June 3, 2012 – Vol.17 No.12
HEAT REFLECTIVE ROOFS, OUTSIDE IN.
by Bruce Mulliken, Green Energy News
In my new neighborhood there are over a thousand homes: More than half have white tile roofs. Talk to any homeowner here and they'll tell you, "White roofs aren't just pretty. They’ll help keep a house cool in the Florida sun."
But not all white roofs here are white. Not all are very pretty either. The neglected ones get dirty, gray and algae covered. I don't think dirt and algae are good sunlight reflectors and do much to cool off a home as a glistening white roof.
One of the initiatives of the U.S. Department of Energy is to install heat reflective materials on the roofs of its own buildings as well as encourage other agencies within the government to follow. The hope is that through its cool roofs initiative that DOE will set an example that will filter down to public and private sector buildings. The effort is not just to cut on air conditioning costs on buildings, but to cut down on the heat island effect of hot roofs in cities. Dark, hot roofs heat up the surrounding air.
DOE's initiative has considerable research from its labs to back up its energy saving, greenhouse gas cutting and heat island reducing claims. That research has helped spawn organizations like the White Roof Project which gathers volunteers to paint roofs white as a way to combat climate change and cool off cities. The group, started in New York City, would like all the world’s roofs painted white.
But white and heat reflecting roof efforts don't emphasize is that painting a roof white is not a one shot deal. Keeping it white or reflective is a lifetime (of the building) commitment. Without a strict regimen of upkeep, white roofs will no longer be white in a few years. Roof maintenance and cleaning, which would include regular inspection, is one of those things building owners might easily forget. Thinking that rain will always wash a roof clean is wrong too. The grayed white roofs of my neighborhood are a testament to that. When the storms come it rains torrents but do little to pressure wash grayed roofs.
It appears as though there's a simple solution: Paint the inside of the roof, the underside of the roof deck, with a heat reflective coating. The inside, in the attic space, protected from the weather, from pollution and from dust, the heat reflecting paint or coating will stay clean. Coating the underside of the roof will still have the much of the same, if not perhaps more, energy-saving qualities as coating the outside roof surface.
There's at least one product that's been on the market for over 25 years and is approved even by the Department of Energy itself as an energy saving product. That product from the Solar Energy Corporation of Ewing, New Jersey is LO/MIT
Here’s how LO/MIT works.
The silver colored radiant barrier is applied to the underside of the roof deck as a building is being built, or sprayed on afterwards to existing buildings of any age. As sunlight strikes the outer roof surface, light is converted to heat, or infrared energy, that is absorbed by the roofing material. As the roof gets hotter as the day builds, heat is radiated into the roof deck material that then also gets hot. WITHOUT the radiant barrier applied, heat from the roof deck will heat the attic, then heat the rooms below. But WITH the barrier applied, heat that penetrates the roof deck, hits the reflective coating of LO/MIT and bounces off. (Reflective materials reflect both heat and light.)
Not only is summer heat gain reduced with LO/MIT, so is winter heat loss. When it’s cold outside, and the heating system is running, the reflective coating on the inside of the roof traps some heat from the building that’s trying to escape. LO/MIT will help cut heating costs in cold weather.
However LO/MIT is not billed as a heat island reducing product, just energy saving, so there’s still a place for sunlight reflective or white, cool roofs. Perhaps for the coolest roof of all, coat the inside with LO/MIT and the outside with white or LO/MIT there too. And please keep it clean.
Recently LO/MIT contributed to making a big splash in history. On May 31, SpaceX's Dragon capsule splashed down in the Pacific Ocean at 11:42 a.m. EDT a few hundred miles west of Baja California, Mexico, marking a successful end to the first mission by a commercial company to resupply the International Space Station. As Dragon fell from orbit it experienced temperatures in excess of 3000 degrees Fahrenheit (1650 degrees Celsius). Helping to keep it cool inside was coating of LO/MIT I radiant barrier coating.
Here on Terra Firma LO/MIT is approved as a building energy efficiency product by:
American Society for Testing and Materials (ASTM)
American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)
American Institute of Architects (AIA)
Electric Power Research Institute (EPRI)
Environmental Protection Agency (EPA)
Florida Power & Light (FPL)
Florida Solar Energy Center
Florida State Energy Code
Insulation Contractors’ Assoc. of America
Lawrence-Berkeley National Lab
Jet Propulsion Laboratory
Oak Ridge National Lab
US Department of Energy
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