Return Air Plenum Component - Ducted Return

[Francisco_Contreras]

Hello all,

I have a simple question. If my design has a fully ducted return air system, should I be using the "Return Air Plenum" component to model my plenums or the "Void" component.

If I should use the "Void" component how does the process look for defining HVAC zones, and HVAC systems.

I couldn't find details regarding the "Return Air Plenum" component in the ApacheHVAC User Guide.

Thanks in advance,
Francisco Contreras

[suyash_vidwans]

Hi Francisco

You are correct, for a ducted return you should model the plenums as voids. When you do not model return air plenums, the software assumes ducted return.
There’s nothing much more to consider about voids. You can add internal gains to voids (if necessary). The voids are unconditioned spaces in the software.

-Suyash

[Timothy]

To be clear, for ducted return, you should model the ceiling cavity spaces in the model as voids, rather than as plenums, as you will not have any plenums. This assumes that there are in fact ceiling cavities (voids) in the real building---typically used to contain the ducts and other items (plumbing, electrical wiring, etc.); however, many buildings with ducted return have exposed ducts, plumbing, etc. mounted on the ceiling within the occupied space. In such cases, there would be no plenums or voids, just ducts. Within ApacheHVAC, you can then use 'Duct thermal properties' components (as differentiated from the air-path segments used to connect all the components together) to model leakage to the space where the duct is located, as well as thermal gains and losses, where you wish to account for these forms of heat transfer.