[Equest-users] usgbc response to outdoor air question

[Patrick J. O'Leary, Jr.]

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> <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

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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