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The current environmental trend right now is electrification, which is part of a broader global strategy to decarbonize economies around the world. In the U.S., the federal government, along with numerous states, has pledged to aggressively reduce — and potentially eliminate — carbon emissions over the next few decades. This typically involves encouraging Americans to replace their fossil fuel appliances like gas furnaces with electric heat pumps. But most heat pumps and air conditioners currently use R-410A refrigerant — or even R-22 in older units — which is a high-GWP HFC that the federal government is in the process of phasing down.

In response to this conundrum, a raft of so-called “clean tech” startups and other research groups are looking for ways to reduce carbon and refrigerant emissions through the use of new cooling technologies. The result is a number of promising innovations, which could bring significant changes to the HVAC industry.

Decarbonized Cooling

One such startup is Blue Frontier in Boca Raton, Florida, which recently made headlines when Bill Gates’ clean energy investment fund, Breakthrough Energy Ventures, announced it was spearheading a $20 million investment to accelerate new company’s ability to bring its “ultra-efficient sustainable air conditioning technology” to market. According to Blue Frontier’s owner and founder, Dr. Daniel Betts, this investment will help the company realize its goal of significantly reducing greenhouse gas emissions by decarbonizing building cooling.

NEW SYSTEM: A prototype of Blue Frontier’s new air conditioning system, which is expected to be commercially available in 2025. (Courtesy of Blue Frontier)

“Blue Frontier solves the problem of the high energy and power consumption of traditional air conditioning and the increasingly high climate change impact due to that energy consumption,” he said. “Blue Frontier air conditioners consume 50% to 90% less energy and also store energy at a fraction of the cost of batteries, so that low-cost, low-emission electricity can be used to provide cooling during evening peak load times.”

Blue Frontier’s packaged rooftop air conditioner contains a novel heat exchanger that both cools and dehumidifies air through the use of a salt solution (liquid desiccant) that removes humidity from the air without increasing its temperature, explained Betts. This dry air can then be cooled through the indirect evaporative cooling process, which separates about 30% of the dry air, flows it adjacent to the rest of the air within the heat exchanger, and subjects it to evaporative cooling. This process cools down the 70% remaining bulk air without increasing its humidity, creating conditioned, low-humidity air.

The water absorbed into the liquid desiccant can then be recovered using a small heat pump that also increases the salt solution’s concentration so that it can be used again. This process requires much less energy and a much lower volume of refrigerant than an equivalent vapor-compression RTU of the same cooling capacity, said Betts.

LOW GWP: The Blue Frontier air conditioning system, shown here being tested at NREL, will use the low-GWP refrigerant, R-454B. (Courtesy of Blue Frontier)

“One of the fantastic side benefits of using liquid desiccant is that it kills airborne pathogens, while maintaining lower humidity indoor conditions in humid climates for the control of mold and bacterial growth,” he said. “In addition, our system is three times more efficient than a conventional air conditioning system and has integrated energy storage that allows us to tie air conditioning electricity consumption to periods when renewable energy is bountiful (e.g., from solar during the middle of the day). Our system also uses the low-GWP refrigerant, R-454B, and the volume needed is less than one-third that of a traditional air conditioner.”

Blue Frontier will initially offer a 5- to 10-ton RTU, which will have a similar size and configuration as existing 10-ton RTUs, with the added technology benefits of energy storage, improved humidity and temperature control, increased outdoor air ventilation, and better air filtration, said Betts. Based on testing to date, the new RTU’s projected IEER will be 38 for the full cooling-regeneration cycle and equivalent to an IEER of 129 when running off energy storage. The RTU can be installed in any new construction or retrofit application and in virtually any climate.

Blue Frontier’s unit can be used as a drop-in replacement for existing 5- to 10-ton RTUs, and Betts expects huge demand from the retrofit market due to its greater energy efficiency. There will be some differences in the installation of the unit, including the requirement to locate the tank containing the desiccant either somewhere else on the roof or at another location in the building. Fluid lines then need to be connected to the RTU. Blue Frontier plans to provide additional training on installation and maintenance procedures in the future.

“Due to the step-change improvements in efficiency, comfort, and health, we expect to increase demand for the retrofit of existing air conditioners, even before the useful life of the existing air conditioner has been exhausted,” said Betts. “That’s because the environmental and occupant benefits are so huge, they outweigh any disadvantage or lost value from removing a functioning RTU. This will increase business for contractors and technicians.”

The Blue Frontier RTU is expected to be commercially available in 2025. In the meantime, the unit is going through pilot, Alpha, and Beta launch phases, with installation in select markets to help validate the real-world performance, benefits, installation, maintenance, and training requirements prior to commercial launch.

As part of the product launch in 2025, Blue Frontier plans to offer “HVAC-as-a-Service,” which will eliminate the upfront cost of the new RTU to building/project owners, encouraging them to try the new technology that will largely be paid for through energy cost savings. Betts said this will make it even easier for contractors to sell.

