Demand Controlled Ventilation and EA Credit 1

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All,

below is a draft letter to the EA Credit 1 TAG chair. I welcome any edits,
or critiques, and if anyone would like to be a co-signer of the letter,
please let me know.

Thanks,

--
Karen

It has come to our attention from a posting on the eQuest list-serve that a
fellow energy-modeling professional has been asked to model proposed design
and baseline design ventilation rates differently where the proposed design
model utilizes demand controlled ventilation. We have searched the ASHRAE
90.1 documentation as well as the LEED reference documentation and
consistently find the requirement that baseline ventilation rates be modeled
the same as the proposed design, and that credit can be taken for demand
controlled ventilation.

We understand that large energy savings can be gained from demand controlled
ventilation and that in certain cases, 'gaming' of the system could result
in abnormally high ventilation rates for the baseline design, while the DCV
system keeps ventilation rates low in the proposed design, however, our main
concern is that energy modelers are being made aware of changes to
guidelines during the design review process. At this stage, the energy
modeler has already completed a significant amount of work in preparing the
proposed and baseline design energy models, and all associated
documentation. Changing the baseline design ventilation rates requires
re-modeling of the building and increases the likelihood that the project
will have to challenge a 'rejected' result if the LEED reviewer is not
satisfied with the energy modeler's response and modeling changes.

We feel that it may be time to develop modeling guidelines for demand
controlled ventilation, and that these guidelines should be developed,
released, and required in a similar fashion to the district energy
guidelines published by LEED for NC 2.2 Furthermore, we feel that any
changes made to EA Credit 1 energy modeling guidelines should be made with
adequate notice to the energy modeling community.

Thank you for your consideration on this issue,

--
Karen Walkerman

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Hi Karen:

I would suggest that you include the original GBCI?"Clarification Required"
comment and their technical advice within the body of your letter.? Then, state
the root issue and suggested resolution.? This way LEED will know the specific
issue that raised this concern.

With regard to the specific LEED comment that started this debate; the LEED
reviewer may be "wrong" or "testing" the modeler.? I've responded to some LEED
review comments with an explanation of the models and their final review
accepted the models as?originally submitted.?

In this case, it may make sense to e-mail GBCI with the explanation before
submitting the EAc1 template?for final review.? They allow you to?submit
questions, which they then forward to the review team for further
clarification.? I think if it's stated that the proposed & baseline design
ventilation rates are the "....same, as required by LEED, page, verse, etc..."
and the DCV credit is "....taken utilizing a different occupancy schedule
between the two models, as required by LEED, page, verse, etc...";?then the LEED
reviewer will either accept this or will have to provide a further explanation
of what they now require.? Especially if you also ask?them to send?you the LEED
requirement for utilizing the ASHRAE 62.1 minimum where-ever DCV is used;
instead of utilizing the same rates?between the baseline and?proposed as
documented in the LEED reference manual, page.....

Each model that I've done for LEED utilizes the same ventilation rates between
the proposed and design; whether it was ASHRAE 62.1 or IMC 2003; however, the
occupancy schedules changed in spaces where DCV was installed.

Having said all this, I've never worked on a project where an Owner has thought
it was a good "energy-efficient / green" idea to provide more outdoor
ventilation than required by code (the increased ventilation point); especially
in a space?where the engineer?would require DCV to make sure the space is not
over ventilated.?

Hope this helps.
?
Ron Lamarre, AIA, NCARB
Architect - LEED AP BD+C

Design ?+??Energy Modeling + LEED Administration

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"Each model that I've done for LEED utilizes the same ventilation rates
between the proposed and design; whether it was ASHRAE 62.1 or IMC 2003;
however, the occupancy schedules changed in spaces where DCV was
installed."

Ron, that's an interesting statement in itself - modifying occupancy
schedules has an impact on the mechanical cooling (not just the cooling
associated with reduced ventilation air), which isn't really fair. Was
that approved by GBCI? If so, I guess it's further proof that there is
still a lot of inconsistency in the review of EAc1.

Karen, I think your letter does a good job of requesting an official
"ruling" from the USGBC.

