Heat pump is a device that can get low-grade heat from the air, water or soil in nature and work through electric power to output usable high-grade heat energy. Now our country mainly uses three kinds of heat pump technology, namely the water source heat pump, the geothermal heat pump, as well as the air source heat pump. Water source heat pump heat extracted from well water at 16 ℃, the working fluid by the power compressor work, you can reach the output hot water temperature 52 ℃, and its output heat input power ratio of 3.51, than the direct use of electric heating to save electricity 72%. This hot water can be used to heat the fan coil to the room. Summer, but also use the same device refrigeration, so that a machine with multiple uses, that is saving the initial investment, but also save operating costs. It is an ideal energy-saving system in the condition of underground water supply. However, in most urban areas, due to the restriction of water resources exploitation, it is very difficult to actually promote the project. Another type of heat pump is the air as a heat source, in theory, can not be resource constraints, in any area. Most of the heating and air conditioning is such a product, which heat is generated by direct hot air or hot water generated after 45 ℃ to achieve hot air. But air-source heat pump in cold climate, due to the evaporation temperature is low, the compressor inlet pressure decreases, the proportion of working fluid increases, so the resistance increases, the compressor intake will become smaller, if still require the same condensate as traditional units Temperature, it will lead to a large compression ratio, will make the compressor overheating, or even burn out, at least not stable operation. To this end, some domestic manufacturers in the outlet power-up heat, some in the water system return pipe plus heaters, some foreign oil, gas for the evaporator heat, or by means of frequency conversion in the cold weather to speed up the compressor operation , While spraying, etc., these practices either make the heat pump efficiency is very low, or make its structure more complex and cost increases, it should be said that these technical routes are not ideal.