From GridLAB-D Wiki
default_outdoor_temperature - Default outdoor air temperature used when climate module is not loaded (Residential)
Synopsis
module residential { default_outdoor_temperature 74.0 degF; }
Remarks
The outdoor air temperature determine the rate of heat gain/loss through the building envelope and as a result of air exchange. When the climate module is loaded, the temperature is read from climate object. However, when no climate object available, the default temperature is used.