Average versus simultaneous climatic data for estimates of natural ventilation cooling potential.

Airflow through houses from onshore coastal breezes in warm humid tropical climates is the principal passive means of achieving indoor thermal comfort when air temperatures exceed 30°C and relative humidity exceeds 60%. Estimates of indoor natural ventilation cooling potential have been based on indoor wind speed coefficients determined from boundary layer wind tunnel tests combined with wind frequency, air temperature and relative humidity data. The paper refers to studies of a naturally ventilated house design proposed for Townsville, a provincial city of 120,000 people in the warm humid tropics on the east coast of northern Australia. One estimate of natural ventilation cooling potential for indoor thermal comfort used 20 year mean dry bulb and wet bulb air temperature at 3 PM together with 20 year wind frequency data. This estimate was compared with natural ventilation cooling based on actual simultaneous temperature and wind data for January 1980. This comparison showed that the estimate of natural ventilation cooling potential based on the long term mean 3 PM dry bulb and wet bulb air temperatures plus one standard deviation compared very well with natural ventilation cooling potential calculated from  actual temperature and wind data for January 1980, suggested by Bureau of Meteorology staff as a "typical year". A similar result was achieved when a comparison was made for 9 PM data when the frequency of calms was significantly higher.