The average AC sold in 2024 was already about 20 percent more efficient than an equivalent model in 2014. However, there’s still plenty of room to grow, as the IEA predicts that “cooling demand” will grow by 1,600 terawatt-hours by 2035—Japan and South Korea’s total electricity combined. But this kind of proximity sensing could also result in marginal energy savings.

“There is a performance improvement you can get if [targeted AC] is done well,” says Vincent Romanin, founder and CTO of San Francisco–based Gradient, which makes 120-volt all-weather window AC/heat pumps. “But we’re going into buildings where we’re reducing the energy by 85 percent and to design another feature that gets us to 87 percent? I personally have never used a product with an occupancy sensor that I feel like worked well.”

Compact Window ACs

For Palm, to reach sustainable home cooling by 2050, we need three major changes: cheaper, compact heat pumps for all home sizes; fewer toxic natural refrigerants (fluids and chemical compounds that absorb and release heat); and newly designed systems with low charge to ensure safety.

Heat pumps have become a modern, efficient option for heating and cooling. For heating, it’s a four-stage process: absorbing outside heat to produce gas via a refrigerant; compressing to raise the temperature; condensing, where heat is passed to the water in your home’s heating system; and cooling back into a liquid via an expansion valve to drop the pressure. When cooling is needed, the reversing valve switches back to run the process from inside to outside for air-conditioning.

The key is to persuade renters and people living in smaller homes to make the overall switch. “For the domestic market, we need heat pumps which fit into an apartment without being too noisy or bulky,” Palm says. It’s also critical to reduce the price.

Gradient units typically use one-third less energy than a standard window AC, mostly for heating but with cooling efficiencies too. They’re a quick self-install option that lets apartment renters get their window back, see lower bills, and run a quieter AC system than older models.

But fixing the form factor only solves part of the equation. Palm’s other criteria—replacing toxic synthetic refrigerants with natural alternatives like propane (R290), as in Bosch’s Climate 6000iP, which launched in September—present a tougher engineering challenge. Leaking refrigerants alone account for an estimated 720 million metric tons of CO2-equivalent emissions every year. Natural refrigerants dramatically curb the potential for global warming, but their flammability demands complex, spark-free redesigns and low-charge systems that US regulators and supply chains are still cautious about embracing.

Reaching sustainable cooling by 2050 won’t be glamorous, Palm says. Ultimately, the future of home cooling won’t hinge on an air conditioner that tracks you to the kitchen for a midnight snack—it depends on the unsexy, invisible mechanical work happening deep inside the compressor.