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Re: [EnergyPlus_Support] Re: Purchased Air variables
You are correct in all 3 statements.
Step 1) PA sets the zone supply inlet conditions according to your
inputs. My responses address this step.
Step 2) Then it calculates the PA inlet conditions, including OA.
Step 3) Using step 1 and 2 above, the required PA capacity is calculated.
anarui.oliveira wrote:
>
> 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
> <mailto:EnergyPlus_Support%40yahoogroups.com>, 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>
> <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 <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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