2023 Volume 25 Issue 2 Pages 47-55
This review aimed to investigate the effects of vertical air temperature differences (VTD) for chair-seated persons, based on human subject tests in a laboratory, on thermal comfort, mental performance, and physiological responses. Recent studies have shown that the acceptable VTD range can be expanded from 3 k/m, as stipulated in ASHRAE Standard 55 (2017) and ISO 7730 (2005), up to 8 k/m. However, females with higher air velocities in the lower body parts and uncovered lower legs should have a narrow range. The VTD for the elderly should be less than 3 k/m because the elderly’s ability to perceive lower body thermal comfort decreases more than that of the young, and the blood pressure of the elderly increases significantly with lower body temperature. A smaller VTD is recommended, particularly in the winter. The effect of VTD on thermal comfort revealed that the preferred temperature of the lower body is several degrees (1.3-6.0°C) higher than that of the upper body. This means that the so-called “cool head and warm feet” condition induces thermal comfort. In addition, lower-body clothing provides less insulation than upper-body clothing, especially for females, and the physiological and morphological characteristics of humans, such as upright bipedal locomotion and a highly developed brain, might influence the thermal responses to VTD. It was shown that more comfortable VTD conditions (the so-called “cool head and warm feet” condition) may induce sleepiness and adversely reduce mental performance. These conclusions, however, may not apply to more complex and long-term (more than 3-hour) mental performance. When evaluating VTD physiologically, measurements of skin temperatures, including peripheral body sites, and blood pressure are essential for the elderly.
