air conditioning

Cooling cities

September 2, 2024 By EarthWise Leave a Comment

As the climate warms, city dwellers tend to suffer from extreme heat more than people in rural areas because of the urban heat island effect. Extensive surfaces of man-made materials like concrete, asphalt, and brick absorb the sun’s energy and lead to temperatures well above those in the surrounding countryside.

Cities can take countermeasures that include creating urban green spaces full of plants that cool the surrounding air and the use of cool roofs that reflect the sun’s energy back into space. Local governments in many cities provide incentives for planting more trees. But more could be accomplished by encouraging the use of cool roofs.

The heat island effect has been well-known for a long time, but scientists are only recently learning what interventions are most effective. A recent study modeled two days of extreme heat in London in 2018 and compared the potential effects of cool roofs, green roofs, roof-top solar panels, and ground level vegetation. They found that cool roofs are the most effective way to lower temperatures and would have reduced London temperatures by 2 degrees on average and as much as 3.6 degrees in some places.

Cool roofs are created by swapping out dark, heat-absorbing roofing materials with reflective materials or simply by painting roofs white. Los Angeles is the first major city to require that all new residential construction includes a cool roof.

Apart from the effectiveness of passive cooling techniques, using them also reduces the reliance upon air conditioning to protect people from heat. Air conditioners themselves contribute considerable amounts of heat to urban environments.

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The surprisingly simple way cities could save people from extreme heat

Photo, posted February 21, 2024, courtesy of Warren LeMay via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Offshore wind and the wake effect

May 28, 2024 By EarthWise Leave a Comment

Electricity demand in the U.S. continues to grow and, in the summer, homes and businesses crank up their air conditioning which drives demand even further. Many East Coast cities are banking on offshore wind projects that are underway in the Atlantic Ocean to help meet that growing demand. The first offshore turbines are now producing power off the coasts of Massachusetts and New York.

Electric power utilities need to know how much power they can get from offshore wind farms, and this is not that easy to predict. Wind is variable, so there is some built-in uncertainty. But there is also a phenomenon known as the wake effect to contend with.

When wind passes through a series of giant turbines, the ones in front extract some energy from the wind and, as a result, the wind slows down and becomes more turbulent behind the turbines. So, the downstream turbines get slower wind and may produce less power.

A study by the University of Colorado has modeled this phenomenon for planned wind farms in the Atlantic Coast region and has found that power output could be reduced by over 30%. Researchers are installing weather monitors and radar sensors in islands off the New England coast to better understand the behavior of the wind in the area and improve prediction models.

The New England grid covers Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont. Even with the wake effect, offshore wind is predicted to be able to provide 60% of the electricity needs of the grid, but it is important to be able to accurately predict what it can produce.

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How much energy can offshore wind farms in the US produce? New study sheds light

Photo, posted August 31, 2022, courtesy of Nina Ali via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Electric Mail Trucks | Earth Wise

January 26, 2023 By EarthWise Leave a Comment

The US Postal Service recently announced that it plans to buy at least 66,000 electric vehicles by 2028. With more than 231,000 total vehicles, the Postal Services operates one of the largest civilian vehicle fleets in the world.

Last February, the Postal Service announced a plan to replace up to 165,000 older mail trucks, many of which are as much as 30 years old. The gas-powered trucks get an estimated 8.6 miles per gallon when air conditioning is running. The plan was for only 10% of the new trucks to be electric, citing the high upfront costs of electric vehicles even though they generally make up the difference by saving on fuel and maintenance costs over time.

Facing strong criticism from the Biden administration, the Postal Service shifted course and in July announced that 40% of the new trucks would be electric. With passage of the Inflation Reduction Act in August, the Postal Service received $3 billion for fleet electrification and has once again changed its plans. It also announced that it intends to stop buying gas-powered delivery trucks altogether after 2026.

As part of the new plan, the Postal Service plans to upgrade hundreds of facilities across the country to accommodate electric vehicles. This will include installing chargers and streamlining delivery operations to reduce unnecessary trips.

The Postal Service is no alone in working to clean up its fleets. FedEx says it plans to completely electrify its pickup and delivery fleet by 2040. Amazon has ordered 100,000 electric vans from the start-up company Rivian.

Electrifying the postal delivery system makes abundant sense. Postal routes are predictable and there is ample charging time to meet the power needs of the fleet.

