(1) Solar gain generally belongs to shortwave (only a small range of
longwave, near-IR). IR needs to be calculated separately.
(2) Radiance calculates radiance within visible range, not full spectrum.
But Gendaylit could output full range spectrum (more precisely, UV, visible,
and near-IR) and then you can convert the radiance back to total
But some issues exist and should be considered if accurate results are
required: (a) calculation of energy needs considering absorbed gain,
currently, as far as I know it is difficult to calculate absorbed energy in
Radiance. (b) visible transmittance and solar transmittance is generally
different. Some glazing, for example, may be spectrally selective. (c)
Sunlight entering into the building may be reflected back. (d) For window,
divider, frame and reveal needs to be considered in energy calculation (e)
Center-of-glazing and edge glazing have different energy performance, This
should also be considered.
(3) For calculation of solar gain, sky needs to be simulated, building
simulation software such as E+ and Radiance uses different algorithms. (a)
gendaylit uses Sky Luminous Model which is developed by Perez (1990); (b) E+
also uses Perez's model in the same paper, but this model is specifically
for calculating irradiance on tilted surface. Since the original purpose of
developing sky luminous model by Perez is to calculate luminance/illuminance
to deal with the daylighting (visible) issue, so it may be better to
consider using Perez's another model to calculate irradiance.
Hope this helps,
On Sun, Jul 17, 2011 at 11:41 PM, Ji Zhang <[email protected]> wrote:
Dear Radiance experts,
May I ask whether it's possible to "isolate" the contribution of short-wave
and long-wave solar radiation using Radiance?
One of our colleagues wants to get these values for the calculation of
"mean radiant temperature" for the purpose of analyzing the implications of
urban geometries on thermal comfort.
Correct me if I'm wrong, the irradiation value obtained in Radiance is the
total solar radiation energy received on a given surface.
So, is this "total" value encompasses the full spectrum of solar radiation,
including the visible part and the short-wave and long-wave parts that are
not visible to human eyes?
If it is, then, is there a way to single out the contribution from
short-wave and long-wave radiation separately?
Clarification and advices are deeply appreciated!
- Cheers, Ji
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