Subjective study of thermal acceptability of novel enhanced displacement ventilation system and implication of occupants' personal control

A novel air distribution principle of cooler air near the floor level being propelled upward via four fans mounted at each corner of a chair was developed to enhance the performance of conventional displacement ventilation (DV) system. Experiments were conducted in a well-controlled climate chamber with DV and constant heat load at different supply air temperatures, namely 20, 22, and 24 °C and room air temperatures, 22, 24, and 26 °C. Subjective assessments were carried out with 32 tropically-acclimatized college students who were given the choice to adjust the fan speed. Subjects' thermal comfort and the implication of personal usage pattern of the enhanced DV system were studied. The results revealed that at the ambient temperature of 26 °C, subjects preferred higher air movement and were satisfied with the cooling provided by the fans. However, the subjects felt cooler at the waists at room air temperatures of 22 and 24 °C when the fans were in operation. It was also found that the Whole Body Thermal Sensation (WBTS) reported by the subjects was correlated with the Local Thermal Sensation (LTS) at the waist, the arms, the calf and the feet when the novel DV system was employed. An expression which allows predicting WBTS based on the LTS was developed. Recommendations for fan speed at different room air temperatures were derived.

► The use of the fans in a DV room improved significantly the thermal sensation.
► The subjects did not frequently change the fan speed.
► The air movement around occupants could help to offset the warm thermal sensation.