James Hansen, PE, LEED AP

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Ron,

In general, I agree with your approach. I too have had reviewers ask me to
do something that is directly contrary to what was required in the
documentation. I cited page numbers and quoted requirements and had my
model accepted. However, in this case, it seems that the modeler asked for
clarification and was still told to model the baseline with a different
outdoor air rate.

I will include the technical advice in the final copy.

Thanks,

--
Karen

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Hi James:

For the record, the occupancy schedule refers to the people present within the
space.? For instance, a?space?within the baseline (not required by ASHRAE to
have DCV) would have the?max number of occupants for the entire occupied-mode
schedule; however, the proposed would have the max number of people?for only as
many hours as?submitted?in the project narrative for FTE usage of the space, and
a minimum number of people (or no one) for the remaining occupied-mode time.?
Thus we create an occupancy (people) schedule for the space.? During the
unoccupied mode the fans would cycle as required?with no people, no lighting
(automatic shut off),?acting on the heating & cooling loads.? We would
not?install DCV if the occupant loads didn't change during the occupied mode.

We also use general lighting schedules that take advantage of installed
occupancy sensors, and process load schedules that take advantage of Energy Star
computers and monitiors.

The HVAC engineer decides the minimum design rate for each space to work
(heating & cooling) if fully occupied with all the lights, process loads, and
people during the occupied mode.? This is normally at or above the 62.1 and/or
other code-required minimums (never below due to the LEED pre-requisite).?
Sharing the reduction schedules placed into eQuest?with a template-narrative to
support the reductions (based on ASHRAE 90.1, Energy Star, etc... %-reductions)
has been accepted by LEED.

We utilize an integrated design team method, where the engineers and
I?review?the models that I construct.? We also get peer reviews?when we think
it's necessary and/or when LEED throws us a curve.? We pay for our peer
reviews.? I'm confident that anything we've?submitted?does?not prove
inconsistency within the review of EAc1.
?
Ron Lamarre, AIA, NCARB
Architect - LEED AP BD+C

Design ?+??Energy Modeling + LEED Administration

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Karen,

Great job on the letter. I got out my special editor's pen, shook the dust
off, and have some suggestions below:

It has come to our attention from a posting on the eQuest listserv that a
fellow energy-modeling professional has been asked to model proposed design
and baseline design ventilation rates differently where the proposed design
model utilizes demand controlled ventilation (DCV). We have researched the
ASHRAE 90.1 documentation, as well as the LEED reference documentation, and
consistently find the requirement that baseline ventilation rates be modeled
the same as the proposed design, and that credit can be taken for demand
controlled ventilation.

We understand that large energy savings can be gained from demand controlled
ventilation and that in certain cases, 'gaming' of the system could result
in abnormally high ventilation rates for the baseline design. We think that
the requirement for the ventilation rate not to change between the baseline
and proposed buildings already limits this possibility, however, and our
main concern is that energy modelers be made aware that changes to the
LEED guidelines
may be made during the design review process. At this stage, the energy
modeler has already completed a significant amount of work in preparing the
proposed and baseline design energy models, and all associated
documentation. Changing the baseline design ventilation rates requires
re-modeling of the building and increases the likelihood that the project
will have to challenge a 'rejected' result if the LEED reviewer is not
satisfied with the energy modeler's response and modeling changes.

We think that it may be time to develop modeling guidelines for demand
controlled ventilation, and that these guidelines should be developed,
released, and required in a similar fashion to the district energy
guidelines published by LEED for NC 2.2 Furthermore, we think that any
changes made to EA Credit 1 energy modeling guidelines should be made with
adequate notice to the energy modeling community.

Thank you for your consideration on this issue,

I would be happy to be a cosigner but since I am not a LEED AP or a BEMP or
anything except a PE you may be able to find someone more impressive.

With respect to James' comment below, I have also modified the occupancy
schedule to model DCV. I simply renamed it "DCV Occ Sch", or something like
that and applied it only to the space that was using DCV. Easy enough to do
and no impact on the mechanical cooling at all. This reminds me of the
discussion the other week about using a schedule to reflect lighting W/sf
reductions vs, just reducing the W/sf itself. When I have some spare time to
mull the costs/benefits of using schedules vs. direct reductions I will. If
others have some thoughts I encourage them to share them.

