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Hillphoenix is launching a new product and partnering with food retailers and others to address charge preservation in CO2 systems.
Sonia Saini

CO2 (R744) is used in commercial refrigeration because of its excellent thermophysical properties (including high energy content, excellent heat transfer coefficient and low viscosity of the liquid phase).

One aspect of these properties is that when the system warms during an extended power loss, the pressure increases.  To protect the piping system, a charge release may occur through a pressure relief valve. The amount of charge released depends on the length of the power outage, but if enough charge is lost it may disrupt the restart and operation of the system.

As transcritical CO2 systems gain more adoption in North America – following their dynamic growth in Europe – OEMs, contractors and end users are increasingly focusing on the need to limit or prevent releases of CO2. The North American Sustainable Refrigeration Council (NASRC) has recently convened a working group of stakeholders to tackle this important issue. There are different strategies to help manage charge preservation and different stakeholders have different views on how to address it.

However, U.S. OEM Hillphoenix is releasing a product designed to help with charge preservation for CO2 systems in a cost-effective manner.

ChargeSecure coming this summer

Hillphoenix is a leading provider of transcritical CO2 systems, with over 1,500 installed in North America (18,000+ units globally). It has already provided some solutions to the charge-release challenge and this summer will release another system to help address charge preservation called ChargeSecure. Powered by a dedicated generator or battery power, this device will prevent pressure buildup by maintaining a CO2 circuit from the flash gas receiver to a compressor and the gas cooler.

The benefit for end users is their CO2 system can maintain a its charge during a power outage or service event, including the normal restart of the system and its operating capabilities.

Powered by an uninterruptible power supply (UPS) battery backup or emergency power, the new ChargeSecure is a 100% natural solution because it uses CO2 from the rack, noted Scott Martin, Senior Director Industry Relations and Compliance for the Georgia-based Hillphoenix.

Hillphoenix and its European affiliate Advansor have pioneered the use of a UPS on the rack to close all valves in the system – including the expansion, high-pressure and flash-gas valves – during a power failure. This will “isolate the refrigerant and not let it migrate and cause relief valves to open prematurely,” said Martin. “It slows the pressure increase.”

Higher pressure ratings debated

Concerns about CO2 charge preservation have led some U.S. foods retailers to ask if the pressure rating of piping in transcritical systems should be raised significantly – up to 90bar (1,305psi) – throughout the system, including in suction piping.

Through science-based and practical approaches, the industry is discussing where in the system pressure rating should be raised. However, more work is believed to be required before a conclusive decision can be made.

There are many factors that could impact the decision to go with high pressure systems. As an example, high-side rack pressure ratings are already at a higher pressure – 120 or 130bar (1,740 or 1,885psi) – but the industry standard for in-store piping such as liquid supply lines is currently 45bar (653psi), with medium-temperature suction piping also at 45bar and low-temperature suction piping at 30bar (435psi).

Martin agrees that liquid-line piping could benefit from a higher-pressure rating – at least 60bar (870psi) and up to 80bar (1,160psi). The liquid line is the most susceptible part of the system to pressure buildup during an outage because the liquid expands to a gas, he noted. By contrast, suction lines already contain mostly gas, which doesn’t increase in pressure nearly as fast.

As a comparison, the majority of European OEMs use 60bar in liquid lines, while 20% employ 80bar. For suction lines, the majority have 60bar medium temperature and 30bar low temperature.

An important factor is the cost-benefit of going to 90bar. Martin pointed out that raising the pressure rating for all in-store piping to 90bar would require the use of copper-alloy piping, upgraded evaporator coils and medium-temperature compressors for low-temperature applications. All of those would add to costs. Other strategies for minimizing charge loss, such as placing the flash-gas receiver in a walk-in cooler, would also increase the price of a transcritical CO2 installation.

“There are many design options that have various application costs; therefore, we should balance effort versus reward,” Martin said.

To further address this issue and provide more information on ChargeSecure, Martin will be participating in a case study presentation on approaches to mitigating CO2 charge loss during power or service events at the ATMOsphere America conference, to be held June 10–11 in Washington D.C. Martin’s presentation will begin at 3:15 p.m. on June 10.

