GBCI comments on DCV (Carol Gardner)

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I've had many comments. They have changed their perspective as the rating
authority and are requiring outside air treatment procedures that are
outside of ASHRAE 90.1 section G procedures. Typically design outside air
volume is the same between the baseline and proposed, but if you are using
DCV they now require you to model the baseline with the minimum ASHRAE 62.1
volume. So, if you have greater OA volume in your proposed model, you may
be penalized depending on your DCV method and diversity schedule for
occupants in the area with DCV control.

Here is an example clarification question:

*1. **CLARIFY:* Demand control ventilation was modeled for credit for
RTU1 and RTU2 in the Proposed case as indicated in Table 1.4 of the
Template; however, the outdoor air volume for RTU1 and RTU2 in the Baseline
model was not modeled at the ASHRAE 62.1-2004 minimum rates (1,066 cfm for
each RTU) as determined in EQp1: Minimum IAQ Performance. Appendix G allows
schedule changes for demand control ventilation as approved by the rating
authority (Table G3.1.4(Baseline)). As the rating authority, GBCI requires
that the outside air ventilation rates for the Baseline Case be modeled
using minimum ASHRAE 62.1-2004 rates wherever credit is taken for demand
control ventilation in the Proposed Case. The Proposed case minimum rates at
design conditions must be modeled as designed.

*TECHNICAL ADVICE:* Revise the Baseline model so the minimum outdoor air
volume is modeled at 1,066 cfm for RTU1 and RTU2 in the Baseline model. In
addition, provide revised SV-A reports for RTU1 and RTU2 reflecting the
changes. Further, 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 must be modeled identically in the Baseline and
Proposed Case).

Thomas Serra

Thomas Serra's picture
Joined: 2011-09-30
Reputation: 0

Can anyone find documentation requiring the baseline to use ASHRAE 62.1
ventilation rates? The table in EA Credit 1 under HVAC System Selection for
the baseline design states:

"Outdoor ventilation rates should be identical to the proposed case"

There are no exceptions listed anywhere in the LEED documentation (I am
currently looking at LEED 2009, but have reviewed this in the past under
LEED 2.2).

We have had DCV be approved in the past with no questions.


No Username provide's picture
Joined: 2011-09-30
Reputation: 200

No documentation exists supporting the new method. GBCI is pulling the
"rating authority" card and implementing their own requirements. I tried
to argue my case that they are going against the procedure in ASHRAE, but
they did not change their requirement. I have expressed my opinion that a
document should be posted on the website that shows this new requirement but
I have yet to see anything new. Otherwise you may be expecting savings from
DCV that will be rejected and then the MEP or modeler will look foolish.
They should have implemented a cut-off date for projects already in the
system similar to the "District Thermal" change they made in May 2008.

In reality the DCV will still result in energy savings but the paper design
savings will be lost. I believe GBCI and USGBC are trying to prevent
"gaming" of the system. A designer could grossly oversize the ventilation
system and then gain tremendous savings by implementing DCV. This new
requirement forces the designer to pursue other ventilation strategies if
they want to claim savings for DCV. Unfortunately the only way we are
learning of this requirement is through clarification questions. This lack
of communication is what really upsets me.

The only solution that I see is that all spaces with demand control
ventilation should be designed to ASHRAE 62.1 minimums. Also, teams should
not pursue the 30% increase ventilation credit.

Thomas Serra

Thomas Serra's picture
Joined: 2011-09-30
Reputation: 0

Tough situation - let me take you where I might go with this one
(hopefully it helps!):

ASHRAE 90.1-2004 and ASHRAE 90.1-2007 state the same thing in Appendix G
regarding energy savings from DCV with the exception of the referenced
mandatory DCV requirement (2004 is Section while 2007 is Section

"G3.1.2.5 Ventilation. Minimum outdoor air ventilation rates shall be
the same for the proposed and baseline building designs.

Exception to G3.1.2.5: When modeling demand-control ventilation in the
proposed design when its use is not required by"

The main difference is in the referenced section. In 2004 the mandatory
requirement was DCV for systems with supply OA exceeding 3000 CFM and
serving areas with occupant densities over 100 people per 1000 SF. In
2007, this was made more stringent: spaces over 500SF with occupant
densities over 40 people per 1000 SF served by systems having an
air-side economizer, automatic modulating control of the OA damper, or a
design OA exceeding 3000 CFM. Remember - these are the criteria that
disallow the exception to G3.1.2.5.

