Outdoor mean radiant temperature estimation in the tropical urban environment

• ISO 7726:1998 formula for Tmrt (mean radiant temperature) was found to be unsuitable for outdoor local use.
• Mean convection coefficient in Tmrt formula was recalibrated.
• Tmrt of 17 points in 2 sites were measured continuously for 2 months.
• Sky view factor has a high correlation with Tmrt exposure.
• Dips in Tmrt at night observed in site with significantly more tree cover.

A large scale estimation of mean radiant temperature (tmrt) is conducted at two sites using customised globe thermometers. The measurement points cover a variety of urban typologies such as high-rise offices, parks, large water bodies and housing apartments. Data is derived using a tmrt formula calibrated to the local climate. Measurements for clear, sunny days are used for the analysis of the average diurnal tmrt profile.The diurnal tmrt profile shows that the tmrt differential between points is most evident during daytime, and is affected most significantly by shade cast by trees and buildings. Results also show that common urban constituents such as greenery and large water bodies, while proven to effectively reduce the ambient temperature of its surroundings throughout the day, do not affect tmrt significantly after nightfall. Further analysis reveals a correlation between sky view factor and tmrt in the day. Measurement points in different parks exhibit contrasting trends in tmrt reduction.Results of the study also provide a realistic threshold for the lowering of outdoor tmrt. Trees, shrubs and green walls may be introduced into the outdoor environment with the intention of reducing tmrt to a desirable level for a specific time range.