Search Results

Heat transfer between the ambient and the air in a vehicle cabin determines the nominal steady state load on the vehicle's heating, ventilation and air conditioning (HVAC) system, a significant factor for vehicle efficiency and greenhouse gas emissions. This paper highlights the effect of glazing (i.e. window) thermal conductivity on steady state heat transfer, with high and low thermal conductivities represented respectively by monolithic glass and standard polycarbonate. Computational fluid dynamics simulations are summarized for a model car cabin including HVAC vents, interior seating, and a rooflite. Passenger and moisture effects are not included. Monthly temperature and radiation data for Phoenix, Arizona and Minneapolis, Minnesota are used to define hot and cold climate scenarios.

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.

Previous papers by the present authors described use of computational fluid dynamics (CFD) to quantify the effect of glazing thermal conductivity on steady-state heating, ventilation and air-conditioning (HVAC) load under wide-ranging climate and state of motion scenarios, and to estimate the significance of this effect for electric battery performance. The CFD simulations yielded the total heat transfer between the ambient and the cabin of a model car, including radiative and convective heat transfer. The five-fold lower inherent thermal conductivity of polycarbonate relative to glass was found to reduce steady-state HVAC load by several percent in all scenarios, leading to reduced greenhouse gas emission or increased electric range, according to the type of vehicle.