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Urban areas are growing hotter as a result of replacing natural vegetation with buildings and roads. “Heat Island Effect” describes this phenomenon. Buildings and pavements absorb solar radiation and become extremely hot warming the surrounding air. As the air temperature rises, so does the demand for air-conditioning (AC), leading to higher emissions from power plants, and increased smog resulting from warmer temperatures.  
Cool surfaces can have a substantial effect on urban air temperature and hence can reduce cooling-energy use and smog. It is estimated that about 20% of the national cooling demand can be avoided through a large-scale implementation of heat-island mitigation measures. This amounts to a 40 Terawatt annual savings that could add up to over $10B per year.

The simplest way to cool cities is using shading, reflective surfaces and trees. Simulations done for Los Angeles, CA show that by cooling about two-thirds of the pavements and rooftops and planting three trees per house would reduce air temperatures equivalent to removing all of the vehicle exhaust for the entire LA basin!  
Rooftops, asphalt and concrete absorb solar energy, raising surface temperature 50-70 degrees Fahrenheit hotter than the ambient temperature and store and release heat even after dark. Rooftops can heat up to as much as 170 degrees Fahrenheit. On the other hand, white rooftops can reflect 65% solar radiation, providing a cooling effect.
In a parking lot and with the sun emitting approximately 1000 watts per square meter at earth's surface it wouldn't seem to unlikely to achieve upwards of 150 F on windless, warm, sunny days., Solar reflectance for old asphalt is about .10, which means 90% of the infrared of the sun heat is being absorbed by the asphalt. Another experiment showed the surface temperature difference between a white car and a black car. The white car was 87 degrees Fahrenheit whereas the black car was 134 degrees Fahrenheit. Without air conditioning, which one would you prefer riding in? The same goes for homes and office buildings. When more air conditioning is required, more energy is consumed. 
Our one MW commercial energy system shades approximately 2.5 acres of asphalt lowering ambient temperatures by at least 30%. The direct effect of this type of heat island mitigation around a building can lower cooling requirement from 10 to 40 percent. This direct cooling effect is immediate to the building and equals the cooling effect to planting over 200 shade trees.  
By using logical techniques such as ecobaun energy plant we can take steps to decentralize commercial power, lower urban temperatures, reduce energy consumption, and increase heath and comfort of the people who live and work here, all while making smart economic sense  
    
(excerpts from Hashem Akbari, Lawrence Berkeley National Laboratory, americanforests.org, )

Also go to: http://www.cleanairpartnership.org/pdf/finalpaper_cheung.pdf for another report on heat island effects.

The Urban Heat Island Effect

 

Our cities and towns are growing hotter as a result of replacing natural vegetation with buildings and roads. A study by the Lawrence Berkeley Laboratory describes what effect urban heat has on business, people and the planet. As the air temperature rises, so do our cooling demands, gasoline consumption, power plant emissions, electrical grid loads and ozone formation or smog. this heat is also linked to various health problems people suffer day and night. 

 

Asphalt and concrete absorb much of this solar energy, raising surface temperatures 50-70 degrees hotter than ambient temperature. This material then stores and releases heat all day and night. A parking lot with the sun emitting 1000 watts per square meter at the surface, can heat to upwards of 150 F on a warm, sunny day. Solar reflectance for old asphalt is about .10, which means 90% of the infrared of suns heat, is being absorbed by the asphalt. Another example is the surface temperature difference between a white car and a black car might exceed 50 degrees. Which one would you prefer riding in? 

 

A study on urban heat island estimates that about 20% of the national cooling demand can be avoided through a large-scale implementation of heat island mitigation. This amounts to a 40TW annual energy savings or over $10B per year in direct cost savings. The study suggests simple methods like reflective surfaces and trees for shade. 

 

Our 1MW energy system covers about 3 acres. It reflects heat at heights to allow cooler air circulation below the canopy and around buildings. By lowering ambient temperatures reduces building cooling demands. Imagine parking under a shade tree that casts a 3 acre shadow! The closest equivalent to our 1MW power plant, would be planting about 300 adult shade trees.

 

By taking the steps like these to reduce urban heat island, we move toward decentralized power, gain power independence and increase the health and comfort of the people who live and work here.

 

(excerpts from Lawrence Berkeley National Laboratory, americanforests.org)