Ceiling space as supply plenum?

[carlosgw]

I have never before used a ceiling space as a supply plenum. The idea does not give me warm fuzzy feelings. I have a situation where I have a 6" ceiling space (including ceiling depth). Above is a rated ceiling/floor assembly with drywall on the bottom. The ceiling is a lay-in acoustical tile ceiling.
Any practical experience using this space as a supply plenum for a room?

 

[MintJulep]

Would you put a three and a half pound weight on each ceiling tile?

 

[KiwiMace]

If you can't fit a duct in the space, then it won't work as a plenum either.

 

[carlosgw]

Supply air plenum (the air pressure will hold the ceiling tiles down).
The 5ish inch space is too small for duct. Why would you say it is too small for a plenum?

 

[MintJulep]

the air pressure will hold the ceiling tiles down

Yes, it certainly will.

 

[317069]

ok let say you use ceiling space as a plenum.
what about return.

 

[KiwiMace]

I meant that I don't think you will get the even pressurisation that you might expect.

Your ceiling tiles and drywall soffit will also reach moisture equilibrium with the ~90%RH supply air - something like 20% moisture content which will promote mould and discolouration.

 

[willard3]

It's a bad idea, don't do it.

 

[RossABQ]

Is this an existing condition, or something still being designed?

 

[carlosgw]

I am not leaning toward the idea.
I can return from the wall. I can supply from the same wall, though it is at the end of the room (actually I have two locations and in only one can I supply from the sidewall). Or I can run duct in the floor assemebly above (which is wood open web and means a bunch of ceiling radiation dampers and awkward transition to the suspended ceiling).

 

[trashcanman]

Willard is right. BAD IDEA. Do you want to trust the Architect to design your ductwork?
Also, how would you balance the air flow?
Drop the idea and go with ductwork.