[Equest-users] Supply Air Temp Reset Interpretation Please...?

Thu Apr 20 15:54:19 PDT 2017

All;

Great discussion.

For context, the text of G3.1.3.12 is: “Supply Air Temperature Reset (System 5 through8). The air temperature for cooling shall be reset higher by 5F under the minimum cooling load conditions.”

Stepping back, the reset is said to occur at ‘the minimum cooling load condition.’ Thinking through how a typlica/real VAV system will control, the terminal box dampers will close towards their minimum as the cooling load in a zone decreases. In a ‘real’ building this should cause the Supply fan to see a pressure increase and slow down to get back to its static pressure setpoint. At some point if all of the boxes are at a minimum position (aka, minimum cooling demand), the Supply Air Temperature should/can be increased.

Looking through the above, this would indicate an Air Flow first reset, before increasing the discharge temperature.

Per the eQuest help file, it would seem to indicate that a ‘Temp-First’ approach attempts to reset the temperature, without modulating the fan down.  This seems fairly odd in a ‘real’ system since in that if any single zone calls for cooling, no reset occurs, no energy saved. Even if it is a Baseline, it should have some sort of gut check to it. If it were a ‘real’ system and going Prescriptive path, it would be subject to Section 6.5.2. I didn’t see any requirement (Mandatory or Prescriptive) for DAT reset….(but I may be missing it….)

Therefore, I’d think in a VAV system the Air-Flow first modulation, then allow the DAT to reset would be the intended path.

Another minor bit of confusion here: The 90.1 ASHREA User’s Manual does not offer much guidance here. There is new guide from PNNL for the 90.1-2010 standard, which is what is also mentioned below. Just want to clarify for readers that these are two separate (and both are useful) guides.

Thanks,
DARIC R. ADAIR  PE, C.E.M.
Henderson Engineers, Inc. | Mechanical Engineer, Energy Analyst
dir 913 742 5530  tel 913 742 5000  fax 913 742 5001  tx id #F-001236  email daric.adair at hei-eng.com  www.hei-eng.com<http://www.hei-eng.com/>
Licensed in KS. 

From: Jennings, Coles via Equest-users [mailto:equest-users at lists.onebuilding.org]
Sent: Thursday, April 20, 2017 10:38 AM
To: PKConsulting <pasha.pkconsulting at gmail.com>; Shaun Martin <smartin at shaunmartinconsulting.com>
Cc: equest-users at onebuilding.org
Subject: Re: [Equest-users] Supply Air Temp Reset Interpretation Please...?

I wanted to chime in quickly, because this is an interesting question that we’ve gone back and forth on in my office as well.

I don’t agree with the stance that, because the section is labelled supply air temperature reset, therefore temperature first is the correct input. Airflow modulation is a given for VAV systems (baseline systems 5 through 8), so the question is not whether airflow modulates, but what takes precedence between the airflow modulation inherent in a VAV system and the temperature modulation also required by 90.1. The three possible combinations are reflected in the available eQUEST inputs: “temperature first,” “airflow first,” or “simultaneous.”

In my view, the correct order of priority between temperature and airflow modulation is not something the standard directly addresses. Absent clear direction in the standard, I would then look for any formal interpretations<https://www.ashrae.org/standards-research--technology/standards-interpretations/interpretation-for-standard-90-1-2010https:/www.ashrae.org/standards-research--technology/standards-interpretations/interpretation-for-standard-90-1-2010> of the standard issued by ASHRAE, and if that still doesn’t clear it up, then a user’s manual may be the next best thing. A user’s manual such as the PNNL manual at least provides specific direction by a neutral third party, which is often a great way to make a case to the reviewing authority (GBCI reviewer, code official, etc...).

Coles Jennings PE, BEMP, LEED AP BD+C
Sr. Energy Engineer, Building Sciences Manager | Mason & Hanger
A Day & Zimmermann Company
D 804.521.7045 | O 804.285.4171 | F 804.217.8520
4880 Sadler Road, Suite 300 | Glen Allen, VA 23060
Mason & Hanger<http://www.masonandhanger.com/>
We do what we say.®

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of PKConsulting via Equest-users
Sent: Thursday, April 20, 2017 11:19 AM
To: Shaun Martin <smartin at shaunmartinconsulting.com<mailto:smartin at shaunmartinconsulting.com>>
Cc: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] Supply Air Temp Reset Interpretation Please...?

