Buildings turn to ‘ice batteries’ for greener air conditioning

Every night, around 74,000 gallons (280,000 litres) of water are frozen at Norton Audubon Hospital in Louisville. Instead of relying solely on traditional air conditioning, the hospital now uses 27 massive ice tanks to cool water that circulates through its network of pipes, keeping operating rooms and patient wards at safe, comfortable temperatures.

This system — known as ice thermal energy storage or "ice batteries" — is gaining popularity across the United States as a sustainable way to provide cooling without increasing carbon emissions. By shifting energy use to nighttime hours when electricity is cheaper and the grid is under less pressure, the technology cuts power demand and costs while easing strain on the grid.

Trane Technologies, a leading manufacturer of heating and cooling systems, said demand for ice batteries has surged in recent years, particularly from schools, government buildings, and commercial facilities. Another company, Nostromo Energy, is developing systems for large energy consumers like data centres, while smaller home units are being produced by Ice Energy.

How the 'ice battery' works

Though designs vary, all ice storage systems operate on the same basic principle: water is frozen overnight using low-cost electricity, and the ice is then melted the next day to cool circulating water that absorbs heat from the building. The chilled air is distributed through existing ventilation systems.

At Norton Audubon Hospital, Trane's system works alongside conventional air conditioners, reducing energy use during peak daytime demand. Because the stored ice thaws naturally, it requires no additional power, cutting electricity costs and reducing emissions.

"Storing energy for future use is where the power grid is heading," said Ted Tiffany, senior technical lead at the Building Decarbonization Coalition. He added that access to cooling is an increasingly urgent public health issue in a warming world, and ice batteries offer a clean, sustainable solution.

Since installing the system in 2018, Norton Audubon Hospital has reduced its annual energy costs by $278,000 and saved nearly $4 million overall since 2016 through broader efficiency upgrades. "The technology has been awesome for us," said Anthony Mathis, a Norton Healthcare executive who oversees sustainability. He said many building operators have expressed interest in adopting the system.

A growing alternative to conventional cooling

Experts say ice thermal energy storage is an effective option for reducing electricity demand, particularly for hospitals and senior homes, where lithium-ion batteries — another energy storage option — may pose fire risks.

The technology is also attracting attention from data centre operators, whose facilities now consume more than 4% of the U.S. electricity supply — a share that could rise to 12% by 2028, according to a U.S. Department of Energy report.

"Data centres are extremely energy-hungry, and 30% to 40% of their electricity use goes to cooling — that's where our solution can really help," said Nostromo Energy CEO Yoram Ashery. The company's systems are already in use at California's Beverly Hilton hotel and are being considered by major data centre firms.

California remains the biggest market for ice batteries because its grid relies heavily on solar power during the day but switches to fossil fuels at night. Ice storage allows buildings to cool air after sunset without drawing power from the grid.

"A lot of utilities are really interested in this kind of load-shifting technology," said Joe Raasch, chief operating officer of Ice Energy. "It's a great innovation for the grid — especially as cooling demand becomes one of the biggest drivers of future electricity use."