Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
The warning is pretty clear: you have surfaces in contact with ground, but you haven't specified ground temperatures in your model.
If you don't want to see this warning, you need to put some ground temperatures. Check out the Input/Output reference, starting at Site:GroundTemperature:BuildingSurface.
As stated:
Caution: The “undisturbed” ground temperatures calculated by the weather converter should not be used in building losses but are appropriate to be used in the Site:GroundTemperature:Shallow and Site:GroundTemperature:Deep objects. The reasoning (for building losses) is that these values are too extreme for the soil under a conditioned building. For best results, use the Slab or Basement program described in this document to calculate custom monthly average ground temperatures (see the Ground Heat Transfer section). This is especially important for residential applications and very small buildings. If one of these ground temperature preprocessors is not used, for typical commercial buildings in the USA, a reasonable default value is 2C less than the average indoor space temperature.
Documentation on how to use the Detailed Ground Heat transfer with the preprocessors Slab or Basement is here.
There's also the option of using @Neal Kruis's Kiva
