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

Mon Apr 24 14:21:50 PDT 2017

One other wrinkle. 

RESET-PRIORITY is a VAV box control.  The DOE2 dictionary describes the RESET-PRIORITY keyword parameters with this example: “if a zone cooling setpoint is 76F with a 2F throttling range, the air flow will first modulate in the range of 77F to 76F and the supply air temperature will reset in the range of 76F to 75F.”  This doesn’t really match real-world operation, either, and may also explain the results Bill got. 

Seems to me, the only way to meet G3.1.3.12 is to use COOL-MAX-RESET-T and COOL-MIN-RESET-T, and let DOE2 do what it wants.  

Shaun

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 Bishop, Bill via Equest-users
Sent: Monday, April 24, 2017 10:01 AM
To: Pasha Korber-Gonzalez <pasha.pkconsulting at gmail.com>; Daric Adair <Daric.Adair at hei-eng.com>
Cc: equest-users at onebuilding.org
Subject: Re: [Equest-users] Supply Air Temp Reset Interpretation Please...?

I agree with Daric’s analysis that an “Airflow First” reset priority should be modeled for baseline VAV systems. I don’t see anything in Appendix G. that implies a temperature-first control strategy. Appendix G. states requirements for both SAT reset and VAV minimum flow. The SAT reset is to be applied “under the minimum cooling load conditions”. That implies that between minimum and design cooling load conditions, airflow rate is adjusted, which means the airflow rate is adjusted first. I tried “TEMP-FIRST” on one of my baseline models and it saved 3.6% cooling energy, added 1.8% fan energy and saved 0.6% heating energy for a net building energy savings of 0.4% versus baseline with AIRFLOW-FIRST. (So AIRFLOW-FIRST is better in my n=1 case for showing savings in the proposed design vs. baseline.)

~Bill

William Bishop, PE, BEMP, BEAP, CEM, LEED AP | Pathfinder Engineers & Architects LLP

Senior Energy Engineer

134 South Fitzhugh Street                 Rochester, NY 14608

T: (585) 698-1956                        F: (585) 325-6005

 <mailto:wbishop at pathfinder-ea.com> bbishop at pathfinder-ea.com              <http://www.pathfinder-ea.com/> www.pathfinder-ea.com

Carbon Fee and Dividend - simple, effective, and market-based.

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Pasha Korber-Gonzalez via Equest-users
Sent: Monday, April 24, 2017 3:43 AM
To: Daric Adair <Daric.Adair at hei-eng.com <mailto:Daric.Adair at hei-eng.com> >
Cc: equest-users at onebuilding.org <mailto:equest-users at onebuilding.org> 
Subject: Re: [Equest-users] Supply Air Temp Reset Interpretation Please...?

Hi All-- Thank you for this in depth discussion and taking time to go over all of this.  (I was away from work for a few days, thus my delayed response.)

I agree with the commentary regarding how REAL LIFE operations happen in VAV systems, and yes modulating airflow is the first approach.  However, i did always find it odd that temp first was stated in Appendix G, but who am I to question Appendix G, right?

As for the discussion of direction from the PNNL User's Manual-- that is interesting, and I hadn't seen that document prior to now because I am still only working on projects that reference ASHRAE 90.1-2007.  Therefore I have had no need or time to look at the 2010 version or any supporting docs...which brings us to the next debate:

Why should anyone be referencing a 2010 version document for guidance for a 2007 version compliance model/project?  Therefore it seems prudent to stand firm to follow exactly what the governed/reference standard states-explicitly which is "temperature reset."  

But then-  Thank you Daric for confirming that the 2007 version User's Manual doesn't specifically guide us on how to meet the criteria of that section.  AND thank you Daric for also conducting a minor experiment on your model.  (I will do the same with a couple of mine this week.) 

So based on what I have learned from this awesome discussion/debate, I will assume that my third party reviewer (non GBCI group) was indeed referencing the PNNL User's Manual for the 2010 version, possibly out of habit, and/or not even aware that the LEED guided project they were contracted for reviewing (my model, which I was contracted to produce by the Architect & owner) is in fact registered as a LEED 2009 project that is referencing and following ASHRAE 90.1-2007 version.

Hmm, I'm in a quandary of how to take action for my model based on this questionable review comment- who is not the actual LEED reviewer.  This seems like a weird situation to be in...

Thanks again for all your input on this topic!

Pasha Korber

Ph 308-763-1593

www.korberenergy.com <http://www.korberenergy.com> 

On Fri, Apr 21, 2017 at 8:49 AM, Daric Adair <Daric.Adair at hei-eng.com <mailto:Daric.Adair at hei-eng.com> > wrote:

Agreed on ventilation. But 90.1 Appendix G addresses the VAV box minimums for Baseline models in G3.1.3.13/G3.1.3.14. The box minimums must take ventilation into account.

