[Equest-users] Two separate outside air streams for a zone

Wed Sep 28 05:55:28 PDT 2011

Jacob,

I've got a fourth possibility to consider. I think you can accomplish
something similar to what you need in "Air-Side HVAC Zone Parameters"
for the zone(s) you're working on. In the outdoor air tab, specify an
exhaust tracking control method and the exhaust schedule to match when
the trucks are in the building. Everything else you've described can be
filled in there. It doesn't sound like an exact match - I believe this
will increase the OA through the main RTUs (shouldn't change the fan
volumes, and just models the conditioning in the main unit rather than
the makeup unit), rather than through separate units.  Check your hourly
reports, but it might be close enough.

Good luck!

Eric O'Neill 
608.785.3328 | MICHAELS ENERGY

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nick
Caton
Sent: Tuesday, September 27, 2011 5:25 PM
To: jacob goodman; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Two separate outside air streams for a zone

Hi Jacob,

My intuition would be something like your 2nd suggestion...  Split the
space geometrically in 2 to get two spaces/zones.  Set the thermal
connection between them as an air wall.

Define your RTU for one zone.  Define your OA vent fans for the other.
Separate scheduling for concurrent/non-concurrent runtimes as
appropriate.  Consider your model now has two thermostats for two
systems, which may or may not match reality.  In any case - make sure
both systems' fan/tstat schedules are defined in relation to each other.
If you  go all out and also model the additional internal loads of a
bunch of tons of blazing hot metal entering in the summertime, you may
expect to encounter a certain "normal" amountNote that some unmet hours
may be normal  

Your 3rd approach seems viable on the surface though... is your supply
fan "all or nothing" (constant volume fan control)?  I think you may
need to swap to something like VSD or maybe explore the PTAC "two-speed"
option to get your "staged" flow work, from your description.  I'd
continue reviewing the hourly results until you can find the golden
combination of tweaks that make it happen ;).

~Nick

NICK CATON, P.E.

SENIOR ENGINEER

Smith & Boucher Engineers

25501 west valley parkway, suite 200

olathe, ks 66061

direct 913.344.0036

fax 913.345.0617

www.smithboucher.com 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of jacob
goodman
Sent: Tuesday, September 27, 2011 4:31 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Two separate outside air streams for a zone

Dear All,
I searched the archives to answer this question and didn't see anything,
but may have missed something. I am trying to model (for LEED 2009) a
warehouse that trucks occasionally drive into. The space has the usual
ventilation air prescribed for a warehouse by 62.1 supplied by RTU's.
Additionally, there are fans that turn on (3.73 kW for 16,000 cfm of
outside air) when trucks are present. I created a schedule for "trucks
present" using fraction type at 1.2 hours per day each weekday. I'm not
sure how to add the outside air or get the extra fans to only run during
those hours. 

Possible solutions:

1.      fans as separate "equipment load" in the zone, on the schedule
and add outside air to the standard ventilation air as a fraction of
16,000 cfm. So new vent = std vent + [(1.2/40)*16,000]. This wouldn't
give the same peak load as having a full 16,000 cfm though. 

2.      create dummy zone with no loads, walls, area, etc. and give that
zone and system the 16,000 cfm and 3.73 kW on the truck schedule. Tried
this and only got a runtime error with no explination. 

3.      change the max OA to std vent + 16,000cfm and change the Min OA
schedule to reflect truck presence (run OA at 7.25% for all hours 1.2
truck hours per day). Also, changed supply flow to system supply=9,000 +
16,000. Tried this, but the supply flow shown in hourly output reports
was always 25,000!

Any suggestions?

Jacob Goodman , LEED AP, Green Building Specialist 
v:509.280.7051  i:www.lseng.com <http://www.lseng.com> 
L&S  Engineering Associates, Inc. 
'High Performance Design' 

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