Minimum Ventilation Air in Proposed and Baseline - Breathing Zone or Outdoor Air Intake

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Hi,

We've received a nice boost in some models in Canada lately as the Proposed
and Baseline designs only need to have the same amount of outdoor air in the
breathing zone under CaGBC Rules. Meaning that if your baseline design is
VAV Reheat and your proposed design is chilled beam and baseboard heating
then your proposed design will have to condition somewhere in the range of
40% less outdoor air due to higher zone effectiveness and system efficiency.
It makes a lot of sense to me and becomes a significant energy savings
measure.

Is this allowed by the USGBC or by ASHRAE? I just read in 90.1 in G.3.1.2.5
that "Minimum outdoor air ventilation rates shall be the same for the
proposed and baseline designs." That doesn't specify whether they mean in
the breathing zone or outdoor air intake but I think most assume it to be
the outdoor air intake.

Aaron Smith, P.Eng

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Aaron,
ASHRAE 90.1-2007 Addendum bj allows modelers to take energy savings credit for HVAC systems that increase air distribution effectiveness and use demand control ventilation. This can therefore result in different ventilation rates between Baseline and Proposed models. USGBC allows modelers to apply any ASHRAE Addenda they want for that version of the standard as long as it is applied uniformly and clearly stated.

Scott P. West, P.E., LEED AP BD+C, BEAP, BEMP

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Scott,

Thanks, I see that came out in 2010 so it didn't make it into 90.1-2010.

It allows you to claim credit for having zone effectiveness greater than 1.0
but doesn't allow you to claim system efficiency gains.

"Baseline ventilation airflow rates in those

zones shall be calculated using the proposed design Ven-

tilation Rate Procedure calculation with the following

change only. Zone air distribution effectiveness shall be

changed to (Ez)=1.0 in each zone having a zone air distri-

bution effectiveness (Ez)>1.0."

So if your Proposed has a DOAS and the Baseline is VAV, the baseline won't
meet Standard 62.

Aaron Smith, P.Eng

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Okay thanks Aaron. I wasn't aware of that development.

Scott P. West, P.E., LEED AP BD+C, BEAP, BEMP

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Scott,

I had thought of that addendum but I don't think it applies in your case since it is meant for UFAD/displacement systems. You may be able to show some savings using G3.1.3.13 and saying that the minimum zone airflow rates are higher for the baseline VAV system since it is not decoupled like your chilled beam/DOAS system. Baseline and proposed would still have the same minimum OA coming into the building but you would need to do a second OA calc to find what the zone minimums would be. I think it makes sense conceptually but I haven't tried it before so not sure if a reviewer would go for it. That being said they are generally pretty good about accepting atypical arguments for energy savings as long as you show your work in a fair amount of detail.

Brendan Hall, PE, LEED AP BD+C

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Thanks Brendan,

This question wasn't for a specific project, it came up because it is
accepted by the CaGBC (in Canada) but didn't seem to be something that the
USGBC or ASHRAE had ruled on.

Regards,

Aaron Smith, P.Eng

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