Page 1 of 2 12 LastLast
Results 1 to 13 of 14
  1. #1
    Join Date
    Jun 2019
    Location
    So Cal
    Posts
    332
    Post Likes

    Cool Request/ web ctrl

    Whats up guys, I had a question in regards to one of our packaged units that supplies VAV's.

    This particular packaged unit provides for 10 separate VAV's/zones and my question is in regards to the cooling request and stages coming on.

    I would like to know, where in the logic can i see how many cooling request does it take for more than one stage to be enabled. Earlier today, only 3 zones were calling for cooling but the packaged unit had 3 stages engaged. Doesnt that sound like over kill? If one of the goals is to implement ems i dont see 3 compressors running to provide cooling for 3 zones as very efficient.

    Can any of you point me towards where i would be able to turn on and off stages as i see fit and not through the logic?

    i have attached some graphics.
    Attached Images Attached Images   

  2. #2
    Join Date
    Apr 2014
    Posts
    141
    Post Likes
    From what that part of the logic shows, you have 6 Cooling callers but the number of significance is your Current SAT Setpt of 55F. Somewhere else on your logic page, there has to be a direct acting PID that shows the cooling demand increasing as your unit stays above the discharge setpoint. The longer the SAT is above 55, the more stages are going to come on. You mention 3 compressors for 3 zones but it shows 6 active callers out of 10. If these zones have some size to them, at 90F outside temp

    If you truly have Supply and Return Fan VFDs as the graphic shows, I would keep an eye on the Static pressure because being half an inch W.C. low seems to indicate the zones are wide open and not satisfying their individual setpoints. If they run at 100% most of the time, the VFDs are just for show.

  3. #3
    Join Date
    Jun 2019
    Location
    So Cal
    Posts
    332
    Post Likes
    Thread Starter
    Quote Originally Posted by controls21 View Post
    From what that part of the logic shows, you have 6 Cooling callers but the number of significance is your Current SAT Setpt of 55F. Somewhere else on your logic page, there has to be a direct acting PID that shows the cooling demand increasing as your unit stays above the discharge setpoint. The longer the SAT is above 55, the more stages are going to come on. You mention 3 compressors for 3 zones but it shows 6 active callers out of 10. If these zones have some size to them, at 90F outside temp

    If you truly have Supply and Return Fan VFDs as the graphic shows, I would keep an eye on the Static pressure because being half an inch W.C. low seems to indicate the zones are wide open and not satisfying their individual setpoints. If they run at 100% most of the time, the VFDs are just for show.
    Hi Controls, thanks for the reply.

    Yes the screen shot i took was after the fact, although i do see that there was at that moment 6 zones calling for cooling.
    I do not believe that SF or EF are on VFDs unless there is an internal one inside the packaged unit?

    Ok, so until the SA hits 55 or lower, multiple stages will remain on? that makes more sense than how i was understanding it.

    Not sure what the deal with the static pressure in the building and ducts are, i have spoken up and brought up this problem but unfortunately im just the middle man.

    ACCO is our service provider.

    Anyways thank you for your input sir.

  4. #4
    Join Date
    Mar 2018
    Location
    Texas
    Posts
    39
    Post Likes
    Hi BuildingMech,

    If you want to follow the trail of the cooling call logic, click that CLREQ label that's storing the request value. It looks like you're dealing with a variable-function SAT setpoint reset, so there may be one of those setpoint reset blocks in there somewhere that parses requests and adds or subtracts from the supply setpoint. Controls is almost definitely correct that your stages will be based on discharge vs setpoint. If you still feel like the response is too aggressive you can slow down the PID loop or add a minimum CLREQ before triggering second and third stage.

    As for the duct static, it doesn't actually look like you have a return fan but rather an exhaust air fan. If it's in tandem with the OAD, you're open 75% and the most comfortable place in the building might be on the roof unfortunately. If you want to save energy I'd start there. I would increase the speed differential between supply and exhaust fans if you're trying to keep up duct static.

  5. #5
    Join Date
    Jun 2019
    Location
    So Cal
    Posts
    332
    Post Likes
    Thread Starter
    Quote Originally Posted by Mikemikemike View Post
    Hi BuildingMech,

    If you want to follow the trail of the cooling call logic, click that CLREQ label that's storing the request value. It looks like you're dealing with a variable-function SAT setpoint reset, so there may be one of those setpoint reset blocks in there somewhere that parses requests and adds or subtracts from the supply setpoint. Controls is almost definitely correct that your stages will be based on discharge vs setpoint. If you still feel like the response is too aggressive you can slow down the PID loop or add a minimum CLREQ before triggering second and third stage.

    As for the duct static, it doesn't actually look like you have a return fan but rather an exhaust air fan. If it's in tandem with the OAD, you're open 75% and the most comfortable place in the building might be on the roof unfortunately. If you want to save energy I'd start there. I would increase the speed differential between supply and exhaust fans if you're trying to keep up duct static.
    Mike, do you mind diving into those points i have highlighted a bit more? Im not sure i follow, i dont understand wha PID loop means.

