DOE Buildings to Get Cool Roofs that Reflect Heat Back into Space

Forums: Environment, Energy, White Roofs, Cool Roofs
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http://solveclimatenews.com/news/20100721/doe-buildings-get-cool-roofs-reflect-heat-back-space?page=show

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The idea that white roofs can both reduce the average temperature of cities and reduce the amount of energy required for cooling buildings received both scientific verification and practical application yesterday.

A report from Lawrence Berkeley National Labs said that if the world’s 100 largest and hottest cities converted to white roofs and lighter colored pavement, they would achieve a one-time offset of 57 gigatons of carbon emissions. That's equivalent to taking all the autos of the world off the road for 11 years, according to Energy Secretary Chu.

Read more at the link.

I have two questions about this:

1. Won't all that reflected heat that is bounced back into space increase the warming of earth's atmosphere, especially on cloudy days?

2. Won't the reflective benefits of all those white roofs and pavement be neutralized by the eventual build up of dust, soot, pigeon poop, and air pollution that will turn the roof and pavement a muddy gray color?

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@Butrflynet,

I don't know the answers to your questions, but I've heard of people changing roofs to white, by whatever means, for energy saving for what seems like at least a decade or two or three - there is probably some data out there.

Ain't pigeon poop white?

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@ossobuco,

ossobuco wrote:

Ain't pigeon poop white?

If I hadn't changed my sig line yesterday this would be my new one.
My architect/business partner Bill will be in tomorrow. I'll ask him about this.

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@Butrflynet,

I wondered this a long time ago, like 20+ years ago, whether making all streets white instead of black would have a positive effect on global warming. I pursued this to some level and was told (I can't remember if I lived in Minnesota or Wisconsin at the time) that part of why roads are black is to help with snowmelt, and that it would be considerably more dangerous/ expensive if they were lighter colored.

Still seems like it could be done in areas without snow, though.

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@ossobuco,

ossobuco wrote:

Ain't pigeon poop white?

I think it depends on what they eat.

http://t3.gstatic.com/images?q=tbn:Y6FLmLKtzrlVLM:http://www.allstarcleaning.us/images/bird_pic/1/PigeonInPoop.jpg&t=1

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@sozobe,

sozobe wrote:

...that part of why roads are black is to help with snowmelt, and that it would be considerably more dangerous/ expensive if they were lighter colored.

Still seems like it could be done in areas without snow, though.

A lot of highways in California have what looks like a light gray cement finish to them rather than the dark asphalt. I remember a lot of eye strain from the sun's reflection and water mirages when driving on those roads. The heat waves rising up off the surface in the distance looked like water flooding the road.

Found a good explanation and photo that shows what I mean. I guess it happens on asphalt surfaces too.

http://4.bp.blogspot.com/_L_GZ4wQqOPw/TDIiaJ3fWaI/AAAAAAAAA3o/2jPq1wgqfHU/s1600/Highway+Mirage+EPOD.usra.edu.jpg

The photo above is from NASA's Earth Science Picture of the Day website, which offers this explanation:

"The effect is caused by a thin layer of hot air just above the ground. The difference in refractive index between the hot air at the road surface and the denser, cooler air above it causes the boundary to act like a mirror: distant objects are reflected...The 'water' is actually a reflection of the blue sky, but a close look at this image also shows reflections of a car, power poles, bushes, a mile marker, and roadside grass. Because the reflection occurs solely at very shallow angles, the mirage appears only in the distance and continually recedes as one moves towards it."

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And concrete (cement is a component of concrete) is routinely white-ish when first poured, and then weathers - at least in my experience. I used to cringe when we would try to replace concrete for safety reasons around old properties with both exposed aggregate and a nice dark color.
The easy answer is to color the concrete, but then that weathers too.
Patience is a virtue..

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@Butrflynet,

Butrflynet wrote:

http://solveclimatenews.com/news/20100721/doe-buildings-get-cool-roofs-reflect-heat-back-space?page=show

Quote:

1. Won't all that reflected heat that is bounced back into space increase the warming of earth's atmosphere, especially on cloudy days?

I'm sure that effect is going to be negligible. Nobody has yet accused the polar snow packs of contributing to global warming. In fact, even minor soot coatings are supposed to add to the general warming.

In winter, sure, there will be increased cooling, but in a global sense that would be more good than bad. I would base the decision on the relative economics of heating in winter vs cooling in summer

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DOE Buildings to Get Cool Roofs that Reflect Heat Back into Space

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