

US Energy Secretary: paint roofs white to fight global warming - daviday
http://www.bloomberg.com/apps/news?pid=20601130&sid=asoQnPxZIsaM&refer=environment

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MichaelApproved
This simple solution was suggested long ago. It'll help keep the building
cooler and the roof will last longer. I'm so bored with these dead simple
suggestions and no action.

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mahmud
They also suggested American school kids hide under their desks in case of a
nuclear attack by the USSR!

Some "solutions" are more of a psychological crutch, or placebo, than
anything.

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steveplace
How is this solution a psychological crutch? If there is evidence that
painting roofs white will help cool off cities and reduce your a/c usage by
15%, why not do it?

The analogy you provided is not applicable.

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ars
"If there is evidence that painting roofs white will help cool off cities and
reduce your a/c usage by 15%, why not do it?"

Is there actually evidence for this? In the real world, not just some
calculations? Various people have pointed out flaws such as: it won't stay
white. In the winter it makes things worse, and depending on where you live
the net is no good.

One reason not to do it is that it costs more than it saves.

And in the places where it's really bad, like Tuscon, they put white rocks on
the roof, so I bet that anyplace where it's worth it - it's already being
done!

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steveplace
Well there's a nice video out there from our most favorite cuddly energy
analyst Amory Lovins; he's talking about parking lots but the same premise
holds (I think):

[http://fora.tv/2009/05/01/Amory_B_Lovins_Big_Savings_Through...](http://fora.tv/2009/05/01/Amory_B_Lovins_Big_Savings_Through_Integrative_Design#Amory_Lovins_on_Integrative_Energy_Solutions)

The entire video is fascinating if you've got 2c of coffee in you.

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delano
I'm not an expert on the matter, but my understanding is that rooftop greenery
is a cheaper and more effective way to reduce cooling in the summer and
heating in the winter.

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Gupie
Perhaps however white roofs or roads etc would increase the amount of heat
reflected back into space, as per the shrinking ice caps.

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olefoo
Even if we made every roof and every road a pure titanium white, it wouldn't
make up for more than a fraction of the albedo change caused by the shrinking
of the ice caps.

In the US roads cover less than 3% of the surface and all artificial
structures together cover less than 10% of the surface.

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yummyfajitas
The relevant quantity is not albedo x area. The relevant quantity is energy
reflected = albedo x area x energy deposition.

Energy deposition is low near the poles. That's why they are cold.

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olefoo
Yes, and surface albedo is only one of many factors affecting the global heat
budget.

Dr. Schneider's site is a reasonably good point to start understanding the
complexities of climate change.
<http://stephenschneider.stanford.edu/index.html>

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8plot
Someone correct me if I'm wrong, but isn't there more energy used to heat
buildings than cool them? Of course it depends on many factors, including
location; so a blanket statement of "white roofs everywhere" seems wrong.

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ars
It strongly depends on where you live.

But very little of the heat from the roof gets in the building in the winter.
Mainly because it's insulated. But also because hot air rises, so little of it
travels down to the building space.

But A/C is with vents, AKA air currents, so may be more effective at capturing
heat from ceilings.

But all that ignores the fact that white paint does not survive. In Tuscon the
roofs would have white rocks on the roof. I strongly doubt you could make a
white roof paint that would survive for more than a few years.

How about shiny aluminium roofs?

As a side note, I always wondered why metal roofs are not more popular.
Aluminium would last pretty much forever, and it doesn't have to be one piece
- you can make it into shingles for easy installation.

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dan_the_welder
As far as shiny aluminum goes, it's my experience that it does not remain
shiny for long. A coating that kept it shiny would increase cost as well as
the process of making it mirror finished in the first place. Once the coating
failed there would be no practical way to re-polish and recoat to anywhere
near factory quality and there goes your efficiency.

In Florida a dull aluminum surface will be much hotter than a white painted
one.

Metal roofs are not as popular as they should be because the capitol cost is
more and they are often considered low class. These days there are several
fancy metal roofing systems that are more popular than 5 V crimp and the
classic corrugated. I personally like the classic standing seam style which I
saw a lot of in Maine and New Hampshire and are installed by skilled
craftspeople.

Asphalt shingles are made from the cheap and plentiful byproducts of the oil
refining process and crushed rock. They are made from dirt and installed by
low skilled labor.

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wmblaettler
I've thought about this a while back when a co-worker and I were discussing
the aesthetics of light colored shingles. Dark ones look better was his
opinion, and probably in the opinion of many others.

If one were to develop a process by which titanium-dioxide (or whatever,
white) paint could be applied to the "top" face of the shingles on a sloped
roof (asphalt shingles are covered with small 3-dimensional granules), while
leaving the lower faces dark, you would have the best of both worlds:
Reflectivity from the summer sun which is high in sky and also heat capture
from a sun in the winter when it is low in the sky, plus the aesthetic of a
darker roof when viewed from ground level.

Just another half-baked idea of mine...

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steveplace
Or we could stop using _black shingles_ on houses.

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ars
Keep in mind that the black singles help in the winter. In hot climates I've
seen white rocks on the roof (with tar or a rubber sheet underneath).

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steveplace
Well i've never lived north of the mason dixon, so I didn't consider that end.

What is this "winter" you speak of?

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mildweed
Sounds a lot like duct tape to stave off chemical attacks.

If dramatic change is the agenda, go after cars more aggressively.

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TriinT
How much energy would be spent on the production of white paint? How much
energy would be saved by painting the roofs white? Unless a detailed
quantitative analysis is provided, this is pretty much nonsensical...

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ars
The article suggests up to 15%. Assume 10%, and a $1000 yearly A/C bill,
that's a savings of $100 a year.

Energy spent is pretty much exactly equal to the price of the paint. So how
much does paint cost? How much to install, and how long does it last?

All theoretical questions, since I don't think paint that can survive on a
roof exists.

I'm going to make some wild guesses:

You need 10 gallons of paint at a cost of $40 per gallon. And it takes about 1
day to install, at a cost of 8 hour*40 $/hour.

So total it would be about $720 to install. And I bet it would last 3 to 5
years. Lets be generous and say 5.

So it costs $144 per year, but saves you $100.

Not a good plan. It uses more energy than it saves.

Of course my numbers are totally guesses. Especially the cost for paint that
does not exist.

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yardie
They have paints that are good for 5-10 years. They are white and you'll find
them on the bottom of your local swimming pool. It's exposed to the sun
everyday with the weight of hundreds of gallons of water on top of it. The
paint does exist, but depending on your location you might not be able to find
it. I'm sure you can get it if your along the south coast.

And it doesn't necessarily have to be paint. Tiles are also useful and they
are good for 20 years or more. Almost all new houses I've seen built in
Florida for the last 15 years have been using white tiles for the roof.

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ars
Paint at the bottom of a pool has all the UV filtered out. I don't think it
would survive full UV from the sun. Don't they use tiles at the top of the
pool?

If they do use paint at the top, I bet it has to be repainted every few years.
You said 5-10 for in the water, I bet that out of it it's more like 3-5. And
that's not anywhere near long enough for a roof.

Of course, I don't actually know. But when I looked for UV resistant paint I
didn't really find anything.

