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Chapter 12: Problem 105

What does the \(\mathrm{SC}\) (shading coefficient) of a device represent? How do the \(\mathrm{SCs}\) of clear glass and heat-absorbing glass compare?

Short Answer

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Answer: The shading coefficients of clear glass generally range from 0.8 to 1.0, while those of heat-absorbing glass range from 0.3 to 0.7. This difference indicates that heat-absorbing glass is more energy-efficient as it transmits less solar heat compared to clear glass, effectively reducing solar heat gain and promoting a comfortable indoor temperature with less reliance on additional cooling systems.

Step by step solution

01

Definition of Shading Coefficient (SC)

The shading coefficient (SC) is a ratio that represents the ability of a window glazing to transmit solar heat compared to a reference 1/8-inch clear, double-strength glass. It is an important parameter used to evaluate and describe the energy efficiency of glass. A lower SC means that a glass transmits less heat than the reference glass and is therefore more energy efficient.
02

Shading Coefficient Values for Clear Glass and Heat-Absorbing Glass

The SC of clear glass depends on its thickness, but it generally ranges from 0.8 to 1.0. Heat-absorbing glass, on the other hand, contains materials that absorb a higher proportion of the incoming solar heat, thus having a lower SC value, ranging from 0.3 to 0.7.
03

Comparison between Clear Glass and Heat-Absorbing Glass

Comparing the shading coefficients of clear glass and heat-absorbing glass, we can conclude that heat-absorbing glass is more effective in reducing solar heat gain as it transmits less solar heat compared to clear glass. The lower SC values of the heat-absorbing glass indicate a better energy efficiency, meaning that it is more capable of maintaining a comfortable indoor temperature and reducing the need for additional cooling systems in buildings.

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Most popular questions from this chapter

A 5-in-diameter spherical ball is known to emit radiation at a rate of \(550 \mathrm{Btu} / \mathrm{h}\) when its surface temperature is \(950 \mathrm{R}\). Determine the average emissivity of the ball at this temperature.

The wavelength at which the blackbody emissive power reaches its maximum value at \(300 \mathrm{~K}\) is (a) \(5.1 \mathrm{\mu m}\) (b) \(9.7 \mu \mathrm{m}\) (c) \(15.5 \mu \mathrm{m}\) (d) \(38.0 \mu \mathrm{m}\) (e) \(73.1 \mu \mathrm{m}\)

Why did we define the blackbody radiation function? What does it represent? For what is it used?

Consider an opaque horizontal plate that is well insulated on the edges and the lower surface. The plate is uniformly irradiated from above while air at \(T_{\infty}=300 \mathrm{~K}\) flows over the surface providing a uniform convection heat transfer coefficient of \(40 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\). Under steady state conditions the surface has a radiosity of \(4000 \mathrm{~W} / \mathrm{m}^{2}\), and the plate temperature is maintained uniformly at \(350 \mathrm{~K}\). If the total absorptivity of the plate is \(0.40\), determine \((a)\) the irradiation on the plate, \((b)\) the total reflectivity of the plate, \((c)\) the emissive power of the plate, and \((d)\) the total emissivity of the plate.

Consider a black spherical ball, with a diameter of \(25 \mathrm{~cm}\), is being suspended in air. Determine the surface temperature of the ball that should be maintained in order to heat \(10 \mathrm{~kg}\) of air from 20 to \(30^{\circ} \mathrm{C}\) in the duration of 5 minutes.
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