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[EnergyPlus_Support] Re: sky temperature

I'm sorry to bother you, but I have a doubt about this argument.

SkyTemp=(DryBulb+TKelvin)*(ESky**.25)-TKelvin

Also in absolute temperatures: Tsky = Tdrybulb * (ESky^0.25)
Isn't it?
What is the physical meaning of that expression?

With Regards



--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Linda Lawrie <linda@...> wrote:
>
> It uses the Horizontal IR from sky as a basis (we calculate this on 
> the weather files and design days)
> 
>          ! 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.
> 
> 
> Linda
> 
> EnergyPlus WebSite: http://www.energyplus.gov
> Owner: EnergyPlus_Support list
> Member: EnergyPlus Development Team
> 
> 
> 
> [Non-text portions of this message have been removed]
>




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