According to the "Solar Irradiation Modeling" document inside the
GenCumulativeSky package (downloaded from https://documents.epfl.ch/groups/u/ur/urbansimulation/www/GenCumSky/GenCumSky.zip),
the GenCumulativeSky.exe program needs a climate file containing two columns
of data, the first column being either the "global horizontal irradiance" or
"direct horizontal irradiance" and the second column being the "diffused
horizontal irradiance".
In a typical EnergyPlus weather file (.epw file), there's the hourly data on
"global horizontal radiation", "direct normal radiation" and "diffuse
horizontal radiation".
May I ask:* Is the "direct horizontal irradiance" as required by
GenCumulativeSky the same as the "direct normal radiation" as recorded in
the EnergyPlus weather file?*
To my understanding, the "direct normal radiation" means the "amount of
solar radiation in Wh/m2 received within a 5.7° field of view centered on
the sun" (refer to http://rredc.nrel.gov/solar/pubs/tmy2/tab3-2.html).
So, the "effective" direct horizontal irradiance, or the effective solar
radiation falling vertically on a horizontal surface, should be a
cosine-weighted "direct normal radiation" according to the solar elevation
angle at a given time. Therefore, the "direct horizontal irradiance" as
required by GenCumulativeSky does NOT mean the same as the "direct normal
radiation" as recorded in the EnergyPlus weather file.
The relationship is: Direct Normal Irradiance = Diffuse Horizontal
Irradiance / Sin(Sun_Altitude)
Regards,
Jia
···
On Thu, Jul 21, 2011 at 6:41 AM, Ji Zhang <hope.zh@gmail.com> wrote:
Dear Radiance experts,
According to the "Solar Irradiation Modeling" document inside the
GenCumulativeSky package (downloaded from https://documents.epfl.ch/groups/u/ur/urbansimulation/www/GenCumSky/GenCumSky.zip),
the GenCumulativeSky.exe program needs a climate file containing two columns
of data, the first column being either the "global horizontal irradiance" or
"direct horizontal irradiance" and the second column being the "diffused
horizontal irradiance".
In a typical EnergyPlus weather file (.epw file), there's the hourly data
on "global horizontal radiation", "direct normal radiation" and "diffuse
horizontal radiation".
May I ask:* Is the "direct horizontal irradiance" as required by
GenCumulativeSky the same as the "direct normal radiation" as recorded in
the EnergyPlus weather file?*
To my understanding, the "direct normal radiation" means the "amount of
solar radiation in Wh/m2 received within a 5.7° field of view centered on
the sun" (refer to http://rredc.nrel.gov/solar/pubs/tmy2/tab3-2.html).
So, the "effective" direct horizontal irradiance, or the effective solar
radiation falling vertically on a horizontal surface, should be a
cosine-weighted "direct normal radiation" according to the solar elevation
angle at a given time. Therefore, the "direct horizontal irradiance" as
required by GenCumulativeSky does NOT mean the same as the "direct normal
radiation" as recorded in the EnergyPlus weather file.
The relationship is: Direct Normal Irradiance = Diffuse Horizontal
Irradiance / Sin(Sun_Altitude)
Regards,
Jia
On Thu, Jul 21, 2011 at 6:41 AM, Ji Zhang <hope.zh@gmail.com> wrote:
Dear Radiance experts,
According to the "Solar Irradiation Modeling" document inside the
GenCumulativeSky package (downloaded from https://documents.epfl.ch/groups/u/ur/urbansimulation/www/GenCumSky/GenCumSky.zip),
the GenCumulativeSky.exe program needs a climate file containing two columns
of data, the first column being either the "global horizontal irradiance" or
"direct horizontal irradiance" and the second column being the "diffused
horizontal irradiance".
In a typical EnergyPlus weather file (.epw file), there's the hourly data
on "global horizontal radiation", "direct normal radiation" and "diffuse
horizontal radiation".
