Black bodies absorb radiation and white surfaces reflect radiation. This is based on the theory of emissivity in Physics.
White painted surface do not absorb heat energy and light energy and reflect them away from their surface. This physical property can be effectively deployed to keep homes cool.
The top surface of the roof of the house is either finished with a coat of white paint or covered with white plastic sheet to serve as a white body reflector. During summer the heat generated by the sun light incident on these white surfaced roof do not retain or absorb the heat due to its reflective property. Thus the internal surface of the house is protected form the hot summer heat and kept cool.
As a consequence the air conditioning charges can be minimized and there is a saving of energy to the tune of minimum 10%. This also helps reduce green house emission and to keep the environment better.
Everybody is aware with the fact that darker materials absorb more heat from sun than white/light colors, but an interesting data I want to share that black surface in the sun can be 40°C (70°F) hotter than the reflective white surface. This phenomenon occurs in the case of roofs also and heated roof then transfer their heat to surrounded air and contribute to heat island effect, while reflective metallic/ ceramic roof can reflect 65-75 %solar light. According to California energy commissioner “White roofs can cut a building’s energy use by 20% and save consumers money,” and “The potential energy savings in the U.S. is in excess of $1 billion annually.”
ReplyDeletehttp://buildinggreenlife.wordpress.com/2009/08/17/magic-of-white-roofs/
That is a very interesting statistics. This also minimizes global warming! Thanks a lot for your comments!
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