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Title: School students find relief from summer heat under new 'fractal' sunshade
Source:
Mainichi Daily News
URL Source: [None]
Published: Aug 21, 2009
Author: Staff
Post Date: 2009-08-26 22:55:36 by Prefrontal Vortex
Keywords: None
Views: 107
Comments: 2
KYOTO -- Students at a Kyoto area high school have a new place to find shelter from the hot summer sun after their school teamed up with Kyoto University and Sekisui Chemical Co. to build a bower-like shady spot dubbed the "Fractal Sunshade." Kyoto Prefectural Kyotoyawata High School worked with Professor Satoshi Sakai of Kyoto University's Graduate School of Human and Environmental Studies and Sekisui on the sunshade. The shade is made of vinyl chloride sheets cut into triangles, and allows sunlight through triangular spaces to dapple the ground below, hence the "fractal" name. The group experimented with a number of different shapes for the sunshade material, measuring the ground temperature beneath, and discovered that the triangle fractal was most effective on a number of fronts. Not only did the fractal design lower the ground temperature more than a design with no holes, but also reduced radiative cooling during the winter, thereby moderating the cold. "It's cooler than being under a regular roof," said one third-year Kyotoyawata student. "It's got good air circulation and feels great." "If built on a regular rooftop, the internal temperature of the building would drop, too," says Sakai. "It's a cheaper option compared to building a green roof."
School students find relief from summer heat under new 'fractal' sunshade
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#1. To: Prefrontal Vortex (#0)
I wonder why that is. .
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First reason I think: Edge effects. A solid roof will get hotter. The bigger it is, the hotter the central portion will get (asymptotically approaching the limit of an infinite roof.) And it radiates heat to the area under the roof, not light. This roof has a lot more edge length, so it won't get as hot. There is a trade-off between sunlight through the holes and heat radiated from the roof surface. Second reason I think: Better convective cooling. The edge effect could also be gotten with a regular pattern of holes, but it wouldn't be as good. The varying size of the solid portions means the amount that they warm will vary. This provides a preferential, non-uniform pattern for convection and convective cooling. Since the pattern is fractal, I think the convective flow will have a greater tendency towards turbulence, and the convection should become turbulent at a lower temperature. Turbulent flow is better for both cooling and drag.
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Not only did the fractal design lower the ground temperature more than a design with no holes,
#2. To: PSUSA (#1)
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