Analysis of the refrigerant-side temperature profiles in the coil of an air-to-water heat pump

Abstract

In this paper, we analyze the refrigerant side temperature profiles in the coil of an air-to-water heat pump. The heat pump unit uses R410A as refrigerant and it works following a flash tank vapor injection cycle (using a vapor-injected compressor). Its main components are a coil as the outdoor heat exchanger, a four-way reversing valve, electronic expansion valves, a plate heat exchanger as the indoor heat exchanger, and a variable speed compressor. The coil consists of 5 refrigerant circuits arranged one on top of the other. Each circuit is made up of 7 hairpins(14 tubes per circuit) and all have similar lengths. In order to estimate the refrigerant temperature profiles in the circuitry of the coil, 48 temperature sensors were attached on the refrigerant tubes of the coil. Experiments were performed at different compressor and air fan speed values with the heat pump unit working in the cooling mode of operation. Result ssuggest that refrigerant distribution is not uniform through each circuit and that some refrigerant accumulation occurs in the lower refrigerant circuits. This refrigerant maldistribution seems to be higher when decreasing the compressor speed, but it is not affected by the air fan speed.