Comparison of thermal comfort performance of two different types of road vehicle climate control systems.

The performance of climate control systems in vehicles becomes more and more important, especially against the background of the important relationship between compartment climate and driver mental condition and, thus, traffic safety. The performance of two different types of climate control systems, an un-air-conditioned heating/cooling device (VW) and an air-conditioning climate control unit (BMW), is compared using modern and practical evaluation techniques quantifying both the dynamic 3-D temperature distribution and the local air refreshment rate. Both systems suffer from considerable temperature gradients: temperature gradients in the U-AC (VW) car up to 8-9 degrees C are encountered, while the AC (BMW) delivers clear improvement resulting in temperature gradients of 5-6 degrees C. The experiments clearly demonstrate the effect of the presence of even a single passenger on the thermal regime, increasing the existing thermal discrepancies in the compartment with 15% independent of ventilation rate. Furthermore, in terms of air refreshment rates in the vehicle compartment, an air-conditioning unit halves the air refreshment time at all positions in the vehicle cabin, delivering a significant improvement in terms of human comfort. Similarly, extra air inlets in the back compartment of a car deliver progress in terms of cabin refreshment rate (93 s down to 50 s).