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  1. #1
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    Carrier Universal Controller Programming

    I am on a job trying to fix up some programming issues on a universal controller. This controller is controlling 3 VFDs. Two of the VFDs are feeding outdoor air into the outdoor air section of some AHUs. The other VFD is controlling a Relief Fan. I am controlling the Relief Fan VFD off of Space pressure. The AHUs are on the first floor of this department store. The outdoor fans are on the roof which is about 25 ft above the AHUs. The outdoor fans pull outside air in and push it into the AHUs. I haven't seen a set up like this before. I need a way to control the fan speed. I am thinking about doing it by tracking the outdoor damper position. I am not sure if that is the best way to do it or not, but it doesn't seem to be too critical. I am having a hard time finding the right algorithm to perform this function. I am looking for some assistance on setting something like this up. Right now they have a Analog Single Loop PID trying to control this function. I tried assigning my damper position to the algorithms setpoint but it will not recognize it as a setpoint. It keeps defaulting to SETPT01. Is there some easy way that I can set something like this up? I have reviewed the manual and cannot locate a similiar situation.

    Thanks for any help on this.
    J. King

  2. #2
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    I don't know that programming, but there is so much slop in most dampers that this isn't a very good approach, but its a cheap way to do it. I've done it but I've had to make multiple resets based on the damper position, ie 0-25% use reset 1, 25-50% use reset 2, etc.
    If budget allows I'd put in a static pressure sensor in the duct between the OA intake and the AHU's OA intake and control to a very slight positive static.
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  3. #3
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    Quote Originally Posted by crab master View Post
    I don't know that programming, but there is so much slop in most dampers that this isn't a very good approach, but its a cheap way to do it. I've done it but I've had to make multiple resets based on the damper position, ie 0-25% use reset 1, 25-50% use reset 2, etc.
    If budget allows I'd put in a static pressure sensor in the duct between the OA intake and the AHU's OA intake and control to a very slight positive static.
    I was considering that idea as well. I think that was the way that is was supposed to be controlled. The customer was just looking for a cheap fix for now, and I thought if I could just track it for now to get them by I would. It probably would just be as easy to use a static pressure sensor on each duct and run the necessary wiring.

    I am still curious on how to set up a fan tracking program on this Carrier controller if someone has the information on this. I would really appreciate it.

    Thanks!
    J. King

  4. #4
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    First thing you will need is the Best ++ manual, email is in my profile

    Quote Originally Posted by apprentice3 View Post
    I was considering that idea as well. I think that was the way that is was supposed to be controlled. The customer was just looking for a cheap fix for now, and I thought if I could just track it for now to get them by I would. It probably would just be as easy to use a static pressure sensor on each duct and run the necessary wiring.

    I am still curious on how to set up a fan tracking program on this Carrier controller if someone has the information on this. I would really appreciate it.

    Thanks!

  5. #5
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    Quote Originally Posted by bdivell View Post
    First thing you will need is the Best ++ manual, email is in my profile
    I have that manual already, but I thought best ++ could only be used on 1600 and 6400 comfort controllers not universal controllers?
    J. King

  6. #6
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    Yes sorry, no Best++ option on the UC


    Quote Originally Posted by apprentice3 View Post
    I have that manual already, but I thought best ++ could only be used on 1600 and 6400 comfort controllers not universal controllers?

  7. #7
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    Just a thought, outside air fan vfd's should have a fixed speed, set and balanced for min outside air requirements and should not need to change speeds. Or install co2 sensors in the space and ramp outside air fans based on co2 readings. Leave the relief air to modulate based on building pressure.

  8. #8
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    You're going to need to put a static pressure sensor in the OSA plenum and control the OSA VFDs to maintain a slightly negative pressure. That's the right way to do it. Also, make sure you have a low static pressure safety switch installed to shut down the fans to prevent the duct work from imploding if something goes wrong.
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  9. #9
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    Quote Originally Posted by air1 View Post
    You're going to need to put a static pressure sensor in the OSA plenum and control the OSA VFDs to maintain a slightly negative pressure. That's the right way to do it. Also, make sure you have a low static pressure safety switch installed to shut down the fans to prevent the duct work from imploding if something goes wrong.
    The OA fans on this job pressurizes there plenums with air. It pulls air off of the roof and pressurizes down into the AHUs OA section. If the dampers were shut it would build up pressure. A static safety switch is a good idea. I will make sure one of those is on there. Based on my sequence of operation described above do you think I should maintain a positive pressure not a negative pressure in the plenum?
    J. King

  10. #10
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    Quote Originally Posted by drj_controls View Post
    Just a thought, outside air fan vfd's should have a fixed speed, set and balanced for min outside air requirements and should not need to change speeds. Or install co2 sensors in the space and ramp outside air fans based on co2 readings. Leave the relief air to modulate based on building pressure.
    I do have Co2 sensors in the space already. I will think about controlling the fans based on Co2. I could do that pretty easily.

    Thanks for the idea.
    J. King

  11. #11
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    Agree w/air1, a slight negative would likely be best to control to, but it depends - the 'shaft' the ductwork is going thru, is there anything that you wouldn't want to pull in that leaks prior to the outside air might mix in via seams/holes in the ductwork? In the setting you described unlikely now that I think about it closer.
    If there is then control to a very slight positive, but keep in mind that slight positive will want to overcome your return air back, short of a return fan controlling to the same...

  12. #12
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    Quote Originally Posted by apprentice3 View Post
    The OA fans on this job pressurizes there plenums with air. It pulls air off of the roof and pressurizes down into the AHUs OA section. If the dampers were shut it would build up pressure. A static safety switch is a good idea. I will make sure one of those is on there. Based on my sequence of operation described above do you think I should maintain a positive pressure not a negative pressure in the plenum?
    It really depends on where you are measuring the pressure and how the duct and dampers are configured. My concern is that if you control to a positive pressure in the mixing box you will force air out thru the return duct or not allow any return air into the mixing chamber.
    "The bitterness of poor quality remains long after the sweetness of low price is forgotten". --Benjamin Franklin
    "Don't argue with an idiot, they will drag you down to their level and beat you with experience". --Mark Twain
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  13. #13
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    Quote Originally Posted by air1 View Post
    It really depends on where you are measuring the pressure and how the duct and dampers are configured. My concern is that if you control to a positive pressure in the mixing box you will force air out thru the return duct or not allow any return air into the mixing chamber.
    I see your point on this. So should I place the pressure sensor in the mixing chamber and not in the OA plenum itself?

    Thanks everyone for all of the advice.
    J. King

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