RE: [EnergyPlus_Support] Daylighting

["Ellis, Peter" <peter_ellis@xxxxxxxx>]

Hello Peter,
 
The sky type is selected using a sky weighting factor determined by SkyClearness and SkyBrightness:
 
3.0 < SkyClearness < 4.0  -->  interpolate between "clear sky" and "clear turbid sky"
    SkyWeight = MIN(1.0,(SkyClearness-3)/3)
    ...if SkyWeight = 1, then it's a clear sky
 
1.2 < SkyClearness < 3.0  -->  interpolate between "clear turbid sky" and "intermediate sky"
    SkyWeight = (SkyClearness - 1.2)/1.8
    ...if SkyWeight = 1, then it's a clear turbid sky
 
1.0 < SkyClearness < 1.2  -->  interpolate between "intermediate sky" and "overcast sky"
    SkyWeight = MIN(1.0, MAX(0.0, (SkyClearness-1)/0.2, (SkyBrightness-0.05)/0.4))
    ...if SkyWeight = 1, then it's an intermediate sky 
    ...if SkyWeight = 0, then it's an overcast sky
 
 
"Sky Clearness for Daylighting Calculation" and "Sky Clearness for Daylighting Calculation" are output variables that you can report out, if you wish.  
 
The final daylighting factors are interpolations/weighted averages (using SkyWeight) between the daylight factors calculated for each discrete sky type.  
 
SkyClearness is calculated using BeamSolarRad and DifSolarRad come from the weather file:
 
      Zeta = 1.041*SunZenith**3
      SkyClearness = ( (DifSolarRad + BeamSolarRad)/(DifSolarRad + 0.0001) + Zeta )/(1.+Zeta)
 
 
SkyBrightness is calculated as follows:
 
SkyBrightness = (DifSolarRad * 93.73)* AirMass / ExtraDirNormIll(Month) 
 
REAL, PARAMETER, DIMENSION(12) :: ExtraDirNormIll=  &     ! Monthly exterrestrial direct normal illuminance (lum/m^2)
      (/131153.,130613.,128992.,126816.,124731.,123240., &
        122652.,123120.,124576.,126658.,128814.,130471./)
 
 
Let me know if you have further questions.
 
Peter Ellis
NREL
 
 
-----Original Message-----
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]On Behalf Of Peter G. Loutzenhiser
Sent: Wednesday, May 11, 2005 1:54 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Daylighting


Dear All,

I am interested in the daylighting algorithm described in the Engineering 
Auxillary manual and by Winkelmann and Sellkowitz (1985).  What is the 
criterion (or what are the criteria) for selecting the sky conditions (there 
are four in EnergyPlus and two in DOE-2.1e), and what specific parameters are 
these conditions a function of?

Many thanks,

Peter





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.




  _____  

Yahoo! Groups Links


*	To visit your group on the web, go to:
http://groups.yahoo.com/group/EnergyPlus_Support/
  

*	To unsubscribe from this group, send an email to:
EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx <mailto:EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx?subject=Unsubscribe> 
  

*	Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service <http://docs.yahoo.com/info/terms/> . 




[Non-text portions of this message have been removed]



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.
 
Yahoo! Groups Links

<*> To visit your group on the web, go to:
    http://groups.yahoo.com/group/EnergyPlus_Support/

<*> 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/