An alternative is the turf roof http://en.wikipedia.org/wiki/Turf_roof, which uses evapotranspiration http://en.wikipedia.org/wiki/Evapotranspiration for cooling. There is also a benefit from thermal mass http://en.wikipedia.org/wiki/Thermal_mass <http://en.wikipedia.org/wiki/Thermal_mass>These are quite heavily promoted in Europe. I understand that they are used in Germany and occasionally in the UK. I think that they are more suitable than white roofing in temperate regions.
A 2009/8/2 Alvia Gaskill <[email protected]> > Regarding the solar gain issue, in the northern states, the impact of > solar heating during the winter is less due to a combination of sun angle > and cloud cover. In the most extreme example for the U.S., the Fairbanks, > Alaska metro area (APX pop. 100,000) would not benefit at all from white or > lighter covered roofs or suffer any loss in heating from having them even > though all the heating and AC is supplied via fossil energy. I'm not sure > if there is any AC in Fairbanks, although temperatures do approach 90 > degrees F in July sometimes. Residents of Seattle and parts of Oregon also > saw temperatures over 100 degrees F this past week, but this is very unusual > and you are correct, few homes in that part of the U.S. have AC. They just > don't need it very often. I think the same analysis applies to Britain, > especially with the large number of cloudy days. > > The article also makes an implied distinction between cities like NYC and > Chicago and rural areas or cities like Minneapolis that get extremely cold > in the winter, such cities although far enough north to require some > additional heating during the winter if white roofs are used, are heat > islands during the summer, less so this year due to the wayward path of the > Polar Jet Stream. So applications of the white roof for commercial > buildings strategy have to take into account a number of variables. > > Note also that the CO2 offsets were done on a state-by-state basis, so > states like Washington and Oregon, which get much of their electricity from > hydroelectric power would benefit less than states like New York and > Pennsylvania which are more dependent on coal and natural gas. It would be > interesting to see the same figure done including residential roofs and > paved surfaces. > > I happened to go by the Sam's Club I mentioned in the article comments last > Friday and noticed that the roof is now a gray color, somewhat worse than in > March. Since most commercial building roofs are flat, the only way they can > maintain their original white color or something close to it is to have them > cleaned periodically. Residential roofs also lose some of the original > lightness (not whiteness, since they are generally not white as the article > notes), but do benefit from the rain and wind washing or blowing away dirt. > I would like to see how many of the 3000 Sam's Club's roofs are really still > white. If not, then their white roof program is a public relations success, > but a global warming failure and the people in charge of calculating the > energy savings need to "roll back" the numbers. > > ----- Original Message ----- > *From:* Andrew Lockley <[email protected]> > *To:* [email protected] > *Cc:* [email protected] > *Sent:* Saturday, August 01, 2009 12:09 PM > *Subject:* Re: [geo] Ceiling the Deal > > I'm confused. The diagram includes chilly Northern states. Don't they > need all the solar gain they can get to cut winter heating bills? I can't > imagine lots of people in Seattle having aircon. In Britain hardly any > homes have it, and most commercial buildings don't either. > A > > 2009/7/30 Alvia Gaskill <[email protected]> > >> http://www.nytimes.com/2009/07/30/science/earth/30degrees.html?_r=1 >> >> >> J. Emilio Flores for The New York Times >> >> A Wal-Mart store in Chino, Calif., has both a cool roof and solar panels >> to cut its energy use. >> >> Jim Wilson/The New York Times >> >> A white roof has helped cool Jon Waldrep’s Sacramento home >> >> >> >> [image: Imagining a Cool-Roof Nation] >> By Degrees*A Cool Shield* >> >> This is one in a series of articles about stopgap measures that could >> limit global warming. >> >> July 30, 2009 >> By Degrees >> White Roofs Catch On as Energy Cost Cutters By FELICITY >> BARRINGER<http://topics.nytimes.com/top/reference/timestopics/people/b/felicity_barringer/index.html?inline=nyt-per> >> >> SAN FRANCISCO — Returning to their ranch-style house in Sacramento after a >> long summer workday, Jon and Kim Waldrep were routinely met by a wall of >> heat. >> >> “We’d