The last thing I want to say is that this listserv is great! I guess I'm a
real nerd cause I love discussions like this one here about DCV where people
have obviously given the matter a lot of thought and feel free to express
their opinion, whether popular or not. We are really a lucky group of
professionals to have such a resource.

Carol

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?For the record, the occupancy schedule refers to the people present within the space. For instance, a space within the baseline (not required by ASHRAE to have DCV) would have the max number of occupants for the entire occupied-mode schedule; however, the proposed would have the max number of people for only as many hours as submitted in the project narrative for FTE usage of the space, and a minimum number of people (or no one) for the remaining occupied-mode time. Thus we create an occupancy (people) schedule for the space. During the unoccupied mode the fans would cycle as required with no people, no lighting (automatic shut off), acting on the heating & cooling loads. We would not install DCV if the occupant loads didn't change during the occupied mode.?

Ron, please educate me if I?m reading your email wrong, but are you saying that your occupancy schedule in the proposed design does not match the baseline design? This is strictly prohibited in App G I thought? You can change schedules to take advantage of non-standard ECMs like DCV, and automatic lighting reductions for the use of occupancy sensors (in rooms NOT already required to have them by code). But having a conference room 100% occupied from 7am-6pm in the baseline model and only 100% occupied from 9am-noon in the proposed model is not a valid way to demonstrate savings from DCV, since there will be energy savings related to the people latent/sensible production that has nothing to do with DCV. Don?t you have to create a minimum outside air schedule to demonstrate DCV savings? If you have received credit for simply reducing the Occupancy Schedule in the proposed model, that is very interesting?

Thanks!

James Hansen, PE, LEED AP

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Ron,
I'm with James on this one. I can see changing lighting or equipment
schedules to capture ECMs but changing occupancy schedules makes no
sense unless you're modeling telecommuting or 4-day work week. You can
capture DCV savings in eQUEST by selecting DCV as the Minimum OA Control
Method for the system and having an occupancy schedule with a varying
percentage (not 100%) during occupied hours. Using the same occupancy
schedule, the model with DCV will heat/cool less OA air and show
savings.
Regards,

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

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Ron and Carol,
Would you please clarify by referencing EQUEST/DOE-2.2 commands? Are you modeling DCV by changing the space occupancy schedule (SPACE: PEOPLE-SCHEDULE)? What are your outside air inputs? Is this the dummy space in a DOAS system? Are you making other creative changes like putting all of your occupant heat gain in as a process load? I am gasping to understand the validity of changing the people schedule.

I have always valid DCV modeling is best done in eQUEST/DOE-2.2 by changing the system minimum outside air schedule (SYSTEM: MIN-AIR-SCH). Even just changing the system minimum outside air control method (SYSTEM: MIN-OA-METHOD) seems iffy because I think the approach that ignores the floor area component of Std 62.1.

Thanks,
Paul Riemer

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Bill and James:

...the proposed would have the max number of people?for only as many hours
as?submitted?in the project narrative for FTE usage of the space, and a minimum
number of people (or no one) for the remaining occupied-mode time....
?
Baseline = 100% of the occupancy for each space not required to have DCV.?
Reducing the occupancy (% of people) within the space to coincide with the FTE
usage provides a reduced OA based on DCV control.? The OA per SF of the space
remains the same in both cases.? The building's occupied/unoccupied schedules
remain the same in both cases.
?
Example:
Baseline = Space occupied 7am to 7pm with 20 people (100% scheduled occupancy
for all 12 hours)
Proposed DCV = Space occupied 7am to 9am with 20 people (100% scheduled
occupancy for 2 hours) and 9am to 5pm with 2 people (10% scheduled occupancy
for?8 hours) and 5pm to 7pm with 0 people (0% schedule occupancy for 2 hours):
based on FTE usage of space.
?
Both models have the same building occupancy schedules 7am to 7pm.

I?thought we were discussing DCV control and OA rates, which refers to spatial
occupancy schedules; not building occupied/unoccupied schedules, so?I don't know
how we got onto the topic of building occupancy schedules.

Ron Lamarre, AIA, NCARB
Architect - LEED AP BD+C

Design ?+??Energy Modeling + LEED Administration

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Sorry to beat a dead horse, but in eQuest, you specify the maximum # of people for a space, and then set up a single occupancy schedule. There?s really no such thing as a ?building occupancy schedule? unless all spaces are occupied the same.

