[Bldg-sim] DOAS and baseline OA

[Patrick J. O'Leary, Jr.]

in reality, i would agree with you.  if you were attempting to compare 
energy simulations for two different types of systems and were comparing 
the difference in outdoor air loads on system size/capacity (and costs 
of different systems) using the minimum per the different system types 
would be beneficial.

in leedality though the approach is a little different.  90.1 app g 
requires the minimum outdoor ventilation be the same to help prevent 
gaming the energy simulations, and is "enforced" by the leed reviewer's 
commenting on it.   the outdoor ventilation rate is the minimum designed 
outdoor ventilation rate.  so if the design is for a DOAS system then 
the minimum outdoor air rate for that system type is to be used in the 
baseline system.  same as if it the design were a packaged system but 
the baseline were VAV based on SF of the building (it happens) - the 
minimum oa rate would be what is designed for the packaged system.

except for the exception noted on page 182 when using dcv in the 
proposed if it is not required in the baseline.

look in the user's manual on page g-26, right column in the 1st 
ventilation paragraph, "outdoor air ventilation can be a major 
contributor to building energy consumption, but i is not considered an 
opportunity for energy savings under the performance rating method.  the 
minimum ventilation rates designed for the proposed building (not 
counting extra ventilation for economizer cooling) must also be modeled 
the same in both the baseline building and the proposed building."

in other words, in order to comply with the energy simulation 
requirements of 90.1 appendix g (the performance rating method) the 
minimum outdoor air rate has to be the same in both the proposed and 
baseline energy simulations (models).  so yes, outside of the one 
exception for dcv systems, the baseline outdoor air rate is the same as 
the proposed if you are only providing the minimum required per ashrae 
62 regardless of what system type the baseline building is required to use.

