Computerised simulation of automotive air conditioning system

Abstract

This study developed a mathematical model for simulating the thermal and energy performance of an automotive air conditioning system in passenger vehicles. The research is divided into two parts: experimental work and computer simulation. The experimental work was conducted to generate data to obtain the off-design air-side evaporator sensible and latent heat transfer correlations. The sensible heat transfer correlation relates the evaporator air off dry bulb temperature to inlet air dry bulb temperature, humidity ratio, evaporator air velocity, condenser inlet air dry bulb temperature, condenser air velocity and compressor speed. Another correlation relates to the coil air off humidity ratio to the same six independent variables. The experimental rig consists of the original components from the air conditioning system of a compact size passenger vehicle. A mathematical model has been developed based on the elegant z- transfer function method. Cooling load calculations are made using heat gain weighting factors. Heat extraction rate and cabin air dry bulb temperature calculationsvare made using air temperature weighting factors. The empirical evaporator sensible and latert heat transfer correlations are embedded in the loads calculation program to enable the determination of evaporator inlet and outlet air conditions and the cabin air condition. The semi-empirical computer program performs transient calculations on a minute-by-minute basis. Comparisons with the road test data indicated the program is capable of predicting the performance of an automotive air-conditioning system with accuracy of about 95%. Parametric studies were conducted to assess the effects of six parameters, that are, air conditioning volumetric air flow rate, number of occupants, glass thickness, vehicle speed, colour of the car and the fractional ventilation air intake on the thermal and energy performance of a 1.6L Proton Wira Aeroback.