They’ve invented a new type of cooling structure at Stanford University (California) which reflects sunlight back into outer space. From the Apr. 16, 2013 news item on Azonano,
A team of researchers at Stanford has designed an entirely new form of cooling structure that cools even when the sun is shining. Such a structure could vastly improve the daylight cooling of buildings, cars and other structures by reflecting sunlight back into the chilly vacuum of space.
The Apr. 15, 2013 Stanford Report by Andrew Myers, which originated the news item, describes the problem the engineers were solving,
The trick, from an engineering standpoint, is twofold. First, the reflector has to reflect as much of the sunlight as possible. Poor reflectors absorb too much sunlight, heating up in the process and defeating the goal of cooling.
The second challenge is that the structure must efficiently radiate heat (from a building, for example) back into space. Thus, the structure must emit thermal radiation very efficiently within a specific wavelength range in which the atmosphere is nearly transparent. Outside this range, the thermal radiation interacts with Earth’s atmosphere. Most people are familiar with this phenomenon. It’s better known as the greenhouse effect – the cause of global climate change.
Here’s the approach they used,
Radiative cooling at nighttime has been studied extensively as a mitigation strategy for climate change, yet peak demand for cooling occurs in the daytime.
“No one had yet been able to surmount the challenges of daytime radiative cooling –of cooling when the sun is shining,” said Eden Rephaeli, a doctoral candidate in Fan’s [Shanhui Fan, a professor of electrical engineering and the paper's senior author] lab and a co-first-author of the paper. “It’s a big hurdle.”
The Stanford team has succeeded where others have come up short by turning to nanostructured photonic materials. These materials can be engineered to enhance or suppress light reflection in certain wavelengths.
“We’ve taken a very different approach compared to previous efforts in this field,” said Aaswath Raman, a doctoral candidate in Fan’s lab and a co-first-author of the paper. “We combine the thermal emitter and solar reflector into one device, making it both higher performance and much more robust and practically relevant. In particular, we’re very excited because this design makes viable both industrial-scale and off-grid applications.”
Using engineered nanophotonic materials, the team was able to strongly suppress how much heat-inducing sunlight the panel absorbs, while it radiates heat very efficiently in the key frequency range necessary to escape Earth’s atmosphere. The material is made of quartz and silicon carbide, both very weak absorbers of sunlight.
This new approach offers both economic and social benefits,
The new device is capable of achieving a net cooling power in excess of 100 watts per square meter. By comparison, today’s standard 10-percent-efficient solar panels generate about the same amount of power. That means Fan’s radiative cooling panels could theoretically be substituted on rooftops where existing solar panels feed electricity to air conditioning systems needed to cool the building.
To put it a different way, a typical one-story, single-family house with just 10 percent of its roof covered by radiative cooling panels could offset 35 percent its entire air conditioning needs during the hottest hours of the summer.
Radiative cooling has another profound advantage over other cooling equipment, such as air conditioners. It is a passive technology. It requires no energy. It has no moving parts. It is easy to maintain. You put it on the roof or the sides of buildings and it starts working immediately.
Beyond the commercial implications, Fan and his collaborators foresee a broad potential social impact. Much of the human population on Earth lives in sun-drenched regions huddled around the equator. Electrical demand to drive air conditioners is skyrocketing in these places, presenting an economic and environmental challenge. These areas tend to be poor and the power necessary to drive cooling usually means fossil-fuel power plants that compound the greenhouse gas problem.
“In addition to these regions, we can foresee applications for radiative cooling in off-the-grid areas of the developing world where air conditioning is not even possible at this time. There are large numbers of people who could benefit from such systems,” Fan said.
Here’s a citation and a link for the paper,
Ultrabroadband Photonic Structures To Achieve High-Performance Daytime Radiative Cooling by Eden Rephaeli, Aaswath Raman, and Shanhui Fan. Nano Lett. [American Chemical Society Nano Letters], 2013, 13 (4), pp 1457–1461
DOI: 10.1021/nl4004283 Publication Date (Web): March 5, 2013
Copyright © 2013 American Chemical Society
The article is behind a paywall.
