[Bldg-sim] Baseline Sizing

[Paul Raftery]

Hi Vinay,

You are getting that error because EnergyPlus does not currently take
exhaust fans into account when autosizing zone airflows. In your case,
EnergyPlus sized the supply airflow for that zone lower than the exhaust
flow rate, and that's why you are getting that error.

To fix this, you can 'force' the supply airflow to be equal to or larger
than the exhaust airflow at all timesteps. You can do this by setting the
autosize value in the airflow parameter for the air terminal unit object for
that zone equal to the exhaust airflow. For example, where you are using
constant volume reheat:

!-   ===========  ALL OBJECTS IN CLASS:
AIRTERMINAL:SINGLEDUCT:CONSTANTVOLUME:REHEAT ===========

AirTerminal:SingleDuct:ConstantVolume:Reheat,
    ObjectName,                        !- Name
    Schedule,                        !- Availability Schedule Name
    OutletNode,                        !- Air Outlet Node Name
    InletNode,                        !- Air Inlet Node Name
    autosize *(change this to exhaust airflow)*,                        !-
Maximum Air Flow Rate {m3/s}
    HWInletNode,                        !- Hot Water or Steam Inlet Node
Name
    RHCoilType,                        !- Reheat Coil Object Type
    RHCoilName,                        !- Reheat Coil Name
    autosize,                        !- Maximum Hot Water or Steam Flow Rate
{m3/s}
    0,                        !- Minimum Hot Water or Steam Flow Rate {m3/s}
    0.001;                   !- Convergence Tolerance

Regards,
Paul

On 12 July 2010 16:46, Vinay Devanathan <vinay.devanathan at gmail.com> wrote:

> Hello All,
>
> I am using EnergyPlus to model a building according to ASHRAE App. G for
> baseline case. I included Zone exhaust fans in the baseline as advised, in a
> fashion similar to what is prescribed in the proposed design. But, when I
> auto-size the model with this Zone Exhaust Fan object, I get a warning
> message saying -
>
> **   ~~~   **   there is unbalanced exhaust air flow.
> **   ~~~   **   Unless there is balancing infiltration / ventilation air
> flow, this will result in
> **   ~~~   **   load due to induced outdoor air being neglected in the
> simulation.
>
> And, I think the design loads are increased due to this, which would
> probably cause over-sizing.
>
> Any help in solving this issue would be greatly appreciated.
>
> Thank you.
>
> Regards,
> Vinay
>
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-- 
Regards,
Paul


=====================
Contact Details
=====================
Paul Raftery, BEng(Hons) (Mech), Fulbright Fellow, IRCSET Scholar
Informatics Research Unit for Sustainable Engineering (IRUSE) Galway,
Department of Civil Engineering,
National University of Ireland, Galway,
University Road,
Galway,
Ireland.

Landline: +353 91 49 3086
Mobile: +353 85 125 4999
Skype: praftery
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