Natural ventilation has served as an effective passive cooling design strategy to reduce energy used by air-con¬ditioning systems. For tropical regions, where the air tem¬perature and relative humidity are generally high, the effectiveness of natural ventilation is always questionable. The vernacular architecture of Thailand, such as the tradi-tional Thai house in Fig. 1a,was designed to take advantage of the prevailing winds. The traditional Thai house is normally built with three notable characteristics: an elevated foor, a steeply pitched roof with long overhangs, and a large open terrace. The elevated foor prevents sudden fooding, protects occupants from dangerous animals, and allows more wind to fow through the living space. The long overhangs provide shade protect the house from rain. There is a thermal stratifcation in the house; the air temperature in the lower part of the house is lower than that in the upper part. The occupant usually stays in the lower, more com¬fortable part of the space. The large open terrace, which occupies approximately 40% of the total foor area, serves as a space for outdoor activities, and was an important space for the typical extended families of the Thai people of the past.