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

[Ruchi Choudhary <ruch@xxxxxxxxx>]

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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