[Bldg-sim] usgbc response to outdoor air question

Patrick J. O'Leary, Jr. poleary1969 at gmail.com
Mon Oct 17 10:37:28 PDT 2011


you're welcome james.  now if i could only get a straight answer on how 
to address baseline system sizing/outdoor air rates when the proposed 
building is evaporatively cooled with 100% outdoor air .... sizing a 
baseline building system of packaged dx just doesn't sit right when the 
proposed is providing 20,000 cfm with 100% outdoor air.  and i get mixed 
comments from reviewers about too much energy savings ... or providing 
too much outdoor air in the baseline ...

On 10/17/11 9:31 AM, Jim Dirkes wrote:
>
> Dear Patrick,
>
> Thank you for sharing this GBCI response!  It is very informative and, 
> while I won't admit that I've been modeling anything incorrectly, I 
> _am_ going to change a couple of things J.
>
> In particular, I have heard on several occasions that the Increased 
> Ventilation credit was a clear case of "IEQ vs. energy"; you make a 
> decision to trade one against the other.  After reading the GBCI 
> response below and then double-checking with ASHRAE 90.1, I find that 
> they are consistent with each other and effectively allow no penalty 
> for the increased energy caused by increased ventilation.  Very 
> curious, considering there is no science which demonstrates a health 
> benefit for outdoor airflows greater than that required by ASHRAE 62.1!
>
> The other item is that I failed to notice (and still can't find) 
> anything in 621.1 which says that unoccupied ventilation should be 
> zero.  I guess that is OK, but is also curious, since a portion of the 
> ventilation calcs in 62.1 include consideration for off-gassing 
> materials (which are always present.)
>
> All in all, I'm smarter than I was as a result of your post, so it's a 
> good day!  Thanks again.
>
> *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] *On Behalf Of *Patrick 
> J. O'Leary, Jr.
> *Sent:* Monday, October 17, 2011 11:46 AM
> *To:* equest-users at lists.onebuilding.org; bldg-sim at lists.onebuilding.org
> *Subject:* [Bldg-sim] usgbc response to outdoor air question
>
> back in september there was a thread about what the outdoor air rate 
> in a baseline simulation should be compared to a proposed simulation, 
> specifically when one is adding 30% more outdoor air to meet the ieqc2 
> requirement and earn 1 leed point.  there were differences of opinions 
> about the flow rates between baseline and proposed being either the 
> same (as required in 90.1 app g) or the baseline being the calculated 
> per 62.1 and the proposed being as designed.
>
> so i submitted a support request to the usgbc and the reply i received 
> is below, but in short the response is that unless you're using dcv 
> optionally the outdoor air rates in the baseline and proposed energy 
> simulations for eac1 should be the same.  the response below gives the 
> standard responses to differing outdoor air rate scenarios.
>
> regards,
> patrick
>
> [Fwd: Case 00531150: General LEED Questions
>
> -------- Original Message --------
>
> *Subject: *
>
> 	
>
> Case 00531150: General LEED Questions [ ref:00D49UeD.5004GN692:ref ]
>
> *Date: *
>
> 	
>
> Mon, 17 Oct 2011 06:54:51 +0000 (GMT)
>
> *From: *
>
> 	
>
> "No reply GBCI" <no-reply at gbci.org> <mailto:no-reply at gbci.org> 
> <no-reply at gbci.org> <mailto:no-reply at gbci.org>
>
> *To: *
>
> 	
>
> patrick@
>
> Dear Patrick,
>
> Thank you for contacting the Green Building Certification Institute.
>
> You ask very good questions related to the relationship between ASHRAE 
> Standards 62.1 and 90.1, and how these standards are applied across 
> multiple LEED Rating System prerequisites and credits.
>
> The simple answer to your question is that, for systems without demand 
> controlled ventilation, the outdoor air included in EA Credit 1 energy 
> simulations must be the same in the Baseline and Proposed cases. If 
> the project is attempting IEQ Credit 2 Increased Ventilation, then the 
> values calculated in IEQc2 must be used in the EAc1 Basline and 
> Proposed case energy models. Note that IEQc2 does not limit the 
> project to providing only 30% more outdoor air than AHRAE 62.1 
> Ventilation Rate Procedure minimums, so higher amounts are acceptable, 
> as long as they are modeled identically in both the Baseline and 
> Proposed case energy models.
>
> The following generic LEED Review Comment applies to ventilation 
> systems that do not have demand controlled ventilation:
>
> It is unclear whether the minimum outside air rates (in CFM) were 
> modeled identically in the Baseline and Proposed case for all zones 
> not having Demand Control Ventilation in the Proposed case. Please 
> confirm that minimum outside airflow (in units of cfm) was modeled 
> identically in the Baseline and Proposed cases using the proposed case 
> rates. Additionally, please verify that all systems in both the 
> baseline and proposed case are modeled with zero outside air flow when 
> fans are cycled on to meet unoccupied setback temperatures unless 
> health or safety regulations mandate an alternate minimum flow during 
> unoccupied periods (in which case, the unoccupied outside air rates 
> should be modeled identically in the Baseline and Proposed case).
>
> The situation becomes a bit more complicated in you have systems that 
> have demand controlled ventilation (often implemented as Carbon 
> Dioxide control of outdoor air or as programmed control of outdoor air 
> based on occupancy sensors.) In this case the Baseline case energy 
> model must include the minimum outdoor air as determined by the ASHRAE 
> 62.1 Ventilation Rate Procedure calculations for all systems having 
> demand controlled ventilation.
>
> The following generic LEED Review Comment applies to ventilation 
> systems that do have demand controlled ventilation:
>
