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Engineering science fair project:
Which roofing material and color offers the best energy efficiency?




Science Fair Project Information
Title: Which roofing material and color offers the best energy efficiency?
Subject: Engineering
Grade level: Elementary School - Grades 4-6
Academic Level: Ordinary
Project Type: Experimental
Cost: Medium
Awards:
1st place, Canada Wide Virtual Science Fair (2010)
Gold medal at Calgary Science School Science Fair
Silver medal at Calgary Youth Science Fair

Affiliation: Canada Wide Virtual Science Fair (VSF)
Year: 2010
Description: The reflectivity of different materials was tested by using a pyranometer - including wood, rigid foam insulation and white and black roofing samples of rubber, concrete, asphalt, steel and plastic. Thermal efficiency tests were conducted to determine which roofing material / colour combination is most energy efficient by recording the temperature differential - temperature difference between the air inside the test unit and the air outside the test unit - over time.
Link: http://www.virtualsciencefair.org/2010/kitaxk2
Short Background

Cool Roof

In the world of industrial and commercial buildings, a roofing system that can deliver high solar reflectance (the ability to reflect the visible, infrared and ultraviolet wavelengths of the sun, reducing heat transfer to the building) and high thermal emittance (the ability to radiate absorbed, or non-reflected solar energy) is a cool roof. Most cool roofs are white or other light colors.

In tropical Australia, zinc-galvanized (silvery) sheeting (usually corrugated) do not reflect heat as well as the truly "cool" color of white, especially as metallic surfaces fail to emit infrared back to the sky. European fashion trends are now using darker-colored aluminium roofing, to pursue consumer fashions.

Cool roofs enhance roof durability and reduce both building cooling loads and the urban heat island effect.

Also known as albedo, solar reflectance is expressed either as a decimal fraction or a percentage. A value of 0 indicates that the surface absorbs all solar radiation, and a value of 1 represents total reflectivity. Thermal emittance is also expressed either as a decimal fraction between 0 and 1, or a percentage. Another method of evaluating coolness is the solar reflectance index (SRI), which incorporates both solar reflectance and emittance in a single value. SRI quantifies how hot a surface would get relative to standard black and standard white surfaces. It is defined such that a standard black (reflectance 0.05, emittance 0.90) is 0 and a standard white (reflectance 0.80, emittance 0.90) is 100. The use of SRI as a combined measurement of reflectance has been disputed, since it has been shown that two different products with identical SRI numbers can yield significantly different energy savings results depending on what geographic region they are applied in, and the climatic conditions present in this region.

Cool roofs are an effective alternative to bulk attic insulation under roofs in humid tropical and subtropical climates. Bulk insulation can be entirely replaced by roofing systems that both reflect solar radiation and provide emission to the sky. This dual function is crucial, and relies on the performance of cool roof materials in both the visible spectrum (which needs to be reflected) and far infra-red which needs to be emitted.

Cool roof can also be used as a geoengineering technique to tackle global warming based on the principle of solar radiation management, provided that the materials used not only reflect solar energy, but also emit infra-red radiation to cool the planet.

Further, it can reduce the need for air conditioning, which causes CO2 emissions which worsen global warming. For this reason alone it is still demonstrably worth pursuing as a geoengineering technique.

See also: http://en.wikipedia.org/wiki/Cool_roof

Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)

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