Analysis of heat pump performance in battery electric buses

Abstract

Battery Electric Buses (BEB) driving range is one of the main challenges limiting their adoption at a massive scale. Heating and air conditioning of the bus cabin is an energy-intensive process that results in additional energy consumption from the sole onboard energy source. The limited capacity of the battery makes it crucial to quantify this load and study its impact on the bus range. Heat pumps (HP) are the main heating, ventilating and air conditioning technology deployed in electric buses due to their superior performance over electric resistance heaters. However, their performance witness major variations at different external temperatures and operating conditions such as air and refrigerant flow rates and compressor speed. This paper quantifies the thermal load in BEB and studies the HP performance at different weather and operating conditions. First, cabin thermal comfort conditions are set, and HP components technological constraints are presented. Then, a HP model is integrated into a BEB model to fulfill its thermal needs. Simulations are conducted at different external temperatures analyzing the HP performance. Moreover, this paper conducts a sensitivity analysis to study the effect of HP operating conditions on the Coefficient of Performance (COP) and energy consumption. The simulation shows that the compressor speed, the air recirculation rate and the mass flow rate of the air blown into the cabin have the most significant impact on the HP COP.