Radiant Fluxes

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Radiant Fluxes
Sd - Solar Diffuse
Sb - Solar Beam
La Sky Thermal
Loe Emitted Outgoing Thermal
Sr - Solar Reflected
Lg Ground Thermal
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Calculating Zenith Angle

• What is the zenith angle?
• Angle of sun with respect to a horizontal plane
  on the earths surface
• Other angles Elevation angle (90 zenith)
• Azimuth angle sun direction with respect to
  cardinal directions
• Calculating zenith angle
• Parameters
• Longitude
• Standard time
• Calendar day
• Solar Declination Position of the sun with
  respect to the equator

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Calculating Zenith Angle

• - Zenith angle
• f - latitude
• d - solar declination

J Julian Day of year
Sp
Zenith angle Y
LC Longitudinal Correction ET Equation of time
Surface
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Calculating Longitudinal Correction and Equation
of Time
Longitudinal Correction 1/15 for each degree
east of std Meridian, -1/15 for each degree
west of std meridian Std. Meridian 0, 15,
30,,345 Example What is LC for Pullman
with 117.2 Longitude? Std. Meridian 120 .
Thus, 117.2 is east of 120 by 2.8 so LC
2.8(1/15)0.19 hours
ET (Equation of Time) Calculation Where f
279.575 0.9856 J J Calendar day of year
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Spo Extraterrestrial Radiation (1360 W m-2) Sp
Direct Irradiance on a perpendicular surface Sb
Beam Radiation (Horizontal Surface) Sd
Diffuse Radiation St Total Radiation (direct
diffuse)
Spo
q
EARTH
m optical air mass
Sb
Sp
Sd
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Sources of Radiation Inputs and Outputs
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Solar Irradiance with Zenith Angle
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Solar Radiation under Cloudy Conditions
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Finding Longwave Emissivities and Shortwave
Adsorptivities
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Example Calculation
Calculate all the inputs and outputs of radiation
above a grass surface during the night, on a
clear day at 1030 am on June 19 in Pullman (Lat
46.77 and Lon 117.2), and on a cloudy day.
Assume ground and sky temperatures are both 10 C
at night and 20 C and during the day, and the
object surface temperature is 27 C.
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Analysis of View Factors
Object A
Object B
FA-B 1 FB-A AreaB/AreaA
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Calculating View Factors
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Analysis of View Factor for Objects
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Putting it all together!!

• The radiation energy balance
• The absorbed radiation
• Question Why does the equation use Sp not Sb?