In order to improve many disadvantages that the heat pump system has when it uses the reverse-cycle defrosting method in the low temperature environment

a new air-water double source composite heat pump system (AWDSHPS-N) was presented. This system has a new preheating and defrosting function. AWDSHPS-N has defrosted for 5 min and has 5 different defrosting ways

such as the condenser outlet refrigerant recooling defrosting

the low temperature-hot water defrosting

and so on. It can be put into different modes by changing some relevant valves or starting and stopping the pump of the low temperature water. In this way

the heat output power of AWDSHPS-N may be reduced dramatically

but the system can produce heating continuously. A test-bed including constant temperature and humidity environment storehouse and a low temperature water tank were set up to get operating data for coefficient of performance (COP) of AWDSHPS-N. The environment storehouse imitates the change in outdoor environment by keeping the temperature and the humidity at a certain level constantly

and the low temperature water tank with two electric heating bars can be thought as a low temperature heating source of a solar energy system or a waste heat system. By heating the water from 18℃ to 51℃

the COP of AWDSHPS-N was tested and analyzed in air source heating mode (ASHM)

water source heating mode (ASHM)

water source heating mode (WSHM) and air-water double source heating mode (AWSHM)

respectively. By calculating

the COP of AWSHM is 6.1%-20.5% higher than ASHM. When the ambient temperature and the low temperature water are both above 15℃

the COP of AWSHM is the best one

and the COP of WSHM is the last one among these three heating modes.