Natural ventilation and thermal comfort: air movement acceptability inside naturally ventilated buildings in Brazilian hot humid zone

The literature on thermal comfort indicates that acceptable indoor air speed in warm climates should range from 0.2 to 1.50 m/s; yet 0.2 m/s has been deemed in ASHRAE Standard 55 to be the threshold of draft perception (i.e. not acceptable) inside air-conditioned buildings where occupants have no direct control over their environment. However, these air velocity ranges have not explicitly addressed air movement acceptability, but have focused mainly on overall thermal sensation and comfort. A large percentage of Brazil is classified as having a hot and humid climate. In such regions, natural ventilation combined with solar protection, is the most efficient building design strategy to achieve thermal comfort without resorting to mechanical cooling. The present research project aims to investigate the relation between air movement acceptability and thermal comfort inside buildings in the north-east of Brazil. The investigation has been developed using university buildings in Maceio city. Questionnaires relating to thermal acceptability were given whilst measurements (air velocity, air temperature, radiant air temperature and humidity), were simultaneously taken inside classrooms. Results indicated that at operative temperatures above 24°C, building occupants preferred mean air speeds up to 1m/s. It was also observed that complaints of draft did not occur in significant numbers until air speeds exceeded 1m/s.