The clock is ticking for fluorinated greenhouse gases, more commonly known as F-gases.

Often deployed as part of data centers’ heating, ventilation, and air conditioning (HVAC) systems, as well as in other areas of the data hall, the use of F-gases is being phased out in markets around the world due to the impact they have on the environment.

In March 2024, the European Union introduced updated F-Gas legislation as part of its goal to move to entirely fossil fuel-free heating and cooling across Europe by 2040.

With that deadline fast approaching, data center companies are looking at alternative gases, with several considering carbon dioxide (CO2) based cooling systems. These have already been successfully installed in a handful of data centers around the world.

F off

The term F-gas refers to a family of fluorine-based gases; hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6), and nitrogen trifluoride (NF3).

HFC is the type of F-gas normally found in HVAC systems. Initially introduced in the 1990s as an alternative to environmentally damaging chlorofluorocarbons (CFCs) used in older chilling units, it was soon discovered that HFCs were not doing the planet any favors, either. The gases are said to exhibit high GWP, or global warming potential (GWP is a measure developed by the United Nations’ Intergovernmental Panel on Climate Change), due to their propensity to hang around in the atmosphere and deplete the ozone layer.

Internationally, there is no agreed date for when the use of F-Gas might end. The Montreal Protocol, drawn up in 1987, is an international treaty that aims to regulate the phasing out of these gases.

This was updated in 2016 with the Kigali amendment, signed by 160 countries plus the European Union, which imposes several different timelines for different countries. Established economies, such as the US and Europe, have agreed to reduce HFC use by 85 percent by 2036 (compared to 2013 levels), while another group of countries, which includes China and Brazil, has until 2045 to cut its HFC consumption by 80 percent. A third batch, comprising India and states in the Middle East, where air conditioning is widely used, have been given a 2047 deadline.

The EU’s F-gas legislation is perhaps the most detailed policy to emerge so far. First proposed in 2006, the version brought into force in March stipulates that the use of HFCs in new small air conditioning units (those drawing 12kW of power or less) must end by 2032, with a 2035 deadline set for new, larger, units such as those used in data centers.

In response to the new regulations, trade body the Institute of Refrigeration Ireland (IRI) said the industry is facing “very significant changes” in the coming years. When manufacturers look for alternatives to HFCs, it argued that “CO2 will undoubtedly feature strongly in mid-size commercial equipment and in industrial systems.”

Great Danes

For Danish native Anders Moensted, this now seemingly inevitable move towards CO2 and other natural cooling products has been 30 years in the making.

“I’ve been working with natural refrigerants since the 1990s,” he says. “Denmark has been a leading country in this area because we had a very progressive environmental minister back then who could already see that F-gas was not the future and put some very tough restrictions in place.”

Indeed, Denmark has had a ban on certain types of F-gases since the early 2000s, way ahead of most of its European counterparts. Moensted is now business development manager for industrial at Advansor, a company that is marketing CO2-based cooling solutions for data centers and other large clients.

Advansor’s core business is in retail, providing cooling systems for supermarkets, but Moensted was hired four years ago to help it push the company into the industrial sector, where data centers are a prime target alongside distribution hubs for large retailers and e-commerce companies. He says businesses are not only looking to move away from F-gas, but also from existing natural alternatives. “Ammonia, for example, is a good natural refrigerant, but it’s toxic and slightly flammable,” he says. “In some use cases, it’s not allowed, so CO2 is a viable alternative.”

For Advansor, pursuing CO2-based systems makes sense because of its versatility, Moensted says. “There are so many ways of configuring a CO2 rack, because we can do freezing, cooling, air conditioning, and heating in the same system, with different temperatures at the same time,” he says.

CO2 in the data center

For data centers, a CO2-based cooling system shares some characteristics with F-gas or ammonia-based systems, Moensted says. “It generates a vapor-compression cycle, and we have a compressor that is compressing the gas, liquefying it, and then evaporating it,” he says. “So that's exactly the same process, but the system is built in a slightly different way with some additional vessels.”

As for its efficiency as a coolant, Moensted says CO2 matches up to comparable F-gas systems, providing the cooling loop is optimized correctly. But he says CO2 is more susceptible to fluctuations in temperature. “When CO2 was new, it was limited in where you could use it, and in areas like Southern Europe it didn’t really work because of the warm climate,” he explains.

“But now we’ve built up a lot more systems around it, and we’re not really limited by climate as we were before. You still have to design for the hottest day of the year, and accept you get the worst efficiencies on those days, as you would with any other refrigerant. So CO2 is a little more punished by warm climates, but then we can enhance the systems with injectors and things which allow us to match the other refrigerants.”

