Reversely-variable circuitry for finned-tube heat exchanger in air source heat pump to enhance its overall energy performance

Abstract

The finned-tube heat exchanger (FTHX) is preferred to contain more circuits as an evaporator but fewer as a condenser, so as to obtain the desired performance in both heating and cooling operation of the air source heat pump (ASHP). However, the conventional FTHX has two-way fixed circuitry with the same refrigerant flowpath in the opposite direction. In this article, the reversely-variable circuitry is proposed for the FTHX to exhibit different flowpath in evaporator and condenser roles flexibly. The original 4-branch distributor in the outdoor FTHX of a nominal 3500-W ASHP is replaced with a 2-branch one and a 3-branch one successively to maintain 4 circuits as an evaporator. Two check valves, however, are added between the two distributors and inside the gas header to change the flowpath to two circuits merging into one as a condenser. Compared with the two-way fixed FTHX, the reversely-variable one yields 5.8% larger cooling capacity and 7.2% higher EER for the ASHP with similar heating performance under nominal conditions. Further simulation shows that fewer circuits of the reversely-variable FTHX increase the overall heat transfer coefficient as a condenser, dominating the increase in the capacity of the FTHX and the overall energy performance of the ASHP. This novel design provides new thoughts to the FTHXs and can be popularized to those with different circuits.