come home in the summer, and the house would be 115 degrees, >> stifling,” said Mr. Waldrep, a regional manager for a national company. >> >> He or his wife would race to the thermostat and turn on the >> air-conditioning as their four small children, just picked up from day care, >> awaited relief. >> >> All that changed last month. “Now we come home on days when it’s over 100 >> degrees outside, and the house is at 80 degrees,” Mr. Waldrep said. >> >> Their solution was a new roof: a shiny plasticized white covering that >> experts say is not only an energy saver but also a way to help cool the >> planet. [But what's it going to look like 5 years from now? AG] >> >> Relying on the centuries-old principle that white objects absorb less heat >> than dark ones, homeowners like the Waldreps are in the vanguard of a >> movement embracing “cool roofs” as one of the most affordable weapons >> against climate >> change<http://topics.nytimes.com/top/news/science/topics/globalwarming/index.html?inline=nyt-classifier>. >> [Exaggeration. This will affect climate change only on the margins. AG] >> >> Studies show that white roofs reduce air-conditioning costs by 20 percent >> or more in hot, sunny weather. Lower energy consumption also means fewer of >> the carbon dioxide emissions that contribute to global warming. >> >> What is more, a white roof can cost as little as 15 percent more than its >> dark counterpart, depending on the materials used, while slashing >> electricity bills. >> >> Energy Secretary Steven >> Chu<http://topics.nytimes.com/top/reference/timestopics/people/c/steven_chu/index.html?inline=nyt-per>, >> a Nobel laureate in physics, has proselytized for cool roofs at home and >> abroad. “Make it white,” he advised a television >> audience<http://www.thedailyshow.com/watch/tue-july-21-2009/steven-chu>on >> Comedy Central’s “Daily Show” last week. >> >> The scientist Mr. Chu calls his hero, Art Rosenfeld, a member of the >> California >> Energy Commission <http://www.energy.ca.gov/> who has been campaigning >> for cool roofs since the 1980s, argues that turning all of the world’s roofs >> “light” over the next 20 years could save the equivalent of 24 billion >> metric tons in carbon dioxide emissions. >> >> “That is what the whole world emitted last year,” Mr. Rosenfeld said. “So, >> in a sense, it’s like turning off the world for a year.” >> >> This month the Waldreps’ three-bedroom house is consuming 10 percent less >> electricity than it did a year ago. (The savings would be greater if the >> family ran its central air during the workday.) >> >> From Dubai to New Delhi to Osaka, Japan, reflective roofs have been >> embraced by local officials seeking to rein in energy costs. In the United >> States, they have been standard equipment for a decade at new Wal-Mart >> stores. More than 75 percent of the chain’s 4,268 outlets in the United >> States have them. [In addition to the picture in the article, remember the >> ones I took of the Sam's Club last spring. AG] >> >> California<http://www.energy.ca.gov/2006publications/CEC-400-2006-015/CEC-400-2006-015.PDF>, >> Florida<http://ecodes.citation.com/cgi-exe/cpage.dll?pg=x&rp=/nonindx/ST/fl/st/b200v07/index.htm&sid=2009072710183304239&aph=0&cid=iccf&ref=/indx/ST/fl/st/b200v07/st_fl_st_b200v07_cover.htm&uid=icsc0418&clrA=005596&clrV=005596&clrX=005596>and >> Georgia have adopted building codes that encourage white-roof >> installations for commercial buildings. [I thought the regulations REQUIRED >> white roofs for commercial buildings. AG] >> >> Drawing on federal stimulus dollars earmarked for energy-efficiency >> projects, state energy offices and local utilities often offer financing for >> cool roofs. The roofs can qualify for tax credits if the roofing materials >> pass muster with the Environmental Protection >> Agency<http://topics.nytimes.com/top/reference/timestopics/organizations/e/environmental_protection_agency/index.html?inline=nyt-org>’s >> Energy Star program <http://www.energystar.gov/>. [They can't have >> offered it for very long. The stimulus money was only approved in >> February. AG] >> >> Still, the ardor of the cool-roof advocates has prompted a bit of a >> backlash. >> >> Some roofing specialists and architects argue that supporters fail to >> account for climate differences or the complexities of roof construction. In >> cooler climates, they say, reflective roofs can mean higher heating bills. >> >> Scientists acknowledge that the extra heating costs may outweigh the >> air-conditioning savings in cities like Detroit or Minneapolis. >> >> But