#1057 directZone tag on VAV Terminals

Leroy Simms Fri 21 Apr 2023

While currently against the Haystack standard, I typically use the directZone tag on VAV terminals. This allows me to quickly find all equipment directly responsible for zone conditions, be it an ahu, fcu, or vav. I have also at times come across VAV terminals which serve sub-vav zones, and this again makes it easy to differntiate them from the ones directly serving zones.

The directZone and vavZone tags are currently a choice under the ahuZoneDelivery tag. I would like to propose the following options:

  1. Modify ahuZoneDelivery tagOn to include airTerminalUnit
  2. Transition from ahuZoneDelivery to airZoneDelivery with tagOn:[airHandlingEquip, airTerminalUnit]
  3. Make airTerminalUnit a subType of airHandlingEquip, many terminal types already fit the existing definition of airTerminalEquip and it would not be hard to broaden that definition slightly.

Interested to hear others thoughts and/or other approaches people have taken.

Jay Herron Sun 23 Apr 2023

I typically use the directZone tag on VAV terminals. This allows me to quickly find all equipment directly responsible for zone conditions, be it an ahu, fcu, or vav.

In the past, I've used the thermostat tag if the equip contains points like zone conditions or setpoints. We could then use that tag to filter for equipment directly responsible for zone conditions. Here's an example. Would that serve your needs?

Frank Smit Mon 24 Apr 2023


I understand what you mean but take care that it become not to complex. We try to keep it so simple as possible. A VAV which serves subzones then in most cases you have a roomstat in each subzones or room. The VAV should have a property tag ahuRef to indentify on which AHU the VAV is physically connected. When we add a VAV as equipment and add a point under that VAV equipment it gets the tag equipRef so we can find very quicly which points are connected. If we have a VAV which is serving more zones we each roomstat has already a relation with that equipment VAV. When I started with Haystack I made it also to complex in my opion if we have a AHU with pumps ,vsd, dampers valves and sensor which are using communication instead of hard i/o we add these as equipments on a floor and adding ahuRef but today we add these under the equipment AHU as sub equipment same like siteMeter and subMeter. An other option is to add reference like deviceRef on the roomStat. The problem what I see is that we want to put to much information in the model. May be we do that beause we are dealing more and more with people how don't know anything of installation only then what google is telling them.

Leroy Simms Wed 26 Apr 2023

Jay - I agree using the thermostat tag on directZone equipment would handle the majority of the cases. But leaves a number of scenarios challenged or requiring "and not" filtering situations which would be resolved by extending the zoneDelivery tag to VAVs.

Going the route of the thermostat tag how do you handle units controlled by return air temperature? Do they still get a thermostat tag? That seems unclear by the docs and is a common situation, which is a non-issue with the zoneDelivery route.

Frank - While using equipment/point relationships can work, it can get a bit messy for a basic ruleOn filter especially for such a common scenario. I have been using the directZone and vavZone tags on VAV terminals for years and it works great, just concerned that with an increased focus on validation I should start pleading my case in any place I've deviated from Haystack standards.

Thanks for the feedback guys, I don't think enough good discussion happens on this forum like it used to. It would be nice to think that is because the standard is really getting flushed out to the point less discussion is needed, but I truly think many have adopted their own ways instead, which sooner or later will be problematic for the standard.

annie dehghani Thu 27 Apr 2023

Leroy - FWIW, we also occasionally use directZone on equipment besides AHUs such as VAVs and FCUs to denote that it's a 1:1 with a zone.

I agree with your suggestions #1 and #2.

Suggestion 3 is interesting. It seems useful to me though to be able to distinguish whether equipment moves air with fans (i.e. an airHandlingEquip) vs something that just controls the end flow of air (i.e. an airTerminalUnit).

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