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[EnergyPlus_Support] Re: ZoneVentilation Volume Standard Density vary

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: ZoneVentilation Volume Standard Density vary
From: "rgen1202" <robin.genoud@xxxxxxxxx>
Date: Thu, 05 May 2011 15:33:22 -0000
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Thank you very much for your answer. So there is definitely a difference between the calculation for the DesignVentilation model, which take constant Volume flow rate in account (an therefore not a constant Mass flow rate = outdoor air density*constant volume flow rate) and the AirLoop model which take constant mass flow rate in account. Hope I am right.

Regards.

Robin



--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Griffith, Brent" <brent.griffith@...> wrote:
>
> Robin,  please note that inside EnergyPlus, the calculations are based on mass flow rate.  The input design volume flow rates are converted to design mass flow rates using a standard density (but with an altitude adjustment).  So even though the models might be referred to as constant volume, they are really constant mass flow rate.  The volume flow rates are available for reporting but are derived from mass flow rates and available with two different options for density.
> 
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of rgen1202
> Sent: Thursday, May 05, 2011 2:16 AM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> Subject: [EnergyPlus_Support] Re: ZoneVentilation Volume Standard Density vary
> 
> 
> 
> Lixing,
> 
> I think my last problrm comes from the Actuator Node of the OutdoorAir Mixer of my loop. In fact, I have an Outdoor Air Node for Actuator Node (called Outdoor Air Inlet Node). When I look at the features of this node (current density, temperature, pressure) they are the same as the oudoor air, which is what I want. But when I look at this Node MassFlowRate, I have a constant value and the flow seams to be calculated with a constant density of 1.1704 kg/m3. I don't understand why EE+ doesn't take the current outdoor air density to calcul the MassFlow. I have uploaded my file, called venti_ailloop_1zone.idf
> 
> Thanks in advance.
> 
> Robin
> 
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support%40yahoogroups.com>, "rgen1202" <robin.genoud@> wrote:
> >
> > Lixing,
> >
> > I am aware of this density calculation. But I am still surprized of the way EnergyPlus model the ventilation(and the infiltration too) because if I model the mechanical ventilation with an Air Loop containing one exhaust fan constant volume and a 100% OA mixer, I get a constant Mechanical Ventilation Volume Standard Density. Therefore, the MassFlowRate in this case isn't calculated with the outdoor air density but with the standard density and I don't understant why.
> >
> > In fact, I am interested in the building energy consumption, and I don't know which model is the more accurate, since I have a significative difference in the cooling load due to outdoor air.
> >
> > Robin
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support%40yahoogroups.com>, Lixing Gu <gu@> wrote:
> > >
> > > Robin:
> > >
> > > This is caused by air density calculations using different pressures,
> > > temperature, and humidity ratio.
> > >
> > > In the calculation subroutine, the mass flow rate is required in the
> > > calculations and is equal to the volumetric flow rate from your input times
> > > air density as a function of outdoor conditions (T, P, and W). In the report
> > > subroutine, the volumetric flow is calculated using the mass flow rate
> > > divided by the air density as a function of standard condition. The
> > > different densities are used in calculation and reporting. That is why you
> > > see minor differences shown in outputs.
> > >
> > > Hope this helps.
> > >
> > > Lixing
> > >
> > > -----Original Message-----
> > > From: EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support%40yahoogroups.com>
> > > [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support%40yahoogroups.com>] On Behalf Of rgen1202
> > > Sent: Wednesday, May 04, 2011 3:17 PM
> > > To: EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support%40yahoogroups.com>
> > > Subject: [EnergyPlus_Support] Re: ZoneVentilation Volume Standard Density
> > > vary
> > >
> > > Lixing,
> > >
> > > Thanks for your answer. I uploaded the file in Files>Problem_Submittals
> > > http://tech.groups.yahoo.com/group/EnergyPlus_Support/files/_Problem_Submitt
> > > als/.
> > > Its called ventilation_mech.idf . Its a single zone building with only
> > > ZoneVentilationDesign Flow Rate. I used the FRA_LYON_IWEC.epw for the
