Coupled analysis of windshield defogging and thermal management system operation in electric vehicles under high-humidity conditions

Windshield defogging is a safety-related humidity-control requirement for electric vehicles (EVs), in which the thermal management system must recover visibility. However, the quantitative effects of supply air temperature and dew point on windshield defogging have not been sufficiently clarified, making it difficult to determine the appropriate supply air state for thermal management operating modes. To address this issue, this study developed a coupled evaluation framework combining a three-dimensional CFD cabin model and a GT-SUITE EV CO 2 thermal management model. Preliminary CFD simulations were first conducted to decouple the effects of supply air temperature, humidity ratio, relative humidity and air mass flow rate on windshield defogging. Then, the transient supply air temperature, dew point and mass flow rate under direct heating and dehumidification-reheating modes were imposed on the CFD model as dynamic boundary conditions. The A-zone and B-zone defogged area ratios, 80% and 90% defogging times, compressor specific energy consumption and dew point safety margin were used for evaluation. Results showed that direct heating reduced the relative humidity but kept the supply air dew point nearly unchanged. Increasing the target supply air temperature from 25 to 45 °C shortened the A-zone 90% defogging time from 311 to 159 s. in the dehumidification-reheating mode, lowering the supply air dew point further improved defogging, reducing the A-zone 90% defogging time to 113–77 s for D9 and 86–71 s for D6. Compared with the direct heating reference M1-T45, D6-T35 reduced both defogging time and compressor specific energy consumption from 159 s and 84.2 Wh/m 2 to 86 s and 64.7 Wh/m 2 . These results provide a reference for selecting energy efficient defogging oriented thermal management operating modes in EVs