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[EnergyPlus_Support] Re: ATUs - Insufflated vs. Exhaust Air flows

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: ATUs - Insufflated vs. Exhaust Air flows
From: "anarui.oliveira" <anarui.oliveira@xxxxxxxxx>
Date: Tue, 15 Jan 2008 12:11:21 -0000
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Thank you for the "nodes" view of the model. It was enlightening.

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Richard Raustad 
<RRaustad@...> wrote:
>
> Only the inlet/exhaust nodes entered in the Controlled Zone Equip 
> Configuration object are used to calculate the Return Air mass flow 
> rate. Note that the mixing and cross-mixing objects only use "zone" 
node 
> information. This node is not the same as the inlet/outlet nodes of 
a 
> zone.  For the actual inlet/outlet nodes, the return air node mass 
flow 
> rate is equal to the sum of the supply (inlet) mass flow rates 
minus the 
> sum of the exhaust (outlet) mass flow rates. You can check this by 
> setting the mixing object mass flow rate to a constant. Then 
reporting 
> all the supply inlet and exhaust outlet mass flow rates and the 
return 
> air node mass flow rate. You can set the exhaust air mass flow 
rates to 
> 0 to make this easier. Calculate the total zone return air flow 
rate by 
> summing the supply (inlet) and subtracting the exhaust (outlet) 
node 
> mass flow rates. Then subtract this value from the return node mass 
flow 
> rate. Is this calculated value ever greater than zero? Since the 
return 
> air mass flow rate is not allowed to be negative, you may see some 
> negative values when the exhaust air mass flow rate is greater than 
the 
> supply air mass flow rate. Also verify that the sum of the supply 
> (inlet) node mass flow rate is 0 at some point in the simulation.
> 
> anarui.oliveira wrote:
> >
> > I understand now about the source zone.
> >
> > But what about the RECEIVING zone of a MIXING object? This inlet 
flow
> > is accounted for to balance the supply and return air flows of an 
ATU?
> >
> > In this case, could I have a zero supply air flow and a non-zero
> > return air flow, based on the inlet flow of the MIXING object?
> >
> > Always thankful for your help,
> > Ana Rui.
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx 
> > <mailto:EnergyPlus_Support%40yahoogroups.com>, "Michael J. Witte"
> > <mjwitte@> wrote:
> > >
> > > Cross mixing simply exchanges and equal amount of air between 
two
> > zones. It is
> > > a zone heat balance function and the air handling system knows
> > nothing of it.
> > >
> > > On 11 Jan 2008 at 17:52, anarui.oliveira wrote:
> > >
> > > > Thanks a lot for all your answers.
> > > >
> > > > Regarding option 4:
> > > > - If I use Cross-mixing instead, doesn't the program account 
for
> > the
> > > > corresponding outgoing flow in the source zone?
> > > >
> > > > Thanks again,
> > > > Ana Rui.
> > > >
> > > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx 
> > <mailto:EnergyPlus_Support%40yahoogroups.com>, "Michael J. Witte"
> > > > <mjwitte@> wrote:
> > > > >
> > > > > 1. First, I will clarify some terminology:
> > > > > Return air flow - air leaving the zone and returning to the
> > HVAC
> > > > system
> > > > >
> > > > > Exhaust air flow - air leaving the zone and exhausted to
> > outdoors
> > > > >
> > > > > Return air flow rate is computed as Supply air flow minus
> > Exhast
> > > > air flow
> > > > >
> > > > > I am not sure when you say "exhaust" if you mean return or
> > exahust
> > > > as defined
> > > > > above. I will use my definitions below.
> > > > >
> > > > > 2. The systems created by Compact HVAC assume that return 
air
> > flow
> > > > is equal to
> > > > > supply air flow.
> > > > >
> > > > > 3. If you want to add exhaust air flow, you can add ZONE
