Dear Vinay,
Keep in mind that it is a “warning”, not an “error”.
Its purpose is to make sure you are aware that the imbalance is
occurring and not that there is necessarily a problem.
In a real building, two things will occur if this imbalance
arises:
·
infiltration will increase due to the slightly lower
building pressure that is a result of too little outdoor air compared to the
exhaust fan capacity
·
Exhaust fan flow will decrease due to the reduction of
the inlet (building) pressure
Each of these is difficult to predict because you probably have
no realistic idea of the building tightness (which affects infiltration rate)
and the exact fan characteristics.
I am inclined to think that it’s beyond the scope of a
typical energy model to simulate this interaction with any accuracy, so I
normally ignore it other than to:
·
Make sure the fan schedules are correct (e.g., Does the exhaust
fan really operate when the zone fan is off?)
·
Make sure airflow for outdoor and exhaust are correct. (e.g.,
Autosizing outdoor air amounts may not give enough airflow to match exhaust
flow. In that case outdoor air should be manually sized.)
If anyone has a better approach, I’d like to know about
it!
The Building Performance Team
James V. Dirkes II, P.E., LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653
From: EnergyPlus_Support@xxxxxxxxxxxxxxx
[mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Vinay
Devanathan
Sent: Friday, September 24, 2010 2:23 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Airloop Error
Mr.
Dirkes,
I have been having this problem too and I would like to know if there is any
way to correct this warning (occurring because of points 2 & 3 as
mentioned by you).
Thank you.
Regards,
Vinay
On Fri, Sep 24, 2010 at 1:54 PM,
James V Dirkes II, PE <jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
wrote:
Here
are a couple of things to consider:
· You must have an exhaust fan in the zone.
Its airflow rate must match the amount of outdoor air introduced to the zone by
each air loop. Normally that zone outdoor airflow rate is controlled in
the Controller:OutdoorAir object, but it is also influenced by the outdoor air
fields in Sizing:Zone. If you have an ERV or other zone object which introduces
outdoor air, that also affects the balance.
· If your zone fan is not operating at the
exact same times as the exhaust fan(s), the “unbalanced exhaust”
message will occur when the zone fan is off (and exhaust is on)
· Finally if your zone fan is the OnOff
style, the warning will occur during times that the zone fan cycles off and the
exhaust fan remains on.
p.s.,
Most of this information is from having the same problem and getting excellent
assistance from Mike Witte
The Building Performance Team
James V. Dirkes II, P.E., LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
On Behalf Of grandocu
Sent: Friday, September 24, 2010 10:52 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Airloop Error
Hello,
I'm getting the following error:
** Warning ** In AirLoopHVAC AHU-B-5 there is unbalanced exhaust air flow.
** ~~~ ** During Warmup, Environment=SUMMERSIZINGDAY, at Simulation time=07/20
19:40 - 19:50
** ~~~ ** Unless there is balancing infiltration / ventilation air flow, this
will result in
** ~~~ ** load due to induced outdoor air being neglected in the simulation.
I don't see a problem with my connections but I did supply airflow rate myself.
I am also getting a "maximum iterations" error for this airloop. Has
anyone ever had this problem before? Thank you.
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