Influence of Refrigerant Charge Amount and EEV Opening on the Performance of a Transcritical CO2 Heat Pump Water Heater

Ze Zhang,Zheng Ren,Yu Hou,Xiaojun Dong,Tianwei Lai

doi:10.3390/en10101521

Abstract

Besides compressor rotary speed and parameters of water flowing through gas cooler and evaporator, refrigerant charge amount and electronic expansion valve (EEV) opening are two important parameters that have significant effects on the performance of a transcritical CO2 heat pump system. In this study, the effects of refrigerant charge amount on the performance of a transcritical CO2 heat pump water heater were investigated experimentally at different EEV openings. An optimal coefficient of performance (COP) was found that corresponded to a specific refrigerant charge and a specific EEV opening. Based on the experiment, the COP peaked at charge of 1.8 kg when EEV opening was 40% of full opening. The heating capacity and the COP increased at first, reached peaks and then decreased with increase of charge amount. The COP decreased 14.95% as the CO2 charge amount was reduced by 22.2% from the optimal charge at 50% EEV opening. As EEV opening varied from 40% to 60% at the same charge amount, the heating capacity decreased more than 30%.

Highlights

Since chlorofluorocarbon (CFC) and hydro-chlorofluorocarbons (HCFC) were restricted because of the environmental issues, researchers are working on feasible and effective alternative refrigerants.Substantially, carbon dioxide (CO2, R744) is one of the representatives [1,2]
CO2 transcritical refrigeration technology is wildly applied in vehicles [4], water heaters [5,6], heat pumps [6,7] and low temperature cascade refrigeration systems [8], and so on
The results show that the capillary tube system has lower coefficient of performance (COP) than that of the electronic expansion valve (EEV) system at the same operating conditions

Summary

Introduction

Carbon dioxide (CO2 , R744) is one of the representatives [1,2]. Owing to some properties such as zero ozone depletion potential (ODP), negligible global warming potential (GWP), excellent heat transfer properties, high volumetric capacity and cheap price, carbon dioxide has been widely acknowledged as the most competitive alternative refrigerant. In 1993, a CO2 transcritical refrigeration system in automotive air conditioning was built and tested [3]. CO2 transcritical refrigeration technology is wildly applied in vehicles [4], water heaters [5,6], heat pumps [6,7] and low temperature cascade refrigeration systems [8], and so on. The coefficient of performance (COP) of a heat pump system is affected by many factors

Methods

Results

Conclusion