Abstract
Determining "equivalent temperature" is an accepted means for assessing the thermal conditions inside of a vehicle passenger compartment. The equivalent temperature is defined as the "temperature of a homogenous space, with [zero solar load,] mean radiant temperature equal to air temperature and zero air velocity in which a person exchanges the same heat by convection and radiation as in the actual conditions under assessment" [1].
Passenger thermal comfort can be improved by adjusting the vehicle compartment air temperature to compensate for the asymmetric heating or cooling that is present in an automotive environment. It follows that a vehicle compartment HVAC control strategy that is based on controlling air temperature to a constant value, without considering differences in mean radiant temperature, will not result in optimal passenger comfort without the manual manipulation of the air set-point temperature. Similarly, a control strategy that is based on the measurement of air and surface temperatures will not be optimal in the presence of solar loading that is directly experienced by the passenger.
A methodology for estimating real-time, in situ passenger compartment equivalent temperature for use in a thermal control strategy has previously been described [2]. As is the case when using equivalent temperature for comfort assessment, this control strategy is appropriate for asymmetric-but-steady environments. This paper reviews the simulation and calculation of human thermal comfort in asymmetric environments and also considers the prediction of comfort under widely varying transient thermal conditions.
Keywords: simulation, thermal comfort, HVAC, solar load, radiation