#24 Enthalpy tags

Sean Hyrich Thu 7 Jul 2011

Would like to propose the following tags:

returnEnthalpy

Kind: Marker

Used With: point, unit

Return enthalpy point for an ahu, boiler, or chiller measured in BTU/lb. Could apply to gas or liquid depending on equipment type.

outsideEnthalpy

Kind: Marker

Used With: point, unit

Outside air enthalpy point for an ahu measured in BTU/lb.

Alper Üzmezler Thu 7 Jul 2011

That is a good tag.

Brian Frank Mon 18 Jul 2011

Any other comments or votes?

John Petze Fri 22 Jul 2011

It’s always helpful to understand the intended usage of a tag and this post brings up a couple of items that I would like to discuss in more detail to insure we have an adequate shared understanding so we can pick the right approach.

The outsideEnthalpy tag that was proposed a while back had a fairly common use case. Enthalpy of outside air is typically used to measure the total heat (latent and sensible) of the air stream. Commercially available sensors combine dry bulb temperature and humidity to calculate enthalpy. Control systems then use this value to determine which air stream – outside air or return air will require the least energy to cool. As a commonly used item it makes sense to be available as a tag. Is the suggestion to include a tag for the “return air enthalpy” for this same application? Or are you suggesting at additional uses?

Enthalpy as an engineering measurement has a wide variety of uses with other gases and liquids, (chemical reactions, heat transfer calculations) but am not familiar with common use cases for them that are directly related to the subjects we are discussing. It would be helpful to offer some additional use cases here to help educate me (and others) so we can assess the best way to model this measurement. Also, do enthalpy sensors exist for those liquids or gases or would you typically derive the enthalpy value from a calculation of other sensed elements?

Just to confirm, the necessary units for enthalpy (BTU, Joules) are available in the library.

Aakash Kumar Wed 6 Jan 2016

My suggestion is to add an enthalpy tag. rather than outsideEnthalpy or returnEnthalpy. The enthalpy tag can be used in sync with return, outside to show return air or outside air enthalpy. Enthalpy sensors are available, but the points are usually calculated values using temperature and humidity. They can be tagged as sp or sensor based on the context.

Denis OConnor Thu 7 Jan 2016

I agree with the proposal to make enthalpy a separate tag.

This addresses the point John raises regarding the use of enthalpy for substances other than air.

Jason Whittier Thu 21 Jan 2016

Another vote to add enthalpy as a separate tag. This is something we are already doing and it would be great to see it part of the haystack library.

Jingkun Gao Wed 2 Mar 2016

Agreed. I am currently use humidity temp energy together as enthalpy. Would be nice if this tag is available.

Leroy Simms Mon 11 Jul 2016

+1 for enthalpy as a separate tag. That keeps things flexible/standardized and prevents the need for a bunch of unnecessary tags (outsideEnthalpy, returnEnthaply, mixedEnthalpy, exhaustEnthalpy, ect.) In fact I had always assumed it was already a tag and surprised to see it is not.

Ronald Breijer Fri 16 Nov

+1 for enthalpy seperate tag

Brent Fleisher Wed 21 Nov

I concur there should be a singular tag for Enthalpy, and used together with other modifiers such as return air or outside air, etc. In my opinion, this is the simplest presentation and provides both clarity and flexibility.

Joseph Firrantello Mon 26 Nov

Glad to see this is getting some renewed attention.

I'm currently setting up tagging for an install where multiple OA enthalpy points are available from the BAS (e.g., one per AHU plus a central "overall building" value). I have already been using a custom enthalpy tag for those points, and would support an official independent enthalpy tag based on my limited knowledge and use case.

Side note for thread context:

John Petze's comment from 2011 reminded me that the industry convention is to typically use the word enthalpy for specific enthalpy, for better or for worse. For example, the ASHRAE Terminology resource makes the distinction.

However, it seems this issue has been decided in the unit system definition:

-- enthalpy --
joules_per_gram,J/g
joules_per_kilogram,J/kg
joules_per_kilogram_dry_air,J/kg_dry
btu_per_pound,BTU/lb
btus_per_pound_dry_air,btu/lb_dry
kilojoules_per_kilogram,kJ/kg
kilojoules_per_kilogram_dry_air,kJ/kg_dry
megajoules_per_kilogram_dry_air,MJ/kg_dry
calorie_per_gram,cal/g

Brian Frank Sat 1 Dec

To move this forward it needs to get merged into a working group and someone needs to champion the actual definitions. Probably the best one is 514 which originally talked about enthalpy, but its not currently in the working proposal. Other options might be to make 626 more about air measurements rather just air quality. Or maybe 609 as part of AHUs.

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