Effect of the Number of Circuits on a Finned-Tube Heat Exchanger Performance and Its Improvement by a Reversely Variable Circuitry

Abstract

The finned-tube heat exchanger (FTHX) works better with more circuits as an evaporator but fewer as a condenser in air-source heat pumps (ASHPs). In this article, a reversely variable circuitry is proposed to address this contradiction. The effects of the circuit number on the performance of an outdoor FTHX in an ASHP prototype was first studied numerically using the EVAP-COND 4.0 software. We showed that the evaporator capacity reached its peak with four circuits, but the condenser capacity decreased monotonously as the circuit number increased. A reversely variable circuitry was obtained by combining distributors and check valves, so that the FTHX exhibited four circuits in the evaporator mode but one and a half (two circuits merging into one) in the condenser mode, thus better matching the respective requirements of the two modes. Comparative tests showed that in the ASHP, the reversely variable FTHX had a 6.1% higher cooling capacity than the four-circuit reversely fixed exchanger and a 3.9% higher heating capacity than the 1.5-circuit reversely fixed one. Therefore, the novel design of the FTHX enhanced both the heating and the cooling performance of the ASHP.