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

[Yates, Christopher]

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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