What’s Next for Cool Roofs?

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In July 2010, Secretary of Energy Steven Chu launched an initiative to install cool roofs on DOE and government buildings. Recognition of the benefits of cool roofs like those from Conklin and the development of emerging technologies promises to transform the future marketplace. Several laboratories, universities and companies are already conducting research on new cool roof products, from self-cleaning to thermally sensitive materials to solar panels that take advantage of cool roofs.

Although they may seem like conflicting technologies, cool roofs can be complimentary to solar photovoltaic panels. According to the DOE, a cool roof can keep the roof surface 50% cooler than a dark roof under the same conditions. Solar panels may perform more efficiently and for a longer lifespan under the cooler conditions provided by a cool roof. Panels by California solar photovoltaic manufacturers Solyndra have even been developed with curved surfaces to take advantage of light refracted off the cool roof.

The Lawrence Berkeley National Laboratory’s Heat Island Group is conducting research on the effects of dirt and algae on the roof surface over time, and it is working to develop an accelerated aging process. This can significantly decrease the aged testing timeline, allowing roofing manufacturers to design and improve product formulas without waiting three years for the aged performance. The Heat Island Group is also working on a self-cleaning surface for roofing materials to reduce the effects of weathering on solar reflectance values. The scientists at United Environment and Energy LLC are developing a coating that can recognize temperature changes to either reflect or absorb solar energy depending on what would be more advantageous for the building. The coating is created using waste cooking oil from restaurants and can be adapted to different climates with preset temperature thresholds. A team at the Massachusetts Institute of Technology has focused on a similar concept, designing a roof tile that changes colors according to temperature. The tiles are made of common polymers encapsulated by a clear plastic top layer and black back layer. These are just a few examples of new technologies that are pushing roofing materials to have the ability to maintain high-performance after weathering while decreasing both cooling and heating loads for a building.

Despite the benefits of cool roofing, it is still a ways off from being adopted as a standard building practice. In the U.S., it faces barriers from misconceptions, aesthetic design concerns and moisture issues caused by non-comprehensive installations. Yet, cool roofing is a simple design measure that can provide significant energy savings and environmental rewards. The Lawrence Berkeley National Laboratory’s Heat Island Group estimates that buildings with cool roofs use up to 40% less cooling energy than buildings with dark colored roofs. A designer specifying a rooftop now has several resources available to make informed and confident cool roof choices.

With increasingly rigorous roofing code and program standards, and promising emerging technologies on the horizon, cool roofs are quickly becoming one of the most effective ways to save energy and help mitigate global warming.

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Cool Roof Resources

There are thousands of product options just for cool roofing (including Conklin), so specifying an appropriate roof can be a daunting task. Cool roofs are available in all colors for virtually every roofing type, although white is still the most efficient option.

You can gauge the energy performance abilities by understanding how a cool roof reflects and emits the sun’s heat back to the sky instead of transferring it to the building below. Once you understand the basic technology of cool roofing, there are several resources available to help you make a confident, informed decision on your next project.

Solar reflectance and thermal emittance are the two key metrics determining how “cool” a roof will stay by its ability to reflect solar energy and emit absorbed heat. Solar reflectance and thermal emittance will appear as a value between 0 and 1, with a higher value signifying a “cooler” roof. Solar Reflectance Index (SRI) is a third metric that is calculated using a product’s solar reflectance and thermal emittance values. It is measured on a scale of 0 to 100 with a higher number symbolizing a more energy-efficient roof. SRI is sometimes used by code bodies or green building programs in place of solar reflectance and thermal emittance as a single-value alternative. Cool roof standards often specify higher reflectance requirements for low-slope, flat rooftops versus steep-slope, pitched rooftops. This difference in values is due to the energy impact the surface type faces, as the flat surface of a low-slope rooftop is exposed to greater solar radiation than a pitched roof.

