[Bldg-rate] [Bldg-sim] usgbc response to outdoor air question
KKyte at watts-ae.com
Thu Sep 19 12:59:24 PDT 2013
Ok, so I received this comment. The one with the provide ASHRAE minimums in the Baseline for spaces with DCV. I understand this is a generic comment - Ok.
However, LEED IEQ Credit 2 is not being pursued and the ASHRAE minimum ventilation requirements are what is being Proposed for in each space that has DCV.
Does this not mean that the Baseline ventilation rate and the Proposed ventilation rate will still be equal?
Not sure how to respond other than to simply say what is stated here.
From: Reba Schaber [mailto:Rschaber at PHMECH.com]
Sent: Tuesday, November 15, 2011 9:42 PM
To: Jim Dirkes; equest-users at lists.onebuilding.org; 'bldg-sim at lists.onebuilding.org'
Subject: Re: [Bldg-sim] usgbc response to outdoor air question
RE: ". . . can't find) anything in 621.1 which says that unoccupied ventilation should be zero."
I think this requirement comes from the mandatory provisions of 90.1.
188.8.131.52.3 Shutoff Damper Controls. Both outdoor
air supply and exhaust systems shall be equipped with motorized
dampers that will automatically shut when the systems or
spaces served are not in use. Ventilation outdoor air dampers
shall be capable of automatically shutting off during preoccupancy
building warm-up, cool down, and setback, except
when ventilation reduces energy costs (e.g., night purge) or
when ventilation must be supplied to meet code requirements.
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 Jim Dirkes
Sent: Monday, October 17, 2011 9:32 AM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>; 'bldg-sim at lists.onebuilding.org'
Subject: Re: [Bldg-sim] usgbc response to outdoor air question
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 :).
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> [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<mailto:equest-users at lists.onebuilding.org>; bldg-sim at lists.onebuilding.org<mailto: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.
[Fwd: Case 00531150: General LEED Questions
-------- Original Message --------
Case 00531150: General LEED Questions [ ref:00D49UeD.5004GN692:ref ]
Mon, 17 Oct 2011 06:54:51 +0000 (GMT)
"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>
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.
Dan Katzenberger, P.E., CEM, BEMP, LEED-AP BD+C
Green Building Certification Institute
2101 L Street NW, Suite 500
Washington, DC 20037
202 828-5110 (fax)
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:
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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