Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
While the Input Output Reference explains the intent of the Green Roof object and its input fields, if you want to investigate these kinds of details related to calculations then you should review the Engineering Reference. Here, we can see that there is transpiration from the vegetation calculated separately from the transpiration from the soil. They both depend upon complex factors like stomatal resistance of vegetation, soil moisture content, vapor pressure difference between vegetation or soil and outside air, etc.
As this post mentions, EnergyPlus applies the Site:Precipitation object to green roofs -- the precipitation data in the EPW weather file is not used. Hopefully when you say that you "removed the rainfall data" you mean that you removed this object from your input file, since setting precipitation columns in the EPW weather file will not have an impact. You may want to add output variables for Green Roof Soil Near Surface Moisture Ratio and/or Green Roof Current Evapotranspiration Depth for further investigation.
You can also read this post for more information on the Green Roof object in EnergyPlus.
