Achievement of Superior Cabin Comfort and Maximising Energy Efficiency Using EXV in BEVs

Abstract

<div class="section abstract"><div class="htmlview paragraph">The global and Indian automotive industry is transitioning from use of Internal Combustion Engine (ICE) vehicles towards Battery Electric Vehicles (BEVs). BEV applications with high voltage (HV) battery require optimal thermal management to have a longer life, higher efficiency and to deliver superior year-round performance. In most electric vehicles, the Heating Ventilation and Air Conditioning (HVAC) system operates thru a dual loop; one loop for maintaining desired cabin comfort and a second loop to ensure optimum cell temperature for HV battery operation at varying climatic conditions, which the vehicle experiences over different seasons of the year</div><div class="htmlview paragraph">This paper evaluates the limitations of a baseline system, in which the HVAC system consists of two parallel low-pressure cooling lines, one for maintaining cabin comfort and another for the purpose of battery cooling. The activation/deactivation of refrigerant flow in each cooling line is controlled through two independent Solenoid Operated Thermostatic Expansion Valves (SO-TxV). With the existing SO-TxV configuration, it is challenging to precisely balance the refrigerant flow between the two cooling lines for meeting the combined objectives of superior cabin comfort and optimum cell temperature, during dual operation. To mitigate the issue of unbalanced refrigerant flow distribution, Electronic Expansion Valve (ExV) is a viable option, as it performs the intended function of throttling the refrigerant with added benefit of precise control of refrigerant flow, arising from battery cooling demand</div><div class="htmlview paragraph">The experimental evaluation of ExV is initially performed on a system bench wherein, multiple DoE’s have been conducted to finalize an optimum opening level in the ExV, where the rise in breath level temperature can be minimized (therefore lesser discomfort) during dual operation. Further, trials were conducted at the vehicle level with optimal opening signature finalized on bench and it is observed that breath level temperatures reduce by ~2.3°C leading to enhanced passenger comfort. The suction pressure is also reduced by ~0.4-0.8 bar leading to the added benefit of energy saving. With use of ExV and optimized compressor operating strategy ~8-12% of energy saving is achieved without any compromise in cabin comfort during dual operation. The case study in this paper and results obtained hereof reinforce the multiple benefits of using an EXV in place of SO-TxV in the battery cooling loop, for superior cabin comfort and maximizing of energy efficiency.</div></div>