This is a break out from post `/forum/topic/6` which digests the whole comment trail into a concrete proposal for additions to the standard tag library:

CO2 Sensors

My understanding is that CO2 sensors are common, but only for the zone and return air. Assuming everybody agrees with that, then I propose two new AHU tags:

• returnCO2: return air carbon dioxide level measured as "ppm" (parts_per_million)
• zoneCO2: zone air carbon dioxide level measured as "ppm" (parts_per_million)

Zone Humidity

I think we are missing:

• zoneHumidity: air humidity of a building zone measured from 0% to 100%.

Outside Flow Setpoint

There was some discussion about outside flow, dampers, and setpoints. What we have today:

• outsideDamper: damper point used to control the outside fresh air feed of an ahu measured from 0% (closed) to 100% (open).
• minOutsideDamper: A secondary damper point used to ensure proper level of fresh air to an ahu measured from 0% to 100%.
• outsideFlow: outside air volumetric flow point of an ahu measured in "cfm" or "L/s"

The current model acknowledges that in some AHUs there are two physical dampers. Sometime an smaller minOutsideDamper is used to separately ensure fresh air. But there is only one sensor - the outsideFlow sensor which would measure air intake through both of these dampers. Assuming that correctly models all cases, then I would propose one new point:

• outsideFlowSp: the desired setpoint for outsideFlow in an ahu measured in "cfm" or "L/S". This setpoint is used to control the the minimum level of fresh air taken into the AHU.

Zone Temp Setpoints

Today there is one zoneTempSp which is probably too simplistic for most modeling and analytical requirements. I propose to clarify the role of zoneTempSp as the effective setpoint and add two new two points:

• zoneTempSp the effective space temperature setpoint of a zone measured in °C or °F. This setpoint is often derived from zoneTempCoolSp and zoneTempHeatSp based on whether the zone is in heating or cooling mode.
• zoneTempCoolSp: the cooling space temperature setpoint of a zone measured in °C or °F
• zoneTempHeatSp: the cooling space temperature setpoint of a zone measured in °C or °F

Heat Wheel

My understand is that a heat wheel would be modeled as a simple bool point:

• heatWheel: a bool point which models the on or off state of a ahu heat wheel

Outdoor vs Weather Tags

Several notes on outdoor temp/humidity sensors. I originally omitted these because of potential confusion with weatherTemp and the overall weather model. Also it was a case where many AHUs might share one outside air sensor across multiple pieces of equipment. So they aren't necessary a point associated with one piece of equip. But I think we can put together a comphrensive model using these principles:

• in general weatherX tags are weather observations from an official weather station or feed
• outsideX tags are sensors local to the facility
• in cases where multiple pieces of equipment share an outdoor air sensor they will use a outsideXRef tag (join from equip side instead of point side)

Having this model allows us to do some nice things like:

• run analytics between weatherTemp and outsideTemp to check for broken sensors
• often degree-day calculations used for billing purposes might need to use an official weather source vs local sensor

Assuming everybody is in agreement with that strategy, then we would have four new tags:

• outsideTemp: Outside air temperature point measured in in °C or °F.
• outsideHumidity: Outside air humidity point measured from 0% to 100%.
• outsideTempRef: reference to an outsideTemp point, often used on an equip like an ahu to indicate a shared sensor.
• outsideHumidityRef: reference to an outsideHumidity point, often used on an equip like an ahu to indicate a shared sensor.

Next Steps

The above changes are an official proposal to update the standard library using the tag names, descriptions, and units as specified. Please share any issues you have with proposed design or any refinements you think might be useful.

I have reviewed this summary of additions and refinements and had a few conversations with people on the phone as well. I view all of these additions as ready to go.

Okay this proposal has been out for a couple of weeks, and no comments - so let's assume everyone is on board with these changes. I will add them to the docs and publish updated model in next week or so.

Brian, A side issue with respect to "Outdoor Air", the term fresh is avoided due to the fact that it is not "always fresh" as the name implies and the determination of freshness can site and condition determined. Outdoor Air may be contaminated with smoke or other fumes from nearby conditions. As such the use off the term "Outdoor Air" is preferred. You might also consider the tag name to similarly be "OAD, OutdoorAirDamper". From another perspective one might ask "outside what". The OutDoor term eliminates any confusion.

Winston