Cool Roofs: A Hot Idea
Part 1: Cool Roof A Simple Solution For Recover, Replacement Projects
Part 2: Facilities With Cool Roofs Less Affected By Urban Heat Islands
Part 3: Cool Roofs Can Be Disadvantage Above Certain Latitudes
Part 4: Vegetation Another Holistic Approach To Cool Roofing
Cool Roofs Can Be Disadvantage Above Certain Latitudes
By Lacey Muszynski, Associate Editor - June 2010
The Great Debate
The energy savings and benefit to the environment of cool roofs in tropical and temperate regions of the world is clear, but what about colder areas? Expert opinions are mixed on whether there's a benefit to cool roofs in northern climates, and some argue that there comes a point when having a cool roof becomes a disadvantage. "North of Chicago, you'll end up paying more for heating in winter," says Desjarlais. "A cool roof will reduce your cooling load, but increase your heating load. Once you reach a certain latitude, the net impact is that you're going to use more energy."
Akbari, however, contends that a cool roof will be beneficial anywhere that air conditioning is used. "Our analysis has shown that any place in the world that you need heating and cooling, a cool roof will save you money."
The answer really comes down to each individual facility, its location, utility rates and demand charges, and the roof in question.
A study by Lawrence Berkley National Laboratories shows that cool roofs can reap energy savings in northern cities like Chicago, New York and Philadelphia. The study, funded by the U.S. Environmental Protection Agency, examined the energy cost savings of light-colored roofs in 11 U.S. cities, taking into account both the savings in cooling and any penalties for heating. The results showed that southern cities, such as Phoenix, Houston and Miami benefit the most from cool roofs, as expected. But Chicago could also see an annual savings of $10 million with cool roofs, New York a $16 million savings, and Philadelphia $3 million.
Whether your main motivation is environmental stewardship or energy savings, it's well worth considering a cool roof when it comes time to recover or replace an existing roof. "You can measure the energy savings, they don't cost much and they last longer," says Akbari. "It's all money in your pocket. What facility manager wouldn't be interested in that?"
Comments
John_Archibald wrote re: cool climate ... reflective roof III
on 6/11/2010 10:45:59 PM
There is no question that Cool Roofs can be useful when roofs are used as "passive" barriers to solar heat gain.
But to take full advantage of the roofing investment, the roofs need to be used as "active solar heating and cooling surfaces".
Nationally, US buildings use more energy for heating than any other purpose, ... about 65% of all residential, industrial and commercial energy use in buildings. Capturing and using that Solar Heat from the roof, either through Solar Air Heat Recovery from the roof surface or solar air to water heat recovery, provides an enourous energy saving resource. On many buildings, it far outweighs the reduction in air conditioning energy use that can be achieved by cool roofs.
The risk in today's cool roofing push is that standards are being set without consideration of the Solar Heat Recovery techniques that are being implemented. The adoption of a "one color fits all" cool roof approach will drive many buildings to install cool 'white' roofs in order to meet code requirements, while they continued to burn fossil fuels or use electric heat for the internal domestic, commercial, or industrial heating needs.
Active solar heat recovery used for a variety of heating, dehumidification, and cooling purposes holds too much promise for too many buildings to be restricted by a singular drive to cut air conditoning energy use with universally required cool roofs..
