Re: [EnergyPlus_Support] sky model in EnergyPlus

[Linda Lawrie <linda@xxxxxxxxxx>]

 From the code:

        ! 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/m^2

        !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.


(It would normally be in the Auxiliary programs document as we intend that 
the epw files will have this information but it looks like it isn't there).

It may be a little dated -- someone proposed some different methods shortly 
before the last release but were unable to lead us to a definitive 
algorithm nor could we determine universiality.

At 03:32 AM 5/6/2004, g_kokogiannakis wrote:

>was looking the engineering reference for this but could not find
>something.
>I took the sky temperatures from the results in EnergyPlus and
>compared them with the predictions of some models from the literature
>(Cole's, Clarke's, Czeplak, e.t.c. - for the same weather file).

Linda

EnergyPlus WebSite: http://www.energyplus.gov
Owner: EnergyPlus_Support list
Member: EnergyPlus Development Team



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