[BLDG-SIM] strange behavior in simulating the solar radiation

[Harry BOYER]

Hello,

I encountered a similar problem when calculating Direct radiation on an
arbitrary oriented and tilted surface, from horizontal diffuse and direct
radiation. If solar height is Hs and Dh hourly horizontal energy recived, it
appears that the term that causes unexpected values of radiation in the
formula was Dh/sin(Hs), when the sun is going down (Hs goes to 0).
Specifically, it is well known these two values represents for the first one
an hourly energy and for the second an instantaned position of the sun.
It is then necessary to know how theses two values where computed (or
mesured) to correct and eventually filter these anormal values.

Harry BOYER
Reunion Island University


-----Message d'origine-----
De : postman at gard.com [mailto:postman at gard.com]De la part de Danni Wang
Envoye : mardi 19 avril 2005 02:13
A : BLDG-SIM at gard.com
Objet : [BLDG-SIM] strange behavior in simulating the solar radiation


I used the formula from ASHRAE Fundamentals 2001,
Chapter 30 Fenestration, Section Determining Incident
Solar Flux, Equation 10~24,  to simulate the direct,
diffuse, and reflect solar radiation on a south wall
in Sacramento in June.

The result seems close to, or at an acceptable scale
of, the measured solar data (as recorded in nrel.gov
website) for 5~19:00 hr of a day. But there are sharp
spikes before 4:00 and after 20:00. The maximal value
of the spikes for direct radiation gets to 5000w/m2,
for diffuse radiation gets to 1200w/m2. This is
unexpected to me. I tried someone else's code and
result was very similar. May there be an explanation
for this?


Thank you very much.

-- Danni



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