Effects of Expansion Devices on the Transient Response Characteristics of The Air-Source Heat Pump during the Reverse Cycle Defrost

摘要

The effects of the defrost expansion device on the transient performance of the air source heat pump during the reverse cycle defrost was investigated. A base case test was established using an average response thermal expansion valve in the experimental setup. The base case test was compared to tests using fast and slow response TXVs and different diameter orifices. The overall performance of each test was analyzed as well as a detailed investigation of the refrigerant dynamics. The results of the investigation for TXVs indicated bulb/suction line contact was more critical to the response of the TXV than the internal bulb charge. The orifice investigation showed a general trend of faster defrost times with larger orifices, although the largest orifices allowed liquid refrigerant to enter the compressor intake. The investigation also described the different refrigerant flow control of the TXV and the orifice. Theses. (mjm)