AHU Coil Condensate Drainage
R. L. Beldon
We have a recurring problem in our campus Science Building
AHU's. These AHU's handle high OA ratios for make-up to fume
hood/laboratory areas and therefore have a higher than normal
latent cooling coil load. Each AHU has a draw-thru fan arrangement
which places the chilled water coils in the negative static
pressure region of the fan(most fans in the 50hp+ range).
The Problem: During summer operation, all of these AHU's
not only retain their condensate in the drain pans but
fill the entire enclosure with 3-6" of water. It actually
looks like a cooling tower basin! On a daily basis, we must
shut down the fans(which is very unsafe) and open the access
doors to let the condensate drain out. We have also tried
increasing the condensate drain pipe size to 1.25" and
relocating the traps as low as possible, sometimes to below
the penthouse mechanical room floor deck. Does anyone
have any constructive suggestions? Post here and/or E-mail.
Please excuse this inquiry if it has been discussed previously.
Ronald L. Beldon, P.E. Mechanical Engineer
ef0...@wpo.cso.niu.edu
Mike Hardy
>We have a recurring problem in our campus Science Building
>AHU's. These AHU's handle high OA ratios for make-up to fume
>hood/laboratory areas and therefore have a higher than normal
>latent cooling coil load. Each AHU has a draw-thru fan arrangement
>which places the chilled water coils in the negative static
>pressure region of the fan(most fans in the 50hp+ range).
>The Problem: During summer operation, all of these AHU's
>not only retain their condensate in the drain pans but
>fill the entire enclosure with 3-6" of water. I
It sounds like the fan static pressure is causing air to be sucked up
your condensate drains and not allowing the condensate to drain
away.The drains should be trapped to prevent this and the height of
the trap should be more than the fan static pressure so the condensate
will drain by gravity uninfluenced by the fan pressure.
If you had blow through air handling units this would not normally be
a problem.
Hope this is of help and good luck
Mike
William J. Lakos
R. L. Beldon wrote:
>
> We have a recurring problem in our campus Science Building
> AHU's.
> The Problem: During summer operation, all of these AHU's
> not only retain their condensate in the drain pans but
> fill the entire enclosure with 3-6" of water.
> On a daily basis, we must
> shut down the fans(which is very unsafe) and open the access
> doors to let the condensate drain out.
Fine for temporary measures, but bad for science labs...
> We have also tried
> increasing the condensate drain pipe size to 1.25" and
> relocating the traps as low as possible, sometimes to below
> the penthouse mechanical room floor deck. Does anyone
> have any constructive suggestions?
Just remember, the distance between the BOTTOM of the "inlet"
side of the trap and the BOTTOM of the "outlet" side of the trap
is a measure of its "strength" against the suction side of the
fan. If operating static is 6", give the trap at least 6"
plus what ever safety factor you want to build in. In tight
situations, where you don't have the luxury of sufficient room
below the drain pan, a smaller (not larger) pipe size might get
you the extra distance you need, otherwise you have to get
creative with piping, etc.
With a poorly designed drain system, you can actually suck the
water through the trap and out of the drain line, unless its
vertical component exceeds the negative pressure.
Also, if there the line is vented before the vertical drop is
achieved, you will experience venting of your waste system
into the fan... which could be an even worse problem for the
occupants! Not to mention any mold (or worse) growth due to
the standing water in a drain pan.
Hope this helps!
Bill Lakos - Systems Analyst wjl...@pplant.msu.edu
HVAC Central Control (517)353-1760x362
Michigan State University
East Lansing, MI 48823
....................................................................
D
R. L. Beldon wrote:
>
> We have a recurring problem in our campus Science Building
> hood/laboratory areas and therefore have a higher than normal
> latent cooling coil load. Each AHU has a draw-thru fan arrangement
> which places the chilled water coils in the negative static
> pressure region of the fan(most fans in the 50hp+ range).
> not only retain their condensate in the drain pans but
> fill the entire enclosure with 3-6" of water.
I have seen this before, but the client did not see the need for a
solution so we never developed one.
Hhmmmm. What would happen if the _discharge_ of the drain was moved to
a lower point. If you could achieve a tall enough 'column' of water in
the drain pipe, would you not be able to overcome the negative static of
the intake plenum?
