One of the most fundamental parameters for designing an automotive HVAC system is the thermal load, also known as cooling load. The major contributors to the thermal load inside the cabin of an automobile are solar loads, occupant loads, infiltration loads and loads due to various electrical fittings and the engine. Simple but accurate predictions of the thermal load inside the cabin will help engineers in designing and developing an efficient mobile air conditioning system.
While commercial software are available for simulating these loads, such tools require tedious and time-consuming modeling of components involving many parameters as well as multiple iterations. A simple method for computation of the vehicle thermal load that requires a minimum of input parameters will be useful in situations where a full-scale analysis is not required.
A computer model has been prepared for this purpose at Mahindra & Mahindra. The model calculates total thermal load by considering four major sources of heat: solar radiation, air leakage, electrical fittings and the occupants.
For the solar load, the location and time specific solar irradiance (both direct and diffuse) and the angle of incidence with different panels are considered. The heat transfer coefficients are calculated for all panels considering boundary layer conditions.
The model's accuracy is verified with test results from wind tunnel tests.