Yes!  Thanks Shaun- even one count of validation makes me feel not so crazy 😜,  especially from an old colleague.  Thank you- thank you.  Why is there too much room for interpretation on these things?  I accept that the User Manual is helpful in most scenarios- but this is one instance that just seems backwards.  If it is supposed to airflow reset controls,  then why is the section written with "Supply Air Temperature Reset"?

I appreciate your validation of my interpretation.

Pasha
Ph: 308-763-1593

On Apr 20, 2017, at 8:29 AM, Shaun Martin <smartin at shaunmartinconsulting.com<mailto:smartin at shaunmartinconsulting.com>> wrote:
Hi,

I think the Standard is quite clear about resetting temperature, and says nothing about modulating airflow.  The user manual seems to be wrong.

Shaun Martin LEED-AP, BEMP
Principal
Shaun Martin Consulting
#90 – 425 Carrall Street
Vancouver, BC  V6B 6E3
p. 604-789-1095

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of PKConsulting via Equest-users
Sent: Thursday, April 20, 2017 7:12 AM
To: Jones, Christopher <Christopher.r.Jones at wspgroup.com<mailto:Christopher.r.Jones at wspgroup.com>>
Cc: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] Supply Air Temp Reset Interpretation Please...?

Thanks for the feedback-  so if the justification for the approach is solely based on the user manual explanation- I can accept that.  I'll cross reference it for the 2007 user manual to put it in my notes.

I've always used air-flow first as a standard reset for all my design energy models, What is counter-intuitive here is that the title of the Appendix G section specifically states 'reset-temp', so why should we not take the section text literally?  I've always humbly assumed that the ASHRAE standard writers know more than me.  After all these years of creating Baseline conforming models (or so I thought),  this makes me feel lost all over again.  AND is it not possible to apply code standard requirements without the use of the User Manual?

Thankful- but-frustrated,
Pasha
Ph: 308-763-1593

On Apr 20, 2017, at 6:48 AM, Jones, Christopher <Christopher.r.Jones at wspgroup.com<mailto:Christopher.r.Jones at wspgroup.com>> wrote:
I had always assumed temperature first but reading the PNNL 90.1-2010 Performance Rating Method Reference Manual, 3.121 (pdf page 151), it states “For systems 5 through 8, the air temperature for cooling shall be reset higher by 5°F under the minimum cooling load conditions using a reset by warmest zone, airflow first strategy.”

The manual states that the airflow first strategy minimizes zone reheat coil energy ( or overcooling) and central chiller energy consumption at the cost of possible increased fan energy.

Unfortunately, the reviewer may have a case.

<image001.jpg>

Christopher R. Jones, P.Eng.
Technical Specialist

WSP Canada Inc.
2300 Yonge Street, Suite 2300
Toronto, ON M4P 1E4 Canada
T +1 416-644-0252

www.wspgroup.ca<https://urldefense.proofpoint.com/v2/url?u=http-3A__www.wspgroup.ca_&d=DwMFaQ&c=xB5UQg5qXm2axe_t44neldV-XNditz6D2ZXZLA0vHlE&r=JrIPsTq2z-_669uhqn51VqSZFL7dpX6NqxKBTKpeQZ9m5XksAJHnQhCI_rEcbMFG&m=TUl4CO4lm0_JnjocmrzLbupzOeFu-9zJ4Wttnq-IxpY&s=wcUq0_D9t-Xi40LrszT5MooY6bxaUqaU8_S_1WcmUOY&e=>

Please consider the environment before printing...

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Pasha Korber-Gonzalez via Equest-users
Sent: Thursday, April 20, 2017 3:59 AM
To: eQUEST Users List <equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>>
Subject: [Equest-users] Supply Air Temp Reset Interpretation Please...?

Hello--- I received this note from a fellow energy model reviewer (non-LEED review comment) regarding my Baseline energy model that is supposed to be compliant with Appendix G.  I disagree with what they are saying.  I appreciate your feedback please and verification if in fact I am wrong in how I am interpreting Section G3.1.3.12.

"We believe TEMP-FIRST supply air reset control strategy is not the correct interpretation of G3.1.3.12 – rather, AIRFLOW-FIRST should be used."

Thanks!

Pasha

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