This is consistent with part of what your review comment states - ASHRAE
90.1 does not require you to model the DCV rates the same in the
baseline and proposed case and the rating authority (ASHRAE's term, not
the GBCI's or USGBC's term) can take a position that the exception is or
is not allowed.

That said, I would specifically take issue with the GBCI stating that
they are the "rating authority". They are only allowed to determine if
the project has complied with the LEED standard as the USGBC has
published it. If the reference guide and rating system in effect at the
time your project was registered do not state what the reviewers did,
file a customer service request with both the USGBC and GBCI outside of
the review process to request that they address this. I have been told
the backlog on this type of issue is 4-8 weeks, but you could be lucky
(as I have been on occasion) and get a response quickly.

The GBCI does not write the LEED rating system - they just certify
projects against the standard. I would also request specific
documentation of where that requirement is referenced in ASHRAE 90.1,
ASHRAE 62.1 and/or the LEED rating system and appropriate reference

This is one of those areas we do bring up with clients - more outdoor
air, regardless of why you have it in the building, will carry an energy
premium. The amount of OA for a design needs to be carefully planned.
The credit for exceeding ASHRAE 62.1 by 30% is still only worth 1 point
and the cost/benefit analysis of the extra outdoor air may not make
sense for a given project. We've had a number of clients skip that one,
especially those who cannot use productivity as part of their financial
justification (yup - they are out there!).

The prerequisites trump credits usually in the LEED review, so at the
very least your reviewer is assuming that since the prerequisite
requires you to provide ASHRAE 62.1 minimum OA then any DCV strategy NOT
required by ASHRAE 90.1 would be optional and part of the
design model but not the baseline.

Good luck!


Jeremy Poling's picture
Joined: 2011-09-30
Reputation: 0

Is anyone on this list-serve on the EA Credit 1 committee, or know someone
who is? If the the GBCI or USGBC has changed the modeling requirements and
is only letting modelers know during the documentation review stage, I find
this very disturbing for a number of reasons. It would be great if we can
get some straight answers on this from someone at one of these organizations
who actually knows what is going on.

I am happy to draft an email outlining concerns, but I don't know who to
send it to. If anyone does, or would like to help me with this, please feel
free to contact me directly.


Karen Walkerman

No Username provide's picture
Joined: 2011-09-30
Reputation: 200

I'm not sure I really understand what the fuss is about. If you're
designing and modeling a building that does NOT have DCV, then it seems
entirely fair (and accurate) to model the same ventilation rates in both
the baseline and the proposed. If, however, you are implementing a DCV
strategy, then regardless of what you set your "maximum" OA rate at for
the proposed model, in reality, the DCV system is going to keep OA flow
rates near or below the ASHRAE 62.1 requirements (in real life

If the TAG committee didn't require you to model the baseline building
at ASHRAE 62.1 flow rates when DCV is being implemented, then
theoretically you could input an astronomically high OA flow rate for
both models, knowing that your proposed model would NEVER run at such a
condition and would have an unfair advantage.

This seems like an entirely acceptable and fair ruling. What am I

James Hansen, PE, LEED AP

James Hansen's picture
Joined: 2011-09-30
Reputation: 200

You are missing the fact that the rules are being changed at the REVIEW
stage. This requires the energy modeler to do a-lot of extra work to change
the baseline model during the review stage. It also means that after
changing the model, if the reviewer has any additional comments or
questions, the energy modeler will have to go through an additional review,
and pay an additional fee to have the USGBC look at their documentation

Also, the fact that this rule seems to be implemented for some projects, and
not for others means that buildings are not being rated fairly against each

The debate about whether this makes sense or not should be kept separate
from this discussion. My main concern is that rules are being changed
without letting the players know. Any time they make changes, it needs to
be documented publicly, preferably with changes only applying to projects
registered after the date of publication.

We can debate separately whether this rule change makes sense. Yes, I
understand that some "gaming" of the system could happen, in theorgy, but in
many cases, adding HUGE amounts of outdoor ventilation air as you suggest is
far too costly to implement.


Karen Walkerman

No Username provide's picture
Joined: 2011-09-30
Reputation: 200

I nodded somewhat along with Karen's email but we probably need to sharpen the saber in addition to rattling it.

