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[EnergyPlus_Support] Re: Modifying a weather file to reflect "real" weather
Adding to the discussion, the weather file needs solar radiation data which could be estimated based on the total horizontal solar radiation which could be "cheaply" recorded, but eplus also requires the horizontal IR radiation, for which I have yet to find a method to estimate it using normally reported weather data (like temp, humidity, wind speed and direction, rain).
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Chris <chris@...> wrote:
>
> Assuming you have global horizontal radiation data from a site within,
> say, 10 km of your test location, you need to separate the direct and
> diffuse components, which can be done with one of many possible methods,
> including Maxwell's. Then you have to calculate the sky diffuse and
> reflected diffuse components for your walls and other tilted surfaces.
> These two steps currently rely on empirical models, which have two known
> problems: (i) they introduce considerable random hourly errors and
> sometimes significant bias errors, and (ii) you never know where model A
> will perform better than model B, precisely because of their empirical
> nature.
>
> I recently published on this issue in Solar Energy, using high-class
> measured data from Golden (NREL) to test these various combinations.
> There were many surprises in the results, but for Michigan, North
> Carolina or elsewhere, other combinations of models might have to be
> recommended, since the cloud, aerosol and water vapor regimes are different.
>
> In many instances, particularly for prevailing clear-sky conditions, my
> tests also showed that it is more accurate to use meteorological data to
> calculate the direct and diffuse components directly than to separate
> them from measured global radiation.
>
> Chris
>
> >
> > In North Carolina, we have a series of EcoNet monitoring stations for
> > agricultural research which capture global horizontal radiation. You
> > can map this into direct beam and diffuse radiation with the
> > correlation developed by Maxwell. See:
> >
> > http://www.nrel.gov/rredc/pdfs/3087.pdf
> >
> > I don't know where you can get a ready-made program to do this
> > computation. I wrote one myself. It has given nice results in
> > comparing measured solar thermal yield with modeled predictions under
> > a variety of partly cloudy to full sun conditions using the global
> > horizontal value as the input, so I have come to trust it. My program
> > is proprietary and not validated by external authority, so I'm not in
> > a position to offer it at this point. However, this is one way to
> > accomplish what you want if you have a local source of global
> > horizontal radiation and ability to turn Maxwell's method into a
> > computer program.
> >
>
>
> --
> 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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