“There are many design options that have various application costs; therefore, we should balance effort versus reward.”

– Scott Martin, Senior Director Industry Relations and Compliance for Hillphoenix.

Curated News With Commentary
Source: Modern Retail

[‘An Industry the Internet Hadn’t Reached Yet’: DTC Home Heating & AC Brands Are on the Rise”]

Why It Matters: Direct-to-consumer (DTC) home heating and AC brands are gaining ground in the U.S. as companies attempt to cut out middlemen and reach consumers directly. Three of the big players, heat pump manufacturer Quilt and window air-conditioning brands Windmill and July, all use HFCs. However, in getting consumers comfortable with buying heat pumps and ACs online, they could pave the way for future competitors using natural refrigerants, such as Aira, a Swedish DTC propane (R290) heat pump maker. R290 heat pumps have yet to take off in the U.S. due to charge limits, which ASHRAE said won’t be raised until “2025 or later.”

CEO Peter Hettich spoke with about the new organization and its objectives.
Sonia Saini

As momentum gathered last year for the European Union’s revised F-gas Regulation, one of the loudest voices of dissent in Germany came from the German Association of Refrigeration and Air-Conditioning Contractors (Verband Deutscher Kälte-Klima-Fachbetriebe, VDKF). The Bonn-based trade association counts more than 1,000 HVAC&R contractors as members, and throughout 2023 it raised the alarm, saying the revised regulation’s phase out of HFCs would hurt contractors, damage the economy and even keep the bloc from reaching its climate goals. 

The revised F-gas Regulation became law in March, and with it the clock began ticking on the use of HFCs in heating and cooling equipment.

While the VDKF bemoaned the news, Bluu Unit celebrated it. Bluu Unit is an alliance of German HVAC&R contractors that promotes the use of natural refrigerants. It’s backed by private equity firm Triton Partners and led by CEO Peter Hettich. In a recent interview with ATMOsphere Founder and CEO Marc Chasserot – ATMOsphere is the publisher of – Hettich laid out his goal for the organization.

“We want to be Germany’s leading provider of refrigeration and climatization solutions based on natural refrigerants and sustainable services,” Hettich told

Hettich detailed his plans to reach that goal in a conversation with Chasserot, which took place on the sidelines of the 2024 B2B networking conference Digisustain, held April 29–May 1 in Frankfurt.

Big ambition, big backer

The seed for Bluu Unit was planted in July 2022 when Triton acquired a majority stake in the Kälte Eckert Group, an air-conditioning and refrigeration contractor in Markgröningen, Baden-Württemberg. Triton is active in the business services, industrial tech and healthcare sectors, and the PE firm says it has raised more than €18 billion ($19.5 billion) across three funds since its founding in 1997.

Triton then acquired five more German HVAC&R contractors with the aim of creating “a national market leader for sustainable refrigeration technology.” That market leader became Bluu Unit, which launched this past January at the World Economic Forum in Davos.

“We currently have 10 companies in this alliance, and we’re seeing huge interest [from others],” said Hettich. “Our vision has proven very attractive.”

Part of the appeal of that vision has to do with Bluu Unit’s focus on fostering business development among its member companies.

Building businesses

Bluu Unit tells prospective members – it specifies that it’s looking for medium-sized companies – that it has a “sustainable concept for successful growth based on partnership-based corporate development.” In plain terms, Hettich said the objective of the alliance is to help members build their businesses and grow their skill in working with natural refrigerants through knowledge sharing.

Hettich said Bluu Unit has established training academies for alliance members that offer the opportunity to learn about new systems and technologies. Alliance members also work together on joint projects, and companies can loan out employees to fellow member companies for lengthy projects to truly cement their knowledge of a new system or refrigerant.

Related reading: European Commission Publishes Proposed Natural Refrigerant, F-gas Training Certificate Regulation

“There is support for planning activities, writing tenders and even in digitization,” said Hettich. “The goal is to give members access to the full knowledge of the alliance to then provide the highest customer value in a sustainable manner.”

