chilled water fan coil unit problem

[tradybrad]

hi guys
Have an issue with a chilled water fan coil unit at one of my sites. Fan coil unit is slinging water up out of the internal drain tray and throwing water down down ductwork etc. internal Drain is leaking water ok with no blockages in drain line (Has been cleared a thousand times). Ra filters are clean and not long ago replaced. Coil could do with a clean but not real dirty.If anyone has any ideas to stop this issue im all ears:)

[stufus]

Is there a trap on the drain outlet to prevent siphoning ?
If you pour water into the drip tray the velocity and quantity will more often than not allow that water to escape.
But as the coil will generate condensate at a much slower rate there is only gravity to take it away ,if there is no trap the air velocity can effectively create a vacuum in the drain line and prevent the condensate from leaving the tray where it will be picked up and thrown out in the air stream.You need to clean the coil to be sure as restricted airflow through the coil could compound the issue.
On the other hand is the ductwork insulated ,if not it may be condensation in the duct not condensate.
Cheers
Stu

[tradybrad]

hey stu
thanks for the reply. Yep there is a trap on the unit it has been cleared out and recharged with water.Ductwork is insulated also.Will clean coil to see if helps.Here's hopeing it works because running out of ideas on this one.

[stufus]

No worries
Another thought is the duct work sized correctly.
Increases and decreases in static pressure due to duct work can do strange things.
Cheers
Stu

[install monkey]

blast nitrogen through the coil as the restricted airflow will suck the water off the fins

[tradybrad]

hey
Coil cleaned unit today see how it goes over the few days.Just looking into the unit today has anyone got any thoughts on this fcu coil not sitting directly in drain pan in some sections. Has 10 mm gap in some spots. Could this be causing me an issue? Also done some digging on history of FCU at fault had fan motor changed 1 year ago.Is it posssible if fan is to large in capacity and running to fast. could this cause an issu?. Any thoughts or ideas would be great.

[matt p]

Hey Mate,

When you say some spots to mean it's not an even drop across the bottom to aid the drain away of the condensate water?.

If you can try and create an even drain off for the condensate water to run into the drain pipe.

I've seen this a couple of times mainly with blocked filters and or coils aswell, but it maybe worth dropping the cover plate off to expose the rear of the coil and blast it out from the inside to totally remove all the rubbish.

Also don't rule out a possible split coil due to people over eager tightning up the actuators on the valves.

Regards

Matt

[Greengrocer]

Is this a Fan coil unit or a AHU?
Could be due to high velocities over the coil carrying moisture into duct. Check the fan speeds. If a fan coil unit (direct drive) then it should be able to operate on all selectable fan speeds without a problem. If an AHU (belt drive) then it's possible that the belt / pulley drive may be incorrect.
However, as you say, if someone has replaced the fan motor is it the correct type / speed.

[tradybrad]

Thanks for the reply guys
greengrocer its a fcu with 3 speed direct drive motor.I changed it to low fan speed from high fan speed when i did coil clean the other day. I will find out tomorrow if unit still has issues i will keep you's all posted on how i go>
Regards
Brad

[Wilbert]

Is the drain located in the return fan side? If so.. ensure that the return fan is running faster then the supply fan. Other option is to install a small pump to prevent water from backing up from the drain. installing a check valve with the pump and putting some sort of switch to activate the pump may help in having the pump run continiously... Just a thought.