> > > weather (I uploaded it too).
> > >
> > > Thanks in advance.
> > >
> > > Regards.
> > >
> > > Robin
> > >
> > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support%40yahoogroups.com>, Lixing Gu <gu@> wrote:
> > > >
> > > > Robin:
> > > >
> > > > If you report Zone Ventilation Volume Standard Density, it should give you
> > > a
> > > > constant value. Please upload the input file and tell us the weather file
> > > > name if this weather file is downloaded from the energyplus web site. We
> > > > will take a look.
> > > >
> > > > Lixing
> > > >
> > > > -----Original Message-----
> > > > From: EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support%40yahoogroups.com>] On Behalf Of Lixing Gu
> > > > Sent: Wednesday, May 04, 2011 1:29 PM
> > > > To: EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > Subject: RE: [EnergyPlus_Support] ZoneVentilation Volume Standard Density
> > > > vary
> > > >
> > > > Robin:
> > > >
> > > > I think you may use one of two output variables to report volume flow
> > > rates:
> > > >
> > > > HVAC,Sum,Zone Ventilation Volume Flow Rate Current Density [m3/s]
> > > > HVAC,Sum,Zone Ventilation Volume Flow Rate Standard Density [m3/s]
> > > >
> > > > It was found as a bug to report volume flow rates and was fixed for the
> > > next
> > > > release. It is a report error and has no impact of simulation results.
> > > >
> > > > Lixing
> > > >
> > > > -----Original Message-----
> > > > From: EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support%40yahoogroups.com>] On Behalf Of rgen1202
> > > > Sent: Wednesday, May 04, 2011 11:56 AM
> > > > To: EnergyPlus_Support@xxxxxxxxxxxxxxx<mailto:EnergyPlus_Support%40yahoogroups.com>
> > > > Subject: [EnergyPlus_Support] ZoneVentilation Volume Standard Density vary
> > > >
> > > > Hello,
> > > >
> > > > I have a question about the ZoneVentilation DesignFlowRate.When I set the
> > > > Design Flow Rate to a constant value (assuming 0.086162 m3/s, for a single
> > > > zone), I don't understand why the output variable Zone Ventilation Volume
> > > > Standard Density (hourly) is varying. Can someone explain it? I have
> > > checked
> > > > the settings and I have all minimum and maximum temperature setted to
> > > > default value (this mean no shutoff of ventilation) , the maximum wind
> > > speed
> > > > is 40 m/s (no shutoff) and only the constant term coeeficient is set to 1,
> > > > the other are to 0. Of course, I have tested this setting for a single
> > > zone,
> > > > without any infiltration or other air system.
> > > >
> > > > Thanks in advance.
> > > >
> > > > Robin GENOUD
> > > >
> > > >
> > > >
> > > > ------------------------------------
> > > >
> > > > Primary EnergyPlus support is found at:
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> > > > energyplus-support@
> > > >
> > > > The primary EnergyPlus web site is found at:
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> > > >
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> > > >
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> > > > EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the
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> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > ------------------------------------
> > > >
> > > > Primary EnergyPlus support is found at:
> > > > http://energyplus.helpserve.com or send a message to
> > > > energyplus-support@
> > > >
> > > > The primary EnergyPlus web site is found at:
> > > > http://www.energyplus.gov
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> > > >
> > > > Attachments are currently allowed but be mindful that not everyone has a
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> > >
> > >
> > >
> > >
> > > ------------------------------------
> > >
> > > Primary EnergyPlus support is found at:
> > > http://energyplus.helpserve.com or send a message to
> > > energyplus-support@
> > >
> > > The primary EnergyPlus web site is found at:
> > > http://www.energyplus.gov
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> > > http://groups.yahoo.com/group/EnergyPlus_Support/
> > >
> > > Attachments are currently allowed but be mindful that not everyone has a
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> > >
> > > EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the
> > > Documentation link and press the "search" button.
> > > Yahoo! Groups Links
> > >
> >
>




------------------------------------

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References:
- RE: [EnergyPlus_Support] Re: ZoneVentilation Volume Standard Density vary
  - From: Griffith, Brent

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