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RE: [EnergyPlus_Support] film coefficients

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: RE: [EnergyPlus_Support] film coefficients
From: "Michael J. Witte" <mjwitte@xxxxxxxx>
Date: Mon, 15 May 2006 13:03:43 -0500
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The best approach is to take the combined conv and rad coefficient and 
determine what the convective-only portion is and use that in EnergyPlus.  If 
there are tables of combined coefficients vs. surface emissivity, this might be 
possible.

An alternative approach, just for the sake of comparison, would be to eliminate 
radiant exchange by setting the Absorptance:Thermal field in the interior and 
exterior MATERIAL:* layers to be something very small, such as 0.0001.  This 
causes the radiant exchange to become very small, and then a combined conv and 
rad coefficient can be used.  Note, however, that this will alter the behavior 
of radiant gains from internal loads, and will eliminate night sky radiant 
effects as well.

Mike


On 12 May 2006 at 10:27, Griffith, Brent wrote:

> EnergyPlus uses a very different model for surface heat transfer, which makes
> it inherently difficult to do such a comparison.   It is possible to reprocess
> a number of report variables and get some results to compare.  But it is
> really an apples to oranges comparison (with complex variations over time) and
> is not likely to be a very satisfying effort.  There is plently of ASHRAE
> literature on the Heat Balance Model.  In my opinion it is an important
> improvement over an approach that uses a combined conv and rad coefficient and
> it should eventually become the new "norm." 
>  
>      
> 
>  -----Original Message-----
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx
> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]On Behalf Of karen Allacker
> Sent: Friday, May 12, 2006 9:17 AM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> Subject: Re: [EnergyPlus_Support] film coefficients
> 
> 
> 
> Dear all,
> 
> I understood that the values I interpreted as actual
> values in the calculations are nominal and therefore
> only serve to compare with ASRAE. Therefore there was
> no difference if I chose for 'input values' or for
> 'simulated values'.
> 
> Is it also possible to report the total surface
> coefficients: convection and radiation? The Belgian
> norm for Energy calculations of Buildings only gives
> total surface values (convection and radiaton
> together). I would like to compare these with the
> calculated values of EnergyPlus. But since I can only
> find the surface convection coefficients to report it
> is impossible to make comparisons.
> 
> Kind regards,
> Karen
> 
> --- Linda Lawrie <linda@xxxxxxxxxx> wrote:
> 
> 
> ---------------------------------
> I think what you want to report is the variables:
> Zone,Average,Surface Int Convection Coeff[W/m2-K]
> Zone,Average,Surface Ext Convection Coeff[W/m2-K]
> 
> These would go onto the .eso files.
> 
> The things reported in the .eio are time invariant and
> "nominal" as 
> the title indicates.
> 
> 
> Linda
> 
> EnergyPlus WebSite: http://www.energyplus.gov
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========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx





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References:
- RE: [EnergyPlus_Support] film coefficients
  - From: Griffith, Brent

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