[Bldg-sim] Accounting for plenums/technical ceilings

[Patrick Bivona]

Hi,

Thanks for your answers. I found a specific section, 2.2.9, in the COMNET
guidelines Shanta directed me to:

(...) Because of the leakage through the ceiling (typically suspended), the
> temperature of the plenum tracks
> the temperature of the space, except that it is generally warmer because
> of heat stratification and heat
> produced by lighting fixtures located at the ceiling or in the plenum.
> It is generally recommended that plenums be modeled as separate thermal
> blocks, but at the modeler’s
> discretion, they may be combined with conditioned space below for modeling
> simplicity.


I guess the part I'm interested in is acceptable simplifications. And
perhaps modelling tricks, that might be software specific.

Now a bit of context. I'm working on a 40 storey high building. That's
quite a few plenums to model, which add a lot of surfaces simply by being
there and by breaking up spaces that could have been grouped vertically
into continuous thermal zones. I was wondering if there was a better way of
approaching this to keep the model simple and the surface count down. Or do
I just have to suck it up?

An example of simplification I thought of, with EnergyPlus, is to model
space and plenum as a single space but setting the Ceiling Height field of
the Zone object to the height below plenum. It's acceptable in terms of air
changes in the space according to the documentation. It removes a lot of
surfaces and allows to group spaces into continuous vertical thermal zones.
But a part of the heat transfers through external walls that would normally
affect the plenum will be accounted for in the space itself. Acceptable
simplification? Unnecessary optimisation?

Thanks,
Patrick
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