[Bldg-sim] Baseline Sizing

Vinay Devanathan vinay.devanathan at gmail.com
Tue Jul 13 06:30:19 PDT 2010


Paul,

Thanks for your reply. I understand that the supply airflow should be equal
or greater than the exhaust airflow. But, the design airflow from auto-sized
runs give me higher CFM than my exhaust fan CFM. But, the problem maybe, it
is not higher always. Is there any method using which I can simulate my Zone
Exhaust fan operation proportional to the supply fan operation so that the
exhaust fan doesn't pull out a constant CFM?

Thank you.

Regards,
Vinay

On Tue, Jul 13, 2010 at 4:21 AM, Paul Raftery <p.raftery at gmail.com> wrote:

> 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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