Ray-tracing MRT and human thermophysiology model combination for local discomfort prediction

Abstract

Thermal comfort and discomfort based on the local sensation of different body parts have been an important development in thermal comfort studies from the past decade. The human thermophysiology model can be a handy tool to predict local skin and core temperatures, which can then be projected into diverse human’s local and overall thermal sensation and comfort. When local environmental parameters are incorporated in the thermophysiology model, the degree of modeling information improves. One of the important input parameters is the mean radiant temperature. Variations in radiant heat fluxes when shortwave radiation is present in the room can be significant. Combining novel scanning and thermography methods together with ray-tracing simulation, we derived a high-resolution thermal model to fully characterize the variations of radiant heat fluxes experienced by different body parts of a human, both longwave (LW) and shortwave (SW). The shortwave heat flux varied in the range of 0-216 W/m2 throughout the day in the experiments conducted in an office room prototype on 23/02/2021 in Fribourg, Switzerland. The radiant temperature experienced by different body parts varied widely, from 24 °C to 58 °C, due to uneven exposure to solar radiation through a window, while the air temperature remained relatively uniform, as it was controlled by a mechanical system. To demonstrate the importance of combining detailed MRT modeling together with the thermophysiology model, we input detailed MRT distribution into the human thermophysiology model, along with the environmental parameters from the experimental measurements. The calculated skin temperatures were compared with the measured ones using iButtons and thermal sensation and comfort values with the survey results collected from the human subject. A combination of these detailed methods can be used as a design tool to assess local (dis)comfort and thermal perception of an occupant exposed to shortwave radiation and for dynamic shading and personalized comfort systems control strategies.