Commercial Attic Ventilation

[dblyle]

So, I have large warehouse (~60,000 sq.ft.) in Dallas in which we are installing low temp coolers (36 degrees) in the space. The coolers are 4" IMP (insulated metal panel) and 16' tall. The Warehouse is 37' tall. Think "building in a building". Given that I have a very large "attic", I feel as if I should ventilate this attic, somewhere around 0.7 cfm/sq.ft., however, this seems pretty excessive. The attic will have ductwork in it carrying 36 degree air, so we don't want that sweating at all. My concern is that if i don't ventilate it, we'll collect moisture at the top of the attic.

My initial design was to use a push/pull ventilation system to keep air moving through this attic - although it will be outside air. Any thoughts on this?

-DOUGLAS

 

[Snickster]

Whether you ventilate the attic or not the duct must be insulated very well to prevent condensation on the duct itself. I don't see why condensation would develop on the top of the attic. You mean roof underside? .7 cfm/ sq ft seems very excessive and would give 42,000 cfm and seems odd to put so much ventilation air into an unused space. I believe attic are vented mostly for energy considerations if the warehouse was to be HVAC but even then I believe natural ventilation systems would be used. If it is an unconditioned warehouse then it will just get hotter inside if attic not ventilated, but if warehouse space itself is ventilated then need to include heat gain by from unvented attic to warehouse ventilation air calculation. This is only my opinion as I never came across this situation in HVAC design.

 

[nuuvox000]

Is the warehouse ever occupied? If so, you'll need to provide ventilation per code. If it's not occupied, just heat for freeze protection and insulate the duct more if needed.

 

[dblyle]

Yes, it's a little different design for me as well.

So the attic is a true attic space - it is the space between the cooler ceiling and the roof of the building (about 21') with walls on all 4 sides. The commercial building codes say we need to ventilate at the rate of 1cfm/sq.ft. That's a lot. The client needs to keep air moving on top of those cooler panels so we don't develop condensation.

 

[nuuvox000]

What code are you using? My code only calls for 0.06 CFM/sf so that's a pretty big difference.