Delivering customer value is incredibly important to Hettich. He noted that, despite the importance of educating contractors in the advantages of natural refrigerants and how to use these technologies, success comes from “working your way back from the customers.”

“I see Bluu Unit as more of an enabler, one that helps these companies transform and grow,” Hettich said. “Each of our members has long-lasting and powerful relationships with their customers. We want to preserve these and use them as the foundation to drive this [refrigerant] transformation.”

“We want to be Germany’s leading provider of refrigeration and climatization solutions based on natural refrigerants and sustainable services.”

Peter Hettich, CEO of Bluu Unit

The European Commission’s assent puts the sale, valued at $775 million, one step closer to closing.
Sonia Saini

The European Commission has announced its approval of Chinese OEM Haier Smart Home’s acquisition of Carrier Commercial Refrigeration (CCR), noting that it “would not raise competition concerns, given the companies’ limited combined market position resulting from the proposed transaction.”

Even with the European Commission’s authorization, the sale is still not finalized, although it is expected to close sometime in the second half of 2024.

The deal: U.S.-based manufacturer Carrier originally announced the sale of its European commercial refrigeration business to Haier Smart Home, a division of Haier, in December 2023. Carrier Commercial Refrigeration was sold for $775 million (€705.1 million).

  • European CO2 (R744) refrigeration systems manufacturers Profoid, Celsior and Green & Cool were also included in the deal. Transportation refrigeration company Carrier Transicold, supply chain visibility software maker Sensitech and cold chain monitoring platform Lynx were not included.
  • CCR counts more than 4,000 employees and has a sales and service network that reaches beyond Europe and into the Asia–Pacific region.

A legacy of CO2: Carrier Commercial Refrigeration installed its first transcritical CO2 rack at a supermarket in Switzerland in 2004. In December 2022, it announced the installation of its 20,000 transcritical CO2 rack.

  • In addition to Europe, CCR recently announced that its CO2 racks, heat pumps and condensing units would be available in North America.
  • While Haier does not have CCR’s extensive experience with CO2 refrigeration systems, it’s not entirely unfamiliar with the technology.
  • Carrier and Haier formed a joint venture in China, the Qingdao Haier Carrier Refrigeration Equipment Company, in 2001. In 2020, the company won a contract to supply a transcritical CO2 ice-making system for a speed skating rink at the 2022 Beijing Winter Olympics.

Pivoting to heat pumps: In April of 2023, Carrier announced its acquisition of Viessmann Climate Solutions from the Viessmann Group, establishing the company as a major player in the European heat pump industry.

  • Heat pumps and related services comprise more than 70% of Viessmann Climate Solutions’ business. Viessmann builds both residential and commercial propane (R290) heat pumps and has seen its sales increase 15% annually since 2020, according to Reuters.
  • The €12 billion ($13.1 billion) sale officially closed in January 2024 after receiving approval from the European Commission in December 2023.
  • Haier, through its Haier HVAC Europe division, also sells propane residential heat pumps, water heaters and air conditioners. It showed off an air-to-air split R290 heatpump at Chillventa 2022 in Nuremberg, Germany.
Ejnar Luckmann, the store’s Technical Manager, gave ATMOsphere an exclusive tour of the smart store.
Sonia Saini

Last summer, Danish component manufacturer Danfoss opened a “smart store” next door to its headquarters in Nordborg, Denmark, which provides an opportunity to showcase its latest CO2 refrigeration technology and conduct R&D. The store shows what’s possible with an integrated CO2 system.

The smart store is a working supermarket with 813m2 (8,751ft2) of floor space and a 240m2 (2,583ft2) machine room, which houses the R&D lab, known internally as the application development center (ADC). A major focus of the store is energy savings and efficiency, and to that end its integrated CO2 system provides refrigeration, heating and cooling. In addition, there are 100kW solar panels installed on the roof that supply most of the store’s electrical power.

