A Study of Optimal Refrigerant Charge Amount Determination for Air-Conditioning Heat Pump System in Electric Vehicles

Kang Li,Jun Yu,Lin Su,Mingkang Liu,Dan Xu,Yidong Fang

doi:10.3390/en13030657

Abstract

With regard to concerns about an electric vehicle’s driving range extension in a cold climate, an air-conditioning heat pump (ACHP) shows considerable advantage over thermoelectric heaters for battery energy conservation. The effect of refrigerant charge amount for cooling and heating performance of the ACHP system is significant. The optimal charge, realizing the optimal system performance, is usually determined by experiments of cooling and heating performance. In this paper, the optimal charge determination process based on a newly designed ACHP applied in electric vehicles was introduced. Relationships of characteristics with charge in two modes were investigated by experimental and theoretical methods. Firstly, the performance of the ACHP system was respectively investigated at different charge amounts in cooling and heating operating conditions according to key parameters of system cycles. Secondly, the intersection platforms of subcooling and superheat variation curves with refrigerant charge amount were obtained for determining optimal charge amount of the system further by comprehensive analysis. Finally, the theoretical calculation of charge with three instructive and classical void friction correlation models were applied for better comparisons. It was found that charge amount calculated by the Hughmark model proved to be most consistent with the comprehensive experimental results.

Highlights

Given concerns about greenhouse gas emission reductions and renewable energy conservation, new energy vehicles driven by electric energy have been paid increasing attention due to the substitution of traditional petroleum energy in recent years [1,2,3]
After components are determined, cooling and heating performance of the system needs to be evaluated under off-design conditions, which is an important procedure of system optimization [3,4,5,6,7]
The HVAC module consists of two heat exchangers (HEX2 and HEX3) and one positive temperature coefficient (PTC) for heating air, which is used to adjust the functions of cooling and heating, and to achieve requirements of temperature and humidity control in the passenger compartment

Summary

Introduction

Given concerns about greenhouse gas emission reductions and renewable energy conservation, new energy vehicles driven by electric energy have been paid increasing attention due to the substitution of traditional petroleum energy in recent years [1,2,3]. Since the driving device of EVs cannot provide a heat source like the internal combustion engine, cabin heating in a cold climate occupies a considerable proportion of the electric energy consumption from a battery leading to drastically shortened driving range [4,5]. To meet this challenge, a vapor compression system with cooling and heating functions is required. Refrigerant charge in an ACHP system is an important factor in order to adapt to different working conditions and meet the requirements of cooling and heating capacity of the system

Methods

Results

Conclusion