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Paint it White: One Way to Chill the Electric Bill
Could something as simple as white roofs actually make a dent in our carbon emissions and help curb global warming?
Physicist Steven Chu, our Nobel Prize-winning Secretary of Energy, thinks so. At the St. James's Palace Nobel Laureate Symposium in London last month, he pushed for a global initiative to lighten the color of roofs, roads and pavements to cut carbon emissions by the equivalent of taking all cars off the road for 11 years.
As residents of hot countries have known for centuries, buildings painted white stay cooler because they reflect the sun’s heat. Light colored materials reflect more solar radiation, including visible, ultraviolet and infrared light (which accounts for most of the heat), than dark materials which absorb heat. Albedo, the gauge of solar reflectivity, is calculated from 0.0 to 1.0, with 1.0 being the highest measure of reflectivity.
Maximizing the number of high albedo surfaces around the world could significantly help cool the planet, said Chu, former director of the Lawrence Berkeley National Laboratory (LBNL).
Chu's ideas have been shaped by the work of Dr. Arthur Rosenfeld (formerly at LBNL, now on the California Energy Commission), and fellow LBNL scientists Hashem Akbari and Surabi Menon. In 1985, they began studying how light colored roofs and pavement could mitigate the urban heat island effect – when urban areas are 2˚F to 8˚F warmer than surrounding areas due to the heat absorbed by pavement and buildings.
In 2004, they realized that their research might also help curb climate change.
"When we did the calculations, initially we couldn't believe the results," Akbari said.
They figured that changing 100 square feet of dark roof area to white would have an effect equivalent to offsetting the emission of one ton of CO2. On a global scale, increasing the albedos of urban roofs and paved surfaces would be equivalent to offsetting about 44 billion tons of CO2 emissions.
White roofs and cool roofs, those made from other high albedo materials, result in less carbon emissions because they reflect the sun, and reduce the need for air conditioning and thus the energy from CO2 emitting power plants.
Cool roofs also curtail the heat island effect and its accompanying smog, make buildings more comfortable, ease stress on the energy grid, help buildings comply with energy efficiency codes, and extend the life of roofs because lower temperatures make for less wear and tear.
White roofs, however, are difficult to keep clean and may lose up to 1/3 of their reflectivity within a few years, so resistance to dirt accumulation is important for roof coatings. And some critics have questioned whether white roofs increase winter heating costs in cooler climates. But Michelle van Tijen from the Cool Roof Rating Council, explained,
“In areas with hot summer and cold winters, the energy savings during hot weather are still greater than the incremental loss of heat in the winter.” This is because roofs do not absorb much heat from the sun in winter when days are shorter and cloudier, and the sun is less intense.
Proof Is in the Payoff
Several examples of shifting to dark to white roofs have shown the value.
In 1995, The Florida Solar Energy Center applied a white acrylic coating onto the 12,000-foot roof of Our Savior’s Elementary School in Cocoa Beach, Fla. After a year, the school’s energy consumption was down 13,000 kWh and its power usage had dropped 10 percent for an overall savings of $850.
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air filters
I wanted to thank you for this great read!! I definitely enjoying every little bit of it I have you bookmarked to check out new stuff you post
Nice approach!!
Good post. I’m been looking for topics as interesting as this.Very informative and information presented very well,i really liked reading your blog which has presented a great information about the dealing with the climate changes.I really apprecite the way you have helped us.I have heard before that Light colored materials reflect more solar radiation, including visible, ultraviolet and infrared light.Thanks for the valuable information which will be a great benefit to deal with glabal warming.
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not in the north
It should depend on the heating degree days (HDD) and the cooling degree days CDD of where you live. I wouldn't require white roofs for any location where the CCD is less than 1000. I had a home (well insulated) with dark eves and shingles in Hailey, ID (CCD < 500). The snow would melt away from the edges, while my neighbors had terrible ice dam problems and leaky roofs. I didn't have AC and was fine in the summer.
Also, are white roofs really white? Meaning - do they reflect well all the way down into the far infra red? (say 10 um). If not, then the benefit is not as much as it could be. So the roofing materials should be tested for this and should come with reflectivity specs that show what the infrared performance is (since you cant look at it and tell).
Come to think of it, that
Come to think of it, that does makes a lot of sense! I hope they could also implement the same roof guidelines in our country... although I very much doubt it.
Heat reflective paint
Thanks for the good and hard working blog! heat reflective painted white stay cooler because they reflect the sun’s heat. Light colored materials reflect more solar radiation, including visible, ultraviolet and infrared light , than dark materials which absorb heat.we follow certain practices that help us in reducing our electricity bills without affecting the quality of life.
Nice information
A very good site. sufficient information. never knew roof’s coolness is determined by its solar reflectance and thermal emittance
Paint it White
The image of white roofs at the top of this post is really lovely, but I can also understand how some people might not want to be the first house in their subdivision to add a white roof. There are options. When we roofed our small timber-frame barn with metal, we were given to understand that all the metallic tones were very reflective. The classic silvery one was blinding, so we chose a copper tone. It is the color of a new terra cotta flower pot when the sun is not shining directly on it, and goreous gold when it is. When we build our green-as-we-can-make it house in 2012, we anticipate a copper-colored metal roof on it too -- unless we learn of something better in the mean time.
I am documenting what we are doing and learning as we sustainably manage 44 acres at my blog http://digginginthedriftless.wordpress.com
Denise Thornton
Grow sustainably.....sustainable farming practices
If the leaders of the global political economy continue to recklessly expand the large-scale production of food to feed an already rapidly growing population, then absolute global human population numbers will continue to skyrocket as they are now. The relentless effort to increase the world's food supply appears to be a primary precipitant of a global human population explosion. A billion people are hungry on Earth in our time. More poor people live in our planetary home today than existed on Earth in the year of my birth.
Why not end large-scale agricultural production and everywhere encourage an increase in sustainable farming practices? Why not fairly and equitably distribute the world's abundant food harvests so that the starving can fed? We have hundreds of millions of people who are starving as well as many too many millions of people who suffer from the ravages of gluttony. The human family could move toward more healthful living standards for all by redistributing available food resources.
The family of humanity is going to have to stop sleepwalking through life and immediately awaken, however difficult that may be, to the human-driven global challenges threatening human wellbeing and environmental health in our time.
Perhaps necessary change is in the offing because its occurrence must come soon.
Otherwise, I fear, the human community could reap the Biblical whirlwind, a storm blast of epic proportions, that gives rise to some kind of unimaginably huge and destructive global ecological wreckage.
Steven Earl Salmony
AWAREness Campaign on the Human Population,
established 2001
http://sustainabilityscience.org/content.html?contentid=1176
www.panearth.org
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