So, I just had a conversation with a colleague about VAV construction. The crux of which centered on where air flow is measured and where the damper is placed. As part of their discussion, they brought up the Haystack tagging standards.

I think we have a problem.

I have completely overlooked this in the past, but the VAV doc uses the combinations of discharge air flow and discharge air damper. In addition, the Haystack community uses the tag entering in dealing with VAV boxes. If someone just looks at our standardized tag groups, one would be lead to believe that the damper and the air flow measurement on VAV boxes is on the outlet of the box. Does anyone know of a manufacturer that builds their boxes this way?

After Googling “vav box diagram” and going through many of the images, I am unable to find a VAV box that has an actual discharge air damper or a discharge air flow sensor. I propose that we change the tagging combinations found on the VAV doc under “Other standardized points” to read:

• entering air flow sensor
• entering air flow effective sp
• entering air flow min sp
• entering air flow max sp
• entering air flow reheating max sp
• entering air flow standby sp
• entering air damper cmd

Initially discharge was proposed because it is the primary supply air to the zone or space that is being measured and controlled. Most control manufacturers, box manufacturers and sequences refer to "supply air flow", etc. It could also be confusing to use entering for supply in this regard. So, after discussing it with Keith we feel it would be best to drop discharge / entering for these points as it is redundant and unnecessary.

The new proposal is to eliminate discharge for the air flow and damper points:

• air flow sensor
• air flow effective sp
• air flow min sp
• air flow max sp
• air flow reheating max sp
• air flow standby sp
• air damper cmd

Completely agree. This helps work around what could be seen as an issue without making a completely breaking change from the earlier tag groups.

At the time, there was also a need to distinguish supply air vs discharge air (air entering in the VAV...from the unit for example vs air supplied to the room by the VAV box).

I agree with Paul's assessment as well. In the context of vav terminal equipment there is only one air flow of concern. A dual duct application can be modeled after a heating vav and a cooling vav with a common discharge air temp sensor.

This is a coincidence...........I just had a lengthy discussion with a representative from Ebtron regarding the accuracy of VAV box flow measurements.

Ebtron has an "ELF /D Series" product they refer to as the "Dual Analog Output Electronic Low Flow Measurement Station" for measuring both discharge air temperature and flow.

Page 3 of the Technical Data Sheet recommends installing the flow sensor "1 duct diameter downstream of VAV box transition".

If we come across this application for a "VAV Terminal Box with H /W Reheat", the discharge tag may still be applicable.....with its current definition of:

discharge - Associated with the discharge air an ahu or vav.

.....and I completely agree we should eliminate discharge from our VAV "docs"

http://www.ebtron.com/Web_Pdfs/SPSync/ELF%20-%20ELECTRONIC%20LOW%20FLOW%20INSTRUMENT/ELF%20PRODUCT%20DATA%20SHEETS/TS_ELF-D.pdf

I started to implement this change, and came across the classic qualifying tag problem:

// what we have today
discharge air temp sensor
zone air temp sensor

// proposed
air temp sensor
zone air temp sensor

If we ditch the discharge tag then there is no clean way to qualify the "box point" versus the zone's point when associating the space temp with the VAV.

So my recommendation is to just leave it the way it is unless anybody has a better solution.

Brian, I think discharge would/could be an appropriate tag when applied on temperature sensors. There are often temperature sensors where the air exits the box.

The issue that I was having with the existing tags sets dealt with when discharge was applied to damper or air flow. I do not have any evidence that these concepts exist in production anywhere. However, discharge air temp sensor is a completely valid item.

If discharge works for temp sensors, then there would be no ambiguity stripping it from the rest of the points:

discharge air temp sensor
entering air temp sensor
air pressure sensor
air flow sensor
air flow effective sp
air flow min sp
air flow max sp
air flow reheating max sp
air flow standby sp
air fan cmd
air fan sensor
air damper cmd
reheat cmd
vavMode sp
ductArea sp
perimeterHeat cmd
zone air temp sensor
zone air temp effective sp
zone air temp occ cooling sp
zone air temp occ heating sp
zone air temp unocc cooling sp
zone air temp unocc heating sp
zone air temp standby cooling sp
zone air temp standby heating sp
zone air humidity sensor
zone air co2 sensor
zone air co2 sp

Does everyone agree that works? Is there still notion of entering vs discharge air temp sensor?

Issues may exist but I don't see any. Thanks Brian.

(ok, well, there should also be a zone air humidity sp in certain cases. I think I'm done now)

Are folks using the perimeterHeat tag for items such as auxiliary baseboard heating?

perimeterHeat - Auxiliary heating points associated with a vav.