I like "entering" and "leaving", in lieu of "supply" and "return". When we're referencing individual pieces like boilers, chillers, cooling towers, heat pumps and coils there is no room for confusion.

Another clear alternative, "in" and "out".

Mike Silady - ESI

The same could be said for "Air on" & "air off" with regards to entering air vs leaving air temps for any fan coil unit. "Supply" and "return" tags would not suit, but as Mike says, "entering and leaving" are unambiguous.

As part of the tag rework, now would be a good time to establish conventions for tagging fluids/gases which are entering and leaving a piece of equipment:

• AHU: we have air entering (return/outside) and exiting (exhaust/discharge)
• Chillers: chilled water and water to cooling towers (not sure proper terms)
• Boilers: water, steam, and think lots of others

If we take an AHU example it is important to distinguish the two ways air enter - either return air from the zone or outside fresh air. In this case case outside air and return air makes good sense. Likewise with exiting air: exhaust air and discharge air.

We haven't talked about boilers, chillers, cooling towers, etc. Having standardized conventions for naming would be great. But at least in the AHU it seems like specific names (outside, exhaust, return, discharge) makes more sense.

We have a convention that return air is what is coming back into the system from a space going into a return air fan. The output of that fan is directed to the outside or mixed with outside air as mixed air which is goes into the supply fan.

I'm definitely on board with the AHU/RTU tags of outside, exhaust, return and discharge.

I do not deal a lot with boilers and chillers, but my suggestion would be to try and keep similar tags; return water and discharge water. No need to keep switching out synonyms when changing equipment types.

You can assign the tag "return" to a dictionary item, however Axon returns an error when you try to query on that tag. I think it may get confused with the "return" language construct. When writing rules you get a save error if you try to use "return" in a query. The Axon engine would need to be modified to use "return" as a tag. "entering" and "leaving" may be a better choice.

Yes it is unfortunate that return is both a common term in HVAC/central plant systems and also a keyword in most programming languages.

Paul, for Axon specific handling of this issue please refer to the SkySpark build notes for what we did there.

Very shortly I will kick off a discussion on this whole problem of return/supply, return/discharge, leaving/exiting, etc.