The building location is specified on the Location tab of the Location Weather and Site dialog. When you use the Default City list, the longitude and latitude coordinates of the selected location are compared to an external database of 4400+ World Meteorological Organization (WMO) weather stations derived from the 2005 ASHRAE Handbook of Fundamentals. The closest WMO weather station is selected along with its weather data, and the values display on the Weather tab.
For the cooling loads calculation, a design day is derived for each of the 12 months of the year, with a maximum dry-bulb temperature corresponding to the 1% monthly percentile temperature for the location. This is the temperature that is exceeded on average, during that month, for 1% of the time. The daily range and profile of the dry-bulb temperature, and the corresponding values of wet-bulb temperature, are derived from data in the ASHRAE database. The clearness number is currently set to 1 for all locations. This will be updated in subsequent versions when this data becomes available for specific locations.
For the heating loads calculation, the design outside dry-bulb temperature is set to the 99% annual percentile temperature for the location - the temperature that is exceeded on average over a period of years for 99% of the time.
The selected city, its coordinates, and weather information are stored within the building data object.