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Roof Radiation Kira Bartlett, Ashleigh Hough, Jeannie Ossorio
BE 4120
Purpose
Investigate the heat transfer due to solar radiation through commonly used roofing materials
Why this Project Topic?There is plenty of research and advertising for the “green” vegetative roofing and “cool” light painted roofing because of their effects on energy efficiency. We wanted to see the effects of regular roofing materials have efficiency.
http://ngm.nationalgeographic.com/2009/05/green-roofs/klinkenborg-text http://www.jagarchitect.com/leed.html
The Set Up ● Hobo Data Loggers
o Temperatureo Ambient Airo Solar Radiation
● Types of Roofingo Cedar o Clay o Asphalt o White Tino Tan Tin
Environment● Mix of Sun and Clouds● 73 ⁰F (22.78 ⁰C)● Time: 1:40 pm - 5:45
pm
MATERIAL ANALYSIS Determining the surface absorptivity (αs) of each material
HOBOs: Surface Temperatures Radiation Flux
DimensionsUsing assumed values for thermal
conductivity (k)
Fourier’s Law:
Solar Irradiation:
ANALYTICAL ANALYSIS PROCESS (Asphalt)
Fourier’s Law:
Solar Irradiation:
ANALYSIS OF ASPHALT SHINGLES
Assumed K Value: 0.11 W/mK
Thickness: 0.002 m
q” = 729.85 W/m2K
αS = 0.912
ANALYSIS OF CEDAR SHINGLESAssumed K Value:
0.12 W/mKThickness:
0.0045 m
q” = 9.687 W/m2K
αS = 0.012
ANALYSIS OF CLAY ROOFING TILES
Assumed K Value: 0.163 W/mK
Thickness: 0.01 m
q” = 356.7 W/m2K
αS = 0.45
OVERALL TEMPERATURE COMPARISON
COMSOL ANALYSIS PROCESSModeled as flat plates using assumed thermal conductivity (k) values
Modeled using steady state conditions (3-4:30 PM)
Boundary ConditionsBS1: Calculated Heat FluxBS2: Constant Temperature
right side → temperature of bottom surface
Compared temperature of the exposed side (left) to temperature from HOBO
COMSOL ANALYSIS
ASHALT SHINGLES CLAY TILES CEDAR SHINGLES
TS1 = 304.952 KTS2 = 318.211 K
TS1 = 304.944 KTS2 = 310.606 K
TS1 = 304.947 KTS2 = 305.31 K
Real Time vs. COMSOL
Conclusion ● Tin shingles reflect heat from the sun and they utilize
the dead-air space between the metal ridge and roof deck to minimize some of the heat generated through conduction.
References Vandervort, Don. "Pros & Cons of Metal Roofing." HomeTips.com. HomeTips, 2015. Web. 25 Apr. 2015.
"Thermo-Physical Properties of Construction Materials | CBERD." CBERD. 2011. Web. 25 Apr. 2015.
Drapcho, Caye. “Appendix A” Handout. Heat and Mass Transport in BE. (Dr. Caye Drapcho). Clemson University. Spring 2015. Print (unpublished).
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