G3.1.2.5 Clarification

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Hello,

G3.1.2.5 states that?minimum ventilation rates will be the same for proposed
building and?baseline building. Does it mean that if my?building design OA rate
is increased by 30%, my model will still be based on the minimum OA required by
62.1 and is still equal to the baseline building OA? Meaning my proposed
building wont be penalized by supplying more OA?

Thanks in advance.

Jaigath

Jaigath Chandraprakash's picture
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In my opinion:

For LEED, the OA should increase 30% first. This is the propose requirement.

Then for energy model, the baseline model should equal to proposed, which
means the baseline OA is also 30% more than 62.1 requirement.

grammy's picture
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I agree. Standard 61.1 sets the minimum acceptable ventilation rate.
The design ventilation rate can be higher, and the baseline rate should
be the same as the real design.

Best regards,

Michael L. Kingsley, PhD, PE, LEED AP

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Section G.3.1.2.5 in 90.1-2007 has added an exception to the "shall be the same" for models with demand controlled ventilation in the proposed that is not required by Section 6.4.3.9.

That alone is kind of confusing since it does not address what the values should be when they are allowed to not be the same.

I think they are trying to resolve the intersection of projects that use more OA than Std 62.1 and utilize demand controlled ventilation.
The most recent Trane Engineers broadcast promised more changes coming to this section (as addendum DA?) but I do not have anything published to reference.

Paul Riemer

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In my opinion, the exception is means that keep the "design value" of OA
same in both proposed and basline, but use DCV only in proposed.

Because DCV can modify OA volume by the number of people in zone, and the OA
requirement is dynamics in simulation - which is too hard to keep baseline
same with, and also should not keep the same, if not where does the saving
come from?

grammy's picture
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Baseline building should always be just providing the minimum outdoor air
ventilation rate required by 62.1. It should never be increased. For proposed,
it just means that your OA should never be below the minimum OA requirement of
62.1. Now if the design chooses to pursue 30% more OA. Then you should reflect
in your model what is in the design. G3.1.2.5 just wants to make sure that you
do not model your proposed to be below the minimum OA. Providing 30% more OA can
earn you a credit but it will affect your EAc1.

Jon

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I agree with Jon. The increased Ventilation rate of 130% OA is for comfort
only, and should show an increase in energy usage when compared to the
baseline. this is the approach my firm has always took when solving this
little riddle.

Rob

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There was a major discussion on this topic a few months ago, although it may
have been on the eQuest list-serve, I don't remember. Try searching the
archives.

The general conclusion was that the current requirements are that the
baseline and proposed design models should have the same ventilation rates,
BUT that this doesn't make that much sense as you could over-ventilate to
the point where there is no added benefit to the occupants, and major
additional energy use. The discussion was primarily around LEED EA Credit
1, and there was some correspondence between the simulation group and the
LEED credit chair. I believe that they will be looking at modifying this
requirement for LEED models in the future.

--
Karen

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Joined: 2011-09-30
Reputation: 200

This changes with the soon to be released 90.1-2010 which adds the following;

If the minimum outdoor air intake flow in the proposed
design is provided in excess of the amount required by the
rating authority or building official then the baseline
building design shall be modeled to reflect the greater of
that required by the rating authority or building official
and will be less than the proposed design.

Michael Rosenberg

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For what it's worth, regardless of what the various publications
actually say, the last 5-6 projects of mine have had reviewers that had
me confirm that when I use DCV in the proposed design, that the baseline
design MUST match the minimum ASHRAE 62.1-2004 (or 07) requirements.

So if you don't have DCV (shame on you!), then your baseline and
proposed models can have matching OA, and it can be whatever quantity
you want.

As soon as you incorporate DCV, the baseline model has to go down to
minimum 62.1 rates.

James Hansen, PE, LEED AP

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The previous discussion also touched on the topic of requirements for LEED
models changing at the review stage (your reviewer indicating something that
is reflected NOWHERE in the documentation). This really makes me mad! It
requires extra time on our end because either:

1. The reviewers are not properly educated as to the requirements
2. The reviewers are making up requirements on their own
or,
3. The reviewers are following guidelines provided to them by someone
(USGBC???) that has not been made available to the modeling professionals
who must abide by these rules.

--
Karen

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yes! Hear! Hear!

My experience with submitted LEED projects has been.
1. proposed and baseline use the same OA quantity
2. you can take credit for DCV in the proposed building; however, the baseline
building is also required to use DCV in the spaces that are required to have it
as prescribed in 90.1

Julia Beabout's picture
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there are so many different opinions~

read the 90.1, and also 90.1 user manual and LEED requirement carefully~

grammy's picture
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Allow me to add my two cents...

My understanding and what my logic are telling me (whether they forgot to clearly specify it in the Standard or not) is that OA design values in the Baseline should never be:

1. more than the design values in the Proposed; and

2. more than the code-prescribed values.

independently of DCV or this 30% over-ventilation.

______________
Demba NDIAYE

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I think this idea that the baseline building design ventilation rate
should be equal to the minimum code required rate should be handled
cautiously by energy modelers. Implementing this requirement would
require modelers to do the following:
1.) determine which code(s) are applicable for the mechanical design
(local/state codes and ASHRAE Standard 62.1 for starters)
2.) calculate the minimum design ventilation rates for all zones, for
all applicable codes for the project, and determine the highest minimum
rates if the applicable codes differ
3.) compare the calculated rates to the ventilation rates in the
proposed design, for all zones

This is significant additional scope that is usually not required for an
energy model, including LEED models. This is the responsibility of the
mechanical designer. Unless I know that a project is pursuing LEED IEQc2
credit, or that a proposed mechanical design is using excessive
ventilation for some other reason, I will use the proposed design
ventilation rates in both the proposed and baseline models, which I have
been entering on a zone-by-zone basis to this point to meet my
interpretation of the G3.1.2.5 intent.

Regards,

William Bishop, PE, BEMP, LEED(r) AP

This changes with the soon to be released 90.1-2010 which adds the
following;

If the minimum outdoor air intake flow in the proposed
design is provided in excess of the amount required by the
rating authority or building official then the baseline
building design shall be modeled to reflect the greater of
that required by the rating authority or building official
and will be less than the proposed design.

Michael Rosenberg

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