Demand Controlled Ventilation (DCV) is a control approach. Std 62.1 is a largely about quantitative ventilation thresholds. Std 90.1 requires DCV in some instances but control approach, It does not reference specific maximum or minimum, design or operating ventilation thresholds. So a 90.1 compliant design can use DCV to modulate between thresholds set by professional judgment, local code, exhaust/pressurization concerns, or even an owner requirement such as 30% above Std 62.1.

It really is a complex intersection of LEED, Std 62.1 and Std 90.1 and prone to collusions. Even Standard 62.1 and its users manual essentially throw up their hands on DCV in multi-zone systems.

Consider a project that is required to implement DCV in some space, and it does so but not to the GBCI's interpretation of Std 62.1 values. Do the differences count for and/or against its EAp2 compliance and/or its EAc1 points? What if the project is IEQc2 Increased Ventilation? What if the project is also implementing DCV in spaces not required to have it? Does it matter if it is based on sensing CO2, sensing occupancy, or time of day? What if they proposed and baseline mechanical systems are multi-zone, single zone, or one of each? ...

This is so complex, I can see why they are reacting project by project. I would take the review Thomas shared as one point in the discussion, not universal guidance for all projects. They cannot possibly be smart enough to write guidance for all cases without sacrificing something currently held sacred by someone.

With every model and especially every exceptional calculation the modeler should build reasonable models and be prepared to justify them as reasonable. With DCV the justification probably needs to be in the initial submittal.

Paul Riemer

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Joined: 2011-09-30
Reputation: 0

Paul, et al:

Without going into great detail, I take exception to the statement that
"62.1 and its user's manual throw up their hands on DCV in multi-zone
systems." It seems to me that the 62.1-2004 User's Manual is quite
specific about how the minimum ventilation rates should be determined
when a multi-zone systems serves spaces with and without DCV starting on
page A-5. You may want to review this guidance.

Cam Fitzgerald

Cam Fitzgerald's picture
Joined: 2011-09-30
Reputation: 0

Thank you Bill.

Allow me to clarify "prone to COLLISIONS" and that to note the Appendix A of the 62.1-2007 User's Manual throws up its hands on page A-7 stating that "DCV for multiple zone recirculating systems has not been adequately developed at this time." Appendix A still provides guidance for constant volume single zone systems with or without flow measuring stations.

Paul Riemer

Paul Riemer's picture
Joined: 2011-09-30
Reputation: 0

I believe that the reviewer is correct when requesting the baseline to
have the minimum outside air requirement per ASHRAE 62.1. I would think
that an excel spreadsheet that calculates the minimum ventilation
required by ASHRAE 62.1 would be easy to create and also easy to input
into eQUEST.

ASHRAE 90.1 2007 Appendix G3.1.2.5 states "Minimum outdoor air
ventilation rates shall be the same for the proposed and baseline
building designs."

Exception: "When modeling demand-control ventilation in the proposed
design when its use is not required by Section (9)."

Appendix G does not state what the minimum outdoor air ventilation rates
should be for the baseline model when demand control ventilation is
being used for the proposed model. If the reviewer does not tell you
what to use for ventilation, you could put whatever flow rate you wanted
in the baseline model.

I believe that the issue should be with ASHRAE 90.1 instead of with the

Otto Schwieterman's picture
Joined: 2011-09-30
Reputation: 200


I am a voting member of the USGBC Energy and Atmosphere Technical Advisory
Group (EA-TAG) and I have been reading this discussion with great interest.
I think that the letter that you proposed in your other post is a good one.
I will e-mail you off-list with the requested contact information.

To summarize what I have taken away from this conversation:

- The LEED EAc1 requirements for creating the baseline and proposed
energy models for projects implementing DCV are not clear and complete.

- In absence of clear and complete modeling requirements GBCI has
required, for at least one project, that the baselilne ventilation rates be
set to the ASHRAE 62.1 minimum ventilation rates for the building in
compliance with EQp1: Minimum IAQ Performance.

- There is interest by the energy modeling community in having
USGBC publish guidance for the correct modeling of DCV baseline and proposed

- There are concerns about jurisdiction. Does GBCI act as the
"rating authority" on LEED projects, and do they have the authority to set
requirements that are not specifically written or referenced by LEED

Now that I am involved, guess who will likely be writing the first draft of
the DCV modeling guidelines if the TAG decides to move forward? ;-)

Thank You,

Daniel A. Katzenberger, P.E., CEM, BEMP, LEED-AP

Dan Katzenberger's picture
Joined: 2011-09-30
Reputation: 0

You go Dan!

cmg750's picture
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