[Equest-users] Interior Wall Conduction and why it screws up building heat loads

[Carol Gardner]

Hi James,

I'm not sure exactly what you are running into - would need the files to
determine that -  but here's a section of the documentation that might
contain a hint:

The program determines the heat transfer by conduction across an interior
surface from its area and U-value and the temperature difference across the
surface. This temperature difference is taken to be the previous-hour
difference in the air temperatures of the spaces adjacent to the surface.
This heat transfer can be significant for high U-value surfaces between a
conditioned and unconditioned space, where the temperature difference is
often large. An example is an interior ceiling between an attic or plenum
and the conditioned room below it. Except for interior surfaces between a
sunspace and a non-sunspace, the program assumes the conduction across the
surface is quick (has no time delay).

So possibly it could be between your ceiling and roof, or?

Hope this helps generate some ideas. I'm tapped.

Carol
On Thu, Dec 16, 2010 at 9:14 AM, James Hansen <JHANSEN at ghtltd.com> wrote:

> Thanks for everyone’s help on the custom weather file info the other week.
> Modifying the CSV value using the energy plus weather editor is definitely
> the way to go.
>
>
>
> I have a question about what exactly “interior wall conduction” is.
>
>
>
> This item shows up in the peak building load calculations under the LS-C
> report, and for my project, which is a strange industrial building that only
> needs to maintain 40 degrees, it accounts for 345 KW on the peak day.  At
> first I thought it might have something to do with interior walls and floors
> storing energy.  However, it turns out that when I create an hourly report
> to list this value for ALL hours, it is almost constant throughout the
> entire year.  In fact, it simply bounces back and forth between 345 KW and
> 360 KW for the whole year, with no pattern to the madness.  This makes no
> sense to me.  It is technically listed in the hourly report as:
>
>
>
> *“Building heat load from int wall conduction”*
>
>
>
> How can there be a 345 KW interior wall conduction heat load when its 90
> degrees outside and I’m only trying to maintain 40 degrees (no cooling
> system in the building)?
>
>
>
> Is this a bizarre custom weighting thing, or what?  All of my interior
> walls are set up as “AIR” walls since there are really no walls throughout
> the 12-story complex.
>
>
>
> Also, there is absolutely NO lighting and NO equipment listed.  The only
> heat in/out from the building is as I’ve defined for wall conduction,
> windows, and infiltration.
>
>
>
> Any advice would be appreciated!  I feel like this might be screwing with
> the unit ventilator air system calculations.  In addition, I’m starting to
> think that this might be why a lot of my projects end up having heating
> loads when I don’t think they should….
>
>
>
> OH – and one last thing.  Just because the peak cooling load below doesn’t
> show any cooling load from internal surface conduction doesn’t mean the
> heating component isn’t still showing up for every hour of the year.
>
>
>
>
>
> *GHT Limited
> **James Hansen**, PE, LEED AP*
>
> *Senior Associate***
>
> 1010 N. Glebe Rd, Suite 200
>
> Arlington, VA  22201-4749
>
> 703-338-5754 (Cell)
>
> 703-243-1200 (Office)
>
> 703-276-1376 (Fax)
>
> www.ghtltd.com
>
> * *
>
>
>
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-- 
Carol Gardner PE
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