May I ask:* Is the "direct horizontal irradiance" as required by
GenCumulativeSky the same as the "direct normal radiation" as recorded in
the EnergyPlus weather file?*
To my understanding, the "direct normal radiation" means the "amount of
solar radiation in Wh/m2 received within a 5.7° field of view centered on
the sun" (refer to http://rredc.nrel.gov/solar/pubs/tmy2/tab3-2.html).
So, the "effective" direct horizontal irradiance, or the effective solar
radiation falling vertically on a horizontal surface, should be a
cosine-weighted "direct normal radiation" according to the solar elevation
angle at a given time. Therefore, the "direct horizontal irradiance" as
required by GenCumulativeSky does NOT mean the same as the "direct normal
radiation" as recorded in the EnergyPlus weather file.
The relationship is: Direct Normal Irradiance = Diffuse Horizontal
Irradiance / Sin(Sun_Altitude)
Regards,
Jia
On Thu, Jul 21, 2011 at 6:41 AM, Ji Zhang <hope.zh@gmail.com> wrote:
Dear Radiance experts,
According to the "Solar Irradiation Modeling" document inside the
GenCumulativeSky package (downloaded from https://documents.epfl.ch/groups/u/ur/urbansimulation/www/GenCumSky/GenCumSky.zip),
the GenCumulativeSky.exe program needs a climate file containing two columns
of data, the first column being either the "global horizontal irradiance" or
"direct horizontal irradiance" and the second column being the "diffused
horizontal irradiance".
In a typical EnergyPlus weather file (.epw file), there's the hourly data
on "global horizontal radiation", "direct normal radiation" and "diffuse
horizontal radiation".
May I ask:* Is the "direct horizontal irradiance" as required by
GenCumulativeSky the same as the "direct normal radiation" as recorded in
the EnergyPlus weather file?*
To my understanding, the "direct normal radiation" means the "amount of
solar radiation in Wh/m2 received within a 5.7° field of view centered on
the sun" (refer to http://rredc.nrel.gov/solar/pubs/tmy2/tab3-2.html).
So, the "effective" direct horizontal irradiance, or the effective solar
radiation falling vertically on a horizontal surface, should be a
cosine-weighted "direct normal radiation" according to the solar elevation
angle at a given time. Therefore, the "direct horizontal irradiance" as
required by GenCumulativeSky does NOT mean the same as the "direct normal
radiation" as recorded in the EnergyPlus weather file.
Either
1.GenCumulativeSky requires "direct horizontal irradiance" as input for
calculation, but we can only feed in the "direct normal radiation" as that
is what we can get from EnergyPlus weather file. Then, GenCumulativeSky will
"internally" transform the "direct normal radiation" into "direct horizontal
irradiance" by applying the formula: "Direct Horizontal Irradiance = Direct
Normal Irradiance * Sin(Sun_Altitude)".
Or
2. What is used in GenCumulativeSky's internal calculation is actually
"direct normal irradiance". Then what is stated in the "Solar Irradiation
Modeling" document is not correct.
So, Jia, Can you kindly help to check if the above is correct?
And Dear Darren Robinson, if you can receive this email, can you also kindly
comment?
The relationship is: Direct Normal Irradiance = Diffuse Horizontal
Irradiance / Sin(Sun_Altitude)
Regards,
Jia
On Thu, Jul 21, 2011 at 6:41 AM, Ji Zhang <hope.zh@gmail.com> wrote:
Dear Radiance experts,
According to the "Solar Irradiation Modeling" document inside the
GenCumulativeSky package (downloaded from https://documents.epfl.ch/groups/u/ur/urbansimulation/www/GenCumSky/GenCumSky.zip),
the GenCumulativeSky.exe program needs a climate file containing two columns
of data, the first column being either the "global horizontal irradiance" or
"direct horizontal irradiance" and the second column being the "diffused
horizontal irradiance".
In a typical EnergyPlus weather file (.epw file), there's the hourly
data on "global horizontal radiation", "direct normal radiation" and
"diffuse horizontal radiation".
