[Bldg-sim] usgbc response to outdoor air question

[Jeremy Poling]

There was an earlier discussion on the list about this:

 

62.1-2007, Section 5.4 states "Mechanical ventilation systems shall
include controls, manual or automatic, that enable the fan system to
operate whenever the spaces served are occupied.  The system shall be
designed to maintain the minimum outdoor airflow as required by Section
6 under any load condition."

 

62.1-2007, Section 6.2.6.1 states "Ventilation systems shall be designed
to be capable of providing the required ventilation rates in the
breathing zone whenever the zones served by the system are occupied,
including all full- and part-load conditions."

 

These are generally applied to mean that the system is not required to
operate when spaces are unoccupied.  Yes, the standard does not
explicitly state that unoccupied ventilation should be zero but the
standard does not explicitly state that unoccupied ventilation can't be
zero.  Section 5.4 and 6.2.6.1 only require controls and ventilation
rates "whenever the spaces/zones served by the system are occupied" so
it can be implied that the requirement doesn't apply when the
spaces/zones are unoccupied.  There's a fine interpretive line there,
but many of the official interpretations on 62.1 also lean this
direction.  If in doubt, put in an official interpretation request
specifically on this with ASHRAE on the topic to clarify.

 

Jeremy R. Poling, PE, LEED AP+BDC



 

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Reba
Schaber
Sent: Tuesday, November 15, 2011 8:42 PM
To: Jim Dirkes; equest-users at lists.onebuilding.org;
'bldg-sim at lists.onebuilding.org'
Subject: Re: [Bldg-sim] usgbc response to outdoor air question

 

RE:  ". . . can't find) anything in 621.1 which says that unoccupied
ventilation should be zero."

 

I think this requirement comes from the mandatory provisions of 90.1.

 

6.4.3.4.3 Shutoff Damper Controls. Both outdoor

air supply and exhaust systems shall be equipped with motorized

dampers that will automatically shut when the systems or

spaces served are not in use. Ventilation outdoor air dampers

shall be capable of automatically shutting off during preoccupancy

building warm-up, cool down, and setback, except

when ventilation reduces energy costs (e.g., night purge) or

when ventilation must be supplied to meet code requirements.

 

Thoughts??

 

Reba

 

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Jim Dirkes
Sent: Monday, October 17, 2011 9:32 AM
To: equest-users at lists.onebuilding.org; 'bldg-sim at lists.onebuilding.org'
Subject: Re: [Bldg-sim] usgbc response to outdoor air question

 

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.

 

The Building Performance Team
James V. Dirkes II, P.E., BEMP , LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653

 

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Patrick J.
O'Leary, Jr.
Sent: Monday, October 17, 2011 11:46 AM
To: equest-users at lists.onebuilding.org; bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] usgbc response to outdoor air question

 

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" <no-reply at gbci.org> <mailto:no-reply at gbci.org>
<no-reply at gbci.org> <mailto:no-reply at gbci.org> 

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

Green Building Certification Institute 
2101 L Street NW, Suite 500 
Washington, DC 20037 
800-795-1746 (phone)
202 828-5110 (fax) 
www.gbci.org/contactus

The text above represents a staff opinion of a particular issue, and
does NOT set any precedent to be upheld during a LEED Certification
Review. For official rulings in advance of a LEED Certification Review,
customers should utilize the Formal Inquiries process available in LEED
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.

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