Heat pump air conditioning is based on ordinary air conditioning, and a four-way reversing valve is added. By changing the operation of the valve, the functions of the evaporator and condenser of the original air conditioner can be exchanged, thus changing the function of cooling indoor air into the function of heating indoor air. We use this kind of air conditioner which can extract heat from outdoor low altitude to heat indoor air in winter and take away heat from indoor air in summer. It is called heat pump air conditioning.

The classification of air source heat pump units can be divided into totally enclosed and semi-enclosed piston compressors, scroll compressor, semi-enclosed screw compressors, etc. According to the size of huxing capacity: there are villa-type small huxing and medium-sized large huxing; According to the unit structure: there are integral units and modular units; According to functions: ordinary heat pump unit, heat recovery unit, cold storage and heat storage unit.

From the common sense of life, we can know that hot water can slowly release heat into the air and cool it into cold water, which shows that heat can be transferred from a high-temperature object to a low-temperature object-air. So can we reverse this process and transfer the energy from the air with lower temperature to the cold water? According to the second law of thermodynamics, heat will not be automatically transferred from a low-temperature object to a high-temperature object. That is, heat can be spontaneously transferred from a high-temperature object to a low-temperature object, but not from a low-temperature object to a high-temperature object. But this does not mean that heat cannot be transferred from a low-temperature object to a high-temperature object. As we all know, heat always transfers from high temperature to low temperature and flows from high to low like water. A device that can lift water from a low place to a high place is called a pump. In the same way, the equipment that raises heat from low temperature to high temperature is called "heat pump". Heat pump consumes a certain amount of mechanical energy, and the equipment that "pumps" the low-temperature heat energy in the air to a high-temperature level to supply the heat demand is called "air source heat pump".

Air-cooled heat pump is a kind of air-conditioning unit different from air-cooled chiller in air-conditioning industry. The air-cooled heat pump unit not only has the function of cooling water by air-cooled chillers, but also can be switched to heating mode to make hot water. The basic principle of air-cooled heat pump is based on the compression refrigeration cycle, with refrigerant as the carrier, absorbing heat from the atmosphere or discharging heat through forced heat exchange of fans to meet the needs of refrigeration or heating.