Dear group, This paper was discussed on 20 march 2014, on the 3rd post of "New ideas (1) on how to cool the Planet: developing night radiative *cooling*. <https://groups.google.com/forum/#!searchin/geoengineering/Stanford$20daytime$20cooling/geoengineering/RkEplr56dGw/LMnYvOoqRWQJ> " https://groups.google.com/forum/#!searchin/geoengineering/Stanford$20daytime$20cooling/geoengineering/RkEplr56dGw/LMnYvOoqRWQJ As a matter of fact, the paper describes materials that allow *daytime *radiative cooling. These type of mirrors facilite the escape of more outgoing terrestrial long-wave radiation (more heat energy or infrared radiation escapes to the outer space), cooling Gaïa by *Earth Radiation Management* (ERM). A power point presentation can be found here <http://publications.solar-tower.org.uk/New%20ideas%20(3)%20on%20how%20to%20cool%20the%20Planet%20by%20Radiative%20Cooling%20through%20the%20Atmospheric%20Window%20by%20ERM.pdf> . Cheers Renaud de Richter
Le jeudi 27 novembre 2014 02:34:50 UTC+1, andrewjlockley a écrit : > > Poster's note : this is either a space mirror or a cool roof, depending on > how you look at it! The researcher interviewed claims it's not a > geoengineering solution, but with one or more orders of magnitude price > reduction, and maybe the inclusion of some energy generation, the economics > could change markedly. > > Mirrors could replace air conditioning by beaming heat into space > > http://gu.com/p/43k69 > > conditioning by beaming heat into space > Researchers have created a mirror that not only reflects 97% of light but > also radiates heat into the cold depths of the universe > Follow contributor Ian Sample , science editor > Published: 18:00 GMT Wed 26 November 2014 > 80 > > When the mirror is warmed up, it releases heat at a specific wavelength of > infrared light that passes easily through the atmosphere and out into > space. Photograph: Fan Lab, Stanford Engineering > A mirror that sends heat into the frigid expanse of space has been > designed by scientists to replace air-conditioning units that keep > buildings cool on Earth. > > Researchers believe the mirror could slash the amount of energy used to > control air temperatures in business premises and shopping centres by doing > away with power-hungry cooling systems. > > Around 15% of the energy used by buildings in the US goes on air > conditioning, but the researchers’ calculations suggest that in some cases, > the mirror could completely offset the need for extra cooling. > > In a rooftop comparison of the device in Stanford, California, scientists > found that while a surface painted black reached 60C more than ambient > temperature in sunlight, and bare aluminium reached 40C more, the mirror > was up to 5C cooler than the surrounding air temperature. > > “If you cover significant parts of the roof with this mirror, you can see > how much power it can save. You can significantly offset the electricity > used for air conditioning,” said Shanhui Fan, an expert in photonics at > Stanford University who led the development of the mirror. “In some > situations the computations say you can completely offset the air > conditioning.” > > Buildings warm up in a number of different ways. Hot water boilers and > cooking facilities release heat into their immediate surroundings. In hot > countries, warm air comes in through doors and windows. Then there is > visible light and infra-red radiation from the sun, which also heat up > buildings. > > Advertisement > The Stanford mirror was designed in such a way that it reflects 97% of the > visible light that falls on it. But more importantly, it works as a thermal > radiator. When the mirror is warmed up, it releases heat at a specific > wavelength of infrared light that passes easily through the atmosphere and > out into space. > > To make anything cool requires what engineers call a heat sink: somewhere > to dump unwanted heat. The heat sink has to be cooler than the object that > needs cooling or it will not do its job. For example, a bucket of ice will > cool a bottle of wine because it becomes a sink for heat in the liquid. Use > a bucket of hot coals and the result will the very different. The Stanford > mirror relies on the ultimate heat sink: the universe itself. > > The mirror is built from several layers of wafer-thin materials. The first > layer is reflective silver. On top of this are alternating layers of > silicon dioxide and hafnium oxide. These layers improve the reflectivity, > but also turn the mirror into a thermal radiator. When silicon dioxide > heats up, it radiates the heat as infrared light at a wavelength of around > 10 micrometres. Since there is very little in the atmosphere that absorbs > at that wavelength, the heat passes straight out to space. The total > thickness of the mirror is around two micrometres, or two thousandths of a > millimetre. > > “The cold darkness of the universe can be used as a renewable > thermodynamic resource, even during the hottest hours of the day,” the > scientists write in Nature. In tests, the mirror had a cooling power of 40 > watts per square metre at ambient temperature. > > Writing in the journal, Fan puts the installed cost of mirrors at between > $20 and $70 per square metre and calculates an annual electricity saving of > 100MWh per year on a three storey building. > > Fan said that the mirror could cool buildings – or other objects – simply > by putting it in direct contact with them. Coating the roof of a building > with the mirror would prevent heating from sunlight but do little to remove > heat from its interior. More likely, the mirror would be used to cool water > or some other fluid that would then be pumped around the building. > > He ruled out the idea of using the mirrors to slow down global warming. > “Roof space accounts for only a small portion of the Earth’s surface, so at > this point we don’t think this would be a geoengineering solution. Rather, > our contribution on the green house gas emission issue is simply to reduce > electricity consumption,” he said. > > “I’m really excited by the potential it has and the applications for > cooling,” said Marin Soljačić, a physicist at MIT. “You could use this on > buildings so you have to spend much less on air conditioning or maybe you > wouldn’t need it at all. You could put it on top of shopping malls. With a > large enough surface you could get substantial cooling.” > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/d/optout.
