# [help] how to get short-wave and long-wave solar radiation value?

Hi Ji,

(1) Solar gain generally belongs to shortwave (only a small range of
longwave, near-IR). IR needs to be calculated separately.

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,

Jia

···

On Sun, Jul 17, 2011 at 11:41 PM, Ji Zhang <[email protected]> wrote:

May I ask whether it's possible to "isolate" the contribution of short-wave

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

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

Clarification and advices are deeply appreciated!

- Cheers, Ji

_______________________________________________
[email protected]

It is good to know this! Thanks.

···

On Mon, Jul 18, 2011 at 2:49 AM, Lars O. Grobe <[email protected]> wrote:

Hi Ji Zhang!

May I ask whether it's possible to "isolate" the contribution of

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

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

Clarification and advices are deeply appreciated!

You are (almost) completely free to choose what wavelength range to squeeze
into any of the three channels that we usually refer to as RGB. So instead
of calling the first channel "RED", you could call it "Shortwave". As long
as you use the three channels for the same wavelength ranges when defining
materials, sources, and interpreting results, that is fine for radiative
transfer of energy.

However I would advice not to make use of the possibility of rendering all
these wavelength ranges at once by making use of the three channels. It
would be better to set all three channels to the same wavelength range, so
work with "neutral grey" lights and surfaces. The reason is that there are
some (few) parts of Radiance's code where the channels are weighted
according to human perceiption assuming RGB-like wavelengths.

Another question is how to find how much of the absorped short-wave solar