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Re: [EnergyPlus_Support] Design Loads and Actual Loads

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Design Loads and Actual Loads
From: "Michael J. Witte" <mjwitte@xxxxxxxx>
Date: Wed, 18 Jun 2003 16:54:56 -0500
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Ruchi:

No, this is not typical.  This means that something is inconsistent 
between your sizing parameters and your system description.  What 
exact variable are you comparing against the .zsz values?

Mike


On 18 Jun 2003, at 14:50, Ruchi Choudhary wrote:

> 
> Hi Mike,
> 
> Is it typical for the peak design loads reported in the zone sizing
> file to not match the peak from the heating and cooling rates? I have
> the same day and design day schedules and have not specified any
> sizing parameter....In the case I am simulating, the peak design loads
> in the *.zsz file are more than the heating and cooling rates for all
> zones by a factor ranging from 1.2 to 6.0!
> 
> ruchi.
> 
> 
> On Tue, 13 May 2003, Michael J. Witte wrote:
> 
> > Ruchi:
> >
> > 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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Follow-Ups:
- Re: [EnergyPlus_Support] Design Loads and Actual Loads
  - From: Ruchi Choudhary

References:
- Re: [EnergyPlus_Support] Cooling & Heating Design Air Flow Method
  - From: Michael J. Witte
- [EnergyPlus_Support] Design Loads and Actual Loads
  - From: Ruchi Choudhary

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