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Energy and Buildings, Vol.206, 2020
Comparison of mean radiant and air temperatures in mechanically-conditioned commercial buildings from over 200,000 field and laboratory measurements
We assessed the difference between mean radiant temperature ((t(r)) over bar) and air temperature (t(a)) in conditioned office buildings to provide guidance on whether practitioners should separately measure (t(r)) over bar 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 that compared radiant and all-air cooling. The ASHRAE Global Thermal Comfort Database is the largest of these three datasets and most representative of typical thermal conditions in an office; in this dataset the median absolute difference between (t(r)) over bar and t(a) was 0.4 degrees C (with 5th, 25th, 75th, and 95th percentiles = 0.2, 0.2, 0.6, and 1.6 degrees C). More specifically, the median difference shows that C. was 0.4 degrees C warmer than to (with 5th, 25th, 75th, and 95th percentiles = 0.4 C, 0.2 C, 0.6 C, and 1.6 C). The laboratory experiments revealed that in a radiant cooled space 7; was significantly (p <0.05) cooler than <(t(r))over bar> (average difference 0.1 degrees C), while in the all-air cooled space i; was significantly (p <0.05) warmer than to (average difference +0.3 C). These observations indicate that C. and to are typically closer in radiant cooled spaces than in all-air cooled spaces. Although the differences are significant, the effect sizes are negligible to small based on Cohen's d and Spearman's rho. Therefore, we conclude that measurement of to is sufficient to estimate ttr under typical office conditions, and that separate measurement of I; or operative temperature is not likely to have practical benefits to thermal comfort in most cases- this is especially true for buildings with radiant systems. Furthermore, spatial and temporal variations in to can be greater than or equal to the difference between 1T. and to at any one location in a thermal zone, thus we expect that such variations typically have a greater impact on occupant thermal comfort than the differences between F-r and t(o). (C) 2019 Elsevier B.V. All rights reserved.