SELECTION METHOD FOR COINCIDENT DESIGN WEATHER DATA WITH SOLAR IRRADIATION BASED ON BUILDING CHARACTERISTICS

The selection of design solar irradiance in the current ASHRAE and CIBSE design handbooks isindependent on design dry-bulb and wet-bulb temperatures. The probability that the load would notexceed the system capacity determined on this basis may not match the reliability level that the designweather data were meant to safeguard. Hence, a statistic method was developed for the rationalselection of coincident solar irradiance, dry-bulb and wet-bulb temperatures. The new methodcombines, based on the principle of heat transfer, the three weather parameters and buildingcharacteristics into a single impact factor, which may be called as equivalent temperature. This ensuresthat the joint probability of occurrence of the three coincident weather parameters can match thecapacity reliability level of air-conditioning systems, which may be required by building owners. Themethod was applied to historic weather records of 25 years in Hong Kong to generate coincidentdesign weather data. These new design weather data were compared with those design weather dataproduced by the traditional method. Results show that traditional design solar irradiance, dry-bulb andwet-bulb temperatures may be significantly overestimated in many conditions. Moreover, the newmethod allows HVAC engineers to determine the peak cooling load directly without the need forcalculating 24 hours cooling loads on one design day for every month of each year.