Warm tile roof in winter, cool in summer

The tiles will be white when hot weather allows them to reflect most of the sun's heat. When it is cold they will turn black and absorb more heat.

A group of Massachusetts Institute of Technology graduates (MIT) developed tiles that could change color according to such temperatures.

Anyone who has ever walked on asphalt sidewalks during hot summer days knows this phenomenon well: black surfaces absorb solar heat very efficiently, making the surface hot. In winter, this comes in handy: dark tile roofs warm up in the sun and help reduce electricity bills for heating appliances. But in the summer, it becomes unfavorable: your home becomes hotter and the air conditioner must work harder.

In most areas, the disadvantages in the summer are often greater than the benefits in the winter. That is why many people including US Energy Minister Steven Chu advocated using white roof tiles.

An aura from the hot air gun made the black tile almost turn white.The first model tile designed by graduate students at MIT can change color: black when the weather is cold, white when the weather is warm (Photo: Physorg)

This problem is not small at all. In fact, Mr. Chu said, if turning all of the world's roof tiles to white, for 20 years would help eliminate greenhouse gas emissions with the amount of gas the world emits in a year. But some critics say that in the northern cities, the benefits in winter are greater than the disadvantages in the summer. It means that the dark tile roof will be more useful.

To solve this problem, a bachelor group at MIT developed tiles that could change color according to temperature . These tiles will be white when hot weather allows them to reflect most of the sun's heat. When it is cold they will turn black and absorb more heat.

Laboratory measurements show that in white state, tile roofs reflect about 80% of the light that hits them while in black they reflect only about 30%. This means that in the white state, they can yield about 20% of the cooling effect. The performance kept warm in the black state has not been determined.

The team is called Thermeleon (by the name of the gecko, because the color of the tiles they designed can change color) will be one of the competition of the Fabrication and Design competition. Engineering Design (MADMEC) - a competition for students at MIT this year.

Dr. Nick Orf, one of the members of the Thermeleon team, explained that he and his team have tried their best to develop tiles that change color, using a mixed fluid system, one dark color and a bright color. Their density will vary with temperature: dark pigments will float on when it is cold and white will rise on hot weather. But this system works too complicated. Need to make improvements simpler and cheaper.

They are continuing to study a simpler tile pattern with polymer solutions . The polymer will be a micro- coating of a clean ' paint ' that can be scanned or sprayed on any existing surface. These small films will still have color-changing properties but can take advantage of the existing black tile roofs to sweep up. This method is much cheaper than installing a new tile material.

Although they have not yet developed a detailed plan for forming a business project to commercialize their ideas, TS. Orf said the team decided to pursue this project and develop it into a marketable product.

Because the materials they use are fairly common and inexpensive, the Thermeleon team thinks they can mass-produce these tiles at a cost that can withstand other tile production materials.

The biggest question remaining is sustainability, and to answer this question will take a while to test many materials in repeated hot-cold cycles.

Hashem Akbari, the leader of the Heat Island group at Lawrence Berkely National Laboratory, has long advocated the use of white tiles as an energy-saving method, saying that several other groups including one The University of Athens team also conducted a study on color changing materials for tile production, but their research is still in an experimental phase. ' Cost and sustainability are still a problem .'

The Thermeleon group hopes to address these concerns. ' It will have to withstand harsh environments,' Orf said. 'Types of research to address these issues will have to be done before we can launch an acceptable product .'