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The selection of HVAC system components is often dictated by service requirements and equipment performance under extreme weather conditions. For example, a chiller must be selected with sufficient capacity to meet the peak cooling loads that occur during extremely hot, humid, and possibly sunny conditions. Minimum and maximum peaks for temperature and other weather variables are available for many locations. However, when a system has thermal capacitance due to internal or external energy storage, sequences of hourly weather data for a period on the order of the system's time constant, rather than just the peak conditions, are needed to evaluate the effects of weather variables on system sizing and the resulting energy demands. If statistically possible extreme sequences can be confidently estimated for a given location, the increased costs associated with undersizing or oversizing equipment may be avoided. A methodology and computer program have been developed to synthesize extreme (but statistically possible) hourly weather data for periods of up to one week for a specified month and location. The weather data parameters that are synthesized include hourly values of dry- and wet-bulb temperatures, humidity ratio (or relative humidity), and solar radiation. The program also outputs wind data, although the statistics of extreme wind data were not studied. The program uses readily available monthly average weather data inputs that are provided for 329 North American locations. Extreme conditions are estimated based on the monthly average weather data. The sequences generated by the EXTREMES program should be used as guides only, and climatic records should be consulted if accuracy is judged to be important.

Units: I-P

Citation: ASHRAE Transactions, vol. 106, pt. 1