Automobile Passenger Compartment Thermal Comfort Model - Part II: Human Thermal Comfort Calculation

An automobile passenger compartment thermal comfort model has been developed to aid the automotive engineers in the evaluation and selection of vehicle design parameters so as to optimize human comfort. This model can be used either as a stand alone tool or in conjunction with independently developed HVAC system models. The present model has as a unique feature the calculation of the thermal comfort of each vehicle occupant as a function of the prevailing local passenger compartment conditions of air temperature, mean radiant temperature, air velocity, air relative humidity, direct solar flux as well as the level of activity and clothing type of each individual. The thermal comfort is expressed as a percent of persons dissatisfied under a prevailing set of values for the aforementioned parameters and is based on Fanger's model of thermal comfort with appropriate modifications. The model presented herein takes into account the geometrical configuration of the passenger compartment including glazing surfaces, the pertinent physical and thermal properties of the enclosure with particular emphasis to glass properties, the prevailing environmental conditions, and the inlet air parameters as specified from the HVAC system. Special attention is given to the calculation of direct and diffuse incident solar radiation through the glass areas. The conduction, convection, mass flow, and radiation heat transfer modes are considered in the model, which has both steady state and transient capabilities. The availability of such a model is expected to facilitate significantly the job of designers and engineers in the early phases of the development of a new vehicle platform. Use of the thermal comfort model allows for exploration of different design avenues as they relate to human thermal comfort in a quick and inexpensive manner. It is thus hoped that superior vehicle designs associated with excellent vehicle occupant thermal comfort will result from the implementation of the passenger compartment thermal comfort model.