2. Experimental methods
The experiment was carried out from March to June in 2005. A climate chamber in the Department of Building Science at Tsinghua University was used to maintain a steady and thermally uniform environment and the temperature inside the chamber was maintained with a precision of 0.2C. Personalized ventilation, which attains many attentions due to its high performance on indoor environmental quality, great potential of energy saving and broad applications in both non-uniform environment and dynamic environment [11], was used in the present study to produce nonuniform and dynamic environments by supplying local cooled airflow. Face, as one of the most sensitive segments of human body and the most frequently exposed area while applying personalized ventilation, was locally cooled in the experiment.
Each test consisted of half-an-hour exposure to uniform conditions and half-an-hour exposure to non-uniform conditions. The ambient room temperature was maintained the same and local cooled airflow was supplied only when the exposure to nonuniform conditions started. Three room temperatures, ranging from neutral to warm, were chosen and for each room temperature, three local cooled target temperatures (target temperature means the air temperature at the center of face surface), ranging from neutral to slightly cool, were studied in the present experiment (Table 1). Relative humidity was kept at 40%, and air velocity was less than 0.1m/s in the room air. Air velocity at the outlet of cooling airflow was maintained at 1m/s.
Thirty randomly selected chinese college-age subjects, dressed in short, with a range of height from 163 to 182cm and weight from 55 to 86kg participated in all the experiment and the total duration for each subject was 27h. The sequence of presentation was balanced among subjects. Subjects remained sedentary throughout each exposure. Conversation was permitted but the subjects were not allowed to exchange views concerning the thermal environment.
Subjects reported their local thermal sensations of face, cheek, back and lower body part, overall thermal sensation and overall thermal comfort simultaneously at each voting time. During exposure to uniform conditions, subjects voted twice in the last 5min. During exposure to non-uniform conditions, subjects voted at 1-min intervals for 6min, and then 2-min intervals for 14min and then at 5-min intervals. Thermal sensations were reported on ASHRAE 7-point scale (Fig. 1a). A thermal comfort scale developed by Zhang [18] was applied in the present study to force subjects to make a clear determination about whether their perception falls in the category of ‘‘Comfortable’’ or ‘‘Uncomfortable’’ (Fig. 1b).