I would like to submit the new tag "supply (air)" to the VAV model.

Supply air is what is coming to the VAV... Discharge air ... coming from the VAV.

For the experts ... do people put sensors on the entering air of a VAV as well as the discharge exiting air?

In this case, I think the terms entering/exiting we use for chillers might be clearer

Some VAV boxes have a sensor in the supply wich allow action of the VAV to "reverse"... If air coming to the VAV is hot, then VAV can open to heat the zone if needed. Standard apps use this info to trig the warmup mode on the VAV box.

In practice, most VAV boxes have a network input and you simply link the discharge air temp from the AHU to the supply air variable of the VAV.

I have not seen a lot of VAV softs/boxes. Worked with Siemens and JCI and both used terms supply for entering air, and discharge for exiting air.

In my experience a physical sensor for air entering a VAV is not common. It is always linked thru software from the AHU sensor to help control the VAV better.

Even if it is rare I think it would be beneficial to be able to model it easily. I agree with Brian's suggestion of using the Chiller model terms of entering and leaving. When I agreed with this, it made me think a little more across all of our current models and terms we are using for the orientation of the controlled medium. I think it would make the tagging model's easier if they were the same across the board.

Current model's

• AHU's
  • return and air
  • discharge and air
• VAV's
  • discharge and air
• Chiller's
  • entering and water
  • leaving and water

Suggestion to make all model's more similar

• AHU's
  • entering and return and air
  • entering and outside and air
  • leaving and air // For single discharge air
  • leaving and hotDeck and air // For dual duct AHU's
  • leaving and coldDeck and air // For dual duct AHU's
• VAV's
  • entering and air
  • leaving and air
• Chiller's
  • entering and water
  • leaving and water

This would open it up for all systems to use entering and leaving for its controlled medium. If the system has multiple entering/leaving elements then you only need an extra tag to differentiate them (i.e. return, outside, hotDeck, etc...).

Thoughts?

I can see the point. A standard term across all the tags. Can easily live with this.

But, I would not add tag where they do not add clarity. (God...thinking in french doesn't help me here ! ;) let's proceed by example !

entering return air -> from my point of view, return air can't be leaving... entering is useless. Same thing with outdoor air...

Bref ( :0) ) We don't need to overtag

I would agree with you that there are situations where some tag combinations "should" never happen. I'm also behind not overtagging when its not necessary, but in my opinion it doesn't hurt and only provides more detailed information. With that said we have trade-offs:

1.) Non standard across all system models

• This would save a tag here and there
• Not consistent in all models, not the same pattern. You need to know every model by heart to know the right tagging combinations.

2.) Standard throughout all system models (always using entering / leaving)

• If you know one model you know them all, same pattern
• Would involve some extra tags in some scenarios

Thoughts on this topic? I'm not quite sure I'm 100% either way, just trying to lay out the differences.

@Joe - I think overriding discharge/exhaust to also include leaving tag and overriding outside/return to include the entering tag might be overkill. Although there is a bit of inconsistency with our terminology in order to use the lingo of the domain, I think it would be worse to require tagging that have duplicate semantics. Although that said, there certainly isn't anything wrong with pairing up discharge and leaving (I just don't think we should prescribe it).

Back to Christian's original proposal, what tag/term do we associated with sensors on the input/entering side of the VAV box? I think at all costs we should avoid the term "supply" - its always confusing and in VAV boxes especially confusing. My suggestion is we use the term "entering", but stick with the existing term "discharge". That sort of straddles exiting conventions we already have with AHU and chillers, but I think most matches up with existing terminology engineers use.

Assuming we have agreement with that, then my specific proposal is to add the following point combination to the VAV point list:

entering air temp sensor

It might also be worth creating a little illustration of the entering versus discharge like I've done for AHUs.

I'd be fine with Brian's addition.

With respect to a VAV, the LonMark functional profile uses nviSourceTemp and nvoDischargeAirTemp. As mentioned above, it's used for a central station heat routine where the AHU supply temperature is elevated and the terminal controller must reverse the VAV damper direction of rotation as the source temperature rises above the room temperature.

The AHU leaving air temp can be bound into a VAV controller (and always should be) or in some cases can have a physical duct probe wired to the controller. Where this differentiation becomes important is for dual duct or parallel fan VAVs.

For an SCC AHU profile they also use discharge air temperature. For clarity I've always recommended my guys use Supply Air Temperature for an AHU/MAU if it sends air to another device and discharge if the air enters an occupied space. That means the use of the term discharge only related to a single zone AHU (AKA blower coil unit).

When discussing entering and leaving air temperatures I try to leave that for differential across kind of heat exchanger like a heat wheel or coil. Engineers use entering/leaving air dry/wet bulb for coil selection criteria. For a VAV I'd recommend using LonMark Source and Discharge terminology.

I like the term "source" - it seems clear. However, I'm not sure I like adding yet another term when we already have "entering" that also seems to work just as well. So my vote is still for "entering" and "discharge".