Ejnar Luckmann serves as the store’s Technical Manager, and he gave Marc Chasserot, Founder and CEO of ATMOsphere, a tour of the ADC, highlighting the energy savings realized in the year since the store’s opening and possible further system integrations. ATMOsphere is the publisher of

Heat producers

Luckmann noted that when it comes to heating, the smart store has been self-sufficient. It is equipped with Danfoss’s heat recovery unit, which supplies comfort heating and domestic hot water. The company’s heat recovery unit was nominated for the ATMO 2023 Innovation of the Year Award for North America as part of the 2023 ATMO America Summit.

Excess heat is sold to the local district heating network, and Luckmann said sales have been brisk.

“Since its commissioning in May 2023, the store has bought 87kWh of heat ‒ required for the system startup ‒ and sold over 15,000kWh to district heating,” Luckmann said.

He noted that the system produced one and a half times the heat needed by the store and the ADC in a test conducted during the winter with a −6°C (21.2°F) nighttime temperature and a roughly 0°C (32°F) daytime temperature.

“Being able to create energy at very low temperatures to get the highest performance in our area is what it is about,” Luckmann said. “The CO2 system is a heating machine and a refrigeration system.”

An optimized system

The Danfoss store contains two CO2 refrigeration racks: a standard one and an “energy pack” with all the “bells and whistles,” including parallel compression and ejector technology, Luckmann said.

The energy pack covers refrigeration, heating and comfort cooling in one rack, with connections to a ground-source heat pump and a Danfoss heat recovery unit. The store’s medium-temperature cooling capacity is 30kW (8.5TR), and its low-temperature capacity is13kW (3.7TR).

In addition, a heat recovery wheel in a standard air handling unit recovers heat from the air sucked out of the supermarket.

According to Luckmann, the efficiency of the wheel runs a little above 80% heat recovery, adding that it is not about optimizing the wheel but rather streamlining the entire system.

A total of 50 electrical and heating meters monitor and help optimize the store’s energy usage, with digitalization providing an overview of all the applications. “Optimization is a compromise between the applications and not a suboptimization of one application,” he added.

Suitable to every climate

The Danfoss smart store is equipped with a roof-mounted adiabatic gas cooler despite the absence of high ambient temperatures in Nordborg, with summer temperatures rarely climbing above 26.7°C (80°F).

Luckmann explained that the store experiments with different technologies for different environments. “In a hot climate, an adiabatic gas cooler, using a little bit of water, gives 5‒7K (5‒7°C/9‒12.6°F) extra cooling; CO2 systems operating in countries closer to the equator need that cooling.”

The store contains Danfoss CO2 technologies for colder and hotter climates than those in Denmark and for different-sized stores, including hypermarkets and smaller grocery outlets. “We are showcasing it here, and we can bring customers from around the world to have a good dialogue about what makes sense for them,” Luckmann said.

Additional tech

According to Luckmann, Danfoss has determined the appropriate size for a battery storage unit to add to the system based on the energy stream data for the year. “Battery storage will allow us to optimize electrical energy flow, storing it at low prices and offloading it at high prices,” he said, adding that the company plans to build it this year.

Other technologies in the works include cold and heat storage, car charging stations for electric vehicles and hydronic heating/balancing.

The compressor is the first Vilter-branded subcritical CO2 single-screw compressor installed in Europe.
Sonia Saini

U.S. manufacturer Copeland has published a case study detailing the installation of its first-ever Vilter-branded subcritical CO2 (R744) single-screw compressor in Europe, which replaced two reciprocating CO2 compressors at a Lithuanian food manufacturing facility.

It was installed in 2021, with the screw compressor replacing two reciprocating CO2 compressors on the low side of an industrial ammonia (R717)/CO2 cascade system. The high side’s four Vilter ammonia single-screw compressors continue to operate as part of the refrigeration system.

The decision to install the Vilter subcritical CO2 single-screw compressor was driven by maintenance issues with the reciprocating CO2 compressors.The plant, which manufactures baked goods and snacks, had scheduled twice-yearly preventive maintenance for the compressors, with each visit lasting five days. Despite this, and after addressing an oil carry-over issue, the CO2 reciprocating compressors still required “excessive” maintenance, according to Copeland.

An increasing number of unplanned emergency repairs that disrupted production prompted plant management to seek out a new solution.