“We already have so much demand and interest in our air conditioners, and we believe that demand will only accelerate as people experience the benefits in the real world,” he said.

CO₂ Cooling

Another innovative technology is Dalrada Financial Corp.s’ LikidoONE heat pump, which was recently selected by the U.S. General Services Administration (GSA) and Department of Energy (DOE) as part of the federal Green Proving Ground (GPG) program. The CO₂-based heat pump is now being tested as part of the government’s efforts to find new technologies that use lower-GWP refrigerants and reduce greenhouse emissions from commercial buildings.

The idea for the LikidoONE was born in the United Kingdom, where heat pumps and boilers are ubiquitous in homes and commercial buildings.

“It all started with a few simple questions: how can we decarbonize heat that depends so heavily on fossil fuels? And is it possible to recover the waste energy lost into the atmosphere during this process?” said Jose Arrieta, chief strategy officer and president of Dalrada Technologies in San Diego, California. “So we designed LikidoONE to address these challenges, ensuring capabilities for long-term decarbonization and improved energy efficiency, resulting in a cleaner environment and increased cost savings for the user.”

LikidoONE industrial heat pumps use CO₂ (R-744) as the refrigerant in a closed system. The heating and cooling loads are connected via secondary heat transfer fluids, usually water or glycol. The core technology employs supercritical CO₂ as the working fluid to enable the highly efficient recovery of low-grade heat from air, water, or thermal waste streams, for use in high-grade heating applications.

By using CO₂, the heat pump requires much less energy than traditional methods, said Arrieta. The machine also has the ability to provide more recycled energy, and its modular, origami-like design makes assembly and integration with existing systems easy. Its stainless steel hardware is designed to withstand extreme pressure and temperature fluctuations, and the machine can deliver instant, on-demand hot and cold water.

“This promising technology is great for use in applications that link to local heat networks, where hot and cold coupling is a necessity, such as in IT, server cooling, or district heating,” said Arrieta. “Overall, LikidoONE increases energy efficiency by 75%, making it seven to eight times more efficient than traditional boilers and heat pumps.”

LikidoONE works in virtually any temperature or climate condition and can be used in both retrofit and new construction with minimal modifications, said Arrieta. The installation, service, and maintenance of LikidoONE heat pumps are no different than traditional heat pumps, he added.

“Our goal is to disrupt conventional heating and cooling technology markets, and we’re hopeful our product will directly answer the call for improved heating and cooling efficiency abroad, but especially in the U.S.,” said Arrieta. He anticipates LikidoONE industrial heat pumps will be commercially available very soon, and the company is in the process of developing a residential version, which it hopes will be available in the near future.

Solid Refrigerants

At Harvard University, researchers have developed a new class of solid-state refrigerants that could enable energy-efficient and emission-free cooling. Given the concerns over high-GWP refrigerants typically used in air conditioning equipment, solid refrigerants could be a possible solution.

SOLID STATE: A first-of-its-kind prototype cooling system at Harvard University uses new solid-state barocaloric materials. (Courtesy of Adam Slavney)

Traditional cooling systems, such as air conditioners, work by causing a refrigerant to cycle between being a gas or a liquid. Unlike gases, solids won’t leak into the environment from a/c units. One class of solid refrigerants, called barocaloric materials, work similarly to traditional gas-liquid cooling systems. They use pressure changes to go through heat cycles, but in this case, the pressure drives a solid-to-solid phase change. That means the material remains a solid, but the internal molecular structure changes.

The key structural aspect of these barocaloric solid materials is that they contain long, flexible molecular chains that are typically floppy and disordered. But under pressure, the chains become more ordered and rigid — a change that releases heat. The process of going from an ordered to a relaxed structure is like melting wax, but without it becoming a liquid, said Jarad Mason, Ph.D., the project’s principal investigator, who is at Harvard University. When the pressure is released, the material reabsorbs heat, completing the cycle.

A disadvantage of barocaloric systems, however, is that most of these materials require massive pressures to drive heat cycles. To produce these pressures, the systems need expensive, specialized equipment that’s not practical for real-world cooling applications. Mason and his team recently reported barocaloric materials that can act as refrigerants at much lower pressures. They’ve now shown that the refrigerants, which are called metal-halide perovskites, can work in a cooling system they’ve built from scratch.

The first-of-its-kind prototype demonstrates the use of these new materials in a practical cooling system. “Our system still doesn’t use pressures as low as those of commercial refrigeration systems, but we’re getting closer,” said Mason.

“We’re really hoping to use this machine as a testbed to help us find even better materials,” said Adam Slavney, Ph.D, a chemist and materials scientist at Harvard, including ones that work at lower pressures and that conduct heat better. With an optimal material, the researchers believe solid-state refrigerants could become a viable replacement for current air conditioning and other cooling technologies.