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Your Mail Truck Is Going Electric

Photo, posted January 18, 2017, courtesy of Rusty Clark via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Propane Refrigerants | Earth Wise

September 20, 2022 By EarthWise Leave a Comment

About 10% of the world’s total electricity supply is used for air conditioning. If current temperature trends continue, the energy demands for space cooling will more than triple by the year 2050. Air conditioning is a double threat to the environment. Apart from using lots of energy, ACs also make use of halogenated refrigerants that are extremely powerful greenhouse gases.

The most common space cooling appliances are split-air conditioners, which use an indoor unit and an outdoor unit connected by pipes. These split ACS mostly utilize HCFC-22 and HFC-410 as refrigerants, which have global warming potential scores as high as 2,256 – meaning they trap 2,256 times more heat than carbon dioxide.

A study by the International Institute of Applied Systems Analysis in Austria has shown that propane is a far better choice as an air conditioning refrigerant. Its global warming potential is actually less than 1 meaning it traps less heat than carbon dioxide. According to the study, if air conditioners switched to propane refrigerants, the world would avoid about a tenth of a degree Celsius of additional warming, which is a significant contribution to meeting the goals of the Paris climate agreement.

Propane-based split-ACs are already available commercially in China and India. Elsewhere, many national regulations prohibit their use, primarily due to codes restricting the use of refrigerants with higher flammability. Given the increasingly urgent need for climate action, it seems to be time to reconsider regulations on refrigerants.

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Propane — a solution for more sustainable air conditioning

Photo, posted March 24, 2021, courtesy of Phyxter Home Services via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Saving Lives With Air Conditioning | Earth Wise

August 26, 2022 By EarthWise Leave a Comment

This summer, extreme heatwaves struck the United States, Europe, and Africa. Thousands of people died as a result. In July, the impact of extreme heat in places ill-prepared for it was evident. In the U.K., where air conditioning is uncommon, public transportation shut down, schools and offices closed, and hospitals cancelled non-emergency procedures.

Air conditioning, which we mostly take for granted in this country, is a life-saving tool during extreme heat waves. However, only about 8% of the 2.8 billion people living in the hottest – and often poorest – parts of the world have AC in their homes.

A new study at Harvard modeled the future demand for air conditioning as the number of days with extreme heat continues to increase across the globe. The researchers identified a massive gap between current AC capacity and what will be needed by 2050 to save lives, particularly in low-income and developing countries.

If the rate of greenhouse gas emissions continues on its present course, the study concluded that that at least 70% of the population in several countries will require air conditioning by 2050. The number will be even higher in equatorial countries like India and Indonesia. At this point, even if the goals of the Paris Climate Accords are met, an average of 40-50% of the population in many of the world’s warmest countries will still require AC.

The research looked at various scenarios. One in which emissions continue to increase leads to widespread need for air conditioning even in temperate countries. In Germany, 92% of the population would need it, and here in the U.S., 96% would need it.

Planning for future power systems must take into account the essential needs of a warming world.

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In a hotter world, air conditioning isn’t a luxury, it’s a lifesaver

Photo, posted July 24, 2021, courtesy of Phyxter Home Services via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

A Solar-Powered Target Store | Earth Wise

April 26, 2022 By EarthWise Leave a Comment

Many companies have made sustainability commitments of various types. Environmental organizations have urged big-box and grocery stores to install solar panels on their rooftops and parking lots thereby reducing their energy usage and expanding the country’s supply of renewable energy. These places occupy large areas and therefore are capable of supporting large solar arrays.

According to a report by two environmental advocacy groups, rooftop solar panels on retail stores could generate enough electricity to power the equivalent of nearly 8 million U.S. homes.

Target Stores are one of the retailers that has been making an effort to be a greener company. Target has installed solar panels on about 25% of its approximately 1,900 stores. The Target store in Vista, California, about 40 miles north of San Diego, is the company’s most sustainable store. It already had solar panels on its rooftop, powering a portion of the store.

But now it has installed massive carports topped with solar panels high above its parking lot. With these panels, this Target can now produce enough renewable energy to power the entire store, from its refrigeration to its heating and air conditioning. Adding in some of the other energy-saving features of the store, Target expects to produce 10% more energy than the store needs, which it will return to the local power grid. This is Target’s first net-zero energy store.

Target is not the only big retailer going solar. Home Depot, Lowe’s, and Walmart all have been installing solar panels on some of their rooftops. Even some restaurants are trying to reach sustainability goals with solar panels. This is a trend that hopefully will continue to grow.