  6. #6
    Join Date
    Apr 2007
    Location
    Amarillo by mornin'
    Posts
    1,001
    Post Likes
    What would help is if you can get down in the logic page and take a snippit of the cooling 'chunk' and we can tell you better about what is going on. Also, I would be looking at the building static pressure. That is probably not correct and has your relief fan screaming at 100%.
    "It's not that I'm smart, it's that I stay with the problem longer”
    Albert Einstein

  7. #7
    Join Date
    Jun 2019
    Location
    So Cal
    Posts
    332
    Post Likes
    Thread Starter
    Quote Originally Posted by xarralu View Post
    What would help is if you can get down in the logic page and take a snippit of the cooling 'chunk' and we can tell you better about what is going on. Also, I would be looking at the building static pressure. That is probably not correct and has your relief fan screaming at 100%.
    Hi Xarralu

    Thanks for your input, ok i will insert a few more screen shots.
    Relief fan? is that another term for exhaust fan?

    What changes would you make to fix the static?

  8. #8
    Join Date
    Jun 2019
    Location
    So Cal
    Posts
    332
    Post Likes
    Thread Starter
    Check out these graphics..

    Name:  870 AC1.8.PNG
Views: 96
Size:  99.5 KBName:  870 AC1.6.PNG
Views: 94
Size:  94.1 KBName:  870 AC1.4.PNG
Views: 95
Size:  66.9 KBName:  870 AC1.3.PNG
Views: 95
Size:  94.4 KBName:  870 AC1.2.PNG
Views: 95
Size:  145.0 KB

  9. #9
    Join Date
    Apr 2007
    Location
    Amarillo by mornin'
    Posts
    1,001
    Post Likes
    Oh, that is an interface unit, meaning WebCTRL is only the messenger. WebCTRL tells it to go, how much, and how cold/warm. Everything else that you see on the graphic is coming straight from the unit's internal controls. You might be able to change the time of stage up/down, but that will most likely need to be done at the unit.

    Yes the exhaust fan. Since this is an interface unit, there will be a poly tube coming from the unit's internal pressure transducer. Check the tubing and go from there.

    Edit/add-Looks like a Carrier unit.
    Last edited by xarralu; 08-01-2019 at 07:34 PM.
    "It's not that I'm smart, it's that I stay with the problem longer”
    Albert Einstein

  10. #10
    Join Date
    Jun 2019
    Location
    So Cal
    Posts
    332
    Post Likes
    Thread Starter
    Quote Originally Posted by xarralu View Post
    Oh, that is an interface unit, meaning WebCTRL is only the messenger. WebCTRL tells it to go, how much, and how cold/warm. Everything else that you see on the graphic is coming straight from the unit's internal controls. You might be able to change the time of stage up/down, but that will most likely need to be done at the unit.

    Yes the exhaust fan. Since this is an interface unit, there will be a poly tube coming from the unit's internal pressure transducer. Check the tubing and go from there.

    Edit/add-Looks like a Carrier unit.
    Thank you Sir

  11. #11
    Join Date
    May 2018
    Location
    VA/DC
    Posts
    204
    Post Likes
    the orange microblocks are pid's you take a set point ( say cooling set point) then in input like zone temp. and a command to run, like cool ok and it adjust the output up and down on demand.
    this is a carrier screen shot. ALC and Carrier are the same basically. they coth have functions or micro blocks the other doesn't.


    Name:  cool pid.jpg
Views: 72
Size:  48.3 KB

  12. #12
    Join Date
    Jun 2019
    Location
    So Cal
    Posts
    332
    Post Likes
    Thread Starter
    Quote Originally Posted by Cool breeze 38 View Post
    the orange microblocks are pid's you take a set point ( say cooling set point) then in input like zone temp. and a command to run, like cool ok and it adjust the output up and down on demand.
    this is a carrier screen shot. ALC and Carrier are the same basically. they coth have functions or micro blocks the other doesn't.


    Name:  cool pid.jpg
Views: 72
Size:  48.3 KB
    Thank you sir, appreciate your input.

  13. #13
    Join Date
    Mar 2018
    Location
    Texas
    Posts
    39
    Post Likes
    Can do.

    Supply Air Temperature (SAT) setpoint reset: to save energy, some buildings have a setpoint reset program. When the space is satisfied (few or no cool requests) it will raise the setpoint for supply air from 55 degrees to something like 60 or 62.

    Variable Function SAT reset: You have the option (check out the dropdown menu underneath SAT Setpoint Reset) to use cooling requests to control the reset, or other things like outside air temperature.

    PID loop is a piece of calculus that is used to control outputs based on an input and a setpoint. If I have a room that is 73 degrees, and I want it to be 70, a PID loop will dynamically adjust an output like a chilled water valve or a VFD for a supply fan, or a damper actuator, to try to get the input (room temperature) to equal the setpoint. If you are at this stage in your controls journey, I don't recommend you mess with it just yet. If you want to know more, the help docs for WebCTRL are actually pretty great. Open it up and search for the PID info page and it will give you a rundown of each element in the block.

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •