Pascal cuts the climate impacts of climate control

Heat pumps are almost magic. They steal traces of heat from cold winter air and use it to warm a home. They dump the heat from a grocery store freezer outside into a hot summer day.

It’s more efficient to use energy to move heat than it is to generate heat from scratch, which makes heat pumps a powerful tool to lower the carbon footprint of climate control and even some industrial heat needs. They’re already in use in millions of air conditioners, home heating systems, and refrigerators.

Unfortunately, the refrigerants at the core of most heat pumps today are environmentally persistent fluorocarbon gases. When these materials leak, their global warming impact is hundreds or thousands of times as strong as the same amount of carbon dioxide. According to the Intergovernmental Panel on Climate Change, refrigerant leaks are responsible for 3% or more of human-caused global warming—more than the entire aviation industry.

Pascal, a start-up out of a Harvard University chemistry lab, thinks it can side-step the global warming impact of refrigerants with a heat pump system that uses refrigerants that remain solid throughout the heat transfer cycle, which prevents them from escaping into the atmosphere.

Conventional heat pumps work by compressing a gas into a liquid to release heat and evaporating a liquid into a gas to absorb heat. It’s the same principle that makes a can of aerosol spray cold when used. Heat pumps exploit the phenomenon with valves and pumps, creating cold and hot sides of a refrigerant loop.

In addition to avoiding leaks, the Pascal team projects its technology has the potential to double the efficiency of conventional systems because it won’t require vapor compression. “You throw away a lot of energy in that step,” CEO and cofounder Adam Slavney says.

In May, Pascal secured $8 million from a group of venture capital firms that thinks the company is onto something. Commercial refrigeration is Pascal’s first target market, Slavney says, so it will use the money to advance from bench scale to a 1 kW prototype—about twice the cooling power of a domestic fridge.

Pascal’s solid refrigerants have millions of layers, each a few molecules thick. They alternate between positively charged fatty acid chains and various negatively charged scaffolds. Under pressure, the fatty acid layers move from a crystalline state to a disordered one, absorbing heat. “The structure is still crystalline overall, but it’s got a lot of disorder in the organic component. It’s almost as if you have nanoconfined molten wax,” Slavney says. When the pressure is off, the layers freeze again, releasing heat.

Pascal has been using metal halide perovskites as the negatively charged scaffold. Slavney says the firm is exploring different scaffolds that might help the device operate at a wider range of temperatures or smooth compatibility with components like gaskets or valves. “All of the action is in that long fatty acid tail,” he says.“We can completely get rid of the perovskite layer, put in other kinds of layered structures, and get very similar behavior.”

Academics have studied this class of materials, known as barocaloric refrigerants, for about 20 years, but they worked only at extremely high pressures. Slavney says Pascal’s refrigerants are working below 1,000 kPa, pressures similar to those found in mass-market air conditioners today.

The breakthrough powering Pascal’s technology came from the lab of Harvard chemistry professor and Pascal cofounder Jarad Mason, where Slavney was a postdoc and cofounder Jinyoung Seo was a PhD candidate. Seo and Slavney were working together on test systems they could use to compare barocaloric refrigerants when they realized they had made a fundamental advance on these materials.

Slavney knows that people buying heating and cooling systems aren’t always thinking about the climate, so he hopes to convince them with a financial argument.

“You need to be able to deliver a product that’s going to cut their electricity bill,” he says. “We’re trying to show that in a realistically sized system, we can do that.”