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Re: [EnergyPlus_Support] Re: Question about sky temperature and Horizontal Infrared Radiation?
Here is the calculation we use, maybe that will help. In the below,
! is a comment, not a calculation. IRHoriz is Horizontal IR from Sky
! Calculate sky temperature, use IRHoriz if not missing
IF (IRHoriz == "missing") THEN
! Missing, use sky cover
OSky=OpaqueSkyCover
TDewK=MIN(DryBulb,DewPoint)+TKelvin
ESky= (.787 +.764*LOG((TDewK)/TKelvin))*(1. + .0224*OSky
- 0.0035*(OSky**2) + .00028*(OSky**3))
SkyTemp=(DryBulb+TKelvin)*(ESky**.25)-TKelvin
ELSE ! Valid IR from Sky
SkyTemp=(IRHoriz/Sigma)**.25 -TKelvin
ENDIF
Sky IR is calculated as:
! Determine Sky Temp ==>
! Function of DryBulb, DewPoint, OpaqueSkyCover
! Calculate Sky IR
!HIR = ESKY * SIGMA * (TOUT**4)
!
!where
!
!HIR = horizontal IR intensity (W/m2)
!ESKY = sky emissivity
!SIGMA = Stefan-Boltzmann constant = 5.6697e-8 W/m2-K4
!TOUT = drybulb temperature (K)
!
!The sky emissivity is given by
!
!ESKY = [0.787 + 0.764*ln(TDEW/273)]*[1 + 0.0224*N -
0.0035*(N**2) + 0.00028*(N**3)]
!
!where
!
!TDEW = dewpoint temperature (K)
!N = opaque sky cover (tenths)
!
!Example: Clear sky (N=0), TOUT = 273+20=293K, TDEW = 273+10=283K:
!
!ESKY = 0.787 + 0.764*0.036 = 0.815
!HIR = 0.815*5.6697e-8*(293**4) = 340.6 W/m2
!References:
!
!George N. Walton, "Thermal Analysis Research Program
Reference Manual,"
!NBSIR 83-2655, March 1983, p. 21.
!
!G. Clark and C. Allen, "The Estimation of Atmospheric
Radiation for Clear and
!Cloudy Skies," Proc. 2nd National Passive Solar Conference
(AS/ISES), 1978, pp. 675-678.
At 01:28 AM 5/15/2008, yhleifei wrote:
>I had some field data of some wuhan building energy consumption. I
>want use e+ to calculate wuhan building, to compare .
>The first step is check the weather file .epw . CHN_Wuhan_CSWD.epw
>was created from the "China Standard Weather Data for Analyzing
>Building Thermal Conditions April 2005" (China Meteorological Bureau-
>Climate Information Center-Climate Data Office and Tsinghua
>University-Department of Building Science and Technology). I had the
>data CD of "China Standard Weather Data for Analyzing Building
>Thermal Conditions April 2005" . Compareing .epw with the data CD,
>except the element "Horizontal Infrared Radiation Intensity from Sky
>{Wh/m2}" , other elements are equal.
>In the data CD , there is a element "sky temperature". I guess
>that "Horizontal Infrared Radiation Intensity from Sky {Wh/m2}" data
>could be calculated from the "sky temperature" , according equation
>at InputOutputReference Page57 . (sky temperature=(Horizontal
>IR/sigma)**0.25-273.15 )
>But the calculate result is not same with the CHN_Wuhan_CSWD.epw .
>For example,
>in the data CD , The first line of wuhan ,the "sky temperature" is
>259.21 K . "Horizontal Infrared Radiation Intensity from Sky
>{Wh/m2}" calculated by the equation is 256.2 . but in
>CHN_Wuhan_CSWD.epw, the Horizontal IR is 323.
>How the data "Horizontal Infrared Radiation Intensity from Sky
>{Wh/m2}" of CHN_Wuhan_CSWD.epw be created ?
>Thank you for help again.
>Lei Fei
>
>--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Linda Lawrie <linda@...>
>wrote:
> >
> > If you put in "missing" values (I think it is 9999 but check the
> > documentation in Auxiliary Programs), then the program will
> > recalculate the Horizontal IR from sky as well as the sky
>temperature.
> >
> > What led you to put in those values for Hor IR from sky?
> >
> > Linda
> >
> > At 08:32 AM 5/14/2008, yhleifei wrote:
> > >I had modifyed a .epw file (CHN_Wuhan_CSWD.epw) ,set the data
> > >of "Horizontal Infrared Radiation Intensity from Sky {Wh/m2}" in
> > >weather file as 0,10,100,200,300.
> > >And i output the "sky temperature ". When i run a case
>(case600.idf),
> > >the "Environment:Sky Temperature [C](Hourly)" is -1,-98,-101,-43,-
>13.
> > >What wrong ?
> >
> >
> > [Non-text portions of this message have been removed]
> >
>
>
>
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[Non-text portions of this message have been removed]
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