Designing air conditioners that won’t cook the planet

The Global Cooling Prize awards $1 million to designs that shave energy, reduce global warming and could make AC more affordable and eco-friendly for billions.
By Jeff St. John

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Image credit: RMI

Air conditioning creates a vicious cycle for a warming planet.

The hotter it gets, the more people will need cooling — not just for comfort, but also for health and even survival. But air conditioning is itself a major driver of climate change, using hydrofluorocarbons that act as a potent greenhouse gas when leaked, and adding major electricity loads to power grids striving to move from fossil fuel to carbon-free generation.

This combination is a big problem for the fight against climate change, according to a 2020 report from the United Nations Environment Programme and the International Energy Agency. But it’s also an opportunity for more efficient and environmentally friendly air conditioning to reduce those impacts, if they can find their way into the roughly $60-billion-per-year global residential air conditioner market.

That’s where the Global Cooling Prize comes in. Announced with fanfare by billionaire business magnate Richard Branson two years ago, the contest has drawn eight companies seeking to meet its aggressive target of a residential air conditioner with a fivefold reduction in climate impact, compared to today’s standard models.

On Thursday, the program announced two winners that will split the $1 million grand prize, after proving that their units’ combination of dramatically lower electricity use and lower global warming potential (GWP) refrigerants can meet that target.

Iain Campbell, a three-decade veteran of the air-conditioning industry and senior fellow at nonprofit RMI, said this 5× improvement target made my jaw drop.” RMI partnered with India’s Department of Science and Technology and global initiative Mission Innovation to run the contest.

But this aggressive target is appropriate for a technology that’s set to quadruple in demand over the coming decades, he said.

We have 3 billion people living in the tropics who don’t have access to these technologies today,” Campbell told Canary Media. Major improvements are needed to help mitigate the impact of more access to cooling, which is a utility I don’t think can be, or should be, denied.”

Achieving drastic emissions cuts with split AC units

The winning teams are China-based Gree Electric Appliances with partner Tsinghua University and India-based Daikin with Japan-based partner Nikken Sekkei. Both winners are major global manufacturers of split” air conditioning systems, which use pipes to carry refrigerant between indoor air cooling units and outdoor compressor units. Splits are the residential product of choice for most global markets, unlike the central-air systems or window-mount systems common in the United States.

Each winning unit has unique design elements, Campbell said. For example, the Gree unit has a small solar panel mounted alongside the outdoor compressor unit to provide extra juice on sunny and hot days, while the Daikin unit uses a novel blend of refrigerant with a lower global warming potential, he said.

But both units used common features that combined to dramatically reduce the electricity used to cool rooms, according to Campbell. Those include advanced vapor compression technology,” efficient dehumidification” and integrated direct evaporative cooling,” along with other advanced controls to make the most of those technical features.

Campbell broke down how each feature contributes to lower energy use, starting with the issue of humidity. Air-conditioner testing standards today measure performance in reducing temperature, not in reducing humidity. But humidity plays a major role in how humans are affected by heat, since it inhibits the role of sweat in evaporating heat away from our bodies.

Most air conditioning today simply overcools incoming air to deal with humidity, Campbell said. But the Global Cooling Prize test site, a 14-story apartment building in Bahadurgarh, India, offers conditions of extreme heat and extreme humidity. […] We were testing for things that the standards didn’t test. And we discovered the technologies for the winners were optimized for the conditions we were testing in.”

Specifically, the winning models lowered the speed of their outdoor fans and compressors, and ran even lower temperatures into the indoor evaporator coils that absorb heat and thus cool indoor air, in a way that amounted to a very efficient dehumidification machine,” he said.

This design choice evokes some of the earliest applications of air-conditioning technologies to dehumidify factories and warehouses. This feature alone accounted for about a third of their efficiency improvement and is probably one of the bigger breakthroughs in relation to this prize.”

Both winning designs also add water misting to the air surrounding the outdoor condensers that repressurize refrigerant — the hot part of an air conditioner — to lower its temperature and thus improve the efficiency of that part of the cycle, Campbell said.

Both units also use variable-speed fans, along with advanced sensors to measure indoor and outdoor temperature and humidity, to allow them to better match system operations to real-world conditions, according to Campbell. The result is a system that doesn’t waste energy, unlike the simple thermostat-controlled systems that so often leave homes or offices much chillier than comfort requires.

How to turn high-tech efficiency into mass-market adoption

All of this technological sophistication comes at a price. Both winning units are expected to cost between two and three times the roughly $500 price of a typical residential split unit.

But their much greater efficiency adds up to a lifetime operating cost that’s roughly half that of today’s standard models, with payback on energy savings occurring after about three years, according to accelerated lifecycle testing data. And that’s not counting the increased comfort and control they provide, Campbell noted.

As for the climate change benefits, last year’s UNEP and IEA report found that doubling the efficiency of air conditioning could reduce global electricity demand by 1.3 terawatts, the equivalent of coal-fired power in China and India combined. Now that technologies that can do even better than that have been proven in field trials, the next steps will be to find ways for global markets to reward their long-range benefits despite their higher up-front cost, Campbell said.

The biggest challenge on this front is redesigning testing and rating systems to make the lifetime value of these advanced designs apparent to the builders, landlords and everyday consumers that will be buying them.

You’ve got two main challenges in the air conditioner space,” Campbell said. One is that the ratings systems only test about two-thirds of the load” because they don’t test for the impact of humidity on how air conditioners operate.

The other is that most testing regimes have minimum energy performance standards that are way below what’s possible,” with performance ladders” that fail to make clear the additional value of highly efficient units.

The testing systems are lagging behind what we can see the technology is able to do,” he said. RMI intends to work with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory and CEPT University in India, its Global Cooling Prize testing partner, to develop methods to translate the results of its tests into guidance for better standards on this front, he said.

Beyond its $1 million grand prize, the eight finalists each earned $200,000 for their contributions. But as a cohort that collectively serves about 20 percent of the global residential air conditioning market, they’ll need to see testing and certification regimes that capture these values to start manufacturing them at large volumes.

Two participants — Gree and China-based Qingdao Haier, which partnered with Transera — have pledged to bring units based on these designs to market by mid-decade as part of their announced intention to join the COP26 Race to Zero Breakthrough” initiative for the cooling sector. Other participants, including Daikin, may follow suit.

As more efficient units are introduced into the market, government agencies and utilities could offer subsidies, on-bill financing and other incentives to spur their adoption, Campbell said. There’s good reason to consider such investments to be as important to combatting global warming as investing in renewable energy, he noted, given that the growth in air-conditioning load could well outpace the growth in solar power in the years ahead.

(Article image courtesy of RMI

Jeff St. John is director of news and special projects at Canary Media. He covers innovative grid technologies, rooftop solar and batteries, clean hydrogen, EV charging and more.