Re: [EnergyPlus_Support] ground heat transfer modeling for unconditioned spaces

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

Presently, the recommended approach would be #1, an iterative approach.  I 
think that you will find it to converge rather quickly.  

If you have many cases like this, you may want to compare option 2 with option 
1 for a couple of climates (warmer and colder) and see how much difference 
there is.  

I will add a more integrated approach for such applications to the overall 
enhancement wish list.

Mike



On 25 Apr 2007 at 10:17, Spencer, Justin wrote:

> I'm looking for a good way to model ground heat transfer from
> unconditioned spaces.  The basement and slab programs require an input
> temperature for the space.  This isn't too hard to provide when you have
> a conditioned space - you should be able to get close.  Since the ground
> transfer is driven by a small temperature difference between the space
> and the ground temperature, getting this temperature wrong will have a
> big impact on the resulting ground temperatures and energy balance in
> the space.  
> 
> 
> 
> In particular, a ventilated crawlspace with some amount of duct leakage
> into the space creates a real modeling conundrum, since the ground
> transfer is one small part of the temperature in the space.  I can think
> of 2 possible solutions:
> 
> 1.	Use an iterative approach.  Run the basement model with a guess
> at the temperatures in the space, then run the resulting ground
> temperatures in the full simulation, make a new guess at the
> temperatures in the space, run the basement model, until convergence is
> reached.  (iterative approach)
> 2.	Abandon the basement model.  Ignore ground transfer through the
> floor.  Model the walls with regular 1-D walls, with wall properties
> that approximate the soil and wall performance.  (Perimeter conduction
> approach)
> 
> In the long run, if the basement model ran with the actual building,
> instead of needing space temperatures as an input, then the basement
> model could be run once, instead of requiring exhaustive iteration.  
> 
> 
> 
> What's the best workaround to use in the short term?
> 
> 
> 
> Justin Spencer
> 
> 
> 
> 
> 
> 
> 
> [Non-text portions of this message have been removed]
> 
> 
> 
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> 
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> 
> Attachments are not allowed -- please post any files to the appropriate folder
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> 
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> Documentation link and press the "search" button.
> 
> Yahoo! Groups Links
> 
> 
> 
> 
> 


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





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