Another factor in which roofing products are unique is that they are exposed to outdoor conditions that may alter the energy performing ability of the product. Each product is therefore tested initially as available straight off the shelf, as well as after it has been weathered by outdoor elements. A study by the Oak Ridge National Laboratory and DLR consultants found that the loss of effectiveness of solar reflectance for most roof types leveled out at around three years, so it is an industry standard to test roofing materials after three years of aging to determine their aged value. Code bodies sometimes reference this aged value, as it more accurately reflects the performance of the roof through its life cycle.

The Cool Roof Rating Council (CRRC) is a third-party rating program that works with manufacturers to rate their products’ solar reflectance and thermal emittance. The Rated Products Directory is a free online database of roofing products rated by the CRRC. Code bodies and voluntary green building programs define a cool roof by specifying a minimum value for initial and aged solar reflectance, thermal emittance and SRI, or a combination thereof. The CRRC does not set minimum standards for products to be listed on its Rated Products Directory, but provides unbiased and credible ratings for all products. You can search through more than 2,000 products by categories such as material type, color or manufacturer. You can even search by minimum initial or aged solar reflectance, thermal emittance or SRI value in order to fine-tune your search to products that meet a specific code or program standard.

While code bodies set cool roof minimum standards as guidelines, many people find it more realistic to specify a cool roof based on quantifiable benefits. The U.S. Department of Energy (DOE) and the Environmental Protection Agency (EPA) have both created cool roof calculators to determine energy and monetary savings based on climate, building size, HVAC equipment and other important factors.

• The DOE Cool Roof Calculator offers savings estimates for small- and medium-sized facilities with flat roofs.
• The EPA Roof Savings Calculator is designed for both residential and commercial buildings, and it allows you to define information about your existing and proposed roofs for comparison.

The cool roof calculators show the tangible savings gained from cool roofs, yet cool roofs offer several other environmental benefits. Eco-conscious designers may also want to consider the cradle-to-cradle aspects of their material choices, including recycled content, end of life recyclability and toxicity of materials.

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ROOFING CONTRACTORS NEEDED IN MULTIPLE STATES!

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Cool Roofs Also Beneficial in Cold Climates

One of the goals of the U.S. Department of Energy's Cool Roofs Roadmap is to answer one of the most fundamental cool roof-related questions: Are cool roofs beneficial in cold climates?

Andre O. Desjarlais and P. Marc LaFrance both say they think so - if not from strictly an energy standpoint, then from the fact that they can help reduce the urban heat island effect.

"If you put a cool roof on a building in a cold climate and run the calculator strictly on energy, it may not save energy because of the heating penalty," says LaFrance. "But if you take into account the urban heat island effect, the indirect benefits may make cool roofs worthwhile."

This is often a tough sell for facility managers only worried about their own bottom lines. But research has already shown the effectiveness of cool roofs like those from Conklin at reducing urban heat islands, pollution and smog. For instance, the Heat Island Group at LBNL showed that Los Angeles spends about $100 million in extra energy costs to mitigate its urban heat island.

Reducing the temperature citywide means less air conditioning energy is required everywhere, which also means fewer greenhouse gas emissions. For this reason, many northern cities like Chicago, Philadelphia and New York City, have mandated cool roofs in their building codes. Utilities in northern states like Wyoming, Minnesota and Oregon offer rebates for the use of cool roofs. And the voluntary LEED rating system specifies cool roofs for a point explicitly for "urban heat island reduction." LaFrance says he hopes the research planned in the Cool Roofs Roadmap will more firmly establish a link between widespread use of cool roofs and reduced air conditioning energy use, pollution and greenhouse gas emissions.

One specific initiative, on which the Department of Energy is already working in conjunction with two other organizations (the White Roofs Alliance and Local Governments for Sustainability), is called the 100 Cool Cities initiative. DOE hopes to engage 100 cities around the world to commit to widespread installation of reflective surfaces by 2020. New York City, Taipei and Athens were the first three cities to sign up.

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