Why CO₂?

As industries and policymakers seek to reduce greenhouse gas emissions and phase out harmful refrigerants, like hydrofluorocarbons (HFCs), CO₂ presents an increasingly viable solution.

CO₂ refrigeration, also known as R-744, is a naturally occurring gas with several key advantages over traditional refrigerants. The primary benefit is its low global warming potential (GWP). Unlike HFCs, which can have a GWP in the thousands, CO₂ has a GWP of 1, making it an environmentally superior alternative. Beyond its sustainability, R-744 is nonflammable and nontoxic in short-term exposures, eliminating the need for extensive safety infrastructure that other refrigerants require.

Supercritical CO₂ Technology

As CO₂ continues to make headway, supercritical technologies are at the heart of this evolution. Operating at high pressures, supercritical CO₂ can exist in both liquid and gas states, making it highly efficient for heat exchange processes.

Pittsburgh, Pennsylvania-based Clean Heat Technologies, a Thar Company, has spent years studying supercritical CO₂ and is now utilizing that expertise to push the limits of modern technology. In 2008, the company began experimenting with CO₂-infused geothermal projects, and, today, it continues its experimental approach through numerous CO₂-based solutions, including heat pumps, high-temperature steam systems, and more.

CO₂ STEAM DREAM: Lalit Chordia, founder and CEO, Thar Energy LLC and Clean Heat Technologies, stands next to a CO₂ steam/hot water system. These systems have many uses, including tall buildings, hospitals, pools, and more. (Courtesy of Clean Heat Technologies)

“Our understanding of the properties of supercritical CO₂ allows us to manipulate CO₂ from a liquid to supercritical to a gas and then to recycle it,” said Todd Palcic, chief commercial officer, Clean Heat Technologies. “Ultimately, we’re able to produce high-pressure systems with superior heat transfer properties within smaller footprints.”

Palcic said Clean Heat Technologies focuses on reducing clients' operating costs while minimizing their environmental impact when developing solutions, and CO₂ refrigeration continues to aid the company on that journey.

“CO₂ is nonflammable, which helps keep infrastructure costs down,” said Palcic. “Also, with CO₂, we’re not as worried about leaks because it has such a low GWP, and short-term exposure for humans is not an overly dangerous situation.”

The company recently built a CO₂ supercritical extraction unit that included an air-source heat pump, which Palcic deemed extremely successful.

“We sold that system to a large nutraceutical company, and it is currently in operation in Arizona,” he said. “The combined heating and cooling solution reduced the existing comfort footprint by approximately two-thirds and energy usage by about 50%.”

Clean Heat Technologies also utilizes supercritical CO₂ for extraction purposes, such as cleaning up polymers in waterproofing materials and extracting essential oils contained in fragrances.

“CO₂ has a low viscosity, a high diffusivity, and a low surface tension that provides selective extraction, fractionation, and purification,” said Palcic. “This allows it to penetrate micro-and macro-porous materials exceptionally well.”

Upcycling

Beyond supercritical technology, companies like Clean Heat Technologies are finding additional ways to harness the power of CO₂ refrigeration systems through upcycling. Upcycling is the process of improving or repurposing existing refrigeration systems that use CO₂, making them more efficient or environmentally friendly.

“I consider upcycling a way to make an existing process better – replacing a 20^th-century technology with a 21^st-century technology,” said Palcic. “For example, entrepreneurs aren’t as focused on improving combustion engines anymore – they’re focused on electric vehicles or hydrogen systems, electric planes, flying cars, etc. The same can be said about hydrocarbons or HFCs — we’re not looking to go backward; rather, we’re only interested in moving forward.”

The Future Is Near

While upcycling is one way to improve today’s CO₂ refrigeration systems, the future holds even more promise. Palcic predicts CO₂ will expand far beyond its current applications, revolutionizing industries ranging from biodiesel processing to data centers in the coming years.

“CO₂ refrigeration will be huge in the processing of vegetable oil, biodiesel, and acetyl extraction,” he said. “There are numerous $200-$400 million plants being built, and I believe many of them will utilize supercritical CO₂. Anywhere there’s a press involved, or cooling in the extraction process, you can expect CO₂ to be on-site.”

He also believes the dual capabilities of CO₂ heat pumps will have a major role in various industries.

“The hybrid heat pump approach offers advantages for nearly every facility that has a need for both cooling and heating,” he said. “From grocery stores to pharmaceutical facilities, hospitals, and more, the demand is there. Laboratories and manufacturing are great examples of industries that may benefit from packaged cooling, heating, and hot water solutions. Other industries, like data centers, may benefit from supercritical CO₂ as well.”

As CO₂ refrigeration continues to make inroads in the U.S., Palcic encourages contractors to dive in as soon as possible, as those who have yet to adopt it may find themselves playing catch-up sooner than later.

“Contractors may have concerns about pressure and leakage; however, if they’re skilled in the refrigeration cycle, with a little training, they can handle CO₂ — it’s not that much different,” said Palcic. “Supercritical CO₂ represents a significant leap toward a more sustainable future. Those who invest in CO₂ expertise now will be the leaders in tomorrow’s refrigerant industry, and Clean Heat Technologies is here to help.”