Advanced thermal management of hybrid electric vehicles in cold climates using heat pump and waste heat recovery

Hybrid electric vehicles (HEVs) tend to experience degraded fuel economy in cold climates, primarily because the engine is frequently used to provide heat to cabins, even when it is not essential for driving. To address this issue, this paper proposed an advanced thermal management system that integrates a heat pump capable of operating during cabin heating by utilizing engine waste heat. The system was designed to deliver sufficient heat to the engine coolant, thereby reducing unnecessary engine operation. The fuel economy was evaluated under various ambient temperatures and heat pump operating conditions using the federal test procedure −75 driving cycle. Consequently, employing a heat pump for cabin heating reduced the operating time of the engine by approximately 10.1 %, which appeared to have contributed to a 9.7 % gain in fuel economy. In addition, supplying more heat to the coolant than that required for cabin heating led to further improvements. The degree of improvement varied depending on the ambient temperature, with a maximum fuel economy improvement of 13.4 % observed at 0 °C. These findings demonstrated that the proposed heat pump is effective in improving the cold-climate fuel economy of HEVs by minimizing engine usage through an efficient thermal management system.