Effect of direct solar projected area factor on outdoor thermal comfort evaluation: A case study in Shanghai, China

Abstract

The outdoor mean radiant temperature (Tmrt) is largely influenced by the direct solar radiation incident on the human body, mainly affected by the projected area factor (fp). The fp has been calculated by different methods and compared by some studies. However, how the fp quantitatively affects outdoor thermal comfort has rarely been studied. Therefore, this study established sitting, standing, and walking human models to calculate the fp in different solar positions through Monte Carlo ray-tracing technology. A case study has been taken in Shanghai to analyze the effect of the fp on outdoor thermal comfort. The Fanger, Jendritzky, and Underwood models' applicability in Shanghai was compared. The fp of sitting, standing, and walking postures have been obtained, respectively. The results show that more than 0.05 fp difference may cause half of the thermal grade deviation for outdoor thermal comfort evaluation. The fp is more sensitive to solar altitude (β) in three postures than solar azimuth (α). The fp difference from different postures can cause more than half of thermal grade deviation. Fanger's model for sitting posture may cause one thermal grade deviation; Jendritzky's model has acceptable performance for three postures; Underwood's model for sitting and walking postures may result in nearly one thermal grade deviation.