A numerical evaluation of a novel recovery fresh air heat pump concept for a generic electric bus

Abstract

Since the outbreak of the worldwide COVID-19 pandemic, public transportation networks have faced unprecedented challenges and have looked for practical solutions to address the safety concerns. In the wintertime, when natural ventilation is not an option, implementing an all-fresh air heating policy could be a viable solution to lower the transmission of such infectious disease, by reducing the density of pathogens and exposure time. Even though this will expectedly increase the energy demand, it is particularly crucial when the people safety is the first priority to operate any public transportation systems. To tackle the transmission issue, in this paper two concepts of an all-fresh-air Heat Pump (HP), namely a Baseline (BHP) and a novel Recovery (RHP) concepts were investigated. These two HP’s concepts could provide better ventilation inside the bus, compared to a Conventional (CHP) concept where the cabin air is re-circulated. To address the energy consumption concerns, the RHP concept is proposed to improve the performance of the system by recovering part of the cabin waste heat, without using any additional heat exchangers. Three different coupled models of a generic single-deck cabin and a heat pump system for each concept were developed in the Simscape environment of MATLAB (R2020b). The performance of these HPs was investigated to evaluate how an all-fresh air policy could affect the performance of the system in the BHP, and the energy-saving potential of the RHP concepts. The performance of the system was studied under different ambient temperatures ranging from -5 to 5 °C, and for low and moderate occupancy levels. Results show that employing the RHP and BHP significantly improved the ventilation rate per person by at least 102% and at most 125%, compared to a CHP concept with 50% of re-circulated air. Moreover, adopting the RHP concept also reduced the power demand by at least 8% and at most 11%, compared to the BHP for the selected fan and blower flow rates.