Tag Archives: air conditioning

‘Smart’ windows from Australia

My obsession with smart windows has been lying dormant until now. This February 25, 2018 RMIT University (Australia) press release on EurekAlert has reawkened it,

Researchers from RMIT University in Melbourne Australia have developed a new ultra-thin coating that responds to heat and cold, opening the door to “smart windows”.

The self-modifying coating, which is a thousand times thinner than a human hair, works by automatically letting in more heat when it’s cold and blocking the sun’s rays when it’s hot.

Smart windows have the ability to naturally regulate temperatures inside a building, leading to major environmental benefits and significant financial savings.

Lead investigator Associate Professor Madhu Bhaskaran said the breakthrough will help meet future energy needs and create temperature-responsive buildings.

“We are making it possible to manufacture smart windows that block heat during summer and retain heat inside when the weather cools,” Bhaskaran said.

“We lose most of our energy in buildings through windows. This makes maintaining buildings at a certain temperature a very wasteful and unavoidable process.

“Our technology will potentially cut the rising costs of air-conditioning and heating, as well as dramatically reduce the carbon footprint of buildings of all sizes.

“Solutions to our energy crisis do not come only from using renewables; smarter technology that eliminates energy waste is absolutely vital.”

Smart glass windows are about 70 per cent more energy efficient during summer and 45 per cent more efficient in the winter compared to standard dual-pane glass.

New York’s Empire State Building reported energy savings of US$2.4 million and cut carbon emissions by 4,000 metric tonnes after installing smart glass windows. This was using a less effective form of technology.

“The Empire State Building used glass that still required some energy to operate,” Bhaskaran said. “Our coating doesn’t require energy and responds directly to changes in temperature.”

Co-researcher and PhD student Mohammad Taha said that while the coating reacts to temperature it can also be overridden with a simple switch.

“This switch is similar to a dimmer and can be used to control the level of transparency on the window and therefore the intensity of lighting in a room,” Taha said. “This means users have total freedom to operate the smart windows on-demand.”

Windows aren’t the only clear winners when it comes to the new coating. The technology can also be used to control non-harmful radiation that can penetrate plastics and fabrics. This could be applied to medical imaging and security scans.

Bhaskaran said that the team was looking to roll the technology out as soon as possible.

“The materials and technology are readily scalable to large area surfaces, with the underlying technology filed as a patent in Australia and the US,” she said.

The research has been carried out at RMIT University’s state-of-the-art Micro Nano Research Facility with colleagues at the University of Adelaide and supported by the Australian Research Council.

How the coating works

The self-regulating coating is created using a material called vanadium dioxide. The coating is 50-150 nanometres in thickness.

At 67 degrees Celsius, vanadium dioxide transforms from being an insulator into a metal, allowing the coating to turn into a versatile optoelectronic material controlled by and sensitive to light.

The coating stays transparent and clear to the human eye but goes opaque to infra-red solar radiation, which humans cannot see and is what causes sun-induced heating.

Until now, it has been impossible to use vanadium dioxide on surfaces of various sizes because the placement of the coating requires the creation of specialised layers, or platforms.

The RMIT researchers have developed a way to create and deposit the ultra-thin coating without the need for these special platforms – meaning it can be directly applied to surfaces like glass windows.

Here’s a link to and a citation for the paper,

Insulator–metal transition in substrate-independent VO2 thin film for phase-change device by Mohammad Taha, Sumeet Walia, Taimur Ahmed, Daniel Headland, Withawat Withayachumnankul, Sharath Sriram, & Madhu Bhaskaran. Scientific Reportsvolume 7, Article number: 17899 (2017) doi:10.1038/s41598-017-17937-3 Published online: 20 December 2017

This paper is open access.

For anyone interested in more ‘smart’ windows, you can try that search term or ‘electrochromic’, ‘photochromic’, and ‘thermochromic’ , as well.

Metamaterial could supply air conditioning with zero energy consumption

This is exciting provided they can scale up the metamaterial for industrial use. A Feb. 9, 2017 news item on Nanowerk announces a new metamaterial that could change air conditioning  from the University of Colorado at Boulder (Note: A link has been removed),

A team of University of Colorado Boulder engineers has developed a scalable manufactured metamaterial — an engineered material with extraordinary properties not found in nature — to act as a kind of air conditioning system for structures. It has the ability to cool objects even under direct sunlight with zero energy and water consumption.

