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100 percent OAU with steam coil

I have a 100 percent Trane OAU with a steam coil. Multiple issues on site corrected but this one unit still having issues. There is a armstrong 812 bucket trap installed 3/4 inch bushed up on both sides to 1 inch. It is being used for space heating a warehouse area.The trap and air handler are outside, the steam trap has a check valve on the outlet and must raise condensate around 15 feet. Inlet pressure is 35-40 per the design blueprints I recently found. The steam trap recently froze up and busted. I do not have any piping diagrams and this has been a problem in the past after speaking with the customer. I need to find the correct best trap to replace with. They had a spare 812 that was installed today and I am looking for recommendations on possibly a better option. 

Comments

  • ratio
    ratio Member Posts: 3,290
    Insulation & heat trace?
    mattmia2everythinghvac
  • pecmsg
    pecmsg Member Posts: 3,336
    Are you saying the trap and piping is outside?

    mattmia2everythinghvac
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 12,658
    That will not work. You can't raise water if the trap and vertical return line is subject to freezing. It will freeze and bust. F & T is the right trap bucket won't work.

    High temp heat trace and covering is the only fix. And that may not fix it.


    Many of these units are installed outside trap piping and everything and will work fine. It's lifting the condensate that's the problem.

    Steam to glycol heat exchanger and convert the unit to glycol and change to a hot water coil may be the only fix
    everythinghvac
  • everythinghvac
    everythinghvac Member Posts: 5
    They half assed insulated the trap and short piece of return all other piping is insulated well. I thought about heat trace, the F&T trap may solve a lot of problems I'm just not sure what was supposed to be there by design their guys just throw whatever trap they have at it. Thanks for the advice. 
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 12,658
    F&Ts pass air much better than a bucket. But like I said the general rule is never lift condensate if the coil and piping are subject to freezing
  • pecmsg
    pecmsg Member Posts: 3,336

    They half assed insulated the trap and short piece of return all other piping is insulated well. I thought about heat trace, the F&T trap may solve a lot of problems I'm just not sure what was supposed to be there by design their guys just throw whatever trap they have at it. Thanks for the advice. 

    With 100% OA you should constantly be pushing HOT condensate!

    1/2 assed insulated?

    Is this the only air handling unit that has the issues?

    Can you find the original blueprints?
  • offdutytech
    offdutytech Member Posts: 79
    Aside from the steam trap how is the steam coil configured? Is it a plain coil or is it a face and bypass configuration? What is the control sequence for the unit? Is it a large unit using 1/3 2/3 steam valves or a single valve? Is the steam valve functioning correctly?

    Typical a 100 OA unit is a face and bypass. Below say 40 deg OAT the steam valve would be 100% open allowing the condensate to flow constantly be pushed through the system. Then the bypass damper is used to temper the air. One of the issues that I have seen is that a heating coil temp sensor is not installed and you get a variation if the discharge air sensor is only used. If the unit is also on a time schedule where it is off and the steam valve is closed it's this will create all sorts of issues below freezing. Couple that with poor sealing outside air dampers and you have more problems. 
    It sounds like in addition to having a few mechanical issues you may have some control issues.
  • everythinghvac
    everythinghvac Member Posts: 5
    It is face and bypass. It's not being controlled well, installed by others with trane Controls. There is no valve/actuator controlling the steam flow. The TGP algorithm is controlling face and bypass dampers by space temp. This causes and issue when the space reaches temperature the dampers close and I would trip the freeze stat. I have cracked the damper slightly to solve this problem without actually changing the program. I have worked out basically all other problems throughout 3 buildings this has been the problem child for obvious reasons, it is the only one that's outside all others sit inside the building. 
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 12,658
    !00% OA the steam valve should be 100% open at 35 degrees OA or below. If the dampers and valve are controlled by the indoor temp it will always trip on freeze. The freeze stat is a safety control it shuts the unit down in an emergency it's not an operating control.

    Perhaps some modern Trane engineer in pursuit of higher efficiency is trying to do something that won't work