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

[Pueltz, Gunter]

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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