Investigation of the integrated fuel cell, battery, and heat pump energy systems

Abstract

The integration of an advanced fuel cell battery electric vehicle was proposed to extend the driving range, increase the overall energy efficiency, and produce an additional cabin space heating service for on-board vehicle application in winter. The adopted heat pump absorbs heat from the fuel cell and battery during charging and discharging scenarios at the heat pump's cold end and transfers it to the cabin supply air for cabin heating. A numerical model for the proposed system was developed and validated by published experimental results. A comprehensive evaluation of the influence of fuel cell output current, battery discharging rate, ambient air temperature, evaporator coolant inlet temperature and refrigerant subcooling degree on the Coefficient of Performance (COP), outlet air temperature, and Equivalent Effective Battery Capacity (EEBC) were conducted. In addition, in this study, a detailed comparison of proposed system to previously published existing systems was carried out in terms of COP, heating capacity, EEBC, and operating price in order to examine the advantages of the proposed system. Results showed that the proposed system was not sensitive to ambient air temperature, but evaporator coolant inlet temperature had the greatest impact on COP, compared to other defined independent variables. A maximum COP of 6.07 could be observed when the evaporator coolant inlet temperature was 32 °C. Although increasing fuel cell output current and battery discharging rate could increase heating capacity, it would decrease outlet air temperature as well. The price of a single charging cycle for running for a 4-hour period was estimated. Compared to conventional Electric Vehicle Air Source Heat Pump (EVASHP) system and Positive Temperature Coefficient (PTC) heaters, the proposed system has the lowest cost which was £10.40per charging cycle while the others are £13.8 and £19.2 respectively when providing the same EEBC and heating capacity. Additionally, the payback period was 10,500 charging cycles. Overall, this study provides a potential solution for efficient cabin heating of electric vehicles in extremely cold weather with twice the EEBC of the existing EVASHP system and with 2.8 times of a PTC system both at −20 °C and the operating price is also 1/3 lower than the existing EVASHP. Meanwhile, the COP of the proposed system is 2.3 times that of the existing systems. It can sufficiently increase the driving range of electrical vehicles in winter and eliminate driving range anxiety.