basement simulation

[nafisse akrami]

hello
How can we simulate basement  exactly? In addition, if we introduce outdoor surface " ground or basement" for EnergyPlus, which ground temperature we have to define for it?
Site:GroundTemperature:BuildingSurface ??
Site:GroundTemperature:Shallow??
or Site:GroundTemperature:Deep?
if we ourselves compute the ground temperature for example for 2.5 depth, which option do we must select?
kind regards

[farhang.tahmasebi]

Hi,

For building surfaces, the only object for defining the ground temperature is Site:GroundTemperature:BuildingSurface. This object defines outside face temperature of the surfaces which have "Ground" outside boundary condition.
So, for buildings where the basement does not have a substantial impact on the overall thermal performance, the easy approach would be to assume some "reasonable" temperatures by rule of thumb. If your model does not have this object, EnergyPlus assume 18°C as default value, which my not be that appropriate for basement surfaces.

But the correct approach to obtain these temperatures is to model the ground heat transfer with the EnergyPlus external program Basement, which is a 3 dimensional heat transfer calculation tool.

This involves:
1) Defining the required objects in the Group: Detailed Ground Heat Transfer;
2) Selecting the right boundary conditions for the surfaces which represent walls and floors of the basement, i.e. GroundBasementPreprocessorAverageFloor, GroundBasementPreprocessorAverageWall.

Step 1 may not be easy at first. But by taking a look at the example file LgOffVAVusingBasement.idf in EnergyPlus ExampleFiles subfolder, and reading the relevant section in the EnergyPlus documentation file "Auxiliary EnergyPlus Programs", it would not be that hard.

Best,

Farhang Tahmasebi
Vienna University of Technology