[Bldg-sim] Accounting for plenums/technical ceilings

[Shanta Tucker]

Hello Patrick,
The plenum areas of the building certainly need to be taken into account in the model and there are cooling and heating loads associatiated with plenums even if they are not conditioned. While they may not be used as a return plenum, there will still be a heat transfer between the plenum and all of the adjacent surfaces, especially the exterior wall and the ceiling. These heat transfers can also affect the occupied space load as there is an exchange through the ceiling. To answer your first question, plenums are typically modeled as separate spaces, yes. The height of the plenum should equal the floor to floor height minus the ceiling height. All of the math should add up so that the exterior wall heat transfers are correctly accounted for.

I recommend consulting the ASHRAE 90.1 users manual for more information on accounting for different definitions of spaces and partition types.

Cheers,

Shanta Tucker
Atelier Ten

T (212) 254-4500 x 210

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Patrick Bivona
Sent: Thursday, October 24, 2013 9:26 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Accounting for plenums/technical ceilings

Hi all,

How do people generally account for plenums or technical ceilings? I'm not referring here to plenums used for air circulation, but closed ceiling space that is not considered as part of a volume to heat or cool for load calculations.

- Do you model them as separate spaces?
- Do you ignore them (but how then do you preserve the building's geometry)?
- Some other option?
- And for those using EnergyPlus, do you use the "ceiling height" field of the Zone object? The documentation says that this generates a warning if the ceiling height and calculated ceiling height differ too much, whatever too much is.

The building I'm working on has a 1.1 m (3.6 ft)  difference between the space ceiling height and the height of the floor above, so it's not something I can ignore.

Thanks for your feedback,
Patrick


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