Researchers figured out why air conditioners consume so much energy

It’s not the heat

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This just in from the laboratory: When it comes to the air conditioner chugging away in the window, it’s not the heat — but the humidity that’s causing it to work overtime.

An analysis by researchers at the National Renewable Energy Laboratory in Golden found that on average more than half of the energy used by residential air conditioning around the globe deals with the moisture hanging in the air on a hot day.

And the projections are that it will become an even bigger challenge as a result of climate change leading to more hot days with warmer air capable of holding more moisture.

The AC is already working hard. In July, a massive heat dome led to heat warnings for more than 100 million people from Portland, Oregon, which saw an unprecedented seven consecutive days above 95 degrees, to Oklahoma City, where it hit 110 degrees.

Denver recorded its second warmest July on record with 16 days at 96 degrees or better, including three days at 100 degrees. On Aug. 3, another heat dome put more than 100 million people under heat warnings and advisories — from Minneapolis to North Texas.

That’s a lot of air conditioning.

The humidity factor does vary from region to region. “Removal of the latent load of moisture will become a bigger issue, though not here in Colorado,” said Iain Campbell, a senior fellow at RMI, an energy think tank. “We live in a desert. If you are in Florida or the tropics, you are out of luck.”

There has been a clear downward trend in humidity since 1980 in the Upper Colorado and Rio Grande basins, including all of western Colorado and the San Luis Valley, Russ Schumacher, the Colorado state climatologist, said in an email.

“On the Front Range and Eastern Plains, it’s not as clear whether there are meaningful trends,” Schumacher said. “Overall, considering that Colorado is far from an ocean, we won’t see the increases in humidity that are expected (and in some places already happening) in coastal areas as the climate continues to warm.”

So for Colorado it is a good news-bad news proposition. There is low humidity in part because we are in a megadrought, with demands to cut water use, reservoirs tapping out, and farm fields shriveling in oppressive heat — but it’s a dry heat.

By way of reference, the average June relative humidity — a measure of how much water vapor is in the air-water mix — in Denver is 46% and in Miami 73%. For every 1 degree Celsius increase in temperature the air can hold 7% more moisture — if there is any moisture around.

Current air conditioning technology is reasonably effective at removing moisture — albeit with some extra energy — up to 60% relative humidity. After that, it’s all heavy lifting.

“In the future there will be places where it will be too hot and too humid to be outdoors,” said Jason Wood, a senior research engineer at NREL, and co-author of the study on air conditioning and humidity.

Still even without humidity, in bone-dry Texas the demand for cooling electricity was so high during the July heat wave that the state’s electric grid operator initiated emergency measures to avoid rolling blackouts.

Texas’ experience is one reason Colorado Public Utilities Commission Chairman Eric Blank asked Xcel Energy, the state’s largest electricity provider, to do some “worst-case scenario” planning for a heat wave.

The real question is: Why, when it is clear that humidity has been a problem hardly anyone has done anything about it, as almost all air conditioners today are using 100-year-old vapor compression technology?

Today’s AC is based on turn of the 20th century tech

To be sure, vast improvements have been made in that technology and today’s units are to the first air conditioners what the BMW 4.4-liter Turbocharged V8 is to the Model-T Ford’s engine.

Still, both the BMW and the Model T have internal combustion engines. Now electric vehicles are poised to send the gasoline-powered car the way of the horse-drawn buggy, and LED lights are banishing Thomas Edison’s incandescent bulbs.

Meanwhile, ever-improving solar panels are decking rooftops and Tesla Powerwalls are being installed to store electricity at home, but the air conditioner is chugging along on the technology invented in Brooklyn, N.Y., at the turn of the 20th century.

“The pace of evolution of the AC industry is alarmingly slow even considering the best available technology,” a report by the RMI concluded.

This may not be the state of affairs for much longer as researchers, including those at NREL, and companies are searching for new AC technologies that in a two-step process remove moisture and then cool the air.

“They are in a very early stage of development,” said Antonio Bouza, a technology manager at the U.S. Department of Energy. “Just as the internal combustion engine is being displaced by EVs, that’s what we want to do with these technologies.”

It was humidity, ironically, not heat that began the march to the window air conditioner, when a 25-year-old engineer named Willis Haviland Carrier experimented in 1902 with humidity controls for a Brooklyn printing plant bedeviled by swelling pages and blurry prints in summer.

By 1933, Carrier had founded the Carrier Air Conditioning Company of America making a unit with technology that became the model for the industry.

It wasn’t until the 1950s that residential air conditioning started to grow in the U.S. Still, in 1952 only 2% of homes had AC and it remained exotic enough to play a role in the 1955 movie “The Seven Year Itch.”

“You have air conditioning! How does it work?” a hot Marilyn Monroe (the story takes place in the summer) breathily asked her lecherous downstairs neighbor as she stands in front of the unit lifting her blouse to bare her midriff.

“The way I feel about air conditioning,” the neighbor, played by Tom Ewell, explains, “no matter how much it costs, if there is no bread in the house, if you have to sell the kid’s bonds, in the summertime in New York City you’ve got to have air conditioning.”

