Condensation on supply grilles
Condensation on supply grilles
(OP)
I have a problem I have never encountered before.
A chilled water system with a series of fan coils. Each fan coil is installed in a bulkhead with a short section of supply duct terminating in a sidewall grille. We are getting condnesation on some of the grilles. Has anyone ever experienced this?
I am figuring it is either caused by warm air in the room passing over the grille and causing the moisture to condense. Another possibility might be that when the unit cycles, the warmer air it blows through the duct is cuasing condensation on the grille which will still be cold.
Any other possibilities of what is causing this and what can be done to prevent it?
A chilled water system with a series of fan coils. Each fan coil is installed in a bulkhead with a short section of supply duct terminating in a sidewall grille. We are getting condnesation on some of the grilles. Has anyone ever experienced this?
I am figuring it is either caused by warm air in the room passing over the grille and causing the moisture to condense. Another possibility might be that when the unit cycles, the warmer air it blows through the duct is cuasing condensation on the grille which will still be cold.
Any other possibilities of what is causing this and what can be done to prevent it?





RE: Condensation on supply grilles
One thing that I have found to be helpful in this situation is the use of plastic grilles. They will tolerate a higher dewpoint without sweating.
---KenRad
RE: Condensation on supply grilles
RE: Condensation on supply grilles
RE: Condensation on supply grilles
Also check for the possibility of any opening above the false ceiling through which there's an ingress of outside air.
HVAC68
RE: Condensation on supply grilles
Were the fancoil coils selected to avoid moisture carry-over?
Is there the possibility that the static pressure from the fan is drawing moisture in from the drain pan?
RE: Condensation on supply grilles
We have reduced the fan speed (3 speed control) and the condensation is not nearlly as bad, but still present.
The outside air mixes with the return air before reaching the coils. There are no obviosu signs of outside air coming in.
It is definitely not moisutre carry over. The water is definitely condensing on to the grilles.
Thanks.
RE: Condensation on supply grilles
HVAC68
RE: Condensation on supply grilles
RE: Condensation on supply grilles
Though this may sound crude and inefficient,it does work!
RE: Condensation on supply grilles
Btu/hr latent load sbsorbed by primary air = CFM primary air x .69143 x 7000 x (lb moisture per lb dry air at room indoor design - lb moisture per lb dry air at entering primary air condition)
Make sure this is equal to or greater than the room latent load (from people, latent equip gain and infiltration if any)
RE: Condensation on supply grilles
Will there be a condition that the chilled fluid valve closes totally during a day? As you already have a fresh air intake, the moisture in fresh air may be condensing on a cold grille. I have seen in many ocassions, condensing of moisture in fresh air upon controlled space walls and ceiling when the chilled water supply is totally cut off.
You can minimize this by crack opening the chilled water bypass.
When you reduce the speed, the fresh air flowrate also gets reduced and that is why there may be less condensation.
Just close the OA damper totally and observe.
Regards,
RE: Condensation on supply grilles
Is there a lot of infiltration in your building. If you are recycling most of your air (i.e. 90%) than the room air will eventually dry out due to you removing the moisture and the space humidity will fall (hopefully to say 50%). If however it is a shop where the doors open constatntly and let in humis air, you have problems.
As already suggested, you would need to cool then reheat to minimise this problem.
I also like the idea of plastic grilles.
Also, try a full recirc unit which is dedicated to dehumidification only to try and lower the space humidity.(we use wall mounted dedicated units for this if we get a problem)
Try a company called Calorex who specialise in this type of unit.
Friar Tuck of Sherwood
RE: Condensation on supply grilles
Yes, the valves will close off from time to time, some more than others as some are oversized because they changed the partiiton layout so some units have a much smaller area to cool than previously. I have not beem able to do it yet, but I plan to increase the water supply temp. to keep the valves open for longer periods. THis may have a benefit of saving some energy too.
Friar,
It is an office building, so there will be some infiltrationdue to doors opening, but it should not be as much as a shop.
I will keep you guys updated as I go on.
RE: Condensation on supply grilles
RE: Condensation on supply grilles
RE: Condensation on supply grilles