Hey all, We have a Trane Climate 1

[imok2]

Hey all,
We have a Trane Climate Changer air handler,chilled water system.The plumbers ran the condensate lines off the unit,due to limited space the traps turn down 5 inches over 4 inches and back up 4 inches then slope to floor drain.The unit has three 1 1/2" nipples all are trapped then tied together to floor drain. Problem is they won't drain properly,unit holds a ton of water and overflows.Trane has a bulletin that shows how to make a proper trap.The unit in question runs at 10 inches of static.So using their formula the trap should go down 18 inches over 4 inches and back up 5.5 inches.The unit is in the penthouse of a hospital so it is possible to drill through the floor to make the trap bigger, but not the easiest thing to do in a hospital.The boss asked why can't we just make the trap wider instead of deeper?Trane says they don't know why it won't work, but they say it can't be done that way.Does anybody have a thought or opinion?

 

[MintJulep]

The water column in the trap must be at least as high as the negative pressure inside the unit, otherwise the suction inside the unit will just suck up the water.

 

[MintJulep]

And I very disappointed to hear that the folks at Trane don't know that.

 

[imok2]

I belong to another web site and from time to time I like to get view points from engineers The other site is mostly questions from service tech in the field. Comments are always welcome

 

[imok2]

MintJulep Thanks for the response. Do you have any thoughts on a solution

 

[quark]

I have a standard practice of maintaining the difference between the two legs of the trap equal to that of the fan static pressure. This arrangement will take care even if your suction damper is closed by accident(this is, actually, to avoid the unfiltered outside air entering into a formulation area). Is there any possibility for taking the pipeline out of the building and then provide the water seal?

Regards,


Believe it or not : Eratosthenes, a 3rd century BC true philologist, calculated circumference of earth with the help of a stick and it's shadow. The error was just 4% to the present day calcuated value.

 

[KenRad]

imok2,

Aside from the trap dimensions, one other thing concerns me. You refer to 3 drain nipples on the unit. One of these should be for the chilled water coil pan, but the other two are probably for other sections (like hot water coil or fan sections). There is no reason for the drain nipples from these other sections to be trapped and run to the floor drain; the traps will stay dry, and you are just providing another source of unfiltered infiltration air.

---KenRad

 

[lilliput1]

Drill through the floor to make the trap deeper. Provide screw on caps for clean-out on the drain piping where the trap goes down & where it goes up. Seal slab opening with fire rated caulking. Make sure bottom of pan slopes down & drain connection is located at this low point otherwize you still will not be able to keep the pan dry. Locate true low point & make drain connection there.

 

[imok2]

Thanks for the responses, I really appreciate all of them!

 

[DouginMB]

imok,

Is this a new installation? I recently had a similar situation with an air handler where the condensate was not draining and was pooling inside the housing. The cause of the back-up was not due to the depth of the trap, but the coil was clogged so badly that the supply fan had to speed-up significantly to overcome the pressure drop across the coil. This caused an excess negative pressure and in turn caused the condensate to stop draining. Just something to consider.

 

[ROCHESTER]

A condensate tank/pump unit, like used for steam systems, should work. You'd need a check valve to prevent backflow.

 

[kck115]

I agree with the solution of drilling thought the floor and lengthen the trap.
One last point, in a unit with multiple drains each drain will often need to be piped with a separate trap. This is due to each section of the unit being under different pressure.
Good Luck

 

[ChasBean1]

Is the coil on the suction side? The 10 in. w.c. of static, is that 10 in. w.c. suction static at the location of the CHW coil or 10 in. delta across the fan? Usually at the suction, all the unit has to overcome are AHU components (OA damper, pre-filter bank, final filter bank, and 2-3 coils) - if all these exceed 4 in w.c., negative pressure, I'd be suprised.

The down & up is key to prevent sucking in sewer or gray water gas, but the delta between the two columns is the key for allowing drainage. If you have 10 in. w.c. negative static at the coil, for example, the trap would serve no purpose unless it goes down and back up at least 10 inches (e.g., 5 down, 5 up). But the key point is that the trap could actually block drainage if the inlet is less than 10 inches higher than the outlet. If this condition exists (which it does in your case), you're better off using a fatter drain pipe and no trap at all.

Think about it, the trap keeps the AHU from sucking in sewer/gray water gases, but only when there's condensate flow. At other times during the season, when the outdoor dewpoint is lower than the coil temperature, the unit happily sucks in gas from the drain line through a totally dry trap... hmmm.

Moral? Question common HVAC convention. (this is a once-though post - I might second-guess it upon later review!). Best of luck, -CB

 

[quark]

CB!

