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

[Jon Hand]

Christopher is correct that most simulation tools default to 1D
conduction. There is, however, the option to turn on 2D and
3D conduction within a model in ESP-r. When this has been used it
has tended to be in the context of external thermal bridges,
but the concept should be applicable to internal portions
of a building (although I know of no one who has reported
trying that). 

It should be noted that 3D conduction implies
additional descriptive detail. Also, such
facilities are typically geared for research use.

-Jon Hand

On Friday 16 Sep 2005 14:34, Yates, Christopher wrote:
> 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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