usgbc response to outdoor air question

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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"

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

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.

Patrick J. O'Leary, Jr.'s picture
Joined: 2011-09-30
Reputation: 0

Dear Patrick,

Thank you for sharing this GBCI response! It is very informative and, while
I won't admit that I've been modeling anything incorrectly, I am going to
change a couple of things J.

In particular, I have heard on several occasions that the Increased
Ventilation credit was a clear case of "IEQ vs. energy"; you make a decision
to trade one against the other. After reading the GBCI response below and
then double-checking with ASHRAE 90.1, I find that they are consistent with
each other and effectively allow no penalty for the increased energy caused
by increased ventilation. Very curious, considering there is no science
which demonstrates a health benefit for outdoor airflows greater than that
required by ASHRAE 62.1!

The other item is that I failed to notice (and still can't find) anything in
621.1 which says that unoccupied ventilation should be zero. I guess that
is OK, but is also curious, since a portion of the ventilation calcs in 62.1
include consideration for off-gassing materials (which are always present.)

All in all, I'm smarter than I was as a result of your post, so it's a good
day! Thanks again.

James V. Dirkes II, P.E., BEMP , LEED AP

James V Dirkes II, PE's picture
Joined: 2011-10-02
Reputation: 203

It's all about the numbers.

LEED Points, that is, not EUI.

Morgan Heater, P.E.

Morgan Heater's picture
Offline
Joined: 2011-10-02
Reputation: 0

you're welcome james. now if i could only get a straight answer on how
to address baseline system sizing/outdoor air rates when the proposed
building is evaporatively cooled with 100% outdoor air .... sizing a
baseline building system of packaged dx just doesn't sit right when the
proposed is providing 20,000 cfm with 100% outdoor air. and i get mixed
comments from reviewers about too much energy savings ... or providing
too much outdoor air in the baseline ...

Patrick J. O'Leary, Jr.'s picture
Joined: 2011-09-30
Reputation: 0

Two quick thoughts:
1. Benefits of increased ventilation: There are actually several studies
that have concluded that increased ventilation rates provide benefits. Here
is a link to two: http://eetd.lbl.gov/news-archives/news-ventilation.html
2. While LEED 2009 and ASHRAE 90.1-2007 (Appendix G) require identical
ventilation rates, that will change with 90.-2010 and LEED 2012. So in LEED
2012, if you take the increased ventilation path, you'll be required to
model the potential energy impact.

--

Chris Schaffner, PE

Christopher Schaffner's picture
Joined: 2011-09-30
Reputation: 0

Dear Patrick,

It sounds as though you are keeping the GBCI folk on their toes! Keep it up
(assuming that your budget doesn't go down the tubes in the process.)

p.s., It's obvious to me that an all-evap system will beat DX into the
ground in an evap-friendly climate. Your reviewer probably lives in Miami
;). Also, If you are not already familiar with www.coolerado.com, check
them out. They have a completely different heat exchanger design that
routinely gets ~95-100% wet bulb effectiveness. (Disclaimer: I consult with
them and get paid for it. I've also done hands-on testing at their factory
and at installations; they really get the performance they claim.)
If an ASHRAE conference paper which discusses this would be helpful, look up
"Energy Simulation of Indirect Evaporative-Assisted-DX" from ASHRAE's Vegas
conference earlier this year. If after looking at it, you think it actually
would be helpful, I mistakenly showed Denver's data for Phoenix and have
since corrected the paper..

James V. Dirkes II, P.E., BEMP , LEED AP

James V Dirkes II, PE's picture
Joined: 2011-10-02
Reputation: 203

Chances are they don't have a "straight answer" to give you. I would
recommend modeling it the way that feels right to you, using your
knowledge of how the building works and your expertise as a modeler, and
providing documentation for the choices you made and why you believe
they are correct. If your arguments hold together you might not have any
trouble at all.

Carol

Carol Gardner's picture
Offline
Joined: 2011-09-30
Reputation: 0

Two quick thoughts:
1. Benefits of increased ventilation: There are actually several studies
that have concluded that increased ventilation rates provide benefits. Here
is a link to two: http://eetd.lbl.gov/news-archives/news-ventilation.html
2. While LEED 2009 and ASHRAE 90.1-2007 (Appendix G) require identical
ventilation rates, that will change with 90.-2010 and LEED 2012. So in LEED
2012, if you take the increased ventilation path, you'll be required to
model the potential energy impact.

--

Chris Schaffner, PE

Christopher Schaffner's picture
Joined: 2011-09-30
Reputation: 0