Experimental and Theoretical Study of Transient Human Thermal Comfort Response in Convective and Radiative Environments

Abstract

Intermittent heating system operation is typically used in spaces occupied on a discontinuous basis. The intermittent operation of the heating system conserves energy at the expense of lessened thermal comfort during the transient period from the time the heating system is turned on until human comfort conditions are reached. In this study, human transient thermal responses and comfort were studied by modeling and experimentation in nonuniform radiant heating and convective heating environments. A simulation model was developed that integrates a space thermal model, a segmental transient bioheat model for the clothed human body that is responsive to radiative asymmetry, and Zhang's transient thermal comfort model (2003) to predict a body's local and overall comfort. The integrated space-human thermal response model for radiative heating was experimentally validated in a full-scale environmental chamber using a sedentary person (who was at a constant metabolic rate) who was subject to changes in environmental condition and clothing insulation. The measured data of the transient human segmental skin temperatures, room mean radiant, and air temperatures agreed well with model predictions of human and environmental thermal response. The model was applied to a selected case study for spaces heated by raditative and convective systems. The focus was on the thermal response due to the change that occurs when a human walking in a cold, outdoor environment at high clothing insulation moves into an unconditioned indoor environment. In the model, the heating system was turned on upon the person's entrance, and it was assumed that some insulated clothing would be removed. The simulation results showed that local comfort is reached much faster with the radiative system than the standard convective system. Overall, comfort was reached 15.5 min after the start of the heating system in the occupied space compared with 25.5 min when using the convective system. For the same transient performance, the convectiv'e system was oversized by 14% compared with peak load size at steady operation to match the transient thermal comfort provided by the radiative system.