U Traps

[frank]

We installed a large above ceiling ducted heat pump unit (25kw) system last summer and had initial problems getting the thing to drain into a condensate tank pump. Having fixed the initial problems, we got a call out today saying that the unit was leaking water, especially after switch off at the end of the day.

It appears that, during winter when the unit is in heating mode the u-trap on the drain evaporates and following a change over to cooling the first cooling cycle cannot drain as the trap is dry. On switch off the unit then floods back and ruins the ceiling. Any ideas as to how we could put in a permanant solution bearing in mind that we cannot use a gravity drain setup.

[Brian_UK]

Just a thought Frank, would it be possible to fit a peristaltic pump that is activated on the cooling cycle?

If this pump discharged into your U trap it may (I only say 'may') pre-fill the trap and repair the water seal.

Any thoughts anyone else ??

[chemi-cool]

this might be dangerows marc,

you will need a spring loaded NRV and may have problems of air pockets in the pipe.

but if ridgid plastic pipe of a large diameter is used, then the water will not create air pockets. an air vent should be installed after the trap.

chemi

[frank]

The drain pipe is 25mm dia and the trap is 100mm away from the outlet. The tank pump is then about 250mm after on a slight slope to allow gravity draining. The idea about a NRV is good but can a gravity drain open the valve - i.e. no pressure applied?

I re-configured the slope and tank pump position today and instructed the staff to only let the system run for 2 hours max when it is switched over from heating in winter to cooling, then to switch the unit off and allow the condensate to drain, filling the trap but not overloading the tank, then to restart the system and all should be ok.

Theory seems good but I have doubts about the reality.

I've heard about u-traps that do not dry out as they are fed with water, quite some time ago and at the time I did not take much notice. Anyone heard of these? They are used on branch pipes into foul drain stacks? Maybe I'll have to ask a plumber friend of mine.

[frank]

I thought of the oil solution, as this tends to sit on top of the water, but with a trap, one side will tend to allow the water to enter and one side will allow the water to pass and so this will eventually leave the trap with one side having oil and the other side not having oil as it would have been carried away with the condensate. This will allow evaporation and eventually a dry trap over the winter months.

What I'm trying to achieve is a long term solution to the problem. OK, it is not long now till the system is out of warranty and then it may become someone else's problem - but I don't work like that - I would rather make the long term solution for peace of mind if nothing else.

[PobodysNerfect]

Frank,
Maybe of interest:
http://www.trenttech.com/dry_trap_syndrome.htm
Saludos
Jan

[Dan]

I would think a pvc gravity swing check valve is all you would need. Just something to keep the air from sweeping up through the pipe until the trap fills. On the other hand, there is the costgard:

http://www.trenttech.com/video_demonstration.htm

[Dan]

Too funny, Pobody. How the heck did you post later than me and get ahead of me? Anyway, there is a bit of simple genius there that I wish I had thought up.

[shogun7]

Frank, Iwas wondering if you used a condensate pump with the discharge line in the drain of the pan and then sealed the part thats still open you may get some back draft but I believe when condensate accumulates in the pan, the pump would over come the negative pressure and solve the problem.

[chemi-cool]

hi frank,

can you make a scatch and post it?

this is a common problem over here as we cool 7 months of the year.

I have somthing that I have done and it made things ok. but I want to see the layout of the unit and how high it is above the false ceiling or where ever you have located it.

one thing that come to my mind, if the condensate tank is located in the cooled erea, even adove the ceiling, why use the U trap at all? why not let the water flow straight into the tank?

chemi

[Peter_1]

That's how we do it.
At the oultlet of the drainpan the suction of the peristaltic pump and seal with that crimp stuff for leads.

[chemi-cool]

hi peter,

i dont think peristaltic pumps are good for this application, the tube which works as a pump has relative short life and the way to find that, is when the ceiling strarts dripping.

chemi

[Peter_1]

It's one of the things we change with the annualy maintenance.
Have such a pumps which we installed 3 or 4 years ago and still with the same tube in it.
They only run when outside machine is running.
Sauermann pumps.

[shogun7]

Frank take a looksee
http://www.plumbingsupply.com/condensatepumps.html

[frank]

Thanks Guy's

Chemi - if you do not use a trap on the drain then the negative pressure within the fan chamber will not allow the condensate to escape as the inrush of air overcomes the force of gravity.


Shogun - we use the tank pumps already, as shown in your link. The pump is not the problem, it is the drying out of the trap during heating season that is the problem.

Dan - good link to the dry trap syndrome site but how does it work?? I suppose you have to buy one to find the answer