Recently, air-source heat pump systems have been brought into the national limelight from a stand point of saving energy and utilizing equipments effectively. However, there are some problems in usual heat pump systems, e. g., 1) the mechanism is complicated, 2) they periodically need defrosting to prevent the efficiency from going down due to frosting on the outdoor coil .during heating operation, 3) liquid floodback to the compressor takes place in heating operation under low ambient temperature, etc.

Some papers have dealt with the frost formation characteristics and their defrosting problems. Several researchers tried to grasp the ambient t..emperature and humidity region for frostingt and attempted to get rid of the defrosting operation. However, there did not seem to be any airsource heat pump systems which successfully prevented frost formation .and removed defrosting operation without using external heat source.

We proposed a new heat pump system to solve the problems accompanied by traditional airsource heat pump systems as mentioned above, and studied its performance experimentally. In this paper, the results of experimental study of the new system are given.