Modeling the Heat Gain of a Window With an Interior Shade ... - inive

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Proceedings of Clima 2007 WellBeing Indoors 750 230 Q gaintot [W/m 2 ] 700 650 600 550 500 SI IP 220 210 200 190 180 170 160 Q gaintotIP [Btu/hr-ft 2 ] 450 150 0.2 0.3 0.4 0.5 0.6 0.7 0.8 τ gn Figure 11. Solar heat gain versus glass transmissivity, reflectivity of 0.11, shade transmissivity of 0.53. 60 Glass Shade 50 40 Temperature, C 30 20 10 0 Heat absorbing glass Clear 1/8 th Figure 8. Temperature of glass/shade systems. Finally, figure 11 shows the impact of the variation of transmissivity of the glass from 0.23 to 0.80, keeping the reflectivity of the glass at 0.11 and the shade tranmissivity at 0.53. The relationship is linear. CONCLUSIONS Modeling results lead to the following conclusions: For the baseline glass/shade system studied here, the temperature of the glass and shade vary with shade transmisivity, the glass varying from 51.4 to 55.5 C (124.6 to 131.8 F) and the shade changing from 34.4 to 37.6 C (95.8-99 F). Again for the baseline glass/shade system, the heat gain through the south façade varies almost linearly with shade transmisivity, ranging from about 416 W/m 2 (132 Btu/hr-ft 2 ) to about 521 W/m 2 (165 Btu/hr-ft 2 ) as the transmissivity varies from 0.1 to 0.85.
Proceedings of Clima 2007 WellBeing Indoors The transmissivity of glass and a shading device do not, by them selves, define the solar heat gain into the room. The reflectance of the glass is equally important. Long wave radiant exchange and convection from the glass and shade to the room are significant components of heat gain. For the hot winter condition studied, the solar heat gain is predicted to be 480 W/m 2 (152 Btu/hr-ft 2 ). The contribution of this heat gain to the cooling load should be calculated using the load calculation methods described in the ASHRAE Handbook of Fundamentals, 2001. FURTHER WORK ASHRAE is currently sponsoring work to develop more complete models and verify them experimentally. REFERENCES ASHRAE Handbook of Fundamentals, SI Edition, pg 22.1, 1993. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. Atlanta GA ASHRAE Handbook of Fundamentals,2005, American Society of Heating, Refrigerating and Air- Conditioning Engineers, Inc. Atlanta GA Brandemuehl, M. J., and W. A. Beckman, Solar Energy, 24, 511 ,1980, “Transmission of Diffuse Radiation Through CPC and Flat-Plate Collector Glazings.” Duffie, J., W.Beckman, “SOLAR ENGINEERING OF THERMAL PROCESSES”, 2 nd ed, 1991, Wiley, NY. Duncan, C. H., et. Al., Solar Energy, 28, 385 (1982). “ Latest Rocket Measurements of the Solar Constant.” Engineering Equation Solver, f-chart Software, Madison Wisconsin, 2005. See http://www.fchart.com/ees/ees.shtml. Fisher, Daniel, and Curtis Pedersen, Advisor “An Experimental Investigation of Mixed Convection Heat Transfer in a Rectangular Enclosure,” Ph.D. Thesis, University of Illinois 1995. See also references by Spitler, Fisher and Pedersen in same. Hickey, J.R., et. Al., Solar Energy, 28, 443 (1982). “Extraterrestrial Solar Irradiance Variability: Two and One-Half Years of Measurements from Nimbus 7.” Hottel, H.C., Solar Energy, 18, 129, (1976). “A Simple Model for Estimating the Transmittance of Direct Solar Radiation Through Clear Atmospheres.” Liu, B. Y. H. and R. C. Jordan, Solar Energy, 4(3), 1 (1960). “The Interrelationship and Characteristic Distribution of Direct, Diffuse and Total Solar Radiation.” Reindl, D. T., W. A. Beckman, and J. A. Duffie, Solar Energy, 45, 1 (1990). “Diffuse Fraction Correlations.” McCluney, R., and L. Mills, ASHRAE Transactions, 99 pt2 , “Effect of Interior Shade on Window Solar Gain.” Thekaedara, M.P, and A. J. Drummond, National Physical Science, 229, 6 (1971). “Standard Values for the Solar Constant and Its Spectral Components.” Thekaedara, M.P, Solar Energy, 18, 309 (1976). “Solar Radiation Measurement: Techniques and Instrumentation.” Willson, R. C., et. Al., Science, 211, 700 (1981). “Observations of Solar Irradiance Variability.”
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