Improving the Fanger model's thermal comfort predictions for naturally ventilated spaces

Abstract

The Fanger model is the official thermal comfort model in U.S. and international standards and is based on the heat balance of the human body with the environment. This investigation focuses on re-specifying the parameters in Fanger's model, the majority of which are empirically-derived coefficients, to improve its thermal comfort predictions for naturally ventilated spaces. A sensitivity analysis revealed that the comfort temperature prediction is by far most sensitive to the comfort value of mean skin temperature. Furthermore, the sensitivity analysis also indicated that for the Fanger model to produce better comfort temperature predictions for naturally ventilated buildings, the comfort mean skin temperature needs to be correlated to an outdoor climate variable, thereby accounting for the psychological adaptations of occupants of naturally ventilated buildings that were largely ignored in the original climate chamber derivation of this parameter. A modified comfort mean skin temperature, that is a function of both metabolic rate and outdoor effective temperature and is applicable to naturally ventilated environments only, produces comfort temperature predictions that agree well with field study data. The thermal sensation transfer coefficient was also updated based on a weighted multiple linear regression of field study data. The results suggest that a Fanger model with a modified comfort mean skin temperature and modified thermal sensation transfer coefficient can significantly improve the thermal comfort predictions for naturally ventilated spaces. However, experiments need to be conducted to determine the true functional forms of both parameters.