On 8/18/11 7:47 AM, Michael A. Eustice wrote:
>
> Unless I'm misunderstanding something, your sentence:
>
> 'when would the baseline be the same?  when you only provide the 
> minimum required outside air per ashrae 62.'
>
> Seems untrue to me.  Just so everyone is clear, under exact same 
> conditions (occupancy, sqft, bldg type etc.), with the only difference 
> being system type (VAV versus DOAS), the minimum required ventilation 
> cfm required by ASHRAE 62.1 will be different.  The VAV system will 
> almost always demand a higher minimum ventilation cfm, sometimes 
> significantly more, since one zone can drive the system towards 100% 
> outside air.
>
> Michael
>
> *From:* bldg-sim-bounces at lists.onebuilding.org 
> [mailto:bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of *Patrick 
> J. O'Leary, Jr.
> *Sent:* Thursday, August 18, 2011 10:33 AM
> *To:* Anne Juran
> *Cc:* bldg-sim at lists.onebuilding.org
> *Subject:* Re: [Bldg-sim] DOAS and baseline OA
>
> note that 90.1 requires the <i>minimum</i> outdoor ventilation rates 
> be the same in both the proposed and baseline models.  this is to 
> prevent gaming of the baseline system sizes by adding 
> capacity/increasing unit sizes which will increase baseline energy cost.
>
> though the baseline ventilation rate(s) can be the same or less than 
> the proposed they can't be more.
>
> when would the baseline be the same?  when you only provide the 
> minimum required outside air per ashrae 62.
>
> when would they be different?  when you provide more outside air in 
> the proposed design than is required by ashrae 62.
> e.g.1  providing 30% more outdoor air than required to obtain 1 leed 
> point via ieqc2 (increased ventilation)   (or using the international 
> mechanical code ventilation rates if your local jurisdiction does not 
> accept ashrae 62)
> e.g.2  using evap cooling systems sized on air change rate by volume & 
> 100% outdoor air.  ashrae 62 may require only 2,000 cfm but if you 
> provide 20,000 cfm (based on space volume) then the proposed would 
> have 20,000 cfm outdoor air and the baseline would have 2,000 cfm.  in 
> a case such as this using 20,000 cfm in the baseline would require a 
> very oversized unit that would use a lot more energy to condition the 
> outdoor air and would reward you with more points under eac1/eap2.
>
> On 8/18/11 7:03 AM, Anne Juran wrote:
>
> I agree that the OA difference is extreme... I just let Trace run wild 
> and do the calculation so I'm sure I have some crazy factors that 
> would be adjusted for a "real" design.  In retrospect, I should have 
> looked at it closer BEFORE submitting to USGBC.  I'm sure it made them 
> closer at it, whereas if I was only slightly different they may have 
> not questioned it.  Lesson learned!
>
> It doesn't look like I'll get anywhere with USGBC, though, as the 
> reviewer explicitly stated, "the total minimum outdoor air ventilation 
> volume in the Baseline model must never be greater than the Proposed 
> model."
>
> Thanks for all the input!
>
> *From:* bldg-sim-bounces at lists.onebuilding.org 
> <mailto:bldg-sim-bounces at lists.onebuilding.org> 
> [mailto:bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of *Jeremy 
> Poling
> *Sent:* Thursday, August 18, 2011 9:40 AM
> *To:* bldg-sim at lists.onebuilding.org 
> <mailto:bldg-sim at lists.onebuilding.org>
> *Subject:* Re: [Bldg-sim] DOAS and baseline OA
>
> While I don't intend to discuss the merits of VAV systems and know I'm 
> part of a minority in that area, this is exactly why DOAS systems are 
> being explored more right now on the research side (take for example 
> the number of ASHRAE Journal articles on the topic over the past few 
> years).  Without seeing your OA calcs I would also agree that the 
> difference is more than I would expect between the two systems, but 
> I'm more inclined to think the DOAS might be a bit low if it is being 
> used in conjunction with FCUs.  VAV systems are typically 
> underventilated due to two common mistakes in the calculations: not 
> analyzing with the correct Ez and not using the minimum expected 
> primary airflow for design purposes (refer to ASHRAE 62.1-2007 Section 
> 6.2.5.1, specifically the note in that section).  When fixing these 
> two typical mistakes in calculations without optimizing the primary 
> airflow rates, I typically see OA requirements double from the 
> incorrectly calculated values.
>
> This situation is a good example of when to do one of two things 
> (possibly both together)
>
> If this is a LEED project, submit a project-specific CIR
>
> Use section ASHRAE 90.1-2007 Section 2.5 Exceptional Calculation 
> Methodology to get around the requirement and document the energy 
> savings from reduced OA requirements for a DOAS system.
>
> *Jeremy R. Poling, PE, LEED AP+BDC*
>
> *From:* bldg-sim-bounces at lists.onebuilding.org 
> <mailto:bldg-sim-bounces at lists.onebuilding.org> 
> [mailto:bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of *Mark 
> Sorensen
> *Sent:* Wednesday, August 17, 2011 11:42 AM
> *To:* bldg-sim at lists.onebuilding.org 
> <mailto:bldg-sim at lists.onebuilding.org>
> *Subject:* Re: [Bldg-sim] DOAS and baseline OA
>
> Anne,
>
> While LEED/ASHRAE 90.1 requires the ventilation rates to be the same 
> in both the Baseline and Proposed systems, the calculated difference 
> for the two systems is much higher than expected. Suggest taking 
> another look at the calculations and confirming that the critical zone 
> for the VAV system has been properly determined and whether 
> appropriate factors for the zone air distribution effectiveness (Ez) 
> and system ventilation efficiency (Ev) have been applied.
>
> Mark Sorensen
> Diversified Energy Services
> Fruitport, Michigan
> 231-578-1264
>
> On 8/16/2011 9:12 AM, Jim Dirkes wrote:
>
> Dear Anne,
>
> I'm not sure why you think the OA requirement varies by system.  I'm 
> not well versed in Standard 62, but my basic understanding is that one 
> of the calculation methods is the result of building area and number 
> of occupants.  Those are unchanged by system selection ... which is 
> why it makes sense for Appendix G to require matching volumes.
>
> *The Building Performance Team
> **James V. Dirkes II, P.E., BEMP , LEED AP
> *1631 Acacia Drive NW
> Grand Rapids, MI 49504
> 616 450 8653
>
> *From:* bldg-sim-bounces at lists.onebuilding.org 
> <mailto:bldg-sim-bounces at lists.onebuilding.org> 
> [mailto:bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of *Anne Juran
> *Sent:* Tuesday, August 16, 2011 8:33 AM
> *To:* bldg-sim at lists.onebuilding.org 
> <mailto:bldg-sim at lists.onebuilding.org>
> *Subject:* [Bldg-sim] DOAS and baseline OA
>
> I'm curious how everyone is handling the OA for Appendix G simulations 
> when using a DOAS in the proposed system.  We have a design that is 
> DOAS + FCU with a  total OA of 8,000 CFM.  When you run the OA calcs 
> for this same building with a VAV system (the baseline), the total OA 
> required to meet Standard 62 is 39,000 CFM.  This difference in OA 
> represents a significant energy savings (in climate zone 4A), yet 
> Appendix G requires the OA volumes to match.  It does not seem "fair" 
> to me that the proposed case cannot take credit for design choice when 
> it comes to OA.  I feel like Appendix G should make an exception for 
> DOAS.  Am I missing something?  Is there a way around this?  Any 
> thoughts are appreciated!
>
> Anne
>
>   
>   
> _______________________________________________
> Bldg-sim mailing list
> http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org
> To unsubscribe from this mailing list send  a blank message toBLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG  <mailto:BLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG>
>
>   
>   
> _______________________________________________
> Bldg-sim mailing list
> http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org
> To unsubscribe from this mailing list send  a blank message toBLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG  <mailto:BLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG>
>    
>
>
> ------------------------------------------------------------------------
> The information contained in this message is intended only for the 
> personal and confidential use of the recipient(s) named above. If the 
> reader of this message is not the intended recipient or an agent 
> responsible for delivering it to the intended recipient, you are 
> hereby notified that you have received this document in error and that 
> any review, dissemination, distribution, or copying of this message is 
> strictly prohibited. If you have received this communication in error, 
> please notify HT Lyons immediately, and delete the original message.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20110818/776f726c/attachment-0002.htm>