I think we should have a new tag for a vavAhu. Currently there isn't away to know if my ahu is a vav ahu, or just a rooftop unit.

I think it would be a bad idea to have a vav tag, and an ahu tag on an VAV AHU, so what if we just created a new tag called vavAhu.

This tag would represent that the AHU had at least 1 VAV under it.

I know you could do this ahu and not rooftop, but I think that's probably a bad idea. It would make much more sense to just have another tag?

Anyone agree?

In our market, there is a lot of rooftops used in VAV systems (sometimes with drive, often with bypass dampers). VAV tag allow us to have VAV Rooftop...

That seems like simpler useful marker tag to add to ahu equipment. I support it. Will put it on todo list unless I hear objections.

It might be better to use variable vs constant to define systems. If new methodologies of flow control is out there, they could be added too. Matthew demonstrated on a job that uses natural ventilation.

I think we need to come up with a better solution for flow control methodologies.

I agree with this. More precise.

But as soon as you add the VAV tag you can no longer just type in vav to find all vavs. You would now have to say vav and not ahu and not rooftop.

Seems like kind of a hack.

I don't think Alper is suggesting we use the vav tag for AHUs. I think is suggesting that we take a more broad approach to describing the terminal units of an AHU. Maybe something like: variableTerminals, constantTerminals, etc. I like the more comprehensive approach, but not enough of a domain expert to enumerate the possibilities and define good terms.

I would prefer constantVolume or variableVolume (those tags are exclusive, can't be both present for one AHU or rooftop)

I agree with constantVolume or variableVolume.

How would you tag a ahu in a VVT system with bypass damper? (crap design in my opinion but we run into it sometimes with customers that don't know better).

Ex: where a much cheaper constant volume unit is installed with a bypass damper (so the AHU, and its core operation are still constant volume at the AHU). Its not until AFTER the bypass damper that the system (ductwork) becomes variable volume.

I also like the idea of being able to take a terminal unit (vav) as constant or variable. (more crap mechanical design), but we still run into some systems that are constant volume with electric reheat (so instead of a VAV box you just have electric heat and a space sensor). Ex: a Reheat running on a warm day isn't as much of a sin (spark) in this type of system, as it would be with a variable volume system, where if you have reheat running on a warm day its defiantly worthy of spark.

Regarding the constant volume AHU with bypass damper, from my point of view, I would tag it variableVolume as the bypass damper is part of the system.

But I can agree with the fact this it is not absolutely exact.

I would not agree more where 1000's of possibilities exist in mechanical layouts. I don't think we will be able to define scopes hacks. Maybe we can add hack tag to the vav to catch that. :) variableVolume and hack :)

I agree with the variableVolume and constantVolume suggestion.

I live in a place where hackers use that everytime ! ;)

Small commercial buildings with VAV terminals I've seen around are all fed by a rooftop w/ bypass damper... with all problems related. [sigh]

I agree with the ( variableVolume | constantVolume ) tag suggestion.

This tag combo really defines a fact about the AHU, where vavAhu is more about the setup of the system.

As far as the hacks listed above go, I think tagging the AHU with the correct tag would still be beneficial in that it could indicate that the "hack" currently in place isn't ideal operation for this type of AHU.

So VVT AHU would be tagged variableVolume? How would I know that the AHU is really a constant volume unit with a bypass damper rather than a true variable volume system?

While we are talking about tagging ahu types, do we have a tag yet for a space comfort unit (return air+min oa or econ) and a 100% outside air makeup unit? Or a 100% outside air lab unit?

I would think if the ahu does not have a vfd attached but has a bypass damper. You would now that it is a vvt.

If we are trying to define the air movement, using variableVolume would make sense. In this case, unit + the bypass damper would be treated as one system.

If we are defining what the equip type is, using constantVolume would make sense.

Make Up Air Units would be attached to ahu and equip. I think I have read about a suggestion making vfd as an equip on its own and attaching it to a fan. I can't find the discussion now. (Brian, We need search functionality on the site.)

Anything that is attached prior to outside air unit could be called in the form of "Make Up Unit" than we can add tags to this equip on how it operates. Somehow we need to reference the MAU, from the AHU that it is connected to?

Any suggestions?

variableVolume = VAV or VVT AHU constantVolume = Normal CV Unit

We do mainly VAV units in our market... it seems that the most of the skyspark demos, and work to date has been on constant volume units with a simple stat control.

What about tags like this.. (throwing out what I need, I'm not 100% on board with the existing tags, so smack me if necessary).

makeupAhu = Makeup AHU (suction of fan is outside air), AHU controls its supply air, to provide neutral or best air to space, not responsible for space temp control sccAhu = Space Comfort AHU (suction of fan is return, return+minoa, or return+airside econ), AHU controls space temp directly (I'm not in love with this name). spaceControl = Unit controls to maintain its space temperature dischargeControl = Unit controls to maintain its discharge air temperature vvtHack = Use Hack tag to denote a mechanical setup that we as a group really think is crap, but is still specified because of cost or customers that have never had one think why not.

So if I had a ahu that was constant vol we would have.. equip ahu constantVolume sccAhu spaceControl (this is what the built in skyspark displays are meant to work with.. correct?)

Real variable volume would be.. equip ahu variableVolume sccAhu supplyControl

VVT variable volume would be.. equip ahu variableVolume sccAhu supplyControl vvtHack

We have a dualDuct ahu as well, which is perfect, I think we should add a multiZone as well.