> > EXHAUST
> > > > FAN objects by
> > > > > editing the expidf file.
> > > > >
> > > > > 4. If you want to model a constant (or scheduled) flow from 
one
> > > > zone to
> > > > > another, you can use a MIXING object to move air from one 
zone
> > to
> > > > another.
> > > > > However, the HVAC system has no knowledge of this and the 
user
> > must
> > > > balance the
> > > > > airflows by adding a dummy ZONE EXHAUST FAN to the source 
zone
> > to
> > > > cause a
> > > > > reduction in return air flow from the source zone.
> > > > >
> > > > > 5. For constant volume systems, you can use
> > > > AIRFLOWNETWORK:DISTRIBUTION:*
> > > > > objects to model the pressure-indcued flows, but this 
feature
> > does
> > > > not yet
> > > > > support VAV systems.
> > > > >
> > > > > Mike
> > > > >
> > > > >
> > > > > On 9 Jan 2008 at 16:23, anarui.oliveira wrote:
> > > > >
> > > > > > Hi.
> > > > > >
> > > > > > The parameters for ATU, such as those cretated by
> > > > > > - Compact HVAC:Zone:VAV,
> > > > > > - Compact HVAC:System:VAV,
> > > > > > only allow the user to define the insufflated air flows
> > (Supply
> > > > air
> > > > > > flow), right?
> > > > > >
> > > > > > What does the simulation assume, in this case, for the
> > exhaust
> > > > air
> > > > > > flows, and how does it deal with the corresponding effect 
on
> > the
> > > > > > inside pressures?
> > > > > >
> > > > > > If the case to model has different insufflated and exhaust
> > flows,
> > > > how
> > > > > > does it affect my model? Wow can I implement this in E+?
> > > > > >
> > > > > > And if a certain zone only has forced exhaust flow, and 
the
> > inlet
> > > > > > flow is assumed to be drawn from adjacent areas by 
pressure
> > > > > > difference?
> > > > > >
> > > > > > Thanks in advanced.
> > > > > >
> > > > > > Best regards,
> > > > > > Ana Rui.
> > > > > >
> > > > > >
> > > > > >
> > > > > > The primary EnergyPlus web site is found at:
> > > > > > http://www.energyplus.gov <http://www.energyplus.gov>
> > > > > >
> > > > > > The group web site is:
> > > > > > http://groups.yahoo.com/group/EnergyPlus_Support/ 
> > <http://groups.yahoo.com/group/EnergyPlus_Support/>
> > > > > >
> > > > > > Attachments are not allowed -- please post any files to 
the
> > > > appropriate folder
> > > > > > in the Files area of the Support Web Site.
> > > > > >
> > > > > > EnergyPlus Documentation is searchable. Open
> > EPlusMainMenu.pdf
> > > > under the
> > > > > > Documentation link and press the "search" button.
> > > > > >
> > > > > > Yahoo! Groups Links
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > >
> > > > >
> > > > > ========================================================
> > > > > Michael J. Witte, GARD Analytics, Inc.
> > > > > EnergyPlus Testing and Support
> > > > > EnergyPlus-Support@
> > > > >
> > > >
> > > >
> > > >
> > > >
> > > > The primary EnergyPlus web site is found at:
> > > > http://www.energyplus.gov <http://www.energyplus.gov>
> > > >
> > > > The group web site is:
> > > > http://groups.yahoo.com/group/EnergyPlus_Support/ 
> > <http://groups.yahoo.com/group/EnergyPlus_Support/>
> > > >
> > > > Attachments are not allowed -- please post any files to the
> > appropriate folder
> > > > in the Files area of the Support Web Site.
> > > >
> > > > EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf
> > under the
> > > > Documentation link and press the "search" button.
> > > >
> > > > Yahoo! Groups Links
> > > >
> > > >
> > > >
> > > >
> > > >
> > >
> >
> >  
> 
> -- 
> 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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References:
- Re: [EnergyPlus_Support] Re: ATUs - Insufflated vs. Exhaust Air flows
  - From: Richard Raustad

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