Direct solar radiation

A = area of the enclosure that i.s exposed to the sun. We have assumed about 50% of the surface area falling outdoors which is exposed to direct solar radiation. 

In fact, it is the solar effect that is causing the maximum heat. The factors considered for the solar effect are also highly conservative. Nevertheless, a canopy over the outdoor part is advisable in the above case. This will ensure the same size of enclosure for the outdoor as well as the indoor parts and also eliminate the requirement for a thicker enclosure or a forced cooling arrangement. Now there will be no direct solar radiation over the bus system and the total solar effect can be eliminated, except for substituting the indoor ambient temperature of 48 C with the maximum outdoor temperature for the outdoor part of the bus system. 

Piping or vessels blocked in while filled with liquid at or below ambient temperature, and subsequently heated by direct solar radiation. Cryogenic and refrigeration systems must particularly be examined in this respect. 

Direct solar radiation into the cooled space. 

Solar energy is the most abundant permanent energy resource on Earth and it is available for use in its direct (solar radiation) and indirect (wind, biomass, hydro, ocean, etc.) forms. The total annual solar radiation falling on the Earth is more than... 

The path length L for direct solar radiation traveling through the earth s atmosphere to a fixed point on the earth s surface can be estimated geometrically using Fig. 3.14. This flat earth approximation is accurate for zenith angles < 60°. One can approximate L... 

Length of path of direct solar radiation through the atmosphere... 

One can thus estimate the total light intensity incident on a given volume of air in the troposphere due to direct solar radiation, scattering, and reflection. The light absorbed in that volume can then be calculated... 

Not to be confused with insulation, the word insolation (acronym for incoming solar radiation") defines the rate at which direct solar radiation is incident upon a unit horizontal surface at any point on or above the surface of the earth. The unit of insolation is the Langley, named after Samuel Pierpoint Langley (1834-1906). an American astronomer, physicist and pioneer in the utilization of solar energy ... 

Figure 1. Spectral distribution of direct solar radiation through a clear atmosphere of different air masses.

Figure 2. Spectral distribution of scattered solar radiation compared to extraterrestrial and direct solar radiation.

Figure 7. Fraction of direct solar radiation scattered by molecular constituents of the atmosphere (Rayleigh scattering) as a function of wavelength.

Lemeur, R., A method for simulating the direct solar radiation regime in sunflower, Jerusalem artichoke, com and soybean canopies using actual stand structure data, Agric. Meteorol., 12, 229-247, 1973. 

Meteorologists and hydrologists use the term insolation to describe the intensity of direct solar radiation incident on a horizontal surface per unit area and per unit time, designated with the symbol /. Although we shall emphasize other units, it will be helpful to mention a unit that appears in the meterological literature ... 

Gubareff, G. G., J. E. Janssen, and R. H. Torborg Thermal Radiation Properties Survey, 2d ed., Minneapolis Honeywell Regulator Co., Minneapolis, Minn., 1960. Threlkeld, J. L., and R. C. Jordan Direct Solar Radiation Available on Clear Days, ASHAE Trans., vol. 64, pp. 45-56, 1958. 

Dutton E. and De Luisi J., Spectral extinction of direct solar radiation by the El Chichon cloud during December 1982. Geophys. Res. Lett., 10, 1013-1016 (1983). 

Flowers E.C. and Viebrock H.J., Solar radiation an anomalous decrease of direct solar radiation. Science , 148, 493-494 (1965). 

Flat-plate solar collectors are often tilted up toward the sun in order to intercept a greater amount of direct solar radiation. The tilt angle from the horizontal also affects the rate of heat loss from the collector. Consider a 1.5-m-high and 3-m-wide solar collector th.al is lilted at an angle fioin the horizontal. The back side of the absorber is heavily insulated. The absorber plate and the glass cover, which are spaced 2.5 cm from eachother, are maintained at temperatures of 80°( and 40°C, respectively. Determine llie rale of heat loss from the absorber plate by natural convection for 0 = 0°, 30, and 90. ... 

The solar energy incident on a surface on earth is considered to consist of direct and diffuse parts. The part of solar radiation that reaches the earth s surface without being scattered or absorbed by the atmosphere is called direct solar radiation G. The scattered radiation is assumed to reach the earth s surface uniformly from all directions and is called diffuse solar radiation G. ... 

Part of the solar radiation entering the earth s atmosphere is scattered and absorbed by air and water vapor molecules, dust particles, and water droplets in the clouds, and thus the solar radiation incident on earth s surface is less than tlie solar couslanl. The extent of the attenuation of solar radiation depends on the length of the path of the rays through the atmosphere as well as the composition of the atmosphere (the cloud.s, dust, humidity, and smog) along the path. Most ultraviolet radiation is absorbed by the ozone in the upper atmosphere. At a solar altitude of 41.8°, the total energy of direct solar radiation incident at sea level on a clear day consists of about 3 percent ultraviolet, 38 percent visible, and 59 percent infrared radiation. 

We are now going to calculate the attenuation of direct (directional) solar radiation through scattering and absorption in the atmosphere. The atmosphere is assumed to be cloudless for details on the complicated effect of clouds, [5.34] is suggested. We will consider a bundle of rays that goes through an optically turbid, namely absorbent and scattering medium, Fig. 5.42. The reduction dLx of its spectral... 

Fig. 5.43 Passage of directional solar radiation through the earth s atmosphere...

In the calculation of rA it must be taken into account that several independent scattering and absorption processes act in the attenuation of direct solar radiation. 

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