Problem on flooding at AHU Room

[WRNR]

I'm having a problem regarding flooding on the AHU Room, where in we have installed two (2) Packaged Water Cooled Units in a single room.

Water comes out from the floor drain as a result when we run the two units at the same time.

Is it possible that excessive return air can contribute to the flooding? We have installed the 2 units and its individual return air as a plenum return (the whole AHU Room being its plenum box).

What can be done to minimize this?

By the way the room is fully insulated.

Thanks.

 

[imok2]

Apparently, when you are running both units you are creating a negative pressure in the room which is causing the condensate from draining. You may have to stick the drain line in the drain and seal all around it to isolate the negative pressure.

 

[friartuck]

Units should be designed to give a slight POSITIVE room pressure (Filtered air).

Sound like the system needs a good looking at.(commissioning being a key requirement)

What sort of units are they?

Floor mounted top discharge, Floor mounted downward discharge into a suspended floor?

Whose make are they.

Can you turn the extract down (If there is any)

If you are sucking water out of the drains, I would guess that the drains are 'trapped' with a 2" seal.

If so, to pull the water out would need 500Pa of suction...some negative room pressure. I'm surprised the walls haven't caved in.
Have you checked if the drain is blocked, laid to a suitable fall etc.



Friar Tuck of Sherwood

 

[MintJulep]

Bith imok and the good friar read your question and seemed to assume that this is a condensate drain question.

However, reading carefully you seem to be saying that water is coming out of a floor drain in the room. Could you clarify this please.

If you are actually sucking water out of the drain line it is probably because you have high negative pressure in the room. Possibly leaks in the return ducting, or possibly a service access panel left open.

 

[walkes]

I have a question or two, are the units using domestic water for cooling? If so, is the return water from the condenser cooling going to the same floor drain, is it piped properly? What size is the drain? Are both lines causing too much capacity for the drain?

When you say flooding is water continually coming up from the floor drain, if it is it doesn't sound like condensate (unless your mixed air is at 90% RH).

 

[jherbert]

......agree with mintjulep

the OP states he has a sealed room, as return air plenum.

Most likely the relative low room pressure (-) is drawing waste water from the trap into the plant room. Incidentally, that is how SARS outbreak occurred.

Anyway solutions:

- unseal the plenum

- increase the depth of the trap seal [such that the water seal is greater than the negative pressure created in the plenum]

If you have trap top-up devices, check that it is operational.

 

[ChasBean1]

I don't really agree with unsealing the plenum. The room is basically an unconditioned box that should be insulated and sealed from neighboring spaces. If assumptions are correct, this room acts as a mixing chamber for (likely) above ceiling return and make-up air. The room needs to be negative to perform its function. I do agree with the trap seal comment.

1. Ensure that air pathways (return and make-up) are not obstructed by wall construction or faulty dampers.

2. The floor drain needs to be properly sized, trapped, and ideally, a trap primer would be used to keep from drawing in wastewater gases.

 

[WRNR]

SORRY FOR MY LATE REPLY.

I'VE FOLLOWED ALL YOUR SUGGESTIONS, I ALSO MADE TRIAL AND ERRORS, I'VE COMBINED SOME OF YOUR SUGGESTIONS AND IT WORKED ON SOME AREAS USING THIS KIND OF SET-UP.

WE MANAGED TO MINIMIZE THE BACK FLOWING OF WATER FROM THE DRAINS, BUT STILL SOME AREAS ARE HAVING THE SAME SITUATION.

BY THE WAY, THE FLOOR DRAINS ARE CONNECTED IN ONE COMMON DOWNSPOUT 8in Dia. AND THE ROOM DEFINITLY ACTS AS A MIXING CHAMBER.

THANKS TO ALL.

 

[AEBuck]

Follow this link for a good description of this and similar situations:

http://www.hpac.com/member/archive/pdf/2001/1001/brusha.pdf