Air source heat pump is widely used

and a capacity modulation with concentration of mixture refrigerant is a new type modulation of environment protection and energy conservation. In this paper

the state of the art of existing variable concentration devices with mixture refrigerant is presented and their types are described according to their locations in the system. The analysis results indicate that the variable concentration device should be set at the outlet of liquid refrigerant in order to change concentration of mixture refrigerant in air source heat pump. Moreover

a rectification section is more effective to change concentration than a gasliquid separator or liquid reservoir

and the middle throttling apparatus should be an electronic regulation device other than a capillary tube. The improvement and application of variable concentration devices in air source heat pumps are also discussed.