Study Of A Solar-Air Source Heat Pump System For Cold Regions

With the energy and environmental crisis, energy-saving and environmental protections are much more important. Renewable energy has become the subject of next energy strategy. More than 40% of total energy consumption is consumed by buildings. So, building energy efficiency is becoming the focus on energy reduction. Because of their advantages of high efficiency, energy-saving and environmental protection, air source heat pump (ASHP) and solar-assisted heat pump (SAHP) are being concerned. Especially, Multi-source heat pump which can use more than one kind of renewable energy becomes an attention and research hotspot.However, ASHP application is limited in the cold regions because of the low ourdoor temperature. Also, SAHP application is affected by low solar heat flux, solar intermittent and so on. To take full advantages of ASHP and SAHP and to make up their deficiency, we have developed a novel solar-air source heat pump (SASHP) for cold regionss. An ejector is adapted in the system, and the solar collector loop and air-source exchange loop which are accessed to the primary fluid inlet and the secondsry fluid inlet respectively are connected in parallel. The outlet of ejector is connected to the compressor suction port. The SASHP system can work in the following three operating modes:SAHP operating mode, ASHP operating mode and SASHP operating mode. The SASHP system can space heating, space cooling and water heating according to outdoor climate and the users'demands.Build the ejector mathematical model based on the gas dynamics and constant-pressure mixing principle, and then build the ejector outlet pressure prediction model. Also, a steady-state compressor model is built. An experimental setup is established to test the performance of the SASHP operating mode, in which its working fluid is R22. The solar collector loop and air-source exchange loop are simulated by using water-glycol bulk with electric heater. The test bench contains a heat pump system and a data-recorder system. Experimental results show that the compression ratio of the ejector is 1.18, the entrainment ratio is 0.63 and the heating COP of the heat pump is 1.83 while the solar side evaporating temperature is 20℃, the air-source side evaporating temperature is -20℃and condensing temperature is 40.5℃. Also, the off-design performance of the heat pump is presented. Compressor suction pressure is enhanced by making use of ejector to improve the adaptability of traditional air-source heat pump in cold regions. Additionally, there are some improvements according to the problems occurred in the experiment, such as the high discharge temperature of the compressor and the low entrainment ratio of the ejector.Lastly, analysis of exergy and thermal economics is presented. The results show that ejector's exergy loss is the biggest of the system components, followed by the compressor and condenser, which can provide theoretical basis for optimization. Analysis of economics show SASHP has characteristics of economic-saving, energy-saving and environmental protection.