[EnergyPlus_Support] Re: ZoneVentilation Volume Standard Density vary

["rgen1202" <robin.genoud@xxxxxxxxx>]

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, 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@xxxxxxxxxxxxxxx] On Behalf Of rgen1202
> Sent: Wednesday, May 04, 2011 3:17 PM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> 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, 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@xxxxxxxxxxxxxxx] On Behalf Of Lixing Gu
> > Sent: Wednesday, May 04, 2011 1:29 PM
> > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> > 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@xxxxxxxxxxxxxxx] On Behalf Of rgen1202
> > Sent: Wednesday, May 04, 2011 11:56 AM
> > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> > 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
> > 
> > 
> > 
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> > 
> > 
> > 
> > 
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> 
> 
> ------------------------------------
> 
> Primary EnergyPlus support is found at:
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> energyplus-support@...
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> The primary EnergyPlus web site is found at:
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> 
> Attachments are currently allowed but be mindful that not everyone has a
> high speed connection.  Limit attachments to small files.
> 
> EnergyPlus Documentation is searchable.  Open EPlusMainMenu.pdf under the
> Documentation link and press the "search" button.
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