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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: Fri, 9 May 2003 18:27:31 -0400 (EDT)
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Sorry there are typos in my question (very careless of me): here is the
fixed version:

> Thanks very much Mike. Following up on your explaination: I specified the
> flow/zone method in the zone sizing object and noted the resulting  peak
> heating and cooling capacity of the system (from the *.ssz file)
>
> Then, I increased the interior
> space gains in the zone without changing the specified amount of flow/zone.
> I expected the capacity of the system to remain the same because 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 (for the parameters I am interested in):
>
> 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 these "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 as against "design day"
>
> 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 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 at every
> hour of the run period 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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References:
- Re: [EnergyPlus_Support] Cooling & Heating Design Air Flow Method
  - From: Ruchi Choudhary

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