Use the Weather tab of the Location Weather and Site dialog to adjust weather data used for heating and cooling loads analysis.
- Manage tab
Project Location panel
(Location)
For heating and cooling loads analysis, verify the Cooling Design Temperatures, Heating Design Temperature, and the Clearness Number. Adjust these numbers for the project location, if needed.
Use closest weather station
This option displays when you select Default City List on the Location tab.
By default, Revit uses the weather station listed in the 2007 ASHRAE Handbook that is closest to the project location. Data for that weather station populates the Cooling Design Temperatures table.
In some remote locations, however, the nearest ASHRAE weather station can be hundreds of miles or kilometers away. The default weather settings may not be appropriate for these locations or in areas with unique local conditions. For these situations, clear Use closest weather station, and override the default values in the Cooling Design Temperatures table as appropriate.
Use HVAC design data from weather station
This option displays when you select Internet Mapping Service on the Location tab and you select a weather station (for Autodesk subscribers with Internet access only).
By default, Revit uses the weather station selected on the Location tab to populate the Cooling Design Temperatures table.
In most cases, the climate conditions for the selected weather station are comparable to the conditions at the project location. However, if the project location is in an area that has unique local conditions, the default weather settings may not be appropriate. For these situations, clear Use HVAC design data from weather station, and override the default values in the Cooling Design Temperatures table as appropriate.
Cooling design temperatures
Revit uses the nearest or selected weather station to populate the Cooling Design Temperatures table. You cannot modify the values if the option is selected (Use closest weather station or Use HVAC design data from weather station).
If these values are not appropriate for the project location, clear the option, and adjust the values as needed.
| Value | Definition |
| Dry Bulb | The dry bulb temperature, commonly referred to as air temperature, is the temperature measured by a thermometer exposed to air, but protected from direct solar radiation and moisture. |
| Wet Bulb | The wet bulb temperature is the temperature to which air may be cooled by evaporating water into it at constant pressure until it is saturated. The smaller the difference between the wet bulb and dry bulb temperatures, the greater the relative humidity. |
| Mean Daily Range | The mean daily range is the mean of the difference between daily maximum and minimum temperatures. |
Heating design temperature
The heating design temperature is the outdoor dry bulb temperature that is exceeded during at least 99% of the hours in a typical weather year. Depending on the required comfort level in the space under consideration, the percentage (99%) can be varied.
Clearness number
According to the 2007 ASHRAE Handbook - HVAC Applications, Section 33.4, clearness is specified as follows:
- Clear and Dry - greater than 1.2
- Average - 1.0
- Hazy, humid - less than 0.8