“[The] simple and effective design of our Vilter ammonia single-screw compressors had a reputation throughout Europe as a durable compressor requiring minimal maintenance,” Copeland said.

Plant management, working alongside Copeland and the Lithuanian distributor/contractor Genys, sought to deploy a similar approach on the low side with a CO2 single-screw compressor.

The new screw compressor ‒ “ideal” for subcritical applications, according to Copeland ‒ almost doubled the refrigeration capacity of the previous two units with 830kW (236TR) at −40°C (−40°F) evaporation and −7°C (19°F) condensation temperatures.

“Since completing the system upgrade in late 2021, the production facility has enjoyed reduced maintenance demands,” Copeland said, with the CO2 reciprocating compressors “repurposed” for system redundancy.

Along with upgrading the low side of the system, the retrofit addressed the system’s faulty capacity control mechanism that prevented output from matching refrigeration load fluctuations.

“We are proud to contribute to the customer’s efficiency objectives while helping them to achieve their environmental sustainability goals with the first installation of a Vilter CO2 single-screw compressor in Europe,” said Genys CEO Mindaugas Zabiela.

The Vilter subcritical CO2 compressor line, designed for operating pressures up to 52bar (754psi), offers capacities from 528 to 2,972kW (150 to 845TR) for low-temperature applications at −20°F SST/20°F SCT (−28.9°C SST/−6.7°C SCT) and ultra-low temperature at −40°F SST/20°F SCT (−40°C SST/−6.7°C SCT) for capacities from 327 to 1,706kW (93 to 485TR).

TC CO2 screw compressors

Earlier this year, Copeland announced it had commenced production of its first Vilter-branded transcritical CO2 single-screw compressor for industrial applications. The company stated that the unit, now available on the North American market, was “developed in response to increasing industry demand.”

The transcritical CO2 single-screw compressor line, designed for operating pressures up to 124bar (1,800psig), offers capacities from 587.3 to 1,287.2kW (167 to 366TR) for medium temperature at 20°F SST/85°F gas cooler (−6.7°C SST/29.4°C gas cooler) temperature. Double units, sharing common oil management and control systems, provide capacities ranging from 1,174.6 to 2,574.3kW (334 to 732TR).

In a presentation at the IAR 2024 Expo in Orlando, Florida, Lauren MacGowens, Director of Sustainability Engineering for Vilter by Copeland, outlined the advantages of the technology and the potential market.

According to MacGowens, in industrial applications, a single CO2 screw compressor can replace multiple racks of CO2 reciprocating compressors with a system that is easier to install and maintain with less piping and leak points.

“We are seeing a drive to CO2 that is unprecedented,” MacGowens said, with transcritical CO2 offering a future-proof solution without the regulatory requirements of ammonia. Through 2030, Vilter projects a 20% annual growth rate for total market spending on CO2 systems.

At the 2023 ATMOsphere America summit, the Best in Sector/Industrial award went to Canadian utility Hydro-Québec for installing a CO2-based water-to-water heat pump with a Vilter transcritical CO2 screw compressor.

Curated News With Commentary
Source: HPAC (Heating Plumbing Air Conditioning)

[Canada Infrastructure Bank Supporting New Residential District Energy]

Why It Matters: The Canada Infrastructure Bank (CIB) has introduced its Infrastructure for Housing Initiative (IHI), designed to help address the infrastructure constraints limiting new housing construction. This opens up an opportunity for natural refrigerant heat pumps to be used in district energy projects. For example, the Canadian utility Hydro-Québec has developed a 1.3MW (379TR) CO2 (R744) water-to-water heat pump system, in conjunction with U.S-based manufacturer Copeland.

The R290 monoblock provides hot water at up to 75°C while the CO2 monoblock offers hot water at up to 70°C.
Sonia Saini

British boilermaker Ideal Heating has announced the launch of a commercial air-to-water propane (R290) monobloc heat pump line that provides up to 75°C (167°F) hot water along with a CO2 (R744) monobloc offering 70°C (158°F) hot water.