May I ask:* Is the "direct horizontal irradiance" as required by
GenCumulativeSky the same as the "direct normal radiation" as recorded in
the EnergyPlus weather file?*
To my understanding, the "direct normal radiation" means the "amount of
solar radiation in Wh/m2 received within a 5.7° field of view centered on
the sun" (refer to http://rredc.nrel.gov/solar/pubs/tmy2/tab3-2.html).
So, the "effective" direct horizontal irradiance, or the effective solar
radiation falling vertically on a horizontal surface, should be a
cosine-weighted "direct normal radiation" according to the solar elevation
angle at a given time. Therefore, the "direct horizontal irradiance" as
required by GenCumulativeSky does NOT mean the same as the "direct normal
radiation" as recorded in the EnergyPlus weather file.
I am not familiar with this program. I just skim its code. This program use
Horizontal Irradiance values, Not normal. In its "cPerezSkyModel.cpp" file,
you can see this:
if (m_SolarAlt > 0)
Ibn=Ibh/sin(m_SolarAlt);
It converts "direct horizontal" (lbh) to "direct normal" (lbn) and then use
lbn in other parts in this class.It is better to re-calculate "Direct
horizontal irra" which would be served as an input
Another option is to revise some parts of the code. Change the above code to
the follows and rebuild to get a new .exe file:
if (m_SolarAlt > 0)
Ibn=Ibh;
In your input weather file (txt), the first column is "global horizontal"
and the second column is "direct normal". Then you set -G option in its
command.
I have not tested the second method.
Best,
Jia
···
On Thu, Jul 21, 2011 at 2:42 PM, Ji Zhang <hope.zh@gmail.com> wrote:
Hi, Jia, Thanks for the clarification!
Well, if this is the case, does it mean that:
Either
1.GenCumulativeSky requires "direct horizontal irradiance" as input for
calculation, but we can only feed in the "direct normal radiation" as that
is what we can get from EnergyPlus weather file. Then, GenCumulativeSky will
"internally" transform the "direct normal radiation" into "direct horizontal
irradiance" by applying the formula: "Direct Horizontal Irradiance = Direct
Normal Irradiance * Sin(Sun_Altitude)".
Or
2. What is used in GenCumulativeSky's internal calculation is actually
"direct normal irradiance". Then what is stated in the "Solar Irradiation
Modeling" document is not correct.
So, Jia, Can you kindly help to check if the above is correct?
And Dear Darren Robinson, if you can receive this email, can you also
kindly comment?
The relationship is: Direct Normal Irradiance = Diffuse Horizontal
Irradiance / Sin(Sun_Altitude)
Regards,
Jia
On Thu, Jul 21, 2011 at 6:41 AM, Ji Zhang <hope.zh@gmail.com> wrote:
Dear Radiance experts,
According to the "Solar Irradiation Modeling" document inside the
GenCumulativeSky package (downloaded from https://documents.epfl.ch/groups/u/ur/urbansimulation/www/GenCumSky/GenCumSky.zip),
the GenCumulativeSky.exe program needs a climate file containing two columns
of data, the first column being either the "global horizontal irradiance" or
"direct horizontal irradiance" and the second column being the "diffused
horizontal irradiance".
In a typical EnergyPlus weather file (.epw file), there's the hourly
data on "global horizontal radiation", "direct normal radiation" and
"diffuse horizontal radiation".
May I ask:* Is the "direct horizontal irradiance" as required by
GenCumulativeSky the same as the "direct normal radiation" as recorded in
the EnergyPlus weather file?*
To my understanding, the "direct normal radiation" means the "amount of
solar radiation in Wh/m2 received within a 5.7° field of view centered on
the sun" (refer to http://rredc.nrel.gov/solar/pubs/tmy2/tab3-2.html).
So, the "effective" direct horizontal irradiance, or the effective
solar radiation falling vertically on a horizontal surface, should be a
cosine-weighted "direct normal radiation" according to the solar elevation
angle at a given time. Therefore, the "direct horizontal irradiance" as
required by GenCumulativeSky does NOT mean the same as the "direct normal
radiation" as recorded in the EnergyPlus weather file.