Enhancing Heating Performance of Low-Temperature Air Source Heat Pumps Using Compressor Casing Thermal Storage

Zhongbao Liu,Fengfei Lou,Yiyao Shen,Xin Qi

doi:10.3390/en13123269

Abstract

Air source heat pumps (ASHPs) are widely recognized as energy-saving and environmentally friendly heating and air-conditioning equipment with broad applications. However, when conventional ASHPs are operated at a low ambient temperature, they suffer from problems such as high discharge temperature and low heating efficiency. To address these problems, this study designed a new type of dual evaporator combined with a compressor casing thermal storage heat pump system (DE-CCTS) on the basis of a low-temperature air source heat pump water heater with enhanced vapor injection (EVI). The proposed DE-CCTS used thermal storage phase change material (PCM), which was filled in the secondary evaporator (the thermal storage heat exchanger), to recover the waste heat of the compressor casing. Unlike that in the original system under different ambient temperatures, the suction temperature increased by 0.1–1 °C, the discharge temperature decreased by 0.1–0.5 °C, and the coefficient of performance (COP) of DE-CCTS increased by 0.85–4.72% under the proposed system. These effects were especially evident at low temperatures.

Highlights

With the development of the global economy, energy shortage and environmental pollution have become major global problems
The type and mass of thermal storage phase change material (PCM) are the key issues explored in this study
Under the premise that the compressor is maximally insulated and the remaining volume outside the compressor is all occupied by the insulation cotton, the average temperature of the compressor casing is 58 ◦ C when the compressor is continuously operated at low temperatures for multiple cycles

Summary

Introduction

With the development of the global economy, energy shortage and environmental pollution have become major global problems. When ASHPs are used in extreme temperatures, they suffer from problems such as low heating efficiency and excessively high compressor discharge temperature [1,2,3]. Researchers have proposed many solutions to these problems, such as the addition of auxiliary heating systems, the use of two-stage or multistage compression cycles, and the use of enhanced vapor injection (EVI). Wang [6] reported that rotary compressors encounter severe performance degradation at low ambient temperatures, and thereby introduced a rotary compressor prototype with a novel end-plate injection structure. Compared with a single-stage rotary compressor, the proposed rotary compressor with a novel end-plate injection structure enhanced the heating capacity and coefficient of performance (COP) by 16.2–31.6% and 5.1–12.0%, respectively. Chen [7] proposed a new direct-expansion

Methods

Results

Conclusion