Statistic Selection of Coincident Solar Irradiance, Dry-bulb and Wet-bulb Temperatures for Determining Design Cooling Loads

Near-extreme solar irradiance, ambient dry-bulb and wet-bulb temperatures are fundamentaldata for determining the peak building cooling load. Design solar irradiance has beenseparately and independently selected by both ASHRAE and CIBSE. This may result in overestimatedcooling loads, and in turn over-sized air-conditioning systems. Hence, a statisticmethod based on probability theory and heat transfer principles was developed for rationalselection of the three coincident design weather data used for calculating peak cooling loadsin a building with thermal lag less than one hour. The new method was applied to historicweather records of 25 years in Hong Kong to rationally generate design weather data. Thesedata were compared with those produced by the traditional method. Results show thattraditional design solar irradiance, dry-bulb and wet-bulb temperatures may be significantlyoverestimated when a room or building faces east, south and west. Generating sequences ofthree coincident weather variables for heavy buildings is also discussed.