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  1. #1
    Join Date
    Mar 2008
    Posts
    10

    Building Static Pressure

    I have a trane RTU unit serving half a building. The other half is leased out to other people. Well once it gets cool enough for econo mode I have serious pressure issues inside the other residents side of the building and the lobby. The walls are sealed up to the roof but im sure they are not air tight obviously. But my static pressure should not be building up enough to be forcing air into the neighbors space anyhow. I have replaced the static pressure transducer inside the unit and replaced the calibration solonoid and verified that it is zeroing out every minute. Ive adjusted my exhaust fan to be enabled once the economizer reaches at least 20%. The issue is that my exhaust fan still does not come on until the pressure inside the space is already to high. On the intelipack it says my pressure reaches around .5wc. I beleive it is still inaccurate due to the volume of air rushing out of the lobby door. I think my issue is the placement of the tubing for the static pressure transducers. There is a drop cieling in the space with return plenum but the drop ceiling is 18' in the air. The installers installed the tubing to stick 1" thru the drop ceiling into the space. My thought is that I am going to ensure that tubing is in good shape i.e. kinks, holes. and then Im giong to extend the tubing into the space closer to ground level. For some more added information about my issue the drop ceiling has egg crate returns in it along with some some missing ceiling tiles. Not many though. Once my power exhaust comes on my pressure in the space is solid. Its only when the econo initially opens and the exhaust fan delays coming on. Once on the exhaust releif dampers modulate according to pressure and operate perfect. Other then rerouting the tubing is there any other changes that I should be looking into to correct this issue. Im not very optimistic that this rerouting of the tubing is going to solve my problem. Any help is appreciated.
    Model#: SXHFC6040E77G9AD3001GAEKLRT8M

  2. #2
    Join Date
    Feb 2006
    Location
    Atlanta,GA.
    Posts
    896
    have you thought about putting the pressure tube in the supply duct and controlling it that way?

  3. #3
    Join Date
    Mar 2008
    Posts
    10
    Quote Originally Posted by chillerout1 View Post
    have you thought about putting the pressure tube in the supply duct and controlling it that way?
    Thanks for the reply. The system is already set up with a duct static pressure set up with its own transducer. The supply fan has inlet vanes on it as well which are operated off of the supply pressure. Obviously the placement of the tubing affects the reading of the static sensor in the space but do you think it only being stubbed 1" thru the drop ceiling closest to the return would be different then placing it say in the space 6' from the ground? I also am going to upsize the pneaumatic tubing that im going to reroute. Do you think that will make any difference?

  4. #4
    Join Date
    Mar 2008
    Posts
    10
    considering your idea would placing both pressure tubes into the supply duct still allow the system to function properly?

  5. #5
    Join Date
    Jan 2005
    Location
    Houston TX
    Posts
    876
    pmpaaron - your dead give away "cool enough for economizer" check the action or have someone check that as the economizer outdoor air damper opens the return air damper starts to close.
    Once in a while everything falls into place and I am able to move forward, most of the time it just falls all over the place and I can't go anywhere-GEO

  6. #6
    Join Date
    Mar 2008
    Posts
    10
    Quote Originally Posted by ga1279 View Post
    pmpaaron - your dead give away "cool enough for economizer" check the action or have someone check that as the economizer outdoor air damper opens the return air damper starts to close.
    ga1279, I have been thru the linkage and had to make a repair on one of the RTU's becuase that was the initial problem in the beginining. But the issue then was way too much negative pressure at the site due to return damper shutting and econo not opening. Once repaired my issue became positive pressure. Today I have relocated one of the pressure tubes in the space to a more central location but I dont beleive it is going to change my issue. This site has two of the same RTU's on it and they lead lag. At the moment the opposite RTU is operating now and the problem is the same. Possibly not as much positive pressure but definitly still positive. My issue lies in that power exhaust I believe but on the trane intellipack the only operations I can change are when the power exhaust is enabled. Which Ive dialed down to 20%. 20% being how much the econo is open. But the power exhaust still does not come on until my pressure are to high. After that it regulates pressure perfectly. How can I get the exhaust to come on sooner? Or am I on the wrong track? ga1279 I appreciate your reply and I hope that I understood it correctly.

  7. #7
    Join Date
    Mar 2008
    Posts
    10
    well I beleive I have gotten the issue taken care of. Ive adjusted the exhaust fan to be enabled at 0%. I adjusted the space pressure SP down to .04wc and the deadband of .04wc. Ive also adjust the minimum position of the economiser up to 33% which is up from the original SP of 30%. This is allowing enough constant flow of outside air to keep the building pressure up just enough to keep the power exhaust from shutting down due to over shooting its SP. The space is not overcooling at thus far and this may end up being a seasonal adjustment as in the summer time I do not wish to waste money on cooling 33% of FA. Thank you guys for your post. I know there is a better way to repair this but this is the only thing I could get to work.

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