ASHRAE 62 question

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Just going through table 6.4 in ASHRAE 62.1-2007 it looks like the minimum exhaust rates for labs (educational science laboratories) is 1 cfm/ft2. That amounts to an ACH of 6 (for a 10ft ceiling) and 6.7 for a 9ft ceiling.

Am I interpreting that correctly? Does that mean for LEED projects we cannot go below 6 - 7 ACH? Is there a way around it?

Vikram Sami, LEED AP

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Good question...a bit interesting to try and answer.

First, your calculations are correct.

Second, it is interesting that only "educational science laboratories" are mentioned, somehow suggesting that their use is different from corporate and institutional labs.

Third, EH&S often makes this determination and there is no agreement among standards/guidelines dealing with lab ventilation so to impose this bit of Std 62 seems like something that the USGBC should be considering as it moves towards connecting Appendix G to Std 62 rates.

Fourth, related to that last point, while Appendix G does not yet directly require Std 62 rates for the baseline, LEED requires Std 62 rates for the proposed and 90.1 requires the baseline ventilation to match the proposed. So, it would seem that models should be reflecting the 1 cfm/sf requirement.

There is a grey area that I think may also be a point of discussion. Minimum exhaust rates of various types are often only required when the space is occupied. As such, and considering that many university EH&S folks are at least beginning to bat around the notion of, if not adopt, a 4 ACH minimum during unoccupied periods, it seems fair to have a value lower than 1 cfm/sf during unoccupied periods. What's your perspective on this?

It'd be good if others chime in and help develop a consensus.

Paul Erickson LEED(r) AP

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Joined: 2011-09-30
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When we provide energy design assistance for labs, a significant
energy efficiency strategy is to try to get the client to really
consider ventilation requirements and get them down as low as possible.
This can be taken further with good focused ventilation strategies.
After going through this optimization process, though, I really think
the final modeling has to have the same ventilation airflow rates in the
baseline and proposed models (for occupied and unoccupied periods).
Different types of labs will have different ventilation/ exhaust
requirements; I don't see how 1 cfm/SF could be be applied to all
laboratory spaces.
Having more resources to help design teams and clients reduce design
ventilation rates as much as possible would be really useful....maybe
there's a way to use 62.1 & Appendix G modeling to encourage this, but
it would need to be a lot more detailed than 1 cfm/ SF.

*Aleka Pappas*

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Joined: 2011-09-30
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I have taken credit for unoccupied ACH levels in the past, since Appendix G
specific a 50% turndown from peak ACH during unoccupied hours (G3.1.1,
Exception c.). My understanding is that you can take for an unoccupied
turndown above and beyond a 50% reduction from peak.

Also, all of this only applies to systems that are 5,000 cfm or more -
otherwise the baseline building exhaust fan system and operation should be
the same as the proposed design.

Kendra Tupper, PE, LEED AP

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Joined: 2011-09-30
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This is an important discussion, at least it is
timely for my needs both as a reviewer and
submitter. I am very interested in hearing from
other LEED (and other energy program, HPNC,
Manitoby Hydro, etc.), energy simulation reviewers.

And with all due respect, Gord, I do welcome your
consideration and thoughts on this issue, it
needs to be made clear by the CaGBC and USGBC as
to what the intentions are as to the budget case
outdoor air requirements and exactly who "the
authority having juristiction" is?

The first question is about "the authority having
jurisdiction" - as far as labs, health care
facilities, etc. The second question is about
air system design and what constitutes proper
design as far as the outdoor air calculation and
the intended long term purposes of the facility.

So first, "the authority having jurisdiction":

This is an excellent question about ASHRAE 90.1;
without and with Appedix G cases; LEED - USGBC
and that Review Organization and "the authority
having juristiction". For example, from the
Green Care For Health Guide, Version 2.2,
Appendix G, Design Assumptions & Procedures for
Modeling for the GGHC Energy Credits:

"Ventilation, air changes and air pressure
relationships: Use specific ventilation rates,
air changes, and pressure relationships, as
required by authorities having jurisdiction. If
the authorities having jurisdiction have no
specific requirements, use the requirements from
2006 AIA Guidelines for Design and Construction
of Hospital and Health Care Facilities, or most recent version. "

Then forther on, in the same document, it states:
"Process Ventilation loads: Special ventilation
requirements in a health care facility are not
unusual. While Table OCC-1 quantifies the
typical ventilation in a health care facility,
some spaces may require higher ventilation
rates. The higher ventilation rates shall be
simulated in both the Baseline and Proposed
building simulation runs, making this an energy neutral feature. "

From the health care prospective, ventilation is
very specific and the "authority having
jurisdiction" is basically the facility and their
designers. Therefore the calculation of outdoor
air requirements would have to be accompanied by
letters from that authority - whom ever it might
be. In my experience these letters typically are
submitted with a fairly detailed air system
balance calculation noting the standards the designer is following.