A still from the 1955 movie “The Seven Year Itch”

By 2020, more than 88% of the households in the U.S. had air conditioning and in the next 30 years it will be the fastest-growing energy use in buildings, according to the U.S. Energy Information Administration.

Almost all air conditioners deal with humidity by cooling to the dew point, when the moisture in the air drops out as water. This is cooler than need be for comfort and when the water is rung out of the air it releases additional heat with which the air conditioner must cope.

To do the extra work an AC system needs an extra 20% to 30% of capacity, said Eric Kozubal, an NREL researcher developing new cooling technologies and a co-author of the study on AC energy use.

The NREL analysis divided the globe into 60-mile-by-60-mile boxes and within each box added population, a measure of economic activity, air conditioning ownership and weather.

Air conditioning accounts for 4% of the world’s annual greenhouse gas emissions

The study also took into account how much the electric grid depended upon fossil fuels, since the goal was to estimate through computer modeling greenhouse gas emissions from air conditioning.

The researchers calculated that almost 4% of the world’s annual greenhouse gas emissions — 1,950 million tons — come from air conditioning. The bulk of that, 1,190 million tons, were linked to standard air conditioning work cooling and dehumidifying, with the latter accounting for 52% of the emissions.

The rest of the emissions come from refrigerants leaking from units and the releases associated with the manufacture and transport of those units.

The NREL modeling projects that greenhouse gas emissions for temperature and humidity loads will grow five times larger by 2050 as there are more and more air conditioners — particularly in the hottest and most humid places, such as India, Indonesia, China and Southeast Asia.

RMI estimates that providing electricity to the 4.5 billion air conditioners running in 2050, will take 2,000 gigawatts of new electric generating capacity — equal to nearly 2,700 of Colorado’s largest power plant, Comanche 3.

“This is why we need new and better technology,” RMI’s Campbell said.

The federal government sets and periodically increases the minimum energy performance standards for air conditioners, but these do not drive innovation.

“The minimum energy performance standards now are equal to the best available technology 40 or 50 years ago,” Campbell said.

There are versions of the current AC technology that are two times more efficient than what is being sold at the local big box store, but they are more expensive.

One problem is the emphasis on the unit’s upfront price tag rather than its lifetime cost, Campbell said. “Does it help consumers to give them a really cheap piece of equipment that is expensive to run?” he asked. “We’d have to call this a market failure.”

Better AC technology a better solution than a new electric grid

If all the air conditioners in Texas were today’s most efficient units it would have cut the July spike in demand in half and likely avoided any emergency measures or threats of blackout.

“This would also be a much cheaper solution than increasing grid capacity in order to serve an ever-growing base of inefficient air conditioners,” Campbell said.

Another problem is the fact that the industry is heavily concentrated with fewer than 500 manufacturers worldwide, creating a high bar to entry, according to RMI.

In an effort to jump-start technological innovation, RMI and the Indian government offered a Global Cooling Prize with $3 million in prize money.

Two of the world’s top air conditioning manufacturers — Japan’s Daikin Global and China’s Gree Electric  — won with prototypes that improved upon existing technology by adding a second cooling or evaporative coil to deal with humidity, Campbell said.

The second coil and a more finely tuned motor made these prototypes seven times more efficient removing humidity and four times more energy efficient, Campbell said.

Still, they were in essence old-school Carrier technology. Meanwhile around the country, in national labs, universities and startup companies, researchers are working on the next generation of air conditioners.

Using electrostatic charges, membranes and desiccants, which soak up moisture, researchers are trying to develop ways of getting humidity out of the air before cooling — some have received federal funding.

“We aren’t picking a winner. The DOE has funded a lot of technologies with the aim of delivering comfort that is affordable,”Bouza said.

At NREL, Kozubal has been working on twinning cooling with desiccants, which come as solids and liquids.

Using a lithium chloride solution — 10 times saltier than the sea with a strong affinity to absorb water— an NREL team, led by Kozubal, and a start-up company 7AC developed a dehumidifying technology that was ultimately acquired by Emerson, a multinational engineering and industrial services company.

“The Emerson technology is brand new and going into a pilot demonstration phase,” Kozubal said.

The amount of energy such a system could save where it is sticky-humid would be substantial. “You save about 50% of the energy,” Kozubal said. “The added cost of the system could easily be paid for by the energy savings.”

Blue Frontier, a Boca Raton, Florida, startup backed by Bill Gates’ Breakthrough Energy Ventures, is also using NREL patented liquid desiccant technology matched with evaporative cooling, which, when it gets to market, the company says will deliver up to 80% energy savings compared with vapor compression.

Both the Emerson and Blue Frontier air conditioning units are aimed at the commercial market. “Residential, that might be something farther in the future,” Kozubal said.

Still, improvements in air condition technology are needed across the board as days get hotter and heat waves get longer. “Right now, our grid is very stressed, even though renewables are going in. In the immediate future more efficient air conditioning helps us save energy,” Kozubal said.

This story is from The Colorado Sun, a journalist-owned news outlet based in Denver and covering the state. For more, and to support The Colorado Sun, visit coloradosun.com. The Colorado Sun is a partner in the Colorado News Conservancy, owner of Colorado Community Media.

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