You can't measure extraterrestrial unless you're in outer space, but
then it's assumed to be constant anyway. For the various radiation and
illuminance values, they can measured by various instrumentation ranging
from the very cheap to the very expensive. Properly, radiation needs to
be measured with a pyranometer (Eppley), which is pricy, but I'm also
seen people use simpler apparatus (Lycors) that are really photometers.
Direct beam is generally not measured, but derived by subtracting the
diffuse from the global. Diffuse is measured by adding a shadow band
over a pyranometer to block out the direct beam. Pyranometers measure
heat, photometers measure light. Don't know what people in our field do
to measure illuminance. I suppose it must be simple (lots of photometers
around), I just seen any. All the illuminance on the weather files are
derived from the radiation and sky conditions.
Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd. Suite 108D
Moraga CA 94556
(o) +925 388 0265
(c) +510 928 2683
yjhuang@xxxxxxxxxxxxxxxxxxxxxxxx
www.whiteboxtechnologies.com> Illuminance {lux}* *Diffuse Horizontal Illuminance {lux}*
Hu,Jia wrote:
>
> Hello all:
>
> I have a question about the following metrics in weather file.
> Can they be directly measured by some inexpensive devices?
>
> Thank you
>
> *Extraterrestrial Horizontal Radiation {Wh/m2}* *Extraterrestrial
> Direct Normal Radiation {Wh/m2}* *Horizontal Infrared Radiation
> Intensity from Sky {Wh/m2}* *Global Horizontal Radiation {Wh/m2}*
> *Direct Normal Radiation {Wh/m2}* *Diffuse Horizontal Radiation
> {Wh/m2}* *Global Horizontal Illuminance {lux}* *Direct Normal
>
>
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