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Re: [EnergyPlus_Support] Cooling & Heating Design Air Flow Method

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Cooling & Heating Design Air Flow Method
From: Ruchi Choudhary <ruch@xxxxxxxxx>
Date: Tue, 13 May 2003 15:59:01 -0400 (EDT)
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Oh that makes sense! thanks very much...

ruchi.


On Tue, 13 May 2003, Michael J. Witte wrote:

> Ruchi:
>
> When using specified air flows in zone sizing and the "flow/zone"
> method, the central air handler flow rate will be the sum of the
> specified flows, regardless of whether these are adequate to meet the
> load.  The ratio of the specified air flow rate and the calculated
> air flow rate is then applied as a sizing ratio to the remaining
> components.  See bullet number 3 at the top of p. 251 in the Input
> Output Reference for an explanation.  That is why you are seeing
> changes in sizes.
>
> To check the actual loads against the design loads, compare your peak
> zone/sys sensible heating and cooling rates from the simulation
> period against the reported peak heating and cooling loads in the eio
> sizing report.
>
> Mike
>
> On 9 May 2003, at 18:10, Ruchi Choudhary wrote:
>
> >
> >
> > Thanks very much Mike. Following up on your explaination: I specified
> > the flow/zone method in the zone sizing object and noted resulting the
> > peak heating and cooling capacity of the system.
> >
> > Then, I increased the interior
> > space gains in the zone without changing the specified amount of
> > air/zone. I expected the capacity of the system to remain the same
> > because now it should use the flow/zone to size the system capacity.
> > However the peak system capacity also changed.
> >
> > So it seems to me that the output in *ssz is based on loads obtained
> > from the design day simulation no matter what the airflow method
> > specification is. However both from what you say and the text in the
> > "Design Objects" section, it should not? Or is it that the flow/zone
> > is used for sizing components, but the system capacity will always be
> > sized on the basis of the design day simulation? Following are my
> > interpretations of the functional dependencies:
> >
> > System Capacity=f(sys. supply temperature, total massflow rate, total
> > outside air)
> >
> > total mass flow rate=f(sum of mass flow rates of all zones)
> >
> > mass flow rate of a zone = f(zone supply temp., design load)
> >
> > Are any of this "mis"-interpretations? Also, it would be great if you
> > could tell me which of these get affected if I choose the flow/zone
> > method for specifying airflow.
> >
> > also, when I specify the air/zone, the *.eio file outputs both the
> > air/zone calculated on the basis of design day simulation as well as
> > the value computed on the basis of the design day simulation...
> >
> >
> > I also have another question :/
> >
> > How can I make sure that the actual energy use in the zone is close
> > enough to the design load (so the design load is not grossly
> > over-estimated)? Should I check the values of the heating/cooling rate
> > against the design load??
> >
> > thanks very much for your help!
> > ruchi.
> >
> >
> > On Fri, 9 May 2003, Michael J. Witte wrote:
> >
> > > If you specify a volumetric airflow rate in the zone sizing object,
> > > then this overrides the design load calculation for that zone.  The
> > > specified rate is then used when sizing the central air handling
> > > components (fan, coil, etc.)  This does not override the specified
> > > supply air temperature for sizing.  Supply air volumes are sized to
> > > meet the sensible load in the zone based on the design day
> > > simulations.  For hourly details of these loads, see the *.zsz and
> > > *.ssz output files.
> > >
> > > Mike
> > >
> > >
> > >
> > > On 7 May 2003, at 14:32, Ruchi Choudhary wrote:
> > >
> > > >
> > > > Dear All,
> > > >
> > > > In the Zone Sizing Object there are two fields that allow the user
> > > > to either specify the volumetric airflow rate, or compute it on
> > > > the basis of the design day simulation.
> > > >
> > > > My understanding is that the mass flow rates computed by the zone
> > > > sizing object are used in conjunction with the system supply
> > > > temperature and outside air flow rate to compute the system
> > > > capacity.
> > > >
> > > > So if I specify the volumetric airflow rate for a zone, will it be
> > > > used to determine the system capacity rather than the output from
> > > > design day simulation? By doing so, I am implicitly also
> > > > over-riding the design load computed by the zone-sizing object and
> > > > zone supply air temperature specification?
> > > >
> > > > Also, the *.eio file lists the design volumetric air flow rates
> > > > for each zone. I am assuming these are computed on the basis of
> > > > the design load and zone-sizing specs. (supply temperature and
> > > > humidity)?
> > > >
> > > > ruchi.
> > > >
> > > >
> > > >
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- Re: [EnergyPlus_Support] Cooling & Heating Design Air Flow Method
  - From: Michael J. Witte

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