LEED Increased Ventilation Credit and Energy Modeling

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Good day,

I have a question regarding the LEED credit for Increased Ventilation (IEQc2). This is the credit awarded for exceeding ventilation in all spaces by 30% beyond the ASHRAE standard 62.1 requirements. It seems obvious that the design model ventilation rates would be those 30% higher than 62.1 requirements. What then would the baseline model ventilation rates be?

If you strictly follow 90.1 Appendix G, you should always model baseline and proposed equivalent except for when taking credit for demand controlled ventilation. However, it seems in this case that it could also be argued (by LEED) that you should model the ASHRAE 62.1 required ventilation rates in the baseline model, not those that are 30% higher and therefore pay the energy expense( most climates) for increased outside air.

Does anyone have any experience with LEED on this issue? Thanks in advance.

Kind regards,
Joe Chappell

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You are going to follow 90.1 Appendix G for the model. This means both the baseline and proposed design outdoor air flow rates will need to be the same except if you are using demand control ventilation in the proposed and it is not required by 90.1 section 6.

In the case where you have demand controlled ventilation in the proposed and it is not required in the baseline then the USGBC has stated that they would like the baseline to be modeled as compliant with 62.1 without the system level corrections. There also should not be any temperature difference corrections because the other appendix G rules require your CFM sizing to be based up on a 20 ?F delta T.

If demand controlled ventilation is required by 90.1 then it must be modeled in the baseline and proposed with the same design flow.

I personally take credit on my models for where the proposed VAV system has controls to maintain a constant OA flow across from design to minimum supply, by modeling the baseline as just proportional. I have not been flagged for it, but I also have not found any definitive ruling that what I am doing is allowed.

Joe Lewis

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Joe,

Your last bit there about taking credit for constant OA flow from full-load
to part-load conditions on a VAV system is a bit of a red flag for me. The
Baseline system should be minimally compliant with ASHRAE 62.1. ASHRAE
62.1 section 6.2.6.1 requires that ventilation systems shall be designed to
be capable of providing the required ventilation rates in the breathing
zone including all full- and part-load conditions. Outside of Demand
Control Ventilation scenarios, I would always expect the Baseline and
Proposed case to deliver the same outside airflow at all hours.

That being said, I'm not certain how you're actually getting a credit for
what you're saying. What input are you modifying in eQUEST to accomplish
proportional outside air flow control?

-Robby

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Great comments all, and correct for LEED v3.

This is changing in the new LEED v4. It references ASHRAE 90.1 2010 which
does *not *match the baseline Ventilation rate to a proposed design that
exceeds the rates set by the rating authority or building official.

This matches Jim's comments - a high ventilation rate will be penalized
under LEED v4, since the baseline is the minimum, and the proposed matches
the higher value of the design.

Cheers,
Alex

*Alex Krickx* | LEED AP

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Joined: 2012-05-16
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Hi Joe,

What version of LEED are you pursuing?

For LEED 2009 (A90.1-2007 Appendix G), baseline and proposed ventilation rates should be modeled identically except when taking credit for demand controlled ventilation where it's not required by A90.1-2007.

For LEED v4 (A90.1-2010 Appendix G), if you are pursuing the 30% Increased Ventilation credit, the baseline model will have the typical A62.1 ventilation rates, and the proposed model will include the 30% increase in ventilation. I believe this is incorporated in exception (c) of A90.1-2010 section G3.1.2.6. LEED v4 and A90.1-2010 are recognizing the fact that increasing outdoor air volumes will have an energy impact, and thus project teams perusing LEED v4 will have to be cognizant of the IEQc2 credit and its potential impact on EAp2/EAc1.

I haven't seen an official LEED v4 interpretation of this issue yet, but I heard this was coming and the new language in A90.1-2010 Appendix G seems to support this.

Best,

LYLE KECK LEED AP BD+C, EIT

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