COOL OFF WITH COOL ROOFS.

whiteroofgraphic526
Arrow lengths are proportional to heat flow. Graphic: Berkeley Lab.

The walls of my red brick house are hot to the touch in the record-breaking heat of the summer of 2010. I could probably fry an egg on my home’s gray slate tile roof. (If there was a nice frying pan flat spot, of course.)

Just a few months ago when warm moist air from the south met with cold air from the north, that same tired 60-year old roof held a 4-foot drift of record-breaking snow. The roof was damaged later by ice, and it leaked below.

Halfway through the year the planet is now on track to be the hottest yet in modern times.

The planet’s getting warmer because too much energy in sunlight is being trapped by heat reflective gases that man has put there in his foolish assumption that the thin layer of air we live in could somehow absorb those gases without complaint.

We need to find ways to artificially reflect more sunlight back into space.

Reflecting sunlight to cool off makes perfect common sense: A surface that reflects won’t get hot itself. A white shirt and white hat can help keep a body cool in glaring sun. Since thousands of years before the age of air conditioning, cool roofs have helped keep buildings comfortable in hot climates. Even in these days of omnipresent artificial air conditioning, keeping the sun’s heat away – not letting it in – will lessen the load on air conditioning systems, saving energy, saving money.

Not reflecting sunlight makes us hotter than we need to be. Dark, energy-absorbing roofing and pavements can warm local climates – such as the climate in your community – and the global climate as well.

Locally, solar heated surfaces will radiate heat into the air. This heated air, distributed by the wind and trapped by greenhouse gases, can make whole cities warmer than they would be if more sunlight reflective materials were chosen. The hot air of this urban heat island effect of cities can be pushed into the countryside by prevailing winds.

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Globally, the increased use of electric air conditioning to cool buildings in lieu of no energy, passive, reflective methods, has increased the demand on power plants, most of which still burn carbon-emitting fuels. Power plants are working harder, putting more emissions into the air than they need to because we’re not being smart about reflecting unnecessary solar heat.

The US Department of Energy’s Lawrence Berkeley National Laboratory – Berkeley Lab – says in a new study that by itself switching to sunlight-reflective roofing and paving materials won’t save the planet, but it will help.

In a way only scientists could understand, Berkeley says in a news story for the new study that “increasing the reflectivity of roof and pavement materials in cities with a population greater than 1 million would achieve a one-time offset of 57 gigatons (1 gigaton equals 1 billion metric tons) of CO2 emissions (31 Gt from roofs and 26 Gt from pavements). That’s double the worldwide CO2 emissions in 2006 of 28 gigatons.”

The graphic accompanying the story tells it in a way the rest of us might comprehend: On a 99 degree F day the surface of a black roof heats up 78 degrees F above the air temperature, while the surface of the white roof heats up only 12 degrees. You’ll have to imagine how millions of buildings worldwide are affecting the temperature of the atmosphere, depending on the color of their roofs. You’ll have to imagine, too, how hundreds of thousands of miles of black roadways and perhaps billions of square feet of black asphalt parking lots are heating up the air as well.

While it may be true that in colder months the heat absorbent qualities of a dark roof may actually help cut energy consumption by helping to heat a building, scientists still think a heat reflective roof is the better bet. Days are shorter, the sun is lower on the horizon, and more days are cloudy in colder months, so the heating affect of a dark roof doesn’t help heat a building very much. (Let the winter sun shine in the windows, however.)

Fortunately, it may not take a massive global government effort to get home and commercial building owners to switch to heat reflective roofs. The message is simple: reflecting sunlight will cut energy bills. Everyone likes the idea of saving money.

“Cool roofs are one of the quickest and lowest cost ways we can reduce our global carbon emissions and begin the hard work of slowing climate change,” said US Energy Secretary Steven Chu.

Since Secretary Chu believes the federal government should play a leading role in moving the nation toward a more sustainable future, he has directed all Department of Energy (DOE) offices to install cool roofs, whenever cost effective over the lifetime of the roof, when constructing new roofs or replacing old ones at DOE facilities.

Links:

Berkeley Lab
http://www.lbl.gov

Berkeley Lab: Global Model Confirms: Cool Roofs Can Offset Carbon Dioxide Emissions and Mitigate Global Warming.

http://newscenter.lbl.gov/news-releases/2010/07/19/cool-roofs-offset-carbon-dioxide-emissions/

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