> Demand control ventilation was modeled for credit in the proposed 
> case. Appendix G allows schedule changes for demand control 
> ventilation as approved by the rating authority (Table 
> G3.1#4(Baseline)). As the LEED Certification rating authority, GBCI 
> requires that the outside air ventilation rates for the Baseline case 
> be modeled using minimum ASHRAE 62.1-2004 (or 2007 for LEED-NC 2009 
> projects) rates wherever credit is taken for demand control 
> ventilation in the Proposed case. The proposed case minimum rates at 
> design conditions should be modeled as designed. Please verify that 
> the Baseline Case model reflects ASHRAE 62.1-2004 (or 2007) minimum 
> rates for any spaces where credit is taken for demand control 
> ventilation, or revise the model accordingly. For all other spaces, 
> please confirm that minimum outside airflow (in units of cfm) was 
> modeled identically in the Baseline and Proposed cases. Additionally, 
> please verify that all systems in both the baseline and proposed cases 
> are modeled with zero outside air flow when fans are cycled on to meet 
> unoccupied setback temperatures unless health or safety regulations 
> mandate an alternate minimum flow during unoccupied periods (in which 
> case, the unoccupied outside air rates should be modeled identically 
> in the Baseline and Proposed case).
>
> Finally, even though you don't address energy recovery in your 
> question, whether or not you have energy recovery in your ventilation 
> systems may affect how much better (or worse) your Proposed case 
> energy models perform in relation to your Baseline case energy models.
>
> The following generic LEED Review Comment addresses energy recovery in 
> EAc1 energy models as it relates to ventilation systems.
>
> Energy recovery is modeled for credit in the Proposed case. Please 
> provide further information regarding the energy recovery efficiency, 
> verify that outside air is modeled with zero flow in both the Baseline 
> and Proposed cases during unoccupied periods when fans are cycled on 
> to meet unoccupied setback temperatures unless health or safety 
> regulations mandate an alternate minimum flow during unoccupied 
> periods (in which case, the unoccupied outside air rates should be 
> modeled identically in the Baseline and Proposed Case), and indicate 
> the bypass mechanism used to bypass the energy recovery during mild 
> conditions.
>
> I hope that helps, but if you have any further questions or concerns, 
> please feel free to use the contact form at 
> http://www.gbci.org/contactus and select "Follow up to GBCI Response," 
> inputting your case number from this email's subject line.
>
> Best Regards,
>
> Dan Katzenberger, P.E., CEM, BEMP, LEED-AP BD+C
>
> Green Building Certification Institute
> 2101 L Street NW, Suite 500
> Washington, DC 20037
> 800-795-1746 (phone)
> 202 828-5110 (fax)
> www.gbci.org/contactus <http://www.gbci.org/contactus>
>
> The text above represents a staff opinion of a particular issue, and 
> does NOT set any precedent to be upheld during a LEED Certification 
> Review. For official rulings in advance of a LEED Certification 
> Review, customers should utilize the Formal Inquiries process 
> available in LEED Online that results in a Project Credit 
> Interpretation Ruling (Project CIR) and possibly a LEED Interpretation 
> (formerly CIRs or Public Rulings). Applications for LEED Certification 
> will be thoroughly reviewed based on USGBC Member balloted and 
> approved LEED Rating Systems, with addenda, and USGBC approved LEED 
> Interpretations, or Project CIRs administered by GBCI, as applicable. 
> Please note that certain inquiries submitted to USGBC are forwarded to 
> GBCI for reply as appropriate.
>
>
> _______________________________
> CUSTOMER EMAIL ADDRESS:
> patirck@
>
> CUSTOMER INQUIRY:
> I am trying to verify what the minimum outdoor airflow rate required 
> for EAc1 is and am not sure if this requires a CIR.
>
> If the Proposed outdoor air ventilation is a minimum of 30% higher 
> than the minimum required by ASHRAE 62 in order to achieve 1 LEED 
> point for credit IEQC2 is the Baseline outdoor air rate also 30% 
> higher than the minimum required by ASHRAE 62? or would the Baseline 
> outdoor air ventilation rate be the minimum outdoor air rate per 
> ASHRAE 62 calculations.
>
> In other words, if ASHRAE 62 requires a minimum of 1,000 CFM of 
> outdoor air, and 1,300 CFM is provided to attain 1 LEED point via 
> IEQC1, is the Baseline outdoor air flow rate 1,000 CFM or 1,300 CFM in 
> the energy simulation?
>
> 90.1-2007/2004 both say the minimu    m outdoor airflow rates shall be 
> the same for both the proposed and baseline building designs, as does 
> the user manual.
>
> But this logic seems to reward the Proposed simulation by conditioning 
> the additional outdoor air supplied (300 cfm in the example above) to 
> achieve IEQC1 in the Baseline system as well as the proposed.
>
> The logic of using the minimum required in the Baseline case is 
> reflected in EAC1 in the equipment efficiency requirements. Baseline 
> efficiencies are the minimum required, e.g. SEER 13 for packaged units.
>
> It is the intent of the requirement that I am not sure is clear. 
> Increasing the outdoor air ventilation rate increases the energy used 
> to condition the outdoor air, so if the intent is to put the onus on 
> Proposed design to show energy reduction/LEED compliance over the 
> 90.1/62 requirements shouldn't the Baseline outdoor air be the minimum 
> air flow rate per the ASHRAE 62 calculations? This puts the onus on 
> the design team to provide a design that compensates for the increase 
> in energy to meet IEQC2 by providing some method of processing the 
> increase in outdoor air while still reducing energy consumption.
>
>
>
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