for most types of construction, they say, light roofs yield >> significant net benefits as far north as New York or Chicago. Although those >> cities have cold winters, they are heat islands in the summer, with hundreds >> of thousands of square feet of roof surface absorbing energy. >> >> The physics behind cool roofs is simple. Solar energy delivers both light >> and heat, and the heat from sunlight is readily absorbed by dark colors. (An >> asphalt roof in New York can rise to 180 degrees on a hot summer day.) >> Lighter colors, however, reflect back a sizable fraction of the radiation, >> helping to keep a building — and, more broadly, the city and Earth — cooler. >> They also re-emit some of the heat they absorb. [Solar energy doesn't >> deliver heat. It is all shortwave radiation. The heat comes from either >> the GHG emissions of infrared or from the roor itself. AG] >> >> Unlike high-technology solutions to reducing energy use, like light-emitting >> diodes<http://topics.nytimes.com/top/reference/timestopics/subjects/l/lightemitting_diodes/index.html?inline=nyt-classifier>in >> lamp fixtures, white roofs have a long and humble history. Houses in hot >> climates have been whitewashed for centuries. >> >> Before the advent of central air-conditioning in the mid-20th-century, >> white- and cream-colored houses with reflective tin roofs were the norm in >> South Florida, for example. Then central air-conditioning arrived, along >> with dark roofs whose basic ingredients were often asphalt, tar and bitumen, >> or asphalt-based shingles. These materials absorb as much as 90 percent of >> the sun’s heat energy — often useful in New England, but less so in Texas. >> By contrast, a white roof can absorb as little as 10 percent or 15 percent. >> >> “Relative newcomers to the West and South brought a lot of habits and >> products from the Northeast,” said Joe Reilly, the president of American >> Rooftile Coatings <http://www.americanrooftilecoatings.com/>, a supplier. >> “What you see happening now is common sense.” >> >> Around the country, roof makers are racing to develop products in the hope >> of profiting as the movement spreads from the flat roofs of the country’s >> malls to the sloped roofs of its suburbs. >> >> Years of detailed work by scientists at the Lawrence Berkeley >> Laboratory<http://coolcolors.lbl.gov/assets/docs/fact-sheets/Cool-roof-Q%2BA.pdf>have >> provided the roof makers with a rainbow of colors — the equivalent of a >> table of the elements — showing the amount of light that each hue reflects >> and the amount of heat it re-emits. >> >> White is not always a buyer’s first choice of color. So suppliers like >> American Rooftile Coatings have used federal color charts to create “cool” >> but traditional colors, like cream, sienna and gray, that yield savings, >> though less than dazzling white roofs do. >> >> In an >> experiment<http://coolcolors.lbl.gov/assets/docs/PAC-2008-03-06/CoolColorsPAC-2008-03-06-team-final-slides.pdf>, >> the National Laboratory in Oak Ridge, Tenn., <http://www.ornl.gov/> had >> two kinds of terra-cotta-colored cement tiles from American Rooftile >> installed on four new homes at the Fort >> Irwin<http://www.irwin.army.mil/Pages/default.aspx> >> Army<http://topics.nytimes.com/top/reference/timestopics/organizations/a/us_army/index.html?inline=nyt-org>base >> in California. One kind was covered with a special paint and reflected >> 45 percent of the sun’s rays — nearly twice as much as the other kind. The >> two homes with roofs of highly reflective paint used 35 percent less >> electricity last summer than the two with less reflective paint. >> >> Still, William Miller of the Oak Ridge laboratory, who organized the >> experiment, says he distrusts the margin of difference; he wants to figure >> out whether some of it resulted from different family habits. >> >> Hashem Akbari, Dr. Rosenfeld’s colleague at the Lawrence Berkeley >> laboratory, says he is unsure how long it will take cool roofs to truly >> catch on. But he points out that most roofs, whether tile or >> asphalt-shingle, have a life span of 20 to 25 years. >> >> If the roughly 5 percent of all roofs that are replaced each year were >> given cool colors, he said, the country’s transformation would be complete >> in two decades. [That will require regulation as old habits die hard. I >> have some ideas on how to fast tract this and will be reporting on it soon. >> AG] >> >> >> >> >> > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en -~----------~----~----~----~------~----~------~--~---