I think I have to disagree with you if I correctly understood your post. Suppose the static at coil suction is -10 in wc (say), water will be sucked up eventhough you provide 5" down and 5" up, for you have to provide height of water column and not any other linear measurement.

If we provide 12" down and 2" up, water will still flow out. Let us consider the 14" portion of trap filled up with water. With further condensation, water will flow down by gravity and tries to rise the water in 2" portion of the drain leg and drains it.

In dry condition, as there is already water in the loop(condensate from the earlier season), no outside air will be sucked in as the fan can't suck water to a lift of 12".

To all(including CB)!

CB opened a can of worms by asking "Is the coil on suction side?". Though the general practice is to put coil on suction side, what if it is on discharge side? Some points which come into my mind are,

1. Moisture carryover due to high pressure (high pre. may balance liquid particle weight)

2. Better corrosion resistance for the fan.

3. Reduced mass flow through fan (though it is marginal)

Any more ideas, or am I lacking the main idea?

All ideas are appreciated.

Regards,

 

[ChasBean1]

I think we're saying the same thing but my 5" down, 5" up point might have added confusion. That point was simply that there should be a 10" (minimum) delta to keep from taking in sewer gases, regardless of need for flow. But then to achieve flow, the initial downward run needs to exceed 10" and the outlet should be more than 10" lower than the inlet; but a loop is still required for the trap to serve the purpose of preventing infiltration of untreated (or sewer/gray water) air (and also to keep condensate from battling an airflow in the opposite direction coming out of the drain pipe).

Back to imok2's problem, his trap allows for proper drainage of neutral to -1 in. w.c. in the AHU (no good). Looks like the formula (18" down, 5.5" up) would produce a good result if it was correctly applied. Meaning, only the suction static should be considered, not the fan rated static pressure, which is the difference in static pressure across the fan.

Imok2, however many inches over shouldn't matter, but I guess the trap could maybe hold more 'goo' if it has a larger horizontal...

 

[imok2]

update: all have agreed that the floor must be drilled and the traps made 18 inches deep.The traps will be located below the floor and tie into the drain pipe above the ceiling on the floor below.The unit serves three floors so scheduling a shut down will take a couple of weeks of paper work.

 

[imok2]

PS This is 10" -static

 

[ChasBean1]

Good choice! That's very negative...

 

[cjw81]

Wow, you guys are amazing when you sink your teeth into a problem. It is a pleasure to watch you go at it.
I am a practical applications orientated operating engineer and have had this problem with high speed fan systems. One approach that worked was to offset or angle the trap because of the lack of clearance between the condensate fan discharge pan and the floor drain. It required quite a longer run to maintain the static head to keep the trap seal but it worked.Also, between the plenum wall and the trap, install a vertical pipe the same pipe size as the trap diameter about 1' high.Teh top of the pipe is left open to the atmophere, not capped. This will provide you with an "air break" to allow flow even though the negative fan static is trying to pull the condensate back. You are "breaking the siphon." Another way we enured pan drainage was to time how long it took for the pan to fill with condensate (about 1 hour) on a high load day and then shut off the fan and timed how long it took for the pan to drain (make sure you keep the access door closed to simulate "real" operating conditions). We then set the the BMS (building management system) to shut the fan off every hour for 7 minutes (acceptable down time) to allow the pan to drain. It worked beautifully. Another solution we used was to use a small constant duty pump inside the drain pan and connected it to a 5/8" garden hose and discharged it into the drain through a hole we drilled in the plenum wall.Electrode switches and floats proved unreliable for a pump controller due to the amount of particulates you will always accumulate in the water so we devised another method which consisted of using a "Turck" proximity switch ( same as used on an assembly line) which we placed outside of the plenum at the lowest level we wanted to maintain in the pan. We set up the adjustable hysterisis field to sense the level in the pan by starting the sensing field just past the wall thickness of the plenum and the pan wall thickness.Now your switch is not in the difficult wet,dirty, high velocity environment of the plenum. The switch amperage rating was not high enough to operate the pump directly so we added a relay to the circuit between the proximity switch and the pump. The pump had a built in foot valve to prevent reverse flow and naturally we put a meinhoff fitting ( a simple funnel)over the drain to prevent splashover and ensure an air gap of 1" to prevent siphoning. Hope this helps.

 

[ChasBean1]

cjw81 - one thing I got from your post is that there are several ways to do things and I applaud you for that. Don't take this the wrong way, but I see some good fate and fortune working with some of the solutions you mention. I just go back to fluids notes from freshman year (P = rho * g * h).

Most applications I've seen in labs and hospitals wouldn't tolerate a 7-minute shutdown every hour. But the pumping you mention should help drainage.

Thanks for your input & best regards, -CB