According to the company, both units are designed for district heating and domestic hot water applications, with inverter-controlled compressor technology “enhancing building efficiencies” by “accurately” matching heat pump operation to heating demand. In addition, the units can be installed with other Ideal Heating products like the company’s commercial condensing boilers to create “low carbon” hybrid systems.

“We have led the way in commercial heating by ensuring our heating products are at the forefront of technology, quality and design by delivering high efficiency and low running costs,” said Chris Caton, Head of Commercial Product Management at Ideal Heating.

The outdoor R290 unit, dubbed ECOMOD 290HT, comes in three chassis sizes and with five outputs: 15, 18, 27, 40 and 50kW (4.3, 5.1, 7.7, 11.4 and 14.2TR). The company said that up to seven units can be combined in a cascade for applications requiring higher capacities.

The CO2 heat pump, the ECOMOD CO2, is capable of providing 70°C hot water and comes in a standard or a quiet version with three outputs: 65, 95 and 130kW (18.5, 27 and 37TR), with higher outputs available by installing units back-to-back. Per Ideal Heating, the ECOMOD CO2’s “innovative space-saving design” means it can be installed flush against a wall.

Increased domestic manufacturing: Other manufacturers in the United Kingdom are also anticipating a surge in demand for natural refrigerant heat pumps and are responding accordingly.

  • Earlier this year, U.K.-based OEM Claude Engineering Systems announced the expansion of its residential and commercial R290 heat pump lines and the launch of a new line of CO2 units for space heating and hot water.
  • U.S.-based OEM Copeland is adding a 3,500m2 (37,673ft2) building expansion at its compressor manufacturing facility in Cookstown, Northern Ireland. The expansion will add new product lines and increase production capacity to “meet the European demand for sustainable, low-carbon heat pumps,” Copeland said.

Government funding: The U.K. government is providing funding to support heat pump manufacturers and make it easier for consumers to adopt the technology.

  • The government recently announced £1.77 million (€2.06 million/$2.22 million) in grant funding for three natural refrigerant heat pump companies, part of a larger tranche of funding for heat pump manufacturers available through its Heat Pump Ready Initiative.
  • Funding was also recently increased for the government’s Boiler Upgrade Scheme, which provides grants to homeowners replacing boilers with “low-carbon” alternatives such as heat pumps. The grant jumped from £5,000 (€5,809/$6,263) to £7,500 (€8,713/$9,378), with the program lasting to the end of 2027.

Quotable: “This latest, innovative addition to our ECOMOD heat pump range, featuring natural refrigerants with ultra-low GWP, will ensure our customers have the best and most advanced solutions for heating and hot water while helping businesses in the U.K. on their journey to net zero,” said Caton.

According to Ducker Carlisle, OEMs will opt for CO2 or R290 instead of widely-used HFO 1234yf in mobile air-conditioning.
Sonia Saini

Over the next five years, manufacturers of plug-in hybrid electric vehicles (PHEVs) and electric vehicles (EVs) are “highly likely” to opt for natural refrigerants like CO2 (R744) or propane (R290) in place of HFO 1234yf in mobile air-conditioning (MAC) systems, according to a white paper from consulting firm Ducker Carlisle.

“Due to stricter environmental legislation across industries, many OEMs and thermal management suppliers anticipate that the EU will implement a regulation banning R1234yf by 2030,” explained the company, noting that the HFO is used in the majority of today’s PHEVs and EVs.

As a PFAS (per- and polyfluoroalkyl substance), R1234yf could be banned under the EU’s chemicals REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) regulation if the Universal Restriction Proposal – officially known as the Annex XV Restriction Report – is approved by the European Chemical Agency.

“If a ban were to be voted, OEMs would have to shift to either CO2 or propane – provided the safety concern related to the flammability of propane has been addressed,” the consulting firm said.

“Due to stricter environmental legislation across industries, many OEMs and thermal management suppliers anticipate that the EU will implement a regulation banning R1234yf by 2030. If a ban were to be voted, OEMs would have to shift to either CO2 or propane.”

Ducker Carlisle

The transition to natural refrigerants will also be driven by government subsidies that favor the use of low-GWP refrigerants in thermal systems, it added.

