Theory And Experimental Study On High Efficient Cascade Air-Source Pump Of High Section Under Low Temperature Conditions

The smoke and waste produced by the winter coal-fired heating in china is one of the main source of fog and haze. It is an urgent need for a clean and energy-saving heating method. Air-source heat pump, as a heating source of renewable energy, has been widely used in Yangtze river basin in china. But there are some shortages of air source heat pump in low environment temperature, such as high suction specific volume, low suction pressure, high compression ratio, high discharge temperature and so on.In order to make the air-source heat pump system operate efficiency in low temperature, we proposed using cascade air-source heat pump system. Based on the research of the domestic and foreign scholars in this area, cascade heat pump system is put forward to solve the problem of high temperature and high efficiency in low environment temperature. We are aiming to broaden the temperature range of the air-source heat pump application and improve the temperature of heating water. The high temperature and high efficiency heat pump can replace boiler partially and realize energy saving and emission reduction.In this paper, we analyzed the theoretical cycle of the cascade heat pump system and established a mathematical model for the system. According to the principle of refrigerant selection and the comparison of the physical property, R134 a and R507 were selected as the most suitable refrigerant for the cascade heat pump system at design point. In this paper, an theory analysis on the operating performance of the cascade heat pump was carried out. We can get the compression ratio, heating capacity, power consumption of compressor and COP change with the evaporation temperature and condensation temperature. The change rule lays the foundation for the design of cascade air-source heat pump experimental table. According to the results of theory analysis, we designed and built the experimental table. We test the performance of the experimental table at the range of 0 to 10 of environment temperature and the range of 65 to 78 ? ? ? ?of heating water temperature. We analyzed the experimental results and variation of the performance parameters of the experimental table.The experimental results show that: The evaporation temperature, the heat transfer temperature and the power consumption increased with the raise of condensation temperature and heating water temperature. With the decrease of the evaporation temperature, the COP and the heating water temperature will reduced. The discharge temperature will increase with the increase of the evaporation temperature and will raise with the increase of the heating water temperature. In the range of the experimental conditions, the maximum COP of the system close to 3. In the same environment temperature and heating water temperature, the heat pump system has obvious heat economy.