Condensation above false ceiling

[gmcshj]

We have air conditioned a car showroom, having 2" thick sandwich panel roofing. Below the sandwich panel, there is sloping false ceiling, made of aluminum tiles insulated with 10 mm thick closed cell rubber insulation with aluminum facing. The average height between the roof and the false ceiling is about 80 cm. The supply ducting is through a gypsum bulk head below the false ceiling and the return is also taken direct to the AC unit, below the false ceiling. The room design is at 23 deg C DB, 50% RH and the design ambient is 46 deg C DB, 29.44 deg C WB.

We are worried about the possibility of condensation above the false ceiling, especially during the peak summer. Can somebody suggest any solution?

Regards,

gmcshj

 

[KiwiMace]

I can't appreciate why you might be overly concerned about condensation, based on your posting. The supply and return is happening below the false ceiling, if anything the false ceiling space will be warm.

Other than that: Don't direct supply air onto the alloy faced false ceiling and minimize infiltration.

 

[Compositepro]

The problem is you have two layers insulation and the condition of the air between the two layers is undefined. If the gap has air infiltration from the outside it may cause condensation. So you must prevent outside air infiltration and allow some inside air infiltration (ventilation) of the gap. This will slightly reduce total thermal insulation but but does not negate the value of the inner layer of insulation.

 

[walkes]

Keep the building slightly positive to avoid infiltration, an air/vapour barrier building wrap would be helpful.

 

[Drazen]

I am trying to figure out what kind of suggestion are you looking for.

If you are designing, you can calculate duct insulation using higher relative humidity figures.

If that is built already, the best you could do is to open false ceiling space so that some level of natural ventilation occurs there, as humidity will be highest in space which is tight bu not resistant to vapor mass transfer.