Application characteristics of variable refrigerant flow heat pump system with vapor injection in severe cold region

Variable refrigerant flow heat pump system is still restricted in use in severe cold region due to ultra-low outdoor temperature there. With the development of vapor injection technique, applying this technique to it is an effective method to promote its heating performance at low outdoor temperature. To promote the application of variable refrigerant flow heat pump system with vapor injection in severe cold region, a test rig was built in Harbin and used to supply heating for a lab. To prevent excessive discharge temperature at ultra-low outdoor temperature, a novel control strategy was proposed and used in the test rig. The application characteristics of the experimental unit were introduced firstly. Then its application potential was analyzed through comparing with quasi-two stage compression air-water heat pump. Results showed the experimental unit run smoothly in the whole test period, even when outdoor temperature dropped to −28.7 °C. Its heating effect was good at outdoor temperature of −22.5 to 7.5 °C. Besides, mal-defrost had more serious influence on heating capacity shortage than ultra-low outdoor temperature in severe cold region. In addition, comparing with quasi-two stage compression air-water heat pump, the experimental unit had advantage on heating capacity and discharge temperature.