VAV Static Reset Control using AX

[viceman]

ever see a secretary tape cardboard over her diffusers. "the air is giving me a stiff neck". box will be at 100%

[The_USC_2001]

ever see a secretary tape cardboard over her diffusers. "the air is giving me a stiff neck". box will be at 100%

If a box stays open 100% then the static setpoint would just go to the max.

[osiyo]

ever see a secretary tape cardboard over her diffusers. "the air is giving me a stiff neck". box will be at 100%

Yep, as a matter of fact.

To be fair, static pressure reset can work. Just as any number of other strategies can and do work well.

In the grand scheme of things, is a static pressure reset is MAJOR energy saver, as compared to other possibilities and tactics. Probably not.

It is, however, one of the new "in" things. Being touted perhaps more than it deserves to be.

Isn't worth a darn, however, long term unless the maintenance folks sit up and pay attention. Routinely check things out to make sure they're working correctly. A lot of various issues can arise which throw the scheme out of whack.

It's kinda like one school district we work with. Some years ago they had space CO2 sensors installed and used to do an OA reset. Only bring in OA as needed versus some set amount.

They thought it wonderful. And it worked well. For a while.

Took em a while to notice. In-house maintenance wasn't paying that close attention to things. Finally a guy noticed he had a couple air handlers that seemed to be bringing in an awful lot of OA all the time. I got a call. Went and took a look. CO2 sensors were out of whack. I checked and rezeroed them, and they tested okay then.

Just for the heck of it, I took a look at several others. They too were out of whack, causing excess OA to be used, just not so badly that staff noticed.

I inquired about how often they checked em, or if they ever did. They didn't. If someone wasn't *****in, they hardly paid attention at all.

I did a scan of that school, and a dozen more via remote access. And identified a number of suspicious instances. Got hired to do a full check of all of them. They'd had those CO2 sensors in for over 7 years. Ended up needed to rezero about a third of them which were significantly off. And replaced maybe 6 or 7 completely. 3 weeks of work.

They'd been burning up a LOT of energy conditioning excess outside air for an indeterminate, but probably long time.

Demand based duct pressure reset can have the same problem. If you're not checking things out routinely to isolate and identify problems and fixing them, over time it can be a waste. Keep on it, it can work.

Most places don't pay that much attention, tho. Maybe at first, until the "new" wears off.

[sysint]

Osiyo, the problem had nothing to do with the control scheme.

I'm thinking:

• The specifier didn't have anything in the specs about specific PM for critical components.
• The responsible people did not have a baseline correct running conditions and energy consumption specified.
• The HMI was improperly designed because it could not identify an issue with a critical sensor drifting and proper system operation.

So, really the installation group is the biggest failure here and not the building staff or control scheme.

[The_USC_2001]

For those that say the reset scheme I posted would not work, Why would it not work. If you have a bad system design and a VAV that you have to bump static up to get flow or someone blocks register and VAV can't get right CFM and damper goes open 100% the reset will just reset up to the maximum setpoint. Then it would start operating like as if you had a non resetting setpoint. No harm no foul. At least this way if they fix that problem the static setpoint would then be able to go back to resetting lower. So the way I see it this sequence would still compensate for poor airflow as much as any other system would.

[sysint]

I think Crabmaster's point of tracking TL and damper position is an excellent idea. I think you need to do this. Further, Nikko's comment about ignoring 100% position is also a great idea. Face it, if a box is 100% for any extended period of time you have a problem with it.

[viceman]

i used to do a little vvt system called air link. in the logic there was a provision for a "wild zone". if a zone was not being satisfied for a certain period of time it would remove the zone from the voting scheme until it came back under control.

[crab master]

For those that say the reset scheme I posted would not work, Why would it not work. If you have a bad system design and a VAV that you have to bump static up to get flow or someone blocks register and VAV can't get right CFM and damper goes open 100% the reset will just reset up to the maximum setpoint. Then it would start operating like as if you had a non resetting setpoint. No harm no foul. At least this way if they fix that problem the static setpoint would then be able to go back to resetting lower. So the way I see it this sequence would still compensate for poor airflow as much as any other system would.

Mechdorn was the only one opposed from what I am seeing. Everyone else is just stating relying on a single VAV being 100% is not going to get you the savings long term. Yes when all things are operating correctly it will, but we all are saying VAV's have too many issues to simply have one or even a couple of boxes at 100% be able to drive your static reset to max. More savings are to be realized if you add in terminal load and/or throw out boxes that are greater than 98% or have been there over x period of time. Terminal load plus damper position I see being the most 'energy' saving long term for static reset.

[orion242]

I think Crabmaster's point of tracking TL and damper position is an excellent idea. I think you need to do this. Further, Nikko's comment about ignoring 100% position is also a great idea. Face it, if a box is 100% for any extended period of time you have a problem with it.

Ditto.

I typically "hand sort" the bad guys out. Tossing out boxes that are 100% for X minutes is a great idea and automatic to boot.