Re: [EnergyPlus_Support] Ground temperatures pre-processor

["Michael J. Witte" <mjwitte@xxxxxxxx>]

You are correct that the ground temperatures are applied to the outside surface 
of the slab and there should be no layer of soil beneath the slab.

The sensitivity will vary depending on the proportions of the building, but it 
is always advisable to run the preprocessor.  I will make a note that we should 
review the basis of the 2C assumption and qualify its limitations.

Mike


On 7 Sep 2006 at 15:24, carlbauer2000 wrote:

> I have looked through other questions on ground temperature and it
> seems that for slabs on grade the recommendation is to use the
> preprocessor to  determine the ground temperatures under the slab.
> These are then the temperatures immediately on the other side of the
> slab so I assume I should then not use any ground construction under
> the slab.
> 
> I did this excercise for a fairly large office building in Gaborone,
> Botswana and ended up with temperatures of 23 degrees in summer to
> about 19 degrees in winter under the slab. These monthly temperatures
> are always within a degree or so of the indoor temperature for the
> conditioned building ground floor. However, when I adjust these
> temperatures by a few tenths of a degree it has a significant effect
> on the heat flows through the slab.
> 
> This means that the accuracy of these temperatures is critical. Hence
> I was a bit surprised that the standard advice is to use the average
> building inside temperature less 2 degrees. This would give a very
> large difference in heat flows in my case. Even with the small
> difference in temp outside to inside I am getting average heat flows
> out through the slab in summer which are about half of the cooling
> delivered by the HVAC.
> 
> Has anyone else looked into this issue?
> 
> 
> 
> 
> 
> 
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> 
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> 


========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx





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