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Re: [EnergyPlus_Support] Re: VAV:NoReheat and indoor air quality
The VAV box calculates an air flow rate required to meet the load based
on the VAV box inlet and zone temperatures. The calculated air flow rate
can not be higher than the maximum nor lower than the minimum. The OA
controller is used to mix outside air with return air. These
calculations happen independently. Yes the VAV box has a minimum flow
rate input, but you are in control of this value. Your minimum air flow
fraction specified in the VAV object should account for the number of
occupants in each zone and provide the correct amount of outside air
regardless of load. If you specify a minimum fraction of 0.3, then the
VAV box will only close down to 30% of the maximum air flow rate. If you
specify 0.1, then the VAV box will close down to 10% of the maximum air
flow rate. For each of these cases, there should be outside air mixed
with the air stream according to the inputs in the OA controller object.
alexandrevarela2000 wrote:
>
> Dear Richard Raustad,
>
> Thank you very much for your reply. Yes, these objects allow for
> outside air based on a ventilation rate per occupant or ventilation
> rate per floor area.
>
> The thing is that the VAV damper is controlled based on zone load or
> the minimum outside air fraction defined in the VAV object.
>
> EngineeringReference.pdf, pg. 432 of the pdf, indicates total air flow
> to the zone to be function of maximum air flow, minimum air flow
> fraction and zone load. This seems to ignore OA flow rates determined
> by Controller:Outside Air or Controller:Outside Air, and only take the
> VAV:NoReheat inputs into account.
>
> I'm looking for a way for solving this, all help is welcome.
>
> Thanks again. Best regards,
> Alexandre
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx
> <mailto:EnergyPlus_Support%40yahoogroups.com>, Richard Raustad
> <RRaustad@...> wrote:
> >
> > The VENTILATION:MECHANICAL object can provide outside air based on a
> > ventilation rate per occupant or ventilation rate per floor area. See
> > documentation for Controller:Outside Air and Demand Controlled
> > Ventilation in the Engineering Reference. You will find the input
> > requirements for Controller:Outside Air and Ventilation:Mechanical in
> > the Input Output Reference. You can also review the example file named
> > HeatPumpSimpleDCV.idf.
> >
> > alexandrevarela2000 wrote:
> > >
> > > Dear all,
> > >
> > > I need to use a VAV system and to ensure a variable minimum outside
> > > air flow rate. The outside air flow rate is to be varied according to
> > > the number of people in the zone.
> > >
> > > The VAV model only allows to have a fixed outside air flow fraction.
> > > Is it possible to have this minimum outside air fraction changing over
> > > time, with the number of people in the zone?
> > >
> > > Thanks. Best regards,
> > > Alexandre
> > >
> > >
> >
> > --
> > Richard A. Raustad
> > Senior Research Engineer
> > Florida Solar Energy Center
> > University of Central Florida
> > 1679 Clearlake Road
> > Cocoa, FL 32922-5703
> > Phone: (321) 638-1454
> > Fax: (321) 638-1439 or 1010
> > Visit our web site at: http://www.fsec.ucf.edu <http://www.fsec.ucf.edu>
> >
> > UCF - From Promise to Prominence: Celebrating 40 Years
> >
>
>
--
Richard A. Raustad
Senior Research Engineer
Florida Solar Energy Center
University of Central Florida
1679 Clearlake Road
Cocoa, FL 32922-5703
Phone: (321) 638-1454
Fax: (321) 638-1439 or 1010
Visit our web site at: http://www.fsec.ucf.edu
UCF - From Promise to Prominence: Celebrating 40 Years
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