Routing exhaust air

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Some of you might recall the e-mails (below, but probably not necessary
to re-read) from early August. Since then, my problem has simplified, but
the solution is not so clear to me.
Basically, I have exhaust fans for a particular shell located in a
"core" zone made of restrooms and an electrical room. No supply or return
air devices exist in this core zone. Rather, the core zone gets its air
from transfer through doorways (and maybe one passive transfer duct) from a
large open office zone. (Note: Insofar as the core zone does not have an
HVAC system, per se, Vikram's excellent previous answer seems inapplicable
Here are the questions:
1. When using eQuest, shall I deem the core zone "unconditioned" or
"plenum" or "conditioned"?
2. What HVAC system, if any, shall I tell eQuest that the core zone belongs
to? Is there even a way, if appropriate, to tell eQuest that a zone does
not belong to an HVAC system?
3. How can I explain to eQuest that the office zone exhausts (passively) to
the core zone, which then exhausts via fans to the outside?
Thank you all in advance for your help - and to Vikram for his previous

Lars Fetzek, EI


Not sure if this is what you're looking to do. I haven't tried this for
a chain of more than two zones, but you can specify the outside air
coming from a particular zone in eQUEST using the "OA-FROM-SYSTEM"
keyword. You have to be careful with this to define the OA system before
the system it feeds (i.e. if system 1 has an OA-FROM system2, but system
2 has not been defined yet in the INP file, you will get an error.

Another thing to watch out for is that when you use the OA-FROM, I don't
think eQUEST calculates the cooling effect of the ventilation air. You
might have to trick the program into accounting for that using an
internal energy source (process) with a negative value. This is easier
with a constant volume OA supply, but if you really want to you could
write a schedule for the VAV supply - it's pretty tricky.

Vikram Sami, LEED AP
Direct Phone 404-253-1466 | Direct Fax 404-253-1366


equest-users-bounces at
equest-users-bounces at] On Behalf Of Lars
Sent: Monday, August 10, 2009 9:47 AM
equest-users at
Subject: [Equest-users] Exhaust air routes


The building floor that I am presently modeling has several
conditioned zones and two unconditioned zones. The conditioned zones
are various offices. The unconditioned zones are restrooms and an
electrical room. The conditioned zones exhaust to each other and,
ultimately, to the unconditioned zones via hallways, doorways, etc. The
unconditioned zones exhaust to the outside (via fans).

How can I explain to eQuest that, for example, conditioned zone A
exhausts to conditioned zone B? Also, how can I explain to eQuest that
conditioned zone D exhausts X% to the electrical room (and thus to
outdoor exhaust fans) and Y% to conditioned zone C?

In case it matters, the ceiling is open and the return ductwork
terminates in one spot. Accordingly, even return air must flow among
the conditioned zones.

Thanks, as always, for your helpful replies.

Lars Fetzek, EI

Lars Fetzek's picture
Joined: 2011-09-30
Reputation: 0


1) Sounds like it should be "unconditioned" if you have no return air devices in the core zone. Specifying unconditioned vs. plenum depends on whether or not you want eQUEST to consider the zone to be a return air path for its parent system. Plenum is like saying "I'm not conditioned but I do impact the return air temperature" and unconditioned is like saying "I'm not conditioned and I have no impact on supply or return air". From what you described, it's definitely not conditioned.

2) If the zone is unconditioned, the parent system is irrelevant. However, a parent system must always be defined for every zone per DOE2 protocol (no orphan zones, no orphan systems). If it's a plenum, it should be assigned to the system to which the return air goes.

3) My understanding is that eQUEST doesn't believe in passive exhaust between zones. Without seeing the dynamics of the actual design, I would think you could just exhaust directly from the office zone. I believe you're trying to account for 1) exhaust fan power 2) the exhaust's heat extraction from the office zone; exhausting directly from the office zone would accomplish this. Whether the exhaust goes directly outside or through a "middleman" zone isn't very important if the middleman zone is unconditioned. So, I would argue that the core zone creates a low pressure area that has to draw air from somewhere, and that somewhere is the office zone. Yes, there's more of a delay involved with the indirect method, but I wouldn't get too technical with it if we're only talking about a couple hundred CFM. The biggest problem I see with what I've suggested is if you're exhausting more than your OA CFM for the office zone. In that case, the office zone's OA CFM will be increased to match the exhaust CFM.

On the other hand, if we're talking about a big exhaust fan that is passively exhausting a lot of air from multiple zones, you could take my suggestion and break it up so that you're simulating smaller "direct" exhaust fans for the affected zones - just make sure the individual fan powers & flows add up to the real fan's power & flow.


Dakota Kelley

Dakota Kelley's picture
Joined: 2011-09-30
Reputation: 1