'GREEN' Buildings.

The Concept of Energy Efficient Roofs or Cool Roofs

• An energy efficient roof should be designed in such a way that it maximizes the use of the natural energy and minimizes the dependency on the electrical energy for the building.

• Typically, the major portion of the electrical energy consumed in residential buildings is used for heating and cooling of the building, and next comes illumination.

• Ideally an energy efficient roof should minimize the consumption of the electrical energy for all three accounts: heating, cooling, and lighting. But, since illumination consists of such small portions of the electrical energy requirements, the cool roof concepts we will discuss here will only related to the heating and cooling of the building.

• The sun is the major source of heat energy for a home. The heat from the sun increases the refrigeration cost at summer and reduces the heating cost at winter. The heat from the sun reaches us in two forms: via infrared waves and via visible light waves.

• Energy efficient roofs normally employ reflective and/or absorptive paint coating to either reflect or absorb the heat from visible light. The paints coatings work on the principle of "black body radiation." In short this principle says that a body with black color absorbs most of the energy that falls over it, and vice-versa is the case for a white colored body.

• The heat traveled through infrared waves anyways gets absorbed.

• So homes located at the summer regions should use white reflective paints and those at the winter region should use black absorptive paints.

• Problems enter the picture for homes that have exposure to both summer as well as winter seasons. What color of paint should be used for such homes? A simple answer is: white reflective paint, because normally the refrigeration energy requirement is higher than heating energy requirements and the intensity of the sunlight heat energy is far less in winter. Another answer is temperature reactive color roofs, which make the cool roofs more energy efficient for such weather conditions.

• You can find the different cool roof materials, which are already available in the market, from the Cool Roof Rating Council website. The website will give you the manufacturer’s details and the solar reflectivity index for each material.

How Temperature Reactive Color Roofs Work

• A special type of temperature reactive color coating is applied over the temperature reactive color roofs.
• The chemical composition of the temperature reactive coating is such that it turns white at higher temperature (summer) and turns black at lower temperature.
• As the paint turns white at higher temperature, it reflects maximum amounts of solar heat and at lower temperature it absorbs the solar heat as it turns black.
• Few manufacturers are producing the paints, but researches are currently working mainly to reduce the price of such paints. Recently a team of MIT students claimed that they invented roof tiles that can save energy in all conditions. Also, there is a claim from United Environment & Energy of Horseheads (UEE) that they have developed a “smart” coating of this type. The Alsa Corporation is a manufacturer of reactive color coatings.

Conclusion

There are many methods available for making roofs energy efficient, and using temperature reactive color roofs is one of them. Traditionally, the cool roofs use either reflective white paint coating or absorptive black paint coating depending upon the weather conditions. Permanent white paint coatings are energy efficient for summer season, but counter-effective for the winter. Temperature reactive color roofs are effective for both summers as well as winter seasons because they change color with the temperature. The research is on for making the temperature reactive coatings more affordable and durable.
References

• Cool Roof Rating Council
• Science News: Cool Roof Coatings Kept under Wraps
• CleanTechnica: MIT Roof Tiles Save Energy in all Climates

Read more: http://www.brighthub.com/engineering/mechanical/articles/84311.aspx#ixzz1VN1U8PPC