Beyond environmental regulations, vehicle performance is also a driving factor.

As manufacturers increase their production of electric vehicles, many are focusing more on heat pump design concepts and refrigerant selection due to the impact thermal management systems have on vehicle battery range and lifespan. In electric buses, for example, R744-based heat pumps have been found to outperform electric heaters, boosting range by more than 32%.

According to Nina Piesch, a Research Assistant from the Norwegian University of Science and Technology, CO2 heat pumps boast a higher efficiency in EVs because of their increased suction vapor density. They also eliminate the need for an auxiliary heater, which enhances overall efficiency.

While all OEMs are looking at heat pump design and refrigerant selection, it is a particular priority for premium manufacturers as their customers demand a higher level of comfort and performance, explained Ducker Carlisle.

NatRefs in cars

According to Ducker Carlisle, a growing number of automakers are looking into CO2 heat pumps following the announcement that Volkswagen had chosen the technology for its modular electric drive matrix (MEB) platform. Volkswagen has said its goal is to use R744 heat pumps in all of its EVs by 2030.

Volkswagen’s MEB platform underpins several EVs in the group’s portfolio, including the Audi Q4 e-tron, which first began offering CO2 heat pumps as an option in 2021.

“When Volkswagen adopts a strategy, others are likely to follow,” a renowned international thermal management system provider told Ducker Carlisle. “We are currently receiving numerous proposal requests for R744 heat pumps, suggesting that many OEMs seem to be considering a CO2 heat pump.”

Volkswagen’s new ID.5 electric SUV coupe uses a CO2 heat pump.
Volkswagen’s ID.5 electric SUV coupe uses a CO2 heat pump. (Source: Volkswagen)

However, it is unclear whether other OEMs will follow suit and commit to CO2, continue with R1234yf or opt for other solutions like propane. This decision depends on multiple factors, including regulations, subsidies, vehicle type and size, safety concerns and brand positioning, explained Ducker Carlisle.

While propane is a highly efficient and inexpensive refrigerant, there are significant safety concerns due to its flammability, explained Stefan Schäfer, Business Development Manager at Burger Group. However, with the right technology and design, propane can also be a safe refrigerant, he added, noting that systems must be “designed as a closed unit with permanently sealed connections.”

Despite regulators like the U.S. Environmental Protection Agency (EPA) advising against the use of propane in MAC applications, the automotive industry has not ruled it out.

In June 2023, German technology company ZF presented TherMas, a new electric-drive system with a propane heat pump. With one circuit dedicated to the passenger compartment and two additional and separate circuits used for the thermal management of the power electronics and the e-drive, the heat pump doubles the cooling capacity compared to current refrigerants, while safety is ensured through a hermetically sealed system.

To date, no carmaker has announced a plan to adopt R290 for MAC systems.

“Due to the flammability of propane, it is expected that CO2 heat pumps will hold a higher market share for passenger cars,” said Ducker Carlisle.

NatRefs in public transport

With significant heating and cooling demands, buses are more likely to adopt CO2 and R290 in their HVAC systems than passenger cars, explained Ducker Carlisle.

In Germany, CO2 has become the refrigerant of choice for heat pumps in electric buses, with numerous cities opting for the technology in their bus fleets. In fact, as of 2021, more than 60% of Germany’s electric buses used R744 heat pump systems from manufacturer Konvekta.

This trend is extending across Europe.

“Since 2018, we have installed over 3,500 CO2 air/water heat pumps in European buses and anticipate another 2,500 new units this year,” said Karsten Mundt, Sales Director International at Konvekta. “Additionally, the increasing demand for CO2 applications in the automotive sector will drive innovation, lower component prices and ensure safety as well as efficiency for operators.”

Konvekta heat pump-equipped electric bus E bus
Konvekta’s CO2-based heat pumps are used in electric buses across Europe. (Source: Konvekta)

The adoption of propane in buses is also on the rise, with the ability to overcome safety concerns by installing heat pumps on bus roofs rather than alongside engines – as is the case with cars.

“Propane started to be used in buses a few years ago, and use cases are expected to strongly grow in the coming years due to its excellent thermal performance,” explained the unnamed thermal management system provider.

