[bldg-sim] Apache uni-dimensional heat transfer assumption

[Yates, Christopher]

 ASPAM=antispamwpk42

Thanks Gunter,

Are you aware of any guidance for adjusting this external heat transfer
coefficient (I assume you mean surface emissivity) to account for such
things as thermal bridging at corners?

I'll take the comments regarding Apache's thermal radiation model on board -
thank you very much.

Regards, Chris

-----Original Message-----
From: Pueltz, Gunter [mailto:GPueltz at MuellerBBM.de] 
Sent: 16 September 2005 14:52
To: 'christopher.yates at halcrowyolles.com'; bldg-sim at gard.com
Subject: RE: [bldg-sim] Apache uni-dimensional heat transfer assumption

Dear Chris,

the error caused by the 1-D heat conduction of very thick walls can be
minimized by an adjusted (higher) external heat transfer coefficient.

But be aware of following fact:
The main problem with Apache is that the thermal radiation model is a simple
"mean-radient-model" (like TRNSYS), which is not very accurate, and not a
more sophisticated model based upon view-factors (like ESP-r, Eplus, TAS,
etc.).
Thus the errors induced by the minor radiation model will exceed the errors
caused by restricted 1D heat conduction extensively .......

Regards,
Gunter

--------------------------------------------
Dr. Gunter Pültz
Müller-BBM GmbH
Robert-Koch-Straße 11
82152 Planegg
Telefon +49 (0)89 85602 - 336
Telefax +49 (0)89 85602 - 111
http://www.MuellerBBM.de 


> -----Original Message-----
> From: bldg-sim at gard.com [mailto:bldg-sim at gard.com]On Behalf Of Yates, 
> Christopher
> Sent: Friday, September 16, 2005 3:35 PM
> To: bldg-sim at gard.com
> Subject: [bldg-sim] Apache uni-dimensional heat transfer assumption
> 
> 
> Dear All,
> 
> The thermal analysis package Apache (from IES) is a multi zone model 
> type analysis package, utilising finite difference methods to model 
> building performance against weather data. One of the assumptions that 
> it makes is that heat transfer only occurs between adjacent spaces in 
> a direction normal to the adjacent surfaces. I believe that this is a 
> common assumption for most building sim software (e.g. ESP-r).
> 
> The assumption holds true for traditional building types with 
> constructions that are relatively thin when compared to the overall 
> building volume.
> 
> However, we are analysing a building with wall constructions that are 
> quite thick when compared to the overall volume. Common sense tells me 
> that there will be a substantial 3 dimensional component to heat 
> transfer.
> 
> Does anybody have any experience of modelling the thermal response of 
> extremely heavyweight buildings that could give me some advice on the 
> limitations of this type of software (it's a nuclear waste storage 
> facility)?
> 
> It may be possible that this is the preserve of high end CFD, 
> generating large amounts of transient data with the help of super 
> computing facilities.
> However, it is difficult to know this because of the apparent lack of 
> work done on modelling such facilities.
> 
> Facts/ opinions???!
> 
> Thank you in advance
> 
> Chris Yates
> 
> 
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The contents of this email are confidential to 
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