Heat pump technology has been rapidly developed recently as a clean and efficient heating method. Continuous capacity modulation of heat pumps is necessary for enhancing room thermal comfort and reducing start-stop losses. A novel capacity modulation method for the scroll compressor heat pump system based on refrigerant injection and refrigerant release is proposed. The experiments indicate the refrigerant injection increases the heating/cooling capacity by 21.9%/21.4% and enhances the heating COP/cooling EER by 5.6%/9.0% when the glycol inlet temperature of condenser and evaporator is fixed at 40 °C and 0°C, respectively. The tests also show the refrigerant release decreases the heating/cooling capacity by 26.6%/31.4% and enhances the heating COP/cooling EER by 16.0%/8.4% when the condensing and evaporating temperature fix at 40°C and 1.7°C, respectively. To sum up, the technology combining refrigerant injection and refrigerant release is a remarkable capacity modulation method for heat pump systems with scroll compressors, which can modulate the capacity continuously within a wide range as well as increase its energy efficiency ratio.
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