Natural refrigerants are also increasingly being adopted in train HVAC systems, with researchers finding that a CO2-based air conditioner can offer a 14% increase in cooling capacity and a 16% increase in COP over a system using HFC blend R407C.

German train operator Deutsche Bahn has committed to only using natural refrigerant-based heating and cooling systems in its trains from 2020. The company already has a passenger train using propane-based air-conditioning units (alongside “state-of-the-art” electric heaters) and has been testing CO2 heat pumps for both heating and cooling.

Showcasing MAC innovation

In recognition of the rapidly changing landscape in the MAC sector, ATMOsphere, publisher of, will host its first MAC and heat pump summit, ATMO MAC Summit 2024 × TU Berlin, in Berlin September 12–13. ATMOsphere is the publisher of

The two-day event is organized in partnership with Technische Universität Berlin (TU Berlin)’s Department of Heat Transfer and Conversion and will be hosted at the university’s campus.

According to ATMOsphere, the conference will “offer a unique opportunity to engage and exchange insights with industry professionals.” Participants will include manufacturers from across the transport sector, suppliers and policymakers, as well as academics and R&D experts.

The event program will feature presentations and case studies on natural refrigerant-based air-conditioning and heat pump technologies for mobile applications, with a focus on CO2 and propane.

Sessions will cover a range of topics, including research, market and technology trends, electric vehicles, refrigerant charge reduction strategies and system controls and safety. Two panel discussions – one on policy developments and one on OEM experiences – are scheduled for the second day of the summit.

The deadline for submissions from OEMs and suppliers in the automotive, bus, truck and train sectors is June 14.
Sonia Saini

ATMOsphere, publisher of, has issued a call for case studies on natural refrigerant-based mobile air-conditioning (MAC) and heat pump technologies to be presented at the ATMO MAC Summit 2024 × TU Berlin, which will take place in Berlin on September 12–13.

To be considered, case studies must include real-life natural refrigerant applications – with a focus on CO2 (R744) and propane (R290) – and be relevant to air-conditioning or heat pump applications in the automotive, bus, truck or train sectors.

Case studies must be submitted by June 14 using the template provided. Details on how to submit a case study can be found here.

Submissions must include reference to the application’s sustainability, replicability, originality and tangibility, and preference will be given to case studies that include efficiency and cost analyses.

Case studies could be presented by OEMs or suppliers and could examine a range of topics, including reversible air-conditioning and heat pump systems, refrigerant charge reduction strategies, thermal management in battery cooling, implementation of heat and work recovery, system controls and safety.

Each presentation will be allocated a maximum of 12 minutes followed by three minutes for audience questions.

Scaling up NatRef solutions

The two-day conference is ATMOsphere’s first event to focus exclusively on air-conditioning and heat pump systems for mobile applications. It is hosted in partnership with Technische Universität Berlin (TU Berlin)’s Department of Heat Transfer and Conversion and will take place on TU Berlin’s campus.

According to ATMOsphere, the conference will “offer a unique opportunity to engage and exchange insights with industry professionals.” Participants will include manufacturers from across the transport sector, suppliers and policymakers, as well as academics and R&D experts.

“There are already commercial applications available today for cars, buses, trucks and trains using either CO2 or propane,” Marc Chasserot, CEO and Co-Founder of ATMOsphere, told “To accelerate and scale up the adoption of these solutions, we have created the annual ATMO MAC Summit in partnership with [TU] Berlin.”

The event program will feature sessions that cover a range of topics, including research, market and technology trends, and two panel discussions – one on policy developments and one on OEM experiences.

The conference will also include several networking opportunities.

Registration for the summit is now open, and an early bird discount of €150 is available until May 23. OEMs, academics and government representatives can attend the summit for free, and there is a 50% discount for confirmed speakers.

“There are already commercial applications available today for cars, buses, trucks and trains using either CO2 or propane. To accelerate and scale up the adoption of these solutions, we have created the annual ATMO MAC Summit in partnership with [TU] Berlin.”

Marc Chasserot, ATMOsphere

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