I agree with this intent and I believe that the
requirements for heat recovery cover cases like
this where, in reality, HVAC systems often have
in excess of 70% outdoor air and greater than
5000 cfm and therefore the budget case system has
heat recovery as a requirement (at least in
reading 90.1-2004). For smaller systems, the
budget case will perform significantly poorer
than the proposed design that has heat recovery.

I believe that the outdoor air requirements
should be based on the minimums suggested in
ASHRAE 62 and other standards such as CSA-Z317,
but each facility had to determine their outdoor
air requirements and should not be penalized by
artificially restricting the budget case how the
reviewer interprets the requirements of 90.1,
LEED, 62.1, CSA Z317, the ASHRAE Application
Table, Table 7.6.3 Ventilation Requirements for
Areas Affecting Patient Care In Hosptitals and Outpatient Facilities, etc.

For example, in the case of a University facility
with a new medical medical education facility
complete with medical labs, exam areas, etc. The
"Owner" deemed certain spaces, systems as medical
facilities and mandated typical health care,
higher, ventilation rates. While not all the
building falls into this category, a reviewer
must accept the design outdoor air requirements
as meeting the requirements of "the authority
having jurisdiction" and allow the budget case to
have the same outdoor air amounts.

I believe that labs any medical labs fall into
this category. A level 3 lab had very strict
ventilation requirements and the budget case will
necessarily have the same outdoor air
requirements and will have any heat recovery,
ventilation control as required by ASHRAE 90.1,
and the other standards to which the facility is designed.

SECOND - what constitutes "correct design" in
terms of the level of outdoor air delivered.

Example, two examples, one a large long term,
expandable, flexible HVAC system on a university
campus - as the building will have, at one time
or another in the detailed life cycle analysis
for the facility, labs, dense occupant lecture
theatres, offices, perhaps dormitories. At any
rate, the designers have decided, in their wisdom
and I mean that with due respect, that the system
should simply be a 100% OA system with variable
flow control for all current and intended space
functions. So, yes there will be offices with
100% OA. As this is a single fan system, any
critical outdoor air calculation will result in a
100% OA system. It will have variable flow
control, demand ventilation control in zones with
variable occupancy - either CO2 or occupancy
sensor. It will have heat recovery.

In this case, the budget case will indeed be a
100% OA system, with heat recovery as per
90.1-2004 6.5.6 and exhaust air control as per
6.5.7 (as appropriate). I don't believe that the
USGBC, its review arm, the CaGBC, etc. can
mandate that the outdoor air has to be lower
because the system has use a critical zone
calculation that results in more than 20% above
the sum of the space by space, uncorrected
ventilation rates - or some other arbitrary percentage.

In the other case, the facility is a smaller,
fixed use but mixed use facility with a small
portion requiring a 100% OA system and the other
small portion being office, storage, corridors,
etc. The pressure and filtration requirements,
and other design requirements (regardless of what
standards), initial cost, controllability and the
other myriad of design goals, results in a 100%
OA system. It is less than 5000 cfm, and but
more than 70% OA. In this case I believe that
the budget case will should have the same 100% OA
system and the not have heat recovery, exhaust control as per 90.1-2004.

I am very interested in hearing from other LEED
(and other energy programs, 90.1, GGHC, HPNC,
Manitoby Hydro, etc.) energy simulation reviewers.

Note that I am quoting 90.1-2004, that is the
latest I can access, the 2007 electronic version
has the wonderful feature of rendering itself
useless when you upgrade your computer,
apparently I have to contact ASHRAE somehow to
provide an unlocking key, now where did I jot down that password?

a bit interesting to try and answer.

Chris Jones

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