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#1
benbakelaar

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Read this in an NYTimes article:
I?m intrigued by what a friend, an architect, told me: That if just one teensy change were made to New York City ? if all black roofs were painted white or silver, a simple, surprisingly inexpensive fix ? the financial and energy savings would be jaw-dropping, not to mention that it would severely reduce the possibility of blackouts and brownouts. Relatively meager effort, monster bang for the buck.

http://www.nytimes.c...0...00&emc=eta1

My question is, for all you hobbyist meteorologists out there, why is this true? Simple reflection? What would then happen to all that refracted/reflected heat not being absorbed on/near the ground? And if so, why don't we make all our impermeable surfaces - ie roads - white/grey concrete instead of black? Why is "blacktop" so much cheaper than other options?

#2
Hans van der Maarel

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I'm not a meteorologist, but:

- Black surfaces absorb heat. Bad in summer, *good* in winter.
- Reflected heat warms up the atmosphere. Bad idea imho

What exactly are they planning to fix this way? Energy consumtion from airconditioning?

I have a better plan: put grass on the roof. Just plain, simple lawn grass. The layer of soil + the biomass will help insulate the roof (which I think is a much better way of saving energy than any color of paint) and it will produce oxygen. Not on a massive scale, but every little bit helps.

Just my 2 cents. I haven't researched the grass alternative, but it's being used in "eco-friendly" housing here in Holland.
Hans van der Maarel - Cartotalk Editor
Red Geographics
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#3
benbakelaar

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What exactly are they planning to fix this way? Energy consumtion from airconditioning?


The article is basically about global warming, and how the author of the article is very lazy, but even he found ways to quickly and easily reduce the "carbon output" of his house by 1000s of tons per year. And then he throws out this paragraph I posted at the very end. He mentions that the creator of the idea says it would solve blackout/brownouts and the resulting energy savings would be astonishing.

#4
Hans van der Maarel

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The article is basically about global warming, and how the author of the article is very lazy, but even he found ways to quickly and easily reduce the "carbon output" of his house by 1000s of tons per year. And then he throws out this paragraph I posted at the very end. He mentions that the creator of the idea says it would solve blackout/brownouts and the resulting energy savings would be astonishing.


The rest of the article is pretty sound, but I'm simply not buying that "paint the roof black" idea... Like I said, there's gotta be more to it... <_<
Hans van der Maarel - Cartotalk Editor
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#5
danielle

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Greenroofs have been getting some attention in NYC. For example, see http://www.earthpledge.org/WhyGR.html. Not only do they help regulate temperature, but they reduce stormwater runoff. This is a big deal in an old city with a combined sewer system.

The New Yorker had an interesting article on the environmental benefits of high-density cities. "Green Manhattan" is available online here: http://www.greenbelt...enManhattan.pdf.

-Danielle

#6
MapMedia

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This is about energy issues in NYC, but also related to global warming.

Reducing heat gain by a fraction would be a huge, cumulative energy saver for NYC. White, reflective roofs makes mechanical sense - would like to see a pilot project. NYC is home to millions of busy people, so IMHO grass on their roofs is not going to work, except for a few Greenies (count me in) here and there. People may have more open attitudes in Holland, plus any additional 'work' involved in maintaining said grass roof would be considered by NYCers a 'pain in the ***'. Imagine implemnenting this throughout Queens? Wait until the insurance companies get involved too.

I am sure that if the math really holds water, NYC would give it a go - even Mayor Bloomberg might get behind it. Oh course though, its gotta be a real solution.

#7
Hans van der Maarel

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People may have more open attitudes in Holland


On average, we seem to be more eco-aware than the average US citizen. However, we're definately aware of the fact we'll be amoung the first to get wet feet when this whole global warming thing takes off... 50% of the nation below sea level...
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#8
MapMedia

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Thanks for adding the missing context, Hans! Likewise, it may be NYC's brown-outs and energy costs that propell white roofs, or, who knows - anything's possible - if that doesn't work, then maybe they will one-day emrace grass roofs.

#9
Dennis McClendon

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Sunlight does not create heat until it is absorbed by a surface. Reflective roofs prevent much of that heat from being created. Green roofs turn some of the sun's energy into biomass, and additionally cool themselves through evaporation (requiring water inputs of some kind).

Chicago's mayor is pushing green roofs very hard, even when other approaches would make more sense. Every developer now puts a dog run or "Chia Pet" section on the roof and claims the green roof zoning bonus. We have absurdities like a big-box home improvement store putting in a half-acre green roof while paving four acres of asphalt parking out front.
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#10
benbakelaar

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Sunlight does not create heat until it is absorbed by a surface. Reflective roofs prevent much of that heat from being created.


Interesting... so, if that sunlight is reflected in the general direction of "up" (not getting into angles here), when would it be converted into heat? When it re-interacts with moisture in the atmosphere? Does the sunlight lose any energy after reflection?

#11
Dennis McClendon

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if that sunlight is reflected in the general direction of "up" (not getting into angles here), when would it be converted into heat? When it re-interacts with moisture in the atmosphere? Does the sunlight lose any energy after reflection?


Some is converted into heat by atmospheric moisture. Some is reflected back into space as earthlight. Energy can neither be created nor destroyed, only converted into another form, such as heat. On the initial trip through the upper atmosphere, some sunlight (particularly UV wavelengths) goes to break the ozone molecules in the upper atmosphere into oxygen molecules.
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#12
Rick Dey

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Greenroofs have been getting some attention in NYC. For example, see http://www.earthpledge.org/WhyGR.html. Not only do they help regulate temperature, but they reduce stormwater runoff. This is a big deal in an old city with a combined sewer system.


Knowing the way our lovely American thought process goes probably a large number of these greenroofs would end up being sprayed with chemicals to kill the bugs and fertilize them to keep them green. The resulting runoff would end up being even more toxic than the standard hard roof runoff.
Rick Dey

#13
Derek Tonn

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I'm not a meteorologist, but:

- Black surfaces absorb heat. Bad in summer, *good* in winter.
- Reflected heat warms up the atmosphere. Bad idea imho

What exactly are they planning to fix this way? Energy consumtion from airconditioning?

I have a better plan: put grass on the roof. Just plain, simple lawn grass. The layer of soil + the biomass will help insulate the roof (which I think is a much better way of saving energy than any color of paint) and it will produce oxygen. Not on a massive scale, but every little bit helps.

Just my 2 cents. I haven't researched the grass alternative, but it's being used in "eco-friendly" housing here in Holland.


Hans,

It is actually true. Dark colored materials absorb heat on a much greater basis than light colored materials, which do not absorb as much heat. What I've even wondered about is how much more/less expensive it might be to right a big white canvas to "shade" portions of my home in the summertime so that the sun doesn't even reach the green shingles and red brick....cutting our need for cooling our home to almost nothing. A brick home stays surprisingly cool in the summer....EXCEPT on the south side of the home that is exposed to the sun a majority of the day. That side of the house is like a sauna, hence my "canvas" idea. Oh yes, and at least for those of us in the "snow belt", having a white roof in the winter is a non-issue, since most of our roofs here in Minnesota are "white" all winter anyway (covered with snow). :lol:

Here's another small energy saving idea I've had: lamp shades with the interior lined in reflective materials....increasing the output of light cast into the surrounding area by quite a bit (lower watts needed for comparable light output)..........
Derek Tonn
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mapformation, LLC

datonn@mapformation.com
http://www.mapformation.com




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