When applied to a surface, the metamaterial film cools the object underneath by efficiently reflecting incoming solar energy back into space while simultaneously allowing the surface to shed its own heat in the form of infrared thermal radiation.

The new material, which is described today in the journal Science (“Scalable-manufactured randomized glass-polymer hybrid metamaterial for daytime radiative cooling”), could provide an eco-friendly means of supplementary cooling for thermoelectric power plants, which currently require large amounts of water and electricity to maintain the operating temperatures of their machinery.

A Feb. 9, 2017 University of Colorado at Boulder news release (also on EurekAlert), which originated the news item, expands on the theme (Note: Links have been removed),

The researchers’ glass-polymer hybrid material measures just 50 micrometers thick — slightly thicker than the aluminum foil found in a kitchen — and can be manufactured economically on rolls, making it a potentially viable large-scale technology for both residential and commercial applications.

“We feel that this low-cost manufacturing process will be transformative for real-world applications of this radiative cooling technology,” said Xiaobo Yin, co-director of the research and an assistant professor who holds dual appointments in CU Boulder’s Department of Mechanical Engineering and the Materials Science and Engineering Program. Yin received DARPA’s [US Defense Advanced Research Projects Agency] Young Faculty Award in 2015.

The material takes advantage of passive radiative cooling, the process by which objects naturally shed heat in the form of infrared radiation, without consuming energy. Thermal radiation provides some natural nighttime cooling and is used for residential cooling in some areas, but daytime cooling has historically been more of a challenge. For a structure exposed to sunlight, even a small amount of directly-absorbed solar energy is enough to negate passive radiation.

The challenge for the CU Boulder researchers, then, was to create a material that could provide a one-two punch: reflect any incoming solar rays back into the atmosphere while still providing a means of escape for infrared radiation. To solve this, the researchers embedded visibly-scattering but infrared-radiant glass microspheres into a polymer film. They then added a thin silver coating underneath in order to achieve maximum spectral reflectance.

“Both the glass-polymer metamaterial formation and the silver coating are manufactured at scale on roll-to-roll processes,” added Ronggui Yang, also a professor of mechanical engineering and a Fellow of the American Society of Mechanical Engineers.

“Just 10 to 20 square meters of this material on the rooftop could nicely cool down a single-family house in summer,” said Gang Tan, an associate professor in the University of Wyoming’s Department of Civil and Architectural Engineering and a co-author of the paper.

In addition to being useful for cooling of buildings and power plants, the material could also help improve the efficiency and lifetime of solar panels. In direct sunlight, panels can overheat to temperatures that hamper their ability to convert solar rays into electricity.

“Just by applying this material to the surface of a solar panel, we can cool the panel and recover an additional one to two percent of solar efficiency,” said Yin. “That makes a big difference at scale.”

The engineers have applied for a patent for the technology and are working with CU Boulder’s Technology Transfer Office to explore potential commercial applications. They plan to create a 200-square-meter “cooling farm” prototype in Boulder in 2017.

The invention is the result of a $3 million grant awarded in 2015 to Yang, Yin and Tang by the Energy Department’s Advanced Research Projects Agency-Energy (ARPA-E).

“The key advantage of this technology is that it works 24/7 with no electricity or water usage,” said Yang “We’re excited about the opportunity to explore potential uses in the power industry, aerospace, agriculture and more.”

Here’s a link to and a citation for the paper,

Scalable-manufactured randomized glass-polymer hybrid metamaterial for daytime radiative cooling by Yao Zhai, Yaoguang Ma, Sabrina N. David, Dongliang Zhao, Runnan Lou, Gang Tan, Ronggui Yang, Xiaobo Yin. Science  09 Feb 2017: DOI: 10.1126/science.aai7899

This paper is behind a paywall.

Members of the research team show off the metamaterial (?) Courtesy: University of Colorado at Boulder

I added the caption to this image, which was on the University of Colorado at Boulder’s home page where it accompanied the news release headline on the rotating banner.

Bringing home the chilling effects of outer space

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  ?

Burkina Faso

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  ?

The Gambia

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  ?

South Africa

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

Saudi Arabia

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

South America

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?