SOLAR RADIATION Mechanical Engineering（太阳辐射机械工程）.pdfVIP

Chapter 7 Chapter 7 SOLAR RADIATION Solar radiation has important effects on both the heat gain and heat loss of a building. The designer should distinguish between the maximum solar load on a surface which is important for load calculations against an average value that the surface experi- ences. Key issues to be learned: a. Thermal Radiation b. Earth-Sun geometry c. Solar Time, Local Standard Time d. Solar Angles e. Solar Irradiation, Mean Solar Constant • ASHRAE Clear Sky Model f. Heat Gain Through Fenestrations • Solar Heat Gain Coefficients • Simplified Solar Heat Gain Calculations • Shading Coefficient g. Energy Calculations QUESTION Is there any usable solar energy available in Houghton during the month of March? If yes, where is it? ANSWER Yes. Behind the clouds. Very obvious in a clear day! Page 1 Chapter 7 7-1 Thermal Radiation The perfect radiant emitter is also given a name blackbody. For a given temperature T in R (K), a black emitter exhibits a maximum monochromatic emissive power at wavelength lmax, given by 5215.6(2897.6) λmax = microns (7-2) T This equation is known as Wien’s displacement law. For nonblack surfaces, the emittance e, leads to actual energy emitted from a sur- face E = ε Eb (7-3) where 4 E = σT b Table 7-1 Solar Absorptances (See book for more) Surface Absor