Improved Battery Performance in Electric Vehicles via Reduced Glazing Thermal Conductivity 2011-01-1341

Reduced battery discharge rates in electric vehicles (EV) tend to extend single-cycle range as well as battery lifetime. Vehicle features that tend to reduce battery discharge rate thus support viability of EV. Of special interest are features that reduce the load on the heating, ventilation and air conditioning (HVAC) system since that system can in turn impose a significant load on EV batteries. A companion paper quantifies the effect on steady state nominal HVAC load of glazing (i.e. window) thermal conductivity using Computational Fluid Dynamics (CFD) to simulate heat transfer between the ambient and the air in a model car cabin when the cabin air is maintained at a comfortable temperature. For hot and cold climate, and for stationary and moving cars, reductions in HVAC load resulted from replacing a monolithic glass backlite and rooflite with polycarbonate (PC), the latter with a five-fold lower inherent thermal conductivity. This paper estimates percent increases in battery single-cycle discharge time, indicative of EV range, and battery lifetime due to these reductions in HVAC load afforded by the lower thermal conductivity of the PC backlite and rooflite. The focus on percent changes instead of absolute values facilitates an approach largely independent of specific battery and EV parameters. Estimated improvements in these measures of battery performance are 2 to 3% for moving cars without accounting for PC's lower mass density relative to glass, which would also tend to reduce battery discharge rate and further improve battery performance.