Using natural resources vs. your air conditioning to keep cool

Posted by Chuck Harrell on Jan 6, 2015 4:20:00 PM

Air_Conditioning1The invention of air conditioning has transformed the way we live. No longer do we have to sweat day and night in high temperatures. But, unfortunately, our comfort comes at an environmental cost. The HFCs used in cooling and refrigeration is causing the ozone layer to degrade and this in turn causes an increased in global warming and also, the amount of electricity used to keep ourselves cool is an issue that is not discussed a lot.

Recent research, carried out by Dr. Aaswath Raman and his colleagues at Stanford University may change that. This new idea allows buildings to radiate their heat into outer space without using pumps or compressors. The idea is surprisingly simple and mostly relies on natural science. Space is big, so big that you won't believe quite how mind staggeringly big it is. It's also really quite chilly, at a mere 3 degrees Celsius. These conditions make it an ideal heat sink. Earth radiates heat non-stop but thanks to the sun, we never really notice this. The trick that Aaswath has come up with is to develop a system that reflects the sunlight that we get from space back into space.

You can read the full article in Nature, but to summarize, he and his team have developed a material which reflects and radiates 97% of sunlight at the most transparent wavelengths of the atmosphere (eight to 13 microns aka millionths of a meter). Using modern manufacturing techniques, the material uses seven extremely thin (13 to 688 nanometers aka billionth of a meter) layers (four silicon dioxide and three hafnium dioxide) on a 200 nanometer thick layer of silver which acts as a mirror. These layers were then mounted on a silicon wafer to keep them flat and for test purposes they were installed in a specially designed box that minimizes the conduction of heat. The recorded wafer's temperature was 4.9 degrees Centigrade cooler than its surroundings. This isolated unit was proof of concept, but if larger sheets of this material were placed directly on the roof of a building, the result would be to cool the entire surface area by radiating the heat away from the building.

There are some cost issues with the materials used in the project and these need to be resolved before it can go into mass production and since it also needs a direct line of sight to the sky and outer space, it's only really suitable for roofs. Someday, our homes and offices may have reduced electricity bills while maintaining a livable environment.

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