For anyone who might be interested in what constitutes hot temperatures, here’s a sampling from the Wikipedia List of weather records (Note: I have removed links and included only countries which experienced temperatures of 43.9 °C or 111 °F or more; I made one exception: Antarctica),
North America / On Earth†
56.7 °C (134 °F) Furnace Creek Ranch (formerly Greenland Ranch), in Death Valley, California, United States 1913-07-10
45.0 °C (113 °F) Midale, Yellow Grass, Saskatchewan 1937-07-05
52 °C (125.6 °F) San Luis Rio Colorado, Sonora
55.0 °C (131 °F) Kebili, Tunisia 1931-07-07
50.6 °C (123.1 °F) In Salah, Tamanrasset Province 2002-07-12
44.5 °C (112 °F) Kandi ?
47.2 °C (117 °F) Dori ?
47.7 °C (117.9 °F) Kousseri ?
Central African Republic
45 °C (113 °F) Birao ?
47.6 °C (117.7 °F) Faya-Largeau 2010-06-22
49.5 °C (121 °F) Tadjourah ?
50.3 °C (122.6 °F) Kharga ?
48 °C (118.4 °F) Massawa ?
48.9 °C (120 °F) Dallol ?
45.5 °C (114 °F) Basse Santa Su 2008-?-?
43.9 °C (111 °F) Navrongo ?
50.2 °C (122.4 °F) Zuara 1995-06
45 °C (113 °F) Ngabu, Chikwana ?
48.2 °C (118 °F) Gao ?
50.0 °C (122 °F) Akujit ?
49.6 °C (121.3 °F) Marrakech 2012-07-17
47.3 °C (117.2 °F) Chibuto 2009-02-03
47.8 °C (118 °F) Noordoewer 2009-02-06
48.2 °C (118.8 °F) Bilma 2010-06-23
46.4 °C (115.5 °F) Yola 2010-04-03
47.8 °C (118 °F) Berbera ?
50.0 °C (122 °F) Dunbrody, Eastern Cape 1918
49.7 °C (121.5 °F) Dongola 2010-06-25
46.1 °C (115 °F) Sidvokodvo ?
45.6 °C (114 °F) Beitbridge, ?
53.6 °C (128.5 °F) Sulaibya, Kuwait 2012-07-31
45.1 °C (113.2 °F) Rajshahi 1972-04-30
49.7 °C (118 °F) Ading Lake, Turpan, Xinjiang, China 2008-08-03
50 °C (122 °F) Sri, Ganganagar, Rajasthan Dholpur, Rajasthan ?
52.0 °C (125.7 °F) Basra, Ali Air Base, Nasiriyah 2010-06-14
53 °C (127.4 °F) Tirat Zvi, Israel 1942-06-21
47.0 °C (116.6 °F) Myinmu 2010-05-12
53.5 °C (128.3 °F) Mohenjo-daro, Sindh 2010-05-26
50.4 °C (122.7 °F) Doha 2010-07-14
52.0 °C (125.6 °F) Jeddah 2010-06-22
44.5 °C (112.1 °F) Uttaradit 1960-04-27
48.8 °C (119.8 °F) Mardin 1993-08-14
50.7 °C (123.3 °F) Oodnadatta, South Australia, Australia 1960-01-02
49.1 °C (120.4 °F) Villa de María, Argentina 1920-01-02
45 °C (113 °F) Pratts Gill, Boquerón Department 2009-11-14
44 °C (111.2 °F) Paysandú, Paysandú Department 1943-01-20
Central America and Caribbean Islands
45 °C (113 °F) Estanzuela, Zacapa Guatemala ?
48.0 °C or 48.5 °C (118.4 °F or 119.3 °F) Athens, Greece or Catenuova, Italy (Catenanuova’s record is disputed) 1977-07-10 or 1999-08-10;
Bosnia and Herzegovina
46.2 °C (115.16 °F) Mosta (Herzegovina, Federation of Bosnia and Herzegovina) 1900-07-31
46.6 °C (115.9 °F) Letkoniko, Cyprus 2010-08-01
47 °C or 48.5 °C (116.6 or 119.3 °F) Foggia, Apulia or Catenuuova, Sicily (Catenanuova’s record is disputed) 2007-06-25 and 1999-08-10
45.7 °C(114.26 °F) Demir Kapija, Demir Kapija Municipality 2007-07-24
47.4 °C (117.3 °F) Amarelja, Beja 2003-08-01
44.9 °C (112.8 °F) Smederevska Palanka, Podunavlie Distrrict, 2007-07-24
47.2 °C (116.9 °F) Murcia 1994-07-04
14.6 °C (59 °F) Vanda Station, Scott Coast 1974-01-05
It seems a disproportionate number of these hot temperatures have been recorded since 2000, eh?