Should we differentiate between a dualDuct, and a multiZone ahu?

Yes they are different. Added some other information for those of us that haven't ran into this kind of thing before. Do we want to put Ahu or something on all the Ahu tags? Or is it more desirable to have the tags be used by different system types?

Ex: sccAhu or scc (space comfort control unit)

dualDuct = AHU which has two supply ducts, hot and cold. Typically dualDuct would be matched up with a dualDuct VAV box or a mixing box (where terminal mixes hot air and cold air at the terminal) for space comfort control. In our area the age of this type of equipment is where it has been or is being retrofitted to a straight VAV system. You see some pretty crazy terminal boxes with this type of setup. A dualDuct system could be constantVolume or variableVolume.

multiZone = AHU which provides bypass air or cold air from a cooling coil (normally chilled water, which could be controlled with a valve or wild (no valve / always as cold as possible). Each "zone" has its own face and bypass damper (no/nc) which is controlled for space comfort control. Each "zone" may also have electric or hydronic reheat. Typical multi-zone units were pneumatic actuator with a single pneumatic signal operating the face and bypass damper, then staging the heat via PEs on a further drop in temperature. Biggest sin for multi-zone units is having a cold cooling coil when no zone is calling for cooling (face and bypass, especially old ones leak). In our area it seems that people have a harder time getting rid of the multi-zone setup during renovations due to physical constraints. If you can control your cooling temperature (so you don't always overcool then reheat) it isn't that bad a setup. MultiZone units are constantVolume. Control of the multi-zone cooling discarge would be dischargeControl, and control of each zones face and bypass damper and heat would be scc.

Throwing a new one out as well..

induction = Unit (normally would also have "makeup" "constantVolume" tags, (100% outside air)), which feeds fresh air and "powers" induction terminals. (Nozzles in airflow in terminal units "induce" flow from the space, so the primary air from the induction unit mix with induced air (return) from space, is conditioned by an additional heating or cooling coil. We have seen some buildings in our market where unit has airside economizer instead of being 100% outside air. Many induction units will have a wild (no valve) cooling coil, which will be served first by the chiller plant, then rest of chilled water system gets return from the induction coil as its supply).

So Brian,

There is an agreement on the variableVolume | constantVolume tags on ahu. I think we can add this two tags.

Brian and I talked on the phone today, and came up with a couple more scenarios. We will be sending over the rough draft so we can all sign off on it.

I think we want to propose also adding a vavTerminal tag as well to the ahu.

I've tried to assimilate the discussion and boil things down into a concrete proposal. There are basically two somewhat orthongal issues:

1. whether the AHU delivers constant or variable volume
2. whether the terminal units are VAVs (have dampers)

So I propose the following tags for ahu:

• constantVolume or variableVolume based on whether the AHU is designed to deliver a constant volume of air (or if there a preference we can use shorter tags constVolume and varVolume). By definition a AHU with variableVolume tag would have a VFD.
• vavTerminals indicates the AHU terminal units are VAVs

A VVT system is really a combination of constant AHU and VAVs (based on my understanding). So VVT would be implied by the combination of constantVolume and vavTerminals tags on the AHU entity.

Separately from that we have dual duct and multi-zone systems. We already have dualDuct tag for AHUs and coldDeck and hotDeck tags for the associated points. I am not sure I fully understand multi-zone, but propose:

• multiZone: would be a tag on ahu indicating its multi-zone
• neutralDuct: would be tag for points associated with the neutral deck (doesn't sound like there is often sensors associated with the neutral deck, but we'll have it to be consisten with hotDeck and coldDuct)

I like it a lot. Great job Jason & Brian.

FYI - You can have a terminal with dampers that isn't vav (variable air volume), ex a dual duct mixing box (one damper no the other nc) on a hotdeck/colddeck unit.

A typical VVT system will not have a airflow sensor. Min and Max are set either by stops on the actuator or by a % of damper pos on the controller. This is a pressure dependent system (you only have the right flow if your duct static is at design where the system had its min and max flows set). So if your going to tag a VVT terminal with vavTerminals you probably won't have the data for any analytics to do with flow work.

Dan

Brian... I think you meant neutralDeck? coldDeck, hotDeck, and neutralDeck right?

Regarding Brian's summary I would offer one comment we should plan for:

A VAV system does not always have a VFD to modulate fan speed. VFD's have become the "best" solution nowadays, but there are other designs and lots of older systems used them. A common method was to have controllable "inlet vanes" on the fan inlet. This reduced the air the fan moved and reduced the horsepower used by the fan, although not as perfectly linearly as a VFD does. I think we need two tags for the fan control method -- VFD, inletVanes. The control signal to each would typically by 0-10 vdc, or 4-20mA. Newer VFDs of course have direct communication via BacNet etc to control fan speed.

John, there is also a third possibility that I have seen, a Bypass. A separate damper actuator opens a damper on the discharge ductwork, allowing air to be fed back into the return of the unit rather than be supplied to the terminals. This option is less common, but I have seen it on both VAV and VVT systems.

Gentlemen, after reading through many of your comments it seems to me that many are confusing terms used for a Air Handler Unit of the VAV type with Terminal devices (Terminal devices also have several types, VAV, VVT, CV or fan (fractional HP) powered)) of the VAV type also commonly referred to as VAV devices.

I believe that making this distinction for this discussion would help. I think the tag being used here is coonfusing and might be more significant if changed to AHU/VAV.