Revision history [back]

How do you extract the Global radiation from Eplus? I've been looking into the weatherfiles and the data entries for Global radiation does not seem to correspond with those reported by EnergyPlus under following two outputs:

• Site Diffuse Solar Radiation Rate per Area

Diffuse solar is the amount of solar radiation in W/m2 received from the sky (excluding the solar disk) on a horizontal surface.

• Site Direct Solar Radiation Rate per Area

Site Direct Solar Radiation Rate per Area is amount of solar radiation in W/m2 received within a 5.7° field of view centered on the sun. This is also known as Beam Solar.

I'm aware that you have to adjust the direct solar with respect to solar angle, but even then i do not seem to get the same results. I've been using the following formula for the conversion:

G_global = G_direct*cos(90-SolarAltitude)+G_Diffuse.

Thanks in advance for any assistance.

EDIT: By the way, the specific values i see in the weatherfile and from EnergyPlus output is as follows:

At 12:00, the weather file reads: Global radiation: 103 W/m2 Diffuse radiation: 63 W/m2 Direct radiation: 264 W/m2

Energy plus outputs (also 12:00) read: Solar Altitude: 11.2 degrees Site diffuse: 50.5 W/m2 Site direct: 188 W/m2

How do you extract the Global radiation from Eplus? I've been looking into the weatherfiles and the data entries for Global radiation does not seem to correspond with those reported by EnergyPlus under following two outputs:

• Site Diffuse Solar Radiation Rate per Area

Diffuse solar is the amount of solar radiation in W/m2 received from the sky (excluding the solar disk) on a horizontal surface.

• Site Direct Solar Radiation Rate per Area

Site Direct Solar Radiation Rate per Area is amount of solar radiation in W/m2 received within a 5.7° field of view centered on the sun. This is also known as Beam Solar.

I'm aware that you have to adjust the direct solar with respect to solar angle, but even then i do not seem to get the same results. I've been using the following formula for the conversion:

G_global = G_direct*cos(90-SolarAltitude)+G_Diffuse.

Thanks in advance for any assistance.

EDIT: By the way, the specific values i see in the weatherfile and from EnergyPlus output is as follows:

At 12:00, the weather file reads: Global radiation: 103 W/m2 Diffuse radiation: 63 W/m2 Direct radiation: 264 W/m2

Energy plus outputs (also 12:00) read: Solar Altitude: 11.2 degrees Site diffuse: 50.5 W/m2 Site direct: 188 W/m2

How do you extract the Global radiation from Eplus? I've been looking into the weatherfiles and the data entries for Global radiation does not seem to correspond with those reported by EnergyPlus under following two outputs:

• Site Diffuse Solar Radiation Rate per Area

Diffuse solar is the amount of solar radiation in W/m2 received from the sky (excluding the solar disk) on a horizontal surface.

• Site Direct Solar Radiation Rate per Area

Site Direct Solar Radiation Rate per Area is amount of solar radiation in W/m2 received within a 5.7° field of view centered on the sun. This is also known as Beam Solar.

I'm aware that you have to adjust the direct solar with respect to solar angle, but even then i do not seem to get the same results. I've been using the following formula for the conversion:

G_global = G_direct*cos(90-SolarAltitude)+G_Diffuse.

Thanks in advance for any assistance.

EDIT: By the way, the specific values i see in the weatherfile and from EnergyPlus output is as follows:

At 12:00, the weather file reads: Global radiation: 103 W/m2 Diffuse radiation: 63 W/m2 Direct radiation: 264 W/m2

Energy plus outputs (also 12:00) read: Solar Altitude: 11.2 degrees Site diffuse: 50.5 W/m2 Site direct: 188 W/m2

How do you extract the Global radiation from Eplus? I've been looking into the weatherfiles and the data entries for Global radiation does not seem to correspond with those reported by EnergyPlus under following two outputs:

• Site Diffuse Solar Radiation Rate per Area

Diffuse solar is the amount of solar radiation in W/m2 received from the sky (excluding the solar disk) on a horizontal surface.

• Site Direct Solar Radiation Rate per Area

Site Direct Solar Radiation Rate per Area is amount of solar radiation in W/m2 received within a 5.7° field of view centered on the sun. This is also known as Beam Solar.

I'm aware that you have to adjust the direct solar with respect to solar angle, but even then i do not seem to get the same results. I've been using the following formula for the conversion:

G_global = G_direct*cos(90-SolarAltitude)+G_Diffuse.

Thanks in advance for any assistance.

EDIT: By the way, the specific values i see in the weatherfile and from EnergyPlus output is as follows:

At 12:00, the weather file reads: Global radiation: 103 W/m2 Diffuse radiation: 63 W/m2 Direct radiation: 264 W/m2

Energy plus outputs (also 12:00) read: Solar Altitude: 11.2 degrees Site diffuse: 50.5 W/m2 Site direct: 188 W/m2

EDIT 2: Correct answer.

Archmages comment gave the answer to my question. It reads: The weather file value is interpolated down to work for individual EnergyPlus timesteps. Solar data in the weather file is also shifted a half hour compared to the other weather data, making the interpolation tricky. Values inserted into your equation need to be from, and compared to, outputs at the shortest reporting frequency or the time averaging will introduce errors. I am afraid it is all much more complicated that it appears.

How do you extract the Global radiation from Eplus? I've been looking into the weatherfiles and the data entries for Global radiation does not seem to correspond with those reported by EnergyPlus under following two outputs:

• Site Diffuse Solar Radiation Rate per Area

Diffuse solar is the amount of solar radiation in W/m2 received from the sky (excluding the solar disk) on a horizontal surface.

• Site Direct Solar Radiation Rate per Area

Site Direct Solar Radiation Rate per Area is amount of solar radiation in W/m2 received within a 5.7° field of view centered on the sun. This is also known as Beam Solar.

I'm aware that you have to adjust the direct solar with respect to solar angle, but even then i do not seem to get the same results. I've been using the following formula for the conversion:

G_global = G_direct*cos(90-SolarAltitude)+G_Diffuse.

Thanks in advance for any assistance.

EDIT: By the way, the specific values i see in the weatherfile and from EnergyPlus output is as follows:

At 12:00, the weather file reads: Global radiation: 103 W/m2 Diffuse radiation: 63 W/m2 Direct radiation: 264 W/m2

Energy plus outputs (also 12:00) read: Solar Altitude: 11.2 degrees Site diffuse: 50.5 W/m2 Site direct: 188 W/m2

EDIT 2: Correct answer.

Archmages comment gave the answer to my question. It reads: The weather file value is interpolated down to work for individual EnergyPlus timesteps. Solar data in the weather file is also shifted a half hour compared to the other weather data, making the interpolation tricky. Values inserted into your equation need to be from, and compared to, outputs at the shortest reporting frequency or the time averaging will introduce errors. I am afraid it is all much more complicated that it appears.