Sunday, December 5, 2010

Shingle Geometry Reflects Heat in Summer, but Absorbs Heat in Winter

Cool roofs are an efficient design practice to reflect summer sun and conserve air conditioning energy.  That same reflectivity, however, drives away valuable heat energy in the winter.

The angle of incident Sun rays changes throughout the day from East to West with the azimuth of the Sun. More to the point for this idea, however, the altitude/zenith of the Sun rays changes angles between seasons.  One could take advantage of this seasonal variability by constructing a specially angled roof shingle or panel to preferentially cool or heat when needed the most.  (See here to find the Sun's altitude on different dates.) 

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In the summer, the sun has a higher elevation in the sky, and you would face a light-colored, highly reflective surface perpendicular to the rays to ward off heat.  In the winter, the sun has a lower elevation. A different portion of the same roof panel would present a dark-colored, highly absorptive surface to the incident rays to capture heat.

Each installation would require shingles with orientation labels (e.g. "Face this edge South") and a calibration process to optimize for roof pitch and geographic latitude.

CATEGORY: Energy, Construction
IDEATION: November 2010

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