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 Print (unpublished).