Re: [EnergyPlus_Support] Summer Design Day -- Direct Solar Radiation Calculation

[Linda Lawrie <linda@xxxxxxxxxxxxxx>]

It would be nice to include the ASHRAE 2009 calcs BUT there
are some table lookups that won't be appropriate for all
locations.

Will/would be difficult to implement. But gets put into the mix of other
things on the priority list.



At 06:13 PM 7/23/2009, Chris wrote:
> This is not "pure"
> ASHRAE, and seems highly convoluted (diffuse 
> radiation is calculated twice). I'm curious to see how the code selects
> A, B, C and the clearness number (the original ASHRAE coefficients) for
> locations outside of the USA, since they are not defined by ASHRAE in
> such a case. I would not use these calculations for locations in the
> southern hemisphere or in dusty/hazy areas, due to the potentially large
> errors involved.
>
> Anyway, this is in need of complete overhaul. The 2009 ASHRAE Handbook
> of Fundamentals will have a completely new model with worldwide 
> application, which I hope will find its way to E+.
>
> Chris
>
> >
> >
> > It currently uses a really old ASHRAE clearsky model, hopefullly you
> > can read Fortran:
> >
> >          IF(CosZenith
> >= SunIsUpValue) THEN
> >            !
> Sun is up.  Calculate solar values
> >           
> TotHoriz = DesDayInput(EnvrnNum)%SkyClear * A * (C + 
> > CosZenith) * EXP( -B / CosZenith)
> >           
> HO=GlobalSolarConstant*AVSC*CosZenith
> >           
> KT=TotHoriz/HO
> >           
> KT=MIN(KT,.75d0)
> >           
> Wthr%DifSolarRad(Hour) = TotHoriz * (1.0045d0 + KT * 
> > (.04349d0 + &
> >                                                    
> KT * (-3.5227d0 + 
> > 2.6313d0 * KT)))
> >            IF
> (DesDayInput(EnvrnNum)%SkyClear .GT. 0.70d0)    &
> >                     
> Wthr%DifSolarRad(Hour) = TotHoriz*C/(C+CosZenith)
> >           
> Wthr%BeamSolarRad(Hour) = &
> >                                
> > (TotHoriz-Wthr%DifSolarRad(Hour))/CosZenith
> >           
> Wthr%DifSolarRad(Hour) = MAX(0.0d0,Wthr%DifSolarRad(Hour))
> >           
> Wthr%BeamSolarRad(Hour) = MAX(0.0d0,Wthr%BeamSolarRad(Hour))
> >          ELSE
> >
> > when the sun is not up -- these are set to 0.0
> >
>
>
> -- 
> 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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