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Target looks to massive solar panels in a California parking lot as a green model to power its stores

Photo, posted June 30, 2014, courtesy of Mike Mozart via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

A Smart Window | Earth Wise

March 31, 2022 By EarthWise Leave a Comment

Researchers at Oxford University have developed a new adaptable smart window technology that has the potential of reducing the energy usage of the average home by a third.

The technology uses a spectrally tunable low-emissivity coating that can control the amount of heat that comes into a room without affecting the quality of the light that enters.

The thermal energy from the sun’s infrared rays is absorbed by the glass and then is re-emitted as heat. That heat can either be used to warm the room using transparent electrical heaters embedded in the glass or can be reflected away to cool the room. The windows can change according to seasonal needs.

The researchers built a prototype using a material called an active chalcogenide-based phase change material. When it is cold, the infrared rays from the sunlight are harvested and used to heat the building. When it is warm, the new glass can switch state to reflect the heat and reduce the need for air conditioning. The active phase change material is adjustable so that the amount of heat absorbed or reflected can be tuned for precise temperature control. There is essentially no effect on visible light passing through the window. Current low-emissivity glass for windows can reduce heat transfer, but its properties cannot be altered according to seasonal needs.

The researchers estimate that using windows fitted with the new prototype glass – including the energy required to control the film – would save 20 to 34% in energy usage annually compared to double-glazed windows found in many modern homes.

A spinout company from Oxford called Bodle Technologies is collaborating with two existing industrial partners to develop the technology further.

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New adaptable smart window coating could help heat or cool a home and save energy

Photo, posted April 26, 2008, courtesy of Lima Andruska via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Poverty And Climate Change

March 15, 2022 By EarthWise Leave a Comment

According to the World Health Organization, climate change is expected to cause approximately 250,000 extra deaths per year between 2030 and 2050. But climate change does not affect everyone the same. In fact, the poorest people on the planet, who are often the least to blame for climate change, typically bear the worst of the impact.

Wealthier people and countries have more resources to shield themselves from the impacts of climate change. For example, higher incomes allow people to purchase air conditioning as temperatures rise, food as food prices soar, and homes in safer places. Wealthy nations can also compensate citizens when climate change harms livelihoods.

According to new research, people with lower incomes are exposed to heat waves for longer periods of time compared to those with higher incomes due to a combination of factors including location and access to heat adaptations like air conditioning. This inequality is expected to increase as temperatures rise.

The study, which was published in the AGU journal Earth’s Future, found that lower income populations face a 40% higher exposure to heat waves than people with higher incomes. By the end of the century, the poorest 25% of the global population will be exposed to heat waves at a rate equivalent to the rest of the population combined.

On the other hand, the highest-income quarter of the population will experience comparatively little change in exposure to heat waves as their ability to keep up with climate change is generally greater.

The research team hopes its findings will prompt innovations into affordable cooling solutions for the world’s most vulnerable population.

Climate change and poverty are, and will remain, inextricably linked.

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Poorest people bear growing burden of heat waves as temperatures rise

Photo, posted October 27, 2019, courtesy of Jack via Flickr.

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Strategies To Cool Off Cities | Earth Wise

July 2, 2021 By EarthWise Leave a Comment

Heatwaves in cities are becoming increasingly common and increasingly intense. The warming climate is a big factor, but it is the nature of our cities that really drives up temperatures. Solar radiation stored throughout the day on asphalt and buildings is released slowly during the night, which generates significant heat stress.

A study carried out by a major Barcelona university and published in the journal Urban Climate looked at the effectiveness of various ways to mitigate the heating effects in cities. In particular, the study examined the effects of the use of white roofs on buildings and the expansion of urban green areas with daily irrigation in the Barcelona metropolitan area. It simulated various scenarios incorporating combinations of these two mitigation strategies.

The strategy with the greatest impact was a combination of the use of both white roofs and the addition of six urban parks, which is a target set by the Barcelona Urban Master Plan. This scenario resulted in an average temperature reduction of 2.25 degrees Fahrenheit. The maximum reduction occurs during the mid-afternoon with a reduction of 7 degrees and the combination still provides more than 3 degrees of reduction at 9 pm. Reducing temperatures this way also results in a reduction in energy consumption, with 26% less spending on air conditioning.

The 2-pronged strategy combines the benefits of reducing the temperature at night due to more urban green areas with the reduction of daytime heat due to both the increased reflectivity of white roofs as well as the irrigation of the green areas.

The study demonstrates how modeling efforts can help urban planners to counteract the impacts of heatwaves, which are likely to increase with climate change and intensification of urbanization.

