Cool Request/ web ctrl

[BuildingMech88]

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.

[controls21]

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.

[BuildingMech88]

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.

[Mikemikemike]

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.

[BuildingMech88]

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.

[xarralu]

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%.

[BuildingMech88]

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?

[BuildingMech88]

Check out these graphics..

[xarralu]

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.

[BuildingMech88]

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

[Cool breeze 38]

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.

[BuildingMech88]

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.

Thank you sir, appreciate your input.

[Mikemikemike]

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.

[BuildingMech88]

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.

Thanks Mike,

I appreciate the detailed explanation. I will be looking into everything you mentioned here. Thanks for your help!