Heating performance of a coolant-source heat pump using waste heat from stack and electric devices in fuel cell electric vehicles under cold conditions

An efficient heating system for the cabin of fuel cell electric vehicles (FCEVs) is required to minimize the reduction in the driving range. However, studies regarding heat pumps that use waste heat from fuel cell stack and electric devices in FCEVs are limited. In this study, the heating performance of a coolant-source heat pump using waste heat in FCEVs is investigated by varying the inlet air temperature, compressor speed, coolant temperature, and coolant volumetric flow rate. A novel triple-fluid heat exchanger is introduced to recover waste heat from the fuel cell stack and electric devices at different temperatures. The heating performance of the coolant-source heat pump depends significantly on the compressor speed, and the heating capacity is inversely proportional to the COP. The effects of the coolant temperature are also investigated in the stack, electric device, and hybrid coolant modes. The stack coolant mode exhibits a relatively higher heating capacity than the electric device coolant mode owing to the higher refrigerant flow rate resulting from the increased evaporating pressure. The heating performance of the coolant-source heat pumps using the electric device coolant and the stack coolant shows different characteristics owing to the different temperature levels of the coolants. In conclusion, using the coolant-source heat pump improves the driving range of FCEVs by 10.8% compared with using the conventional electric heater under cold ambient conditions.