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