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White roofs and more green areas would mitigate the effects of heat waves in cities

Photo, posted January 16, 2011, courtesy of Sean MacEntee via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Better Paint For Cooler Buildings | Earth Wise

August 20, 2020 By EarthWise 2 Comments

A research team led by scientists at UCLA have developed a super-white paint that reflects as much as 98% of incoming heat from the sun. Such paint, if used on rooftops and other parts of buildings, could have a major impact on reducing the costs of keeping buildings cool.

Passive daytime radiative cooling is a well-known method to keep buildings cooler. By having building surfaces reflect sunlight and radiate heat into space, building temperatures can be significantly lowered. This in turn cuts down on air conditioner use and associated carbon emissions.

A roof painted white will result in lower indoor temperatures than a darker roof. But a white roof will do even more: it can reject heat at infrared wavelengths that are invisible to our eyes. This results in even more radiative cooling.

The best performing white paints currently available reflect about 85% of incoming solar radiation. The rest is absorbed by materials in the paint. The new research has identified simple modifications in paint ingredients that lead to a major increase in reflectivity.

Current reflective white paints use titanium dioxide, which absorbs UV radiation and therefore heats up under sunlight. The researchers studied replacing it with other substances such as barite – an artist’s pigment – or with powdered Teflon, both of which allow the paint to reflect more of the sun’s radiation.

Many cities are encouraging the use of cool-roof technologies on new buildings. Using the most reflective coatings possible on rooftops, if applied on a sufficiently large scale, could have a real impact on climate change as well as saving significant amounts of energy used for running air conditioners in buildings.

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UCLA-led Team Develops Ways to Keep Buildings Cool with Improved Super White Paints

Photo, posted August 15, 2012, courtesy of Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Roofs Going Green

November 21, 2019 By EarthWise Leave a Comment

Green roofs are roofs on buildings that are partially or completely covered with vegetation and a growing medium, generally planted over a waterproofing membrane. The modern version of these roofs began in Germany in the 1960s and spread to many other European countries over time. With concerns about climate change and shrinking natural resources rising, green roofs are becoming increasingly popular across North America. The Toronto-based organization Green Roofs for Healthy Cities estimates that the number in North America has increased by about 15% since 2013.

Replacing black asphalt and shingles with plants can lower the surrounding air temperature, filter dirty storm water, and reduce building energy use. The National Research Council of Canada estimates that a green roof can reduce air conditioning use in a building by as much as 75%. The roofs also help to reduce air pollution and greenhouse gas emissions according to the EPA.

As the benefits of green roofs become more widely known, cities around the world are passing green roof legislation. Copenhagen passed a law in 2010 requiring all new commercial buildings to have green roofs if their roofs are not sloped too much. Toronto was the first city in North America to pass a green roof law in 2009. Over 640 green roofs covering more than five million square feet have since been constructed in Toronto.

Apart from the environmental benefits, green roofs are providing pleasant spaces in the urban environment that may include flower beds, trees, herb gardens, gazebos and picnic tables. As for the economics, studies show that over the course of a roof’s lifetime, green roofs are actually considerably cheaper than conventional roofs taking into account energy savings.

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The Green Revolution Spreading Across Our Rooftops

Photo, posted July 15, 2014, courtesy of Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

A See-Through Heat Shield

January 8, 2019 By EarthWise Leave a Comment

It is estimated that air conditioners use about 6% of all the electricity produced in the United States for an annual cost of $29 billion. With rising temperatures, this expense is only going to get larger.

A significant part of the heat load in buildings arises from heat coming through windows. It turns out that for every square meter of window, about 500 watts of heat energy can be brought in by sunlight, equivalent to 5 old-fashioned light bulbs.

Researchers at MIT and the University of Hong Kong have developed a heat-rejecting film that can applied to a building’s windows that will reflect 70% of the sun’s incoming heat. The film is similar to transparent plastic wrap. It remains highly transparent at temperatures below 89 degrees Fahrenheit. Above that temperature, tiny microparticles embedded in the film shrink and the film becomes more translucent or frosted, still letting in a good amount of light, but rejecting a lot of heat.

There are already so-called smart windows on the market, similar to the electrochromic mirrors in cars that darken to prevent trailing headlights from blinding drivers. But that technology is not very effective in rejecting heat and it requires power to operate, which means you would have to pay to turn windows opaque.

Tests of the new film demonstrated its ability to reject heat and lower temperatures. The researchers estimate that if every exterior-facing window in a building were covered in the heat-rejecting film, the building’s air conditioning and energy costs could drop by 10%. Saving ten percent of tens of billions of dollars is no minor matter.

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