Numerical Analysis of a Recovery Air Conditioning Concept for Electric Buses

Amid the COVID-19 pandemic, the operators of mass transit systems have to take appropriate precautions to address the safety concerns. In this regard, using 100% fresh air and avoiding air recirculation could help to reduce the exposure time and virus density in public transportation systems; however, it makes cooling more challenging, especially in electric buses. In this study, two all-fresh air conditioning (AC) systems were modeled on a generic bus: a baseline (BAC) concept and a recovery air conditioning (RAC) concept. To evaluate the system performance and cabin conditions, these concepts were compared to a Conventional AC (CAC) system with 50% air recirculation. In both BAC and RAC cases, 100% fresh air flows through the evaporator into the cabin. In the BAC, the condenser of the AC unit is exposed to 100% hot ambient air, while in the RAC the cool air from the cabin passes through the condenser before being vented outside. Simulink and Simscape toolbox from MATLAB (R2020a) were used to build up a coupled model by integrating an AC system with a cabin sub-model for each concept. Results showed that both the RAC and BAC concepts improved the ventilation rate by approximately 105%, compared to the CAC. Because of this excess fresh air, as well as the lack of air recirculation within the cabin, air quality is expected to be improved, and this is especially important during the current COVID-19 pandemic. Moreover, results indicated that when an all-fresh air policy was adopted, the RAC showed superior performance and decreased the power demand by 11%, compared to the BAC system.