Fan energy is a major element. Several of my more recent models have had fan energy on par with heating and cooling energy. Both for baseline and proposed models. Fans unload nicely…which is a blessing and a curse.

Running some quick diagnostic tests on a couple of my most recent models, the difference in the two control strategies didn’t yield a massive difference. But one test does not a trend make….in any sense, the Temperature Frist reset set was 0.29% lower on a cost basis…

Another factor specific to eQuest, when using Airflow first control, is the ‘MIN-RESET-FLOW’ variable. This defaults to 0.66. Which from the help files seems to indicate that the it will only allow the fan to reset to this level (0.66 in this case/by default) before starting temperature reset. Modifying this value  impacts when the system will start to modify the DAT. This did have an impact on the results, but not very underwhelming at best from my very limited testing pool….

In short, it gets back to which element should unload first – fans vs chiller/boiler. Fan curves are dictated for Appendix G (and Fan laws). Chiller curves are not provided/dictated for Appendix G, but performance is. Similar for boilers. In a ‘real’ system with actual equipment curves, it would be a balance between savings from the fan slowing vs savings from central plant equipment unloadng (which has more complex relationships).

Thanks,

DARIC R. ADAIR  PE, C.E.M. 
Henderson Engineers, Inc. | Mechanical Engineer, Energy Analyst 
dir 913 742 5530 <tel:(913)%20742-5530>   tel 913 742 5000 <tel:(913)%20742-5000>   fax 913 742 5001 <tel:(913)%20742-5001>   tx id #F-001236  email daric.adair at hei-eng.com <mailto:daric.adair at hei-eng.com>    <http://www.hei-eng.com/> www.hei-eng.com 
Licensed in KS. 

From: Bruce Easterbrook [mailto:bruce5 at bellnet.ca <mailto:bruce5 at bellnet.ca> ] 
Sent: Thursday, April 20, 2017 10:24 PM
To: Daric Adair <Daric.Adair at hei-eng.com <mailto:Daric.Adair at hei-eng.com> >; Jennings, Coles <Coles.Jennings at MasonandHanger.com <mailto:Coles.Jennings at MasonandHanger.com> >; PKConsulting <pasha.pkconsulting at gmail.com <mailto:pasha.pkconsulting at gmail.com> >; Shaun Martin <smartin at shaunmartinconsulting.com <mailto:smartin at shaunmartinconsulting.com> >

Cc: equest-users at onebuilding.org <mailto:equest-users at onebuilding.org> 
Subject: Re: [Equest-users] Supply Air Temp Reset Interpretation Please...?

I may be all wet here but one other consideration is OA.  If there is no DOAS then the VAV system is supplying the OA to the zones.  A drop in flow could reduce the OA below minimum requirements for the zones.  A temp first reset would maintain airflow and the OA air portion.  With energy consumption, cooling and heating are the most expensive components of the flow and then the fan energy.  This is why economizers are very energy efficient in the right conditions.
So ultimately you have to meet ASHRAE 90.1 and also 62.1.  These are also baseline systems, just setting the low bar before we start to tinker.  All points and justification come from the magnitude you can exceed the baseline.  The baseline has been ratcheting up, things are not as easy now and almost all the low hanging fruit is gone.
I was reading an article in the online Journal this morning from 2014.  Part of it concerned fan efficiency, FC, AF and plenum with direct and belt drive.  Now that efficiency is getting right down to belt slippage you know there isn't much left to play with.
Bruce Easterbrook P.Eng.
Abode Engineering

On 4/20/2017 6:54 PM, Daric Adair via Equest-users wrote:

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)%20742-5530>   tel 913 742 5000 <tel:(913)%20742-5000>   fax 913 742 5001 <tel:(913)%20742-5001>   tx id #F-001236  email daric.adair at hei-eng.com <mailto:daric.adair at hei-eng.com>    <http://www.hei-eng.com/> 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  <mailto:pasha.pkconsulting at gmail.com> <pasha.pkconsulting at gmail.com>; Shaun Martin  <mailto:smartin at shaunmartinconsulting.com> <smartin at shaunmartinconsulting.com>
Cc: equest-users at onebuilding.org <mailto: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 <tel:(804)%20521-7045>  | O 804.285.4171 <tel:(804)%20285-4171>  | F 804.217.8520 <tel:(804)%20217-8520>  
4880 Sadler Road, Suite 300 | Glen Allen, VA 23060 
 <http://www.masonandhanger.com/> Mason & Hanger 
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 <tel:(308)%20763-1593> 

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 <tel:(604)%20789-1095> 

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 <tel:(308)%20763-1593> 

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 <tel:(416)%20644-0252> 

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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