condensation on hvac ducts and other metal objects in ceiling plenium. 1

[watter]

I recently installed a new fire alarm system in a new addition of an existing hospital. Once summer time weather begin I have had many call backs due to "false alarms and trouble alarms". Upon inspection of these false alarms I find that the fire alarm devices contain water which as we all know does not mix with electronic equipment. Further investigation turned up evidence of water condensing on all of the HVAC ducts and lines above the ceiling. The HVAC ducts are insulated but they are cool to the touch, the metal deck pans of the roof are insulated on the outside with a finished EPDM rubber membrane roof, but the metal deck is warm to the touch in the plenium space above the ceiling. The plenium space is very warm and feels humid. The moisture is so bad it is collecting on ceiling tiles and light fixtures as well as fire alarm devices and is even dripping out of supply and return air vents. I know when water vapor comes in contact with a surface that has a temperature lower than the dew point of that water vapor it condenses so I know were all the water is coming from the question is how to stop it? Is the duct insulation to thin? Is the roof insulation to thin? Or both? Is the HVAC system not balanced right.... when you open any outside door to the new area of the hospital air gushes in so fast you have no trouble feeling it, this tells me there is negative pressure in the building. I did not create this problem but I would like to help the hospital out by coming up with some possible solutions, mainly so they will quit calling me to come bail water out of the fire alarm system.

 

[brmech]

I don’t know about the negative building pressure, it may be required for hospitals by some health code. The building pressure can certainly be controlled by the HVAC system fans if it has the capacity to do so. The moisture can also be controlled by the HVAC system if it was designed properly. The scenario you describe is not acceptable (or legal by ASHRAE codes I suspect) for any building, especially a hospital.