecological problems become increasingly prominent,people gradually focus on the use and development of renewable energy.Solar energy had catched people’s attention for its clean,pollution-free,no need to transport,lower cost and security,etc.An integrated thermal energy system based on solar energy and air source was studied in this paper.The combination of direct-expansion solar heat pump and air-source heat pump,has solved the defects that solar heat pump can not work properly in rainy days and night,and achieved the functions of refrigeration,heating and production of hot water.Not only that,the efficiency has been ensured at the same time.A systematic study on the key issues in the operation mode of heating,hot water and hot and cold is conducted adopting the approaches consisting of theoretical analysis and experimental research.Firstly,a high-performance flat-panel solar collector/evaporator is developed combining with the current processing technology.The use of high-absorption coating aluminum plate for the heat-absorbing plate,the back of rolling semi-circular groove,and the aluminum tube type welding is used to fix the collector copper tube so that the circumference of the collector tube is in close contact with the heat absorbing plate,which reduces the contact resistance and improves the heat transfer performance of the collector plate and the tube.A test bed for solar-air source heat pump system is built,and environmentally friendly refrigerant R417A was used in the experiment.Secondly,in order to explore the main influencing factors and overall performance of the composite heat pump system,the related mathematical models of the four main components were established,for the solar collector/condenser,condenser,electronic expansion valve and compressor of the composite system.A simulation program of solar air source composite heat pump system was compiled.Through the simulation and experiment,the influence of the three main influencing factors of solar radiation intensity,ambient temperature and inlet temperature on the performance of the system was analyzed.When the environment temperature is 10℃,the temperature difference between the heat absorbing plate and the glass cover becomes larger as the solar radiation intensity increases,indicating that the glass cover can effectively reduce the heat loss of the collector plate when the solar radiation intensity is large in winter.When the solar radiation intensity increase and the other factors stay constant,the heating capacity of the system goes up,while collector efficiency goes down.Based on the simulation results,the biggest decline of the collector efficiency arise when the solar radiation intensity increases from 300W/m2 to 500 W/m2.Most affected by the circulating water temperature is the compressor power consumption,the increase of circulating water temperature raise the compressor suction-exhaust pressure ratio which leading to the compressor power consumption increase quickly,while the COP decrease.The rest of the performance will also be affected by the circulating water temperature,but relatively small.Finally,in order to make a comprehensive evaluation of the multi-mode system performance,the experimental test standards are set according to the corresponding national standard,and a series of experimental tests about the multi-mode performance of the composite heat pump in different weather conditions have been conducted.Under the summer hot and cold water supply conditions,maintaining air-conditioning water inlet water temperature of 12℃,the outlet water temperature of 7℃,when heating the living hot water in the storage tank from 15℃ to 55℃,the system EER gradually declined from 9.4 to 4.0,with an average EER of 6.2.At the same time,experimental situation of using two plate heat exchangers as the condenser is also analyzed.The results show that the heat of living water decreases gradually after the water temperature exceeds 20℃ in the case of air temperature is 20℃,and is reduced to 0 when air temperature is 43℃,indicating that heating in the production of hot water is ineffective,which need to be improved.Through abundant experimental situation and detailed experimental data,this paper provides support for the research and popularization of the solar-air source heat pump system.