Instead of the Slab preprocessor, I would recommend using the Foundation boundary condition for a ground-contact surface in EnergyPlus. Instead of pre-calculating ground-contact temperatures in Slab, this option uses Kiva. There are three key benefits to this:
- Kiva can take EnergyPlus inputs, pre-calculate ground-contact temperatures, then provide ground-contact temperature results as inputs to the EnergyPlus simulation. This is more integrated than running Slab to get temperatures as its own process, then taking outputs from Slab to provide as inputs to EnergyPlus.
- Kiva can calculate ground-contact temperatures every time step. This is much more accurate than using the monthly average ground temperatures calculated by Slab.
- Kiva allows you to simulate insulation placement inside or outside of footing walls that EnergyPlus normally can't handle due to its requirement of continuous material layers spanning entire surfaces.
You can read more about Kiva in Unmet Hours posts here and here.
