Air to water heat pump is a kind of energy-saving device which can make the heat flow from low heat source air to high heat source by using high heat source. Air to water heat pump system has no cooling water system, no cooling water consumption, no cooling water system power consumption. In addition, many cases of Legionella infection caused by cooling water pollution have been reported. From the perspective of safety and health, air source heat pump has obvious advantages. There is no need for boiler, air source and dust removal system due to its safety.