Research On The Heating Performance Of A Single/double Stage Mixed Cascade Air-source Heat Pump

As we all know, air source heat pump application is limited in cold regions. In recent years, scholars have done a lot of research on the air-conditioning units in cold regions. The directions of these studies are as follows:a two-stage compression heat pump system, a quasi-two-stage compression heat pump system, a single and double stage coupled heat pump system, and a cascade heat pump system. This paper presents on a single/double stage mixed cascade air-source heat pump.The unit is mainly made up of a low temperature heat pump system, a high temperature heat pump system and a three-channel tube heat exchanger. It can achieve cascade circle by the three-channel tube heat exchanger. In the cooling case, the system runs by a single circle. In the heating case, the system runs by a single-stage circle at a higher outdoor temperature.While the outdoor temperature is low, the system runs by double-stage cascade circle.Firstly, the paper produces a computer simulation system of a single/double stage mixed cascade air-source heat pump, which is based on the VB language. The the program modules of simulation include a compressor, a condenser, a evaporator, a three-channel tube heat exchanger, a throttle valve, the fluid thermal properties. The structure sizes of the heat exchangers are parameters designed by the author. The simulation of heat exchanger uses the lumped parameter method of partition.Secondly, the simulation is doned for heating in a single-stage and a double-stage of the single/double stage mixed cascade air-source heat pump.And there is a comparison between the single-stage and the double-stage circle.The single-stage circle can not run below-10℃, but the two-stage circle is still run at-30℃which has some heating capacity. In the low temperature, the double-stage system is superior to the single-stage system in the exhaust temperature, pressure ratio, the heat quantity of transferring.Finally, based on the simulation, it is doned for the optimum of the switch temperature and the area of the three-channel tube heat exchanger, further for the performance comparison among several air-source heat pump for low temperature. It is concluded that the switch temperature between the single and double stage is 0℃in the condition that the COP is optimum. The three-channel tube heat exchanger of the most valuable length is 5m in the condition of optimal economic parameter of F. The single/double stage mix cascade heat pump is more reliable in safety, the heating performance is the best among these heat pump systems.