HVAC system operation, consumption and compressor size optimization in urban buses of Mediterranean cities

Abstract

Electric buses are a key element in the transition to sustainable urban mobility. The HVAC system is the primary auxiliary load and significantly affects the efficiency and the driving range. In this work, advanced dynamic models have been developed to simulate accurately and optimize the urban bus energy consumption under real operating and extreme conditions, with a particular emphasis on HVAC systems. This study integrates a 3D city model, a weighted stochastic driving cycle, a climate model, a transient thermal model coupled with a physical HVAC system model using IMST-ART and a battery model. Different bus lines and urban typologies have been analyzed in the city of València. The results indicate that the overall consumption is similar across the different bus lines, around 2.10 kWh/km. The HVAC is the second largest contributor, after the powertrain, and can reduce the driving range by 15%–20% on mild and hot summer days, respectively. Finally, the size of the compressor has been optimized, revealing that a scale factor of 75% is more convenient, since the energy consumption can be reduced by 3% with lower costs in the compressor.