Thermal sensations of the whole body and head under local cooling and heating conditions during step-changes between workstation and ambient environment

This paper examines people’s thermal sensations during step-changes between ambient and workstation environments with a local ventilation device installed to supply-air motion around heads. We conducted human subject tests in a controlled environment chamber for summer and winter conditions. We performed 29 tests. The ambient air temperatures were 28 and 30 °C for summer conditions and 19 °C for winter conditions. The local supply-air temperatures were at 24, 28 and 30 °C for summer and 50 °C for winter. The supply-air velocities of the local ventilation device were at 3, 3.5, and 5 m/s for summer and 3.5 m/s for winter. The air temperatures near heads were 26–30 °C for summer and 32 °C for winter. The velocities along the jet-flow line at a distance of 10 cm from heads were 1.4–2.6 m/s for summer and 1.8 m/s for winter. In total, 23 subjects participated in the tests, and each subject participated in 1∼2 test conditions. Both the dynamic and stable thermal sensations of head and whole body were analyzed. When head is cooled by local ventilation, head thermal sensation has an effect on overall thermal sensation. When subjects moved from the workstation, where local devices were installed, to the ambient environment that was warmer in summer and colder in winter than the workstation, both overshooting and hysteresis were found. These thermal sensation changing trends in non-uniform step-change environments are helpful in personalizing environment control designs and exploring the possibilities of saving energy in buildings.

► Thermal sensations were examined during step-changes with local ventilation.
► Head thermal sensation has a strong effect on overall thermal sensation.
► Obvious overshooting and hysteresis were found during step-changes.
► Re-circulated air supply method is effective for cooling.