[EnergyPlus_Support] Re:About Ground Temperatures

[troy Harvey <taharvey@xxxxxxxxxxxxxxxx>]

I have found the slab program totally unreliable in most circumstances  
because it calculates the temperature of the surface between the slab  
and the ground, or the slab and insulation - rather than buffered by  
insulation/mass of in-between layer(s). In most cases I've found this  
to be totally inappropriate, and it causes the problems with the  
dynamic hourly simulation on the other side of a thin (and conductive)  
slab. As you noted one common problem, is the slab inappropriately  
heats/cools the space when it shouldn't.

I think the energyplus approach is very flawed, and could be improved  
with a simple algorithm that is dynamically calculated by hour. This  
would be more accurate the the pre-calculation method, even if it  
doesn't use the theoretically more accurate 3D FEA. The accuracy of  
the FEA is all thrown out the window once coupled with the dynamics of  
the hourly simulation after the fact. And if the interior temp is  
changing a lot (passive solar), it is near worthless.

This is what we do in the interim: We calculate the ground temperature  
*below* the slab insulation OR if no insulation, below several layers  
of earth using the ISO 13790 ground temp method. Then we enter those  
values into energyplus for ground temps, and build the slab assembly  
with the insulation included or with several layers of earth (or  
both). That way the fixed monthly temperature is buffered from the  
interior space. This seems to give acceptable results. But it would be  
nice to see a real solution built into E+.


Troy Harvey
---------------------
Heliocentric




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