outside air flow during unoccupied/setback hours

6 posts / 0 new
Last post

Dear All,

One of the LEED review comments on a university building project I'm
working on suggests to verify that all systems in baseline and proposed
models contain zero outside air flow when fans are cycled on to meet
setback temperatures during unoccupied hours.

What is the best way to go about verifying this? In the 'Hourly Report
Block' options under a system, I find 'Hourly summed zone OA CFM for DCV
calculation (cfm)' and 'Hourly max zone OA/total flow for DCV calculation
(cfm/cf/). Is one or both of these options under an hourly report, the way
to go or is there a better way of doing it?

Thanks,
Ramana.

Ramana Koti's picture
Offline
Joined: 2011-09-30
Reputation: 0

I normally have a min sch specified at the zone level - 0 for unoccupied
hours and -999 for other hours that takes care of this comment.
There is an hourly report for fan coming on during night cycle flag (or
something similar). If you do not have the fan coming on or do not have the
night cycle control, you should be ok. You can also look at the hourly
report for OA ratio and whether fan is on/off during the unoccupied time.
-Rohini

R B's picture
R B
Offline
Joined: 2011-09-30
Reputation: 4

is this a leed 2.2 or 3.0 project?

i'm guessing, without looking in my leed manuals, this is a usgbc
requirement for at least 2.2. for leed 3, 90.1-2007, appendix g, table
3.1, no. 4 schedules, specifically states the "hvac fans that provide
outdoor air for ventilation shall run continuously whenever spaces are
occupied and shall be cycled on and off to meet heating and cooling
loads during unoccupied hours." 90.1-2004 doesn't specify fans
specifically for outdoor air for ventilation, it just says hvac fans -
which is the same as the system supply fan in a non-doas/economizer
capable of completely closing the outdoor air damper system so the
outdoor air can't be shut off.

so the comment is contrary to the 90.1-2007 (and/or 2004 depending on
systems) simulation requirement. the 90.1-2004 user's manual appendix g
section doesn't address the scheduling for hvac fans during unoccupied
modes.

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

I should have written min OA sch (at the OA tab, system level) instead of
the min sch at the zone level. Thanks to Ramana for pointing this out.
-Rohini

R B's picture
R B
Offline
Joined: 2011-09-30
Reputation: 4

That worked, thanks. It took me while to figure out the schedule type was
Frac/Design but the results showed that my model was using OA during
unoccupied hours.

Ramana.

Ramana Koti's picture
Offline
Joined: 2011-09-30
Reputation: 0

just looking in the advanced energy modeling for leed manual (from aug
2010) i can't find anything about the reviewer's comment, though it does
mention 90.1-2004 addenda for appendix g did change the language for
schedules, outside air, to match the 90.1-2007 appendix requirement i
quoted below.

have you tried contacting the review team thru the project resources?
for leed 3/2009 there is an option buried in the submittal process that
allows some communication w/the review team so either you, or the
project lead, should be able to ask the reviewer to clarify the source
of the comment requirement prior to marking your comment responses as
done & possibly getting the same comment again. i've found it useful to
respond to reviewer's comments by referring to ashrae chapter, section,
and verse (90.1-2007 in this case) and quoting the relevant text so if
there's a usgbc interpretation that is different from the ashrae text,
addenda, or interpretations the reviewer ends up telling what the source
of the comment is.

there could be a usgbc cir addressing the subject, does anyone know?
the usgbc position on simulating non-tradable exterior lighting the same
in both proposed and baseline cases is in an old cir only - not in the
usgbc modeling guide, not in 90.1, not in the usgbc handbooks.

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