Dynamic modelling and performance prediction of a recovery fresh air heat pump for a generic bus

Air circulation inside the buses’ cabin seems to negatively affect the spread of contagious diseases, such as the COVID-19 virus and raises valid health concerns over using public transportations. Employing all-fresh air and avoiding to recirculate it could help with lowering the exposure time and the virus density in buses; however, it makes the heating more challenging, especially in Electric buses. Here a Baseline and a proposed Recovery Heat Pump (BHP and RHP, respectively) systems in a generic single decker bus were modeled to investigate their dynamic performance and the cabin’s conditions using 100% fresh air. Simulink and Simscape toolbox from MATLAB (R2020a) were used to build up the real-time model by integrating an HP system with a cabin sub-model. The cabin is modeled using a moisture air network and is coupled with the HP to exchange heat with the refrigerant through the condenser. For both cases, 100% fresh air flows through the condenser into the cabin. In BHP the evaporator is exposed to 100% cold fresh air, while in RHP the warm air from the cabin passes through the evaporator before being vented outside. Both cases were studied for different ventilation modes in low and medium occupancy levels. Results indicate that RHP shows superior performance compared with BHP. Under the studied operational conditions, RHP reduced the power requirement, warm-up time, and operation time by 36%-6% (at most-at least), 57%-7%, and 39%-13%, respectively.