Thursday, July 30, 2009
White roofs and other easy answers
The New York Times has a story on its front page this morning touting the nascent effort to build roofs with lighter or even reflective material, both to save energy and to increase the reflectivity of the planet's surface, especially in urban "heat islands." This issue has been a hobby horse of mine for years, in no small measure because I believe it to be a low-cost and reversable means of conservation; whether your motivation is to mitigate global warming or to save Adirondack fish or to defund the Wahabbis or simply to avoid waste, gradualist steps like this are good policy (and certainly ought to be tried before "cap and tax").
That said, it disappointed me that the story did not address the problem of local building codes and restrictive covenants for aesthetic purposes, both of which would block the use of new roof technology in communities all over the country. Much as the idea offends my love of freedom of contract, it is hard to see how we will get "cool" roofs in many places without a federal law that preempts regulations or contract provisions insofar as they prevent the installation of energy-efficient materials.
10 Comments:
By 
JPMcT, at
Thu Jul 30, 10:08:00 AM:
This idea has been bashed around for a long time. I suppose it's a good idea if you live in Arizona and want to reduce your air conditioning bill...but as a mechanism to effect climate change it's ineffective.
It shares that characteristic with the "Cap and Fraud" bill.
By the way...has anyone actually looked at the massive...lord, GLOBAL fraud that this legislation is espousing?
Bernie Madoff must be sitting in his jail cell with a misture of AWE and CHAGRIN at what the Democrat Congress is trying to do to the country with Cap & Trade.
By 
, at
Thu Jul 30, 10:44:00 AM:
Can someone explain to me how, when black attracts heat and white REPELS it, it would be a good idea to reflect the heat back up into the atmosphere?
By , at
Thu Jul 30, 10:49:00 AM:
There is certainly no reason why flat industrial roofs on new construction could not be white. However, the Building Code is going to have to get a lot thicker. On my last project one of the subcontractors was worried that contrasting color traffic pads designed to protect the roof from wear could cost us Leadership in Energy Efficient Design points because they were not "white". Small changes like that often lead to a reworking of the energy calculations.
By , at
Thu Jul 30, 10:54:00 AM:
Anon-
White radiates heat back out into space, thus cooling the planet.
I remember in the 70's when global cooling was all the rage there was a plan to spread coal dust on the Arctic sea ice to melt it an save the planet.
By , at
Thu Jul 30, 11:22:00 AM:
Anon at 10:40: The point is that a black roof absorbs heat and, thus heats the building. That means more air conditioning (and thus, more energy) to cool it. White reflects it away from the building.
By Mystery Meat, at
Thu Jul 30, 12:02:00 PM:
I can't recall the source, but a couple of months ago, I read that someone with a lot of time on his hands had estimated the total surface area of the United States that was covered by roofs and roads. The estimate was, as I recall, 1.2%. Incrementalism and gradualism is fine, and I have no objection to it either, but don't expect any significant reduction in temperatures.
By , at
Thu Jul 30, 12:06:00 PM:
TH, You strike me as a microcosm of what is wrong with Congress. You espouse freedom and liberty until your pet cause comes along, and THAT should be made mandatory. Congress is the same way, they all claim to be for freedom until their pet causes come along and then those are passed into law. After awhile, with 535(?) individuals pushing pet causes on an annual basis, there isn't much freedom left for those of us that only want Government to maintain domestic order and defend us from foreigners.
By , at
Fri Jul 31, 11:42:00 AM:
OK, I accept that it reflects back, but won't the atmosphere trap said reflected heat? How does it get past that to return to space?
And as to the effect on the building, I thought we were discussing how to minimize AGW, not control building temps......
By , at
Fri Jul 31, 02:32:00 PM:
Anonymous at 11:42 - Heat is not like CO2. So even though the heat is reflected back up, it will not remain to heat the overall atmosphere, since heat is not stable. CO2, on the other hand, stays in the atmosphere and heats it for a long, long time.
So if we paint roofs white and reduce the amount of energy needed to cool the building, that reduces the CO2 created when we make the energy to power the air conditioners.
By , at
Sat Aug 01, 11:41:00 AM:
The white roof reflects radiation (light) not heat per se. A dark roof absorbs light, heating it up, and raising the temperature of the space below it. The atmosphere doesn't trap reflected heat, but it does absorb some of the reflected light.
A roof will loose heat by radiation. It does so because of the temperature difference between the roof and deep space. The color doesn't really matter all that much. Although just because a color is reflective in the visible spectrum, doesn't mean it's equally reflective (and emissive) in the infrared.
The effect is greater at night because of the atmospheric conditions then. It is greater under a clear sky than overcast. This is why frost is most likely to form on clear night.
Enough thermodynamics for a Saturday morning!