In your proposed model, you can?t model only 2 people in the space from 9am to 5pm if you also aren?t doing this in the baseline. You COULD have an outside air schedule in the proposed DCV model that reduced the OA volume down to 2 peoples-worth, however.

I can?t tell what you are doing, but in your example, you appear to be modifying the occupancy schedule for the space in the proposed model (different than the baseline), but then you immediately go on to say that both models have the same building occupancy schedule (which is the same thing used for the space occupancy schedule). This isn?t possible.

Why is my brain not able to understand this?

There is no difference between a space occupancy schedule and a building occupancy schedule. Maybe a building central plant schedule, or something like that, but your building occupancy schedule is really just the sum of your space occupancy schedules.

-James

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I also do not think that modifying the occupancy schedule is a proper way to account for DCV savings. Doing that, one modifies the loads due to people.

And the Baseline and Proposed should always have the same occupancy schedules.

________________
Demba NDIAYE

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I'm sorry for not being clear, but I've had little sleep in the last few
days cause of a darn project. I don't really change the occupancy schedule,
rather I create a DCV schedule which is sort of based on the occupancy
schedule but w/ hrs reduced to reflect them coming and going from meetings
or whatever the space is used for. It's probably what the new DCV commands
do in eQUEST, I just haven't had the time or opportunity to use them yet.

Carol

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Below is some discussion that we had on the same subject month's ago.

Normally the base model, I set up with the min. percentage amount of OSA
coming in through the air side (air handler) required by code during all
occupied hours and then with this OSA closed by schedule during
unoccupied hours. Typically this is what is required by code (usually
15-20 CFM per person for all occupants), unless you have a CO2 demand
control system installed. Also, make sure the OSA and Exhaust are set
up on the Zone inputs so that the air handler OSA intake is not
overridden by the inputs in the the zones. On each Zone under the
system under Outside Air & Exhaust enter as follows: Under Outside Air
Flow/Person - Leave this blank. Under Outside Air Flow - Leave this
blank. Under Outside Air Changes - Leave this blank. Under Outside
Air/Flow/Area (CFM/FT2) - Leave this blank.

Then when you do the Revised ECM model with the CO2 demand control then
I would suggest that you set the revised model up something like as
noted below on the 3-23-10 e-mail. This set up will vary the amount of
OSA that is brought in based on the occupancy schedule (which would be
the same on both models) but not allow the ventilation rate to go below
the code required 0.06 CFM/FT2 during occupied times. The OSA is again
closed by schedule when the building is unoccupied.

David Bastow dbastow at mcclure-engineering.com

Tue Mar 23 08:50:18 PDT 2010

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________________________________

I have used the DCV ventilation method with OA from the system and it
has worked great, as long as you have inputs in correctly under the zone
outside air & exhaust. If you have inputs under the zone incorrectly
then the OA control on the system will be overridden by the inputs under
the zone.

Inputs in the model would be something like this to get it to work:

-Air side HVAC System under outdoor air - vent & economizer:
-Under Min. outside air (ratio)- set at whatever, such as 0.10
for 10% OSA (if using an economizer the minimum must be set at least to
0.001, or the economizer feature will not work in the model).
-Under Min. OA Method - I always use DCV Return Sensor.

-On each Zone under the system under Outside Air & Exhaust:
-Under Outside Air Flow/Person - Input CFM required by code or
usually 15 to 20 CFM per person.
-Under Outside Air Flow - Leave this blank.
-Under Outside Air Changes - Leave this blank.
-Under Outside Air/Flow/Area (CFM/FT2) - Normally I input 0.06
here, which is typically the amount required by the code.

As long as you have your hourly occupancy schedule set up correctly with
the % of the number of people that are in each zone then these inputs
have always worked for me. The Outside Air entering the system will
vary down to as low as 0.06 CFM/FT2 of the area of the applicable zones
depending on how many people your occupancy schedule shows you have in
each of the applicable zones that you have under the HVAC air system.
The Outside air reduction will, of course, also always be limited by the
amount of exhaust CFM that you have input under the zone. Be careful
with what you enter under the zone regarding the CFM of the ventilation
and the exhaust, as the program will always override what you enter
under the system by what you have entered under the zone.

David A. Bastow

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