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Re: [EnergyPlus_Support] Weather data - DISC Maxwell
Camille,
I ran my code that compares various direct/diffuse separation algorithms.
Normally, I have internal checks that prevent the diffuse/global ratio
to be >1 and therefore DNI to be <0.
I turned this safety off in the case of the DISC/Maxwell algorithm to
see what happens in your case.
Here are the results:
Date Z AM Glob DNIe DNIm DNIo DNIr2 DNIr3
--------------------------------------------------------------------------------------------------------
08Nov 68.400 2.697 314.0 498.7 644.8 483.9 514.8 486.5
01Nov 76.200 4.121 28.0 0.9 -46.7 2.5
0.0 0.1
The DNI subscripts correspond to these various models, which all use Kt
as the independent variable, and some also use AM:
e: Erbs et al. (1982), f(Kt)
m: Maxwell/DISC (1987), f(Kt,AM)
o: Orgill & Hollands (1977), f(Kt)
r2: Reindl et al. (1990), f(Kt,AM)
r3: Reindl et al. (1990), f(Kt)
Note the differences in predicted DNI in the first case between the
various algorithms. As I explained in a previous post, this is due to
the empirical nature of these simplistic algorithms. There is currently
no way of knowing which one is more accurate for a specific location or
time, so this is anyone's guess.
There are other possible algorithms that use additional variables, but
they are empirical too, so we can't be sure whether they are really more
accurate.
Your results with DISC/Maxwell look correct. You just have to add the
rule that the diffuse/global ratio must always be smaller or equal to 1
before calculating DNI.
Chris
>
>
> I add, sun's zenith angle and mass air !
>
> 1 : Lat:50,56 ; long:2,48 ; date:8th Novembre,12h00 ; ETR:1396 ; TZ=1
> ; DayAgle:5,35 ; ZenithAngle:68,4 ; MassAir:2,7 ;
> GlobaleHorizontaleInsulation: 314W/m² ; DirectNormalInsulation:645W/ m²
>
> 2 : lat:50,56 ; long:2,48 ; date:1st Novembre,10h00 ; ETR:1391 ; TZ=1
> ; DayAgle:5,23 ; ZenithAngle:76,2 ; MassAir:4,2 ;GlobaleHorizontaleI
> nsulation: 28W/m² ; DirectNormalInsulat ion:-48W/ m²
>
> Camille T.
>
--
Chris A. Gueymard, PhD
Solar Consulting Services
P.O. Box 392
Colebrook, NH 03576, USA
Tel. (603) 237-8550
Fax (603) 237-5314
http://www.SolarConsultingServices.com
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