1) In the HVAC calculation, the design volumetric flow rates are changed to
design mass flow rates using a standard air density:
StdBaroPress=101.325d0*(1.d0-2.25577D-05*Elevation)**5.2559d0
StdBaroPress=StdBaroPress*1000.d0
StdRhoAir=PsyRhoAirFnPbTdbW(StdBaroPress,constant_twenty,constant_zero)
So the conditions are: a) elevation corrected standard barometric pressure; b) 20 C air temperature
c) dry air (no moisture content)
If Elevation = 0.0, then StdRhoAir = 1.294.
Then all calculations are done in terms of mass flow rate.
2) in the envelope calculation, the density of air is calculated using the outside barometric
pressure and the relevant air temperature and humidity ratio. For instance, in calculating
interior surface convection coefficients, the current zone temperature and humidity ratio
are used.
Fred Buhl
direzionecontraria wrote:
Cz is on page 5. 1.204 kg/m3 is on pages 573 and 603. Regards Francesco --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Fred Buhl <wfbuhl@...> wrote:Could you tell us what section or page of the EngineeringReference youare looking at? Fred Buhl direzionecontraria wrote:Hello! I refer to "Engineering Reference"http://apps1.eere.energy.gov/buildings/energyplus/pdfs/engineeringref erence.pdf In the equations of the heat balance on the zone, for example intheequation (2), there is the term Cz, which is the air capacitance. Cz = (air density )*(volume of the zone) I read that the standard air density is 1.204 kg/m3. What are the standard conditions ? How is the air densitycalculate indifferent conditions from the standard conditions? With Regards Francesco ------------------------------------ The primary EnergyPlus web site is found at: http://www.energyplus.gov The group web site is: http://groups.yahoo.com/group/EnergyPlus_Support/ Attachments are not allowed -- please post any files to theappropriate folder in the Files area of the Support Web Site.EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdfunder the Documentation link and press the "search" button.Yahoo! Groups Links------------------------------------ The primary EnergyPlus web site is found at: http://www.energyplus.gov The group web site is: 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 <*> To visit your group on the web, go to: http://groups.yahoo.com/group/EnergyPlus_Support/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/EnergyPlus_Support/join (Yahoo! ID required) <*> To change settings via email: mailto:EnergyPlus_Support-digest@xxxxxxxxxxxxxxx mailto:EnergyPlus_Support-fullfeatured@xxxxxxxxxxxxxxx <*> To unsubscribe from this group, send an email to: EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
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