EXPERIMENTAL STUDY ON A NOVEL DEFROST CYCLE FOR AIR SOURCE HEAT PUMP

Abstract

On the basis of the hot-gas bypass defrost cycle, a new defrost method for air source heat pump is proposed. In the new defrost cycle, the outdoor heat exchanger is divided into two parts which are connected by a capillary tube. The front and rear parts of the heat exchanger are used as the evaporator and condenser respectively during defrosting, and can be defrosted orderly by using the four-way valve. The defrosting performance of the new cycle is investigated experimentally and the results are compared with that of the reverse-cycle defrost system. The experimental results indicate that the energy is used more efficiently in the new defrost cycle, therefore, the defrosting duration and losses are less than those of the reverse-cycle defrost system. Moreover, it does not extract heat from the indoor space during defrosting in terms of the new defrost cycle. Compared with the reverse-cycle defrost system, it is found that the switching times of the four-way valve in the new defrost system are the same, and the fluctuation of the discharge and suction pressures during the defrosting is much less than that in the reverse-cycle defrosting, hence, the mechanical impact on the system is much less.