Waste Heat Recovery from Cabin Exhaust Air by Use of Heat Pump

Reducing the energy consumption required for heating ventilation and air conditioning for passenger compartment is one of the key challenge for the thermal management system of electric vehicles to extend the driving range. Particularly at low ambient temperature the power demand for cabin heating increases and drains the battery capacity at the cost of the driving range. Due to the high air exchange rate of the vehicle cabin to the environment, a large share of the heated air is released unused into the environment via the rear exhaust vent as warm exhaust air. Consequently, the heat contained in the cabin air remains unused. A new approach considered in this study is to use the thermal energy in the cabin air as a heat source for a heat pump system to reduce the heating power required to heat the fresh intake air from the ambient. In vehicles with rear air-conditioning systems, the basic components, evaporator and fan, are already present. In this study, the potential of waste heat recovery from cabin exhaust air is demonstrated with the help of simulation and evaluated for various boundary conditions. Limiting effects on the performance are identified and critically discussed.