Center for the Built Environment
Comparison of mean radiant and air temperatures in mechanically-conditioned commercial buildings from over 200,000 field and laboratory measurements
- Author(s): Dawe, Megan
- Raftery, Paul
- Woolley, Jonathan
- Schiavon, Stefano
- Bauman, Fred
- et al.
We assessed the difference between mean radiant temperature ((t_r ) ̅) and air temperature (t_a) in conditioned office buildings to provide guidance on whether practitioners should separately measure (t_r ) ̅ or operative temperature to control heating and cooling systems. We used measurements from 48 office buildings in the ASHRAE Global Thermal Comfort Database, five field studies in radiant and all-air buildings, and five test conditions from a laboratory experiment, including both radiant and all-air spaces. Considering only the ASHRAE Global Thermal Comfort Database because it is the largest and most representative dataset, under typical office conditions, the median absolute difference (e.g., disregarding direction of the difference) between (t_r ) ̅ and t_a was 0.4 ℃ (with interquartile range = 0.4 ℃), and more specifically, the median difference shows that (t_r ) ̅ was 0.4 ℃ (with interquartile range = 0.4 °C) warmer than t_a. In the radiant cooled laboratory tests, (t_r ) ̅ was significantly (p<0.05) cooler than t_a (average difference -0.1 ℃) while in the all-air cooled laboratory tests (t_r ) ̅ was significantly (p<0.05) warmer than t_a (average difference +0.3 ℃). While these observations are significant, the effect sizes are negligible to small based on Cohen’s d and Spearman’s rho. These observations indicate that (t_r ) ̅ and t_a are typically closer in radiantly cooled spaces than in all-air cooled spaces. The results suggest that t_a measurements are sufficient to estimate (t_r ) ̅ under typical office conditions, and that separately measuring (t_r ) ̅ or operative temperature is not likely necessary to improve thermal comfort, especially in buildings with radiant systems. Furthermore, spatial and temporal variations in t_a can be greater than the difference between (t_r ) ̅ and t_a at any one location in a thermal zone, thus we expect that such variations have a greater impact on occupant thermal comfort than the differences between (t_r ) ̅ and t_a.