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[EnergyPlus_Support] Re: Purchased Air variables
Thank you.
The variations with supply temperature are actually very small, when
I look at them in terms of percentual differences, and I suppose they
can be overlooked as small differences in simulation conditions.
Regarding the dT and dH terms you mention, I took yet another look at
the Engineering reference, but I'm not sure I understood it correctly:
- The "initial" or departure conditions for determinig the dT and dH
terms are based on the "entering air" conditions (at the inlet of the
virtual PA unit), right?
- and these are based on the recirculated air and on the outside air
conditions?
- if no OA was defined in the PA object (instead it was defined
independently, as a ventilation object), the departure conditions for
dT and dH calculation are the zone conditions (recirculated air)?
Thanks again,
Ana Rui.
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Richard Raustad
<RRaustad@...> wrote:
>
> 2) Sorry, wrong equation - Q=M*dH
>
> Richard Raustad wrote:
> >
> > 1) - the maximum reported heating/cooling rate increases
> > The load met by purchased air should not change IF the zone
conditions
> > have not changed. Mass flow rate should increase. Check the zone
> > conditions.
> > PAOutput = M*Cp*dT
> > 2) - Why, for instance, when cooling, the cooling rate/energy
increases
> > greatly when lowering the supply humidity ratio in Purchased Air
> > definitions?
> > Since you specified a lower humidity ratio, the dH from zone
supply
> > inlet to zone is greater. Q=M*Cp*dH. Mass flow rate should be the
same.
> > 3) - what should be the approach to choosing the supply
temperature and
> > humidity ratio to be set in Purchased Air objects?
> > Choose the SA temp/humrat inputs to closely resemble the supply
air
> > conditions of the "real" system you expect to use to replace PA.
> >
> > anarui.oliveira wrote:
> > >
> > > Hello.
> > > I've been doing some experimenting with Purchased Air and I'd
> > > appreciate some help to better understand why:
> > >
> > > - the maximum reported heating/cooling rate increases as I set
the
> > > supply air temperatures in Purchased Air to be closer to the
zone
> > > setpoint temperatures?
> > >
> > > - Why, for instance, when cooling, the cooling rate/energy
increases
> > > greatly when lowering the supply humidity ratio in Purchased Air
> > > definitions? Does PA actually accounts for the energy necessary
to
> > > force the supply airflow below dew point and then back to the
> > > defined supply temperature again? I was under the ideia that PA
was
> > > much simpler than that?... In the affirmative case, which are
the
> > > departure conditions that PA considers to calculate those extra
> > > energy consumptions due to HR adjustments?
> > >
> > > Considering that I'm using PA for a first approach of thermal
load
> > > estimates and equipment sizing, what should should be the
approach
> > > to choosing the supply temperature and humidity ratio to be set
in
> > > Purchased Air objects (especially HR greatly influences
results)?
> > >
> > > Regards,
> > > Ana Rui Oliveira.
> > >
> > >
> >
> > --
> > 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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