Let us know how it turns out.
--
Your name
R. L. Beldon wrote:
>
> We have a recurring problem in our campus Science Building
> AHU's. These AHU's handle high OA ratios for make-up to fume
> hood/laboratory areas and therefore have a higher than normal
> latent cooling coil load. Each AHU has a draw-thru fan arrangement
> which places the chilled water coils in the negative static
> pressure region of the fan(most fans in the 50hp+ range).
> The Problem: During summer operation, all of these AHU's
> not only retain their condensate in the drain pans but
> shut down the fans(which is very unsafe) and open the access
> increasing the condensate drain pipe size to 1.25" and
> relocating the traps as low as possible, sometimes to below
> the penthouse mechanical room floor deck. Does anyone
> Please excuse this inquiry if it has been discussed previously.
> Ronald L. Beldon, P.E. Mechanical Engineer
> ef0...@wpo.cso.niu.edu
Are the condensate pans slanted toward the drain lines?
"hawkins@ac...@accucomm.net
are drains on negative side of fan?
DTRossi
I have had this problem in several units. My problem was that there was a
plate between the bottem of the coil and the drain pan. The little weep
holes in the plate became blocked, not allowing the condensate into the
drain pan. I drilled them bigger, a my problem went away. I another job
(Carrier 39L) The condensate was being blown off the coils because of
high air volocity caused by the coil being dirty inside even though the
outside had been cleaned and looked OK. We power washed it and the leak
went away.
Hope this helps,
Dale Rossi
dtr...@acrx.com
Little joh
> not only retain their condensate in the drain pans but
> fill the entire enclosure with 3-6" of water. It actually
> looks like a cooling tower basin! On a daily basis, we must
> shut down the fans(which is very unsafe) and open the access
> doors to let the condensate drain out. We have also tried
> increasing the condensate drain pipe size to 1.25" and
> relocating the traps as low as possible, sometimes to below
> the penthouse mechanical room floor deck. Does anyone
> have any constructive suggestions? Post here and/or E-mail.
> Please excuse this inquiry if it has been discussed previously.
> Ronald L. Beldon, P.E. Mechanical Engineer
> ef0...@wpo.cso.niu.edu
>Are the condensate pans slanted toward the drain lines?
I don't know all, haven't been on lately, hope this helps.
My first guess as to the problem for this situation is that the traps are
not deep enough to hold enough water to allow drainage ( the wieght of the
water to over come the I.W.C. draw of the fan.) if the trap is only 2
inches tall (or can only hold 2" of standing water) then a negative static
of 2.1" will pull the water out of the trap and air will follow with
enough force to stop any standing water from draining. The larger you make
the pipe the more air will travel through the pipe. Who Knows where that
air has been being sent from some floor drain or even hard piped into a
drain.
The object off a trap is to allow standing water to flow while still
maintaining a seal to prevent air from flowing. If the outlet of the
condensate is 1" then I normally will put a 3-4" trap on the
system.(office unit). If the unit will have high efficency filters then
increase the trap to acomadate the high neg. static.
Coming out of the unit the pipe can should be elbowed 10" then elbowed
back up 9" then elbowed off to the drain, where you can inset a open Tee
into the system to watch the water drain away and here the gurgle of water
when you don't make the trap deep enough. This will give a proper trap for
6 inches of water on a clean system. But when the filters get dirty and
the neg static goes up it will still work.
I have had to move traps to the floor below and made them deeper not
bigger. One I had to cut a 12 X 12 hole in the concrete floor to give the
trap the depth that it needed.
Little john
John P. Held
Little John (John P.Held)
Taking the problems out of everyday life.
Tom Moore
Apparently, the total external pressure of the fans is exceeding the
'head' presented by the trap. Good practice assunmes a trap whose longest
leg is 1-1\2 times the TESP. This means that if the pressure differential
between the interior of the AHU and the exterior is (for instance)
20"w.c., then the difference between the length of the long trap leg and
short trap leg should be THIRTY inches"
R. L. Beldon wrote:
>
> We have a recurring problem in our campus Science Building
> AHU's. These AHU's handle high OA ratios for make-up to fume
> hood/laboratory areas and therefore have a higher than normal
> latent cooling coil load. Each AHU has a draw-thru fan arrangement
> which places the chilled water coils in the negative static
> pressure region of the fan(most fans in the 50hp+ range).
