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Re: [EnergyPlus_Support] using Ground Calculation
See below for responses from our ground heat transfer expert concerning
basement modeling. Sorry for the delayed response.
> ------- Forwarded message follows -------
> To: <EnergyPlus_Support@xxxxxxxxxxxxxxx>
> From: "Ian Doebber" <idoebber@xxxxxx>
> Date sent: Thu, 13 May 2004 15:06:37 -0400
> Subject: [EnergyPlus_Support] using Ground Calculation Program
> for Basements
> Send reply to: EnergyPlus_Support@xxxxxxxxxxxxxxx
> [ Double-click this line for list subscription options ]
> I am using the Auxiliary Ground Temperature program to calculate the outside
> face temperatures of my walls and floor of the basement for my house. I
> understand that this program was meant for slab on grade but saw that I
> could use the core temps for my basement floor and perimeter temps for my
> basement walls. I know that this will be a lot better then using the ground
> temperatures in the weather file but I am curious about the applicability of
> this program to modeling basement heat transfer.
Just for your information, a basement ground heat transfer program is
presently being readied for inclusion with EnergyPlus. This will use
the same "dividing plane" concept, but will enable the users to have
temperatures that apply to basement walls and floors. This will not
make the summer 2004 release, but should make the one after that.
> I was wondering if anyone had any recommendations on how to specify certain
> inputs into this program to manipulate it more for an unconditioned
> 1. For example, instead of entering my setpoints for my conditioned zones
> as the monthly averages, I use the monthly averaged temperatures of my
> unconditioned basement from a previous EnergyPlus run. As a result, this
> significantly decreasing the calculated monthly ground temperatures.
The first question is: How did you model the unconditioned basements?
The results you get would be heavily influenced by the assumptions
made. For example, you should probably use an interzone partition for
the ceiling/floor above the basement to include the gains from above.
Include other incidental gains as well. In addition, I would suggest
using the core slab ground temperature for the floor, and making a run
with insulated walls. From those results see what monthly average
unconditioned basement temperature results. Then, with those, try
using the perimeter slab temperatures on the basement walls and see
what the effect is.
> 2. I was wondering about using the daily sine wave variation amplitude since
> my basement zone experiences larger daily fluctuations then my conditioned
My experience has been that the daily variations get damped out so they
have little effect on the results.
> 3. Should I specify my slab and soil material properties differently then
> those recommended for the slab on grade.
If you can come up with some information that is more local, definitely
use it. One problem always is that basement excavations are filled
with material, like sand, that is nothing like the earth in the
> 4. How should I specify my insulation configuration (vertical or under the
My suggestion would be under the slab.
> 5. How thick should I specify my slab.
It probably won't have a huge effect in this case, but 4 inches or
100mm is common.
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support
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