usgbc response to outdoor air question

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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. 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.



Reba Schaber's picture
Joined: 2011-09-30
Reputation: 0

In the Model energy code in Canada only up to 20%
more than ASHRAE 62 is allowed in the base
case. Imagine a building with 100% more OA and a
ERV of 70% on the proposed case it can easily
reach 10 EAcr1 point especially in cold climate.


Martin Roy's picture
Joined: 2011-10-02
Reputation: 0

imagine a building with 100% oa and evaporatively cooled ... 10 eac1
points ... unless you're gbci reviewer who doesn't understand evap cooling

Patrick J. O'Leary, Jr.'s picture
Joined: 2011-09-30
Reputation: 200

While ASHRAE 90.1 does a pretty good job of defining higher efficiency
practices, it?s not perfect. On the other hand, that?s why Appendix G is
there; you can show why your idea is better, at least on the energy part of

There are still issues with the general level of knowledge among both the
reviewer community as well as the energy modeling community, and that may
never cease. As is commonly the case, a designer often is facing either
(energy efficiency) / or (greater IAQ & productivity). The challenge is how
to get the best combination of both.

One benefit of LEED certification seems to have been that many engineer
designers have responded to the challenge of greater efficiency and
performance and changed their standard designs in favor of something with
better performance. That?s probably very good, largely because stagnation
is never good.

There certainly is experimentation going on, not all of which is producing
great results, but I still prefer a real attitude of ?continuous
improvement? over stagnation!

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

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

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 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 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

Jeremy Poling2's picture
Joined: 2011-09-30
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