> The Problem: During summer operation, all of these AHU's
Theo van Riet
Little joh <litt...@aol.com> wrote:
> Coming out of the unit the pipe can should be elbowed 10" then elbowed
> back up 9" then elbowed off to the drain, where you can inset a open Tee
> into the system to watch the water drain away and here the gurgle of water
> when you don't make the trap deep enough. This will give a proper trap for
> 6 inches of water on a clean system. But when the filters get dirty and
> the neg static goes up it will still work.
I think you are right, but how do you get the thing working ?
You pour water in it before starting the fan?
I remember once seeing a solution with a table-tennis bal in a drain
pipe. This to prevent the back flow of air out of the sewer system.
This blockage allowed the water to collect on top of the bal, pushing it
down once sufficient head had build up. Then the bal popped up again.
I do not remember the fine details, but it looked smart.
Theo
-----------------------------------
Theo van Riet ----- tvan...@macbel.be (home)
from the purple heather ----- TVR...@JANBELC1.SSW.JNJ.COM (office)
in the north of Belgium -----
Mike Hardy
On Sat, 22 Mar 1997 20:58:19 +0000, tvan...@macbel.be (Theo van Riet)
wrote:
>Little joh <litt...@aol.com> wrote:
>
>
>> Coming out of the unit the pipe can should be elbowed 10" then elbowed
>> back up 9" then elbowed off to the drain, where you can inset a open Tee
>> into the system to watch the water drain away and here the gurgle of water
>> when you don't make the trap deep enough. This will give a proper trap for
>> 6 inches of water on a clean system. But when the filters get dirty and
>> the neg static goes up it will still work.
>The idea of an open Tee is a good one.
>I think you are right, but how do you get the thing working ?
>
>You pour water in it before starting the fan?
>Yes you do and make sure the trap never dries out.
>I remember once seeing a solution with a table-tennis bal in a drain
>pipe. This to prevent the back flow of air out of the sewer system.
>
>This blockage allowed the water to collect on top of the bal, pushing it
>down once sufficient head had build up. Then the bal popped up again.
>
>I do not remember the fine details, but it looked smart.
The idea of the table tennis ball is intriguing but I can't quite see
how it would work. Instead of a 'U' trap I have used a different
arrangement in the past, that is to stick a piece of 4 inch plastic
soil pipe vertically on to the bottom of a tank and have the air
handling unit drain by gravity into the flooded 4 inch pipe. The
condensate spills over into the tank and the drain may then be run by
gravity or pumped from the tank. It is particularly useful in false
ceilings where it may be important to use high level water alarms to
cut the unit off if the pump fails and to provide an element of water
storage when the air handler is shut off by the safety alarm.
Regards Mike
Brendan McFarlane
Theo van Riet wrote in article <1997032220...@pool03-441.innet.be>..
.
>Little joh <litt...@aol.com> wrote:
>
>
>> Coming out of the unit the pipe can should be elbowed 10" then elbowed
>> back up 9" then elbowed off to the drain, where you can inset a open
Tee
>> into the system to watch the water drain away and here the gurgle of
water
>> when you don't make the trap deep enough. This will give a proper trap
for
>> 6 inches of water on a clean system. But when the filters get dirty and
>> the neg static goes up it will still work.
>
>
>You pour water in it before starting the fan?
>
>pipe. This to prevent the back flow of air out of the sewer system.
>
>This blockage allowed the water to collect on top of the bal, pushing it
>down once sufficient head had build up. Then the bal popped up again.
>
>I do not remember the fine details, but it looked smart.
>
>
>
>-----------------------------------
>Theo van Riet ----- tvan...@macbel.be (home)
>from the purple heather ----- TVR...@JANBELC1.SSW.JNJ.COM (office)
>in the north of Belgium -----
>
The ping-pong ball device is made by Holland Heating, who are in Waalwijk,
The Netherlands.