The transient nature of thermal loads generated by people

Available design information on thermal loads generated by people is based on steady-state data. One hour or more can be required for a person to reach a thermal steady state after entering a new environment and/or changing activities. During this time, the thermal load generated depends on prior environmental exposure as well as the current activity and environmental conditions. This long response time makes steady-state information of limited use in the design of environmental control systems for mass transit vehicles, where large numbers of people enter the vehicle at one time and/or there is a rapid turnover of passengers. To obtain quantitative data describing the dynamic nature of the heat and moisture that people dissipate to their surroundings, experiments were conducted in a calorimeter capable of holding 10 people. Test subjects were exposed to controlled conditions and activity levels in a separate environmental chamber prior to entering the calorimeter. Once in the calorimeter, the heat and moisture dissipation from the subjects to the calorimeter environment was measured on a continuous basis. Twenty such experiments were conducted. A computer simulation model that predicts the dynamic sensible and latent loads generated by people was also developed. The model is based on amore » modified version of the Gagge two-node model, which simulates the thermal transients in the human body. The modified model includes a transient simulation of heat and moisture flows and moisture accumulation in clothing, both of which play an important role in determining the mix of sensible and latent heat dissipation, as well as the total heat dissipation, during transience. The model was validated with the experimental data and now provides a tool with which designers can predict the size and nature of human-generated thermal loads in a wide variety of transient situations.« less