When the sun is in occupants' field of view: assessing discomfort glare, thermal comfort, and overall comfort

This study investigates the cross-effects between thermal comfort and discomfort glare in office environments where the sun is in the field of view (FOV). While thermal and visual comfort have been extensively studied independently, their combined effects under real sunlit conditions remain unclear. A 2 × 2 within-subject experiment was conducted in a controlled test facility located in Germany, exposing 36 participants to two thermal conditions (lower temperature: -1 < PMV < 0 and higher temperature: 0 < PMV < +1) and two perceived glare levels (imperceptible and noticeable) under clear and stable sky conditions. Subjective comfort responses and physiological parameters (skin temperature and heart rate variability) were collected alongside environmental data. Results under these stimulus conditions showed no significant effect of temperature on glare discomfort, nor of glare discomfort on thermal perception, suggesting that thermal and visual sensations may not strongly interact under the tested conditions. However, glare discomfort showed a negative effect on overall comfort, while thermal variables (acceptability and sensation) showed weaker but still significant positive associations with overall comfort. Physiological analyses revealed that neither skin temperature nor its spatial variability were significantly associated with glare discomfort or thermal acceptability. However, glare discomfort showed a significant yet non-intuitive negative association with cardiovascular activation. Taken together, these findings suggest that discomfort glare due to the sun in the field of view may play a more prominent role in overall comfort perception than the thermal variations investigated in this study, while emphasizing the value of effective shading to improve occupants' well-being in office spaces.