Comparison of mean radiant and air temperatures in mechanically-conditioned commercial buildings from over 200,000 field and laboratory measurements

Abstract

We assessed the difference between mean radiant temperature (! ) and air temperature (! ) in conditioned office buildings to provide guidance on whether practitioners should separately measure ! 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 ! and ! was 0.4 (with 5 th , 25 th , 75 th , and 95 th percentiles = 0.2, 0.2, 0.6, and 1.6 °C). More specifically, the median difference shows that was 0.4 warmer than (with 5 th , 25 th , 75 th , and 95 th percentiles = -0.4 °C, 0.2 °C, 0.6 °C, and 1.6 °C). The laboratory experiments revealed that in a radiant cooled space ! was significantly (p<0.05) cooler than ! (average difference -0.1 ! ), while in the all-air cooled space ! was significantly (p<0.05) warmer than ! (average difference +0.3 ! ). These observations indicate that ! and ! 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 ! is sufficient to estimate ! under typical office conditions, and that separate measurement of ! 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 ! can be greater than or equal to the difference between ! and ! 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 ! and ! .

Post-Occupancy Evaluation of Indoor Air Quality and Thermal Performance in a Zero Carbon Building

“…According to CIBSE guide A [40], "in well insulated rooms and away from direct radiation from the sun or from other high temperature radiant sources, the difference between air and the mean radiant temperatures (and hence between the air and operative temperatures) is small". The on-site measurements, done by Dawe et al [74] and Walikewitz et al [75], also show that in the absence of a radiative heat source or sink (e.g., radiative heating or cooling system, windows facing south-east and south-west), the air temperature can be used as an estimation of radiant and consequently operative temperature as the difference is around 0.4-0.5 K. Based on that, it can be assumed that the operative temperatures in the CSET building are in proximity to the measured air temperatures. The results are summarized in Figure 7.…”

Targeted occupant surveys: A novel method to effectively relate occupant feedback with environmental conditions

“…It also demonstrates that the radiant system was able to maintain consistent indoor temperatures as the HVAC modes switched. In addition, the median infrared and dry-bulb temperature measured in the occupied zone by our sensor kits were 22.6 °C and 22.8 °C, respectively, indicating that there are negligible differences in air and mean radiant temperatures experienced by occupants in this building (Dawe et al 2020). The subjective thermal satisfaction responses from the small number of subjects indicate that this radiant building exceeds the ASHRAE 80% acceptability criteria ( Figure 5).…”

Improved long-term thermal comfort indices for continuous monitoring

“…Differences between and were small for most floors-less than 0.5°C-with T a T o greater variance in than . An analysis [51] of field measurements in ASHRAE Global T a T o Thermal Comfort Database II [52] and additional laboratory testing reported similar differences in air and radiant temperatures, and they suggested as an appropriate estimate of mean T a radiant temperature when it is not readily available. Moreover, recent studies have reported systematic errors when using traditional globe thermometers to measure radiant temperature [53,54].…”