CO2 is readily available in large quantities. In Europe alone, 2.5 billion tons of CO2 were generated in 2023 as a byproduct of the continent’s various energy systems. “You can liquify this CO2 and use it in our refrigeration systems,” Moensted says. “It needs an industrial process to clean it up, but then you can put it in bottles and use it for refrigeration, or for other things such as soft drinks.”

Certainly, there’s no comparison when it comes to the environmental impact of CO2 versus F-gas. While HFC, the F-gas used most commonly in data center cooling systems, typically has a GWP of somewhere between 1,600 and 4,000, putting it at the high end of the GWP scale, CO2 scores one, the lowest possible ranking.

Bringing CO2 systems to life

So far, CO2-based cooling systems in data centers are few and far between, with the shift to liquid cooling, necessitated by the increasingly powerful servers required for AI and other advanced workloads, meaning operators are more likely to invest in direct-to-chip cooling systems rather than next-generation HVAC.

Canadian operator Telus has installed a CO2-based computer room air conditioning (CRAC) system at its data center in Quebec. US-based vendor M&M Carnot provided the CRAC set-up for the data center, and it was installed as part of a ‘green’ update to the facility. The company told DCD that it had seen “significant annual electrical operating savings” since installation, in addition to being able to effectively cool other parts of its building using the same system.

In Europe, Advansor has been working with Kio Networks on its new data center in Valencia, Spain, which the operator says is the first in the country to run entirely on natural refrigerants. Work began on the 1,000 sqm (10,763 sq ft), €50 million ($55m) facility in February 2023.

The cooling set-up is based on two of Advansor’s medium-temperature SteelXL refrigeration units connected to three of the company’s MiniBooster systems. This combination can provide 1.3MW of cooling capacity for the servers, and 150kW of cooling capacity for the data center’s air-conditioning. Waste heat from the cooling system is set to be siphoned off and sold to district heating systems in the region.

Advansor claims to have enabled additional energy savings of 7-8 percent by adding permanent magnet motors to all 12 of the system’s compressors.

Like Telus, Kio expects to see significant energy savings according to David de Diego Villarrubia, the company’s infrastructure director. “By using CO2 as a refrigerant, our energy efficiency ratio will improve at least three times compared to a system with a non-natural refrigerant, resulting in significant energy savings,” he says. “This will yield an annualized PUE that will be spectacular even at low load levels, ultimately leading to a facility that drastically reduces energy consumption.”

Build your own?

CO2 was a natural choice to cool Kio’s Valencia facility, De Diego Villarrubia says, because it offers the best way to assure the longevity of the data center. “Choosing [CO2] protects our investment by ensuring we do not have to undertake any retrofitting in our facility before the expected life cycles of the equipment due to regulatory obligations related to the decommissioning of refrigerant gases,” he says.

“From a purely regulatory standpoint, we believe that important aspects such as the EU F-gas regulation will eventually impose restrictions on all refrigerant gases that are not natural. The final application of this regulation will inevitably lead to the use of only natural gases.”

De Diego Villarrubia is confident his company has got “ahead of the curve” when it comes to adopting this kind of technology and adds: “We believe that switching to ecological gases was the natural step to take, demonstrating that our industry can be genuinely clean on all levels.

He says Kio is keen to work with other operators wanting to explore the benefits of CO2 cooling, and hopes his company can provide an example that will “help transform our sector for the better, moving it away from harmful greenwashing.”

Despite the environmental benefits of CO2 cooling, data center companies wishing to carry out an installation should bear in mind a number of complicating factors. Telus has noted its new system experiences greater climate-related variation in performance than a set-up based on synthetic coolants, and says great care needs to be taken during installation as the interconnecting pipes are more sensitive to slope gradient than traditional systems.

CO2 cooling systems also operate at much higher pressure than their F-gas equivalent, meaning the potential for a costly leak is higher, and that leak detection equipment is much more likely to be required.

But such factors are unlikely to hold the shift to natural refrigerants like CO2 back for too long, says Advansor’s Moensted. “Some data center companies are already demanding 100 percent natural refrigerants,” he says. “Data centers have not been a focus segment for us until now, so we are still developing the components we need because the temperature profile in a data center is a bit higher than the food processing environments we have usually worked in.

“The Kio Networks project was a big system when we built it, but today we could already make something double that size. So we’re developing our offering all the time and the CO2 technology itself is coming on rapidly.”

He agrees with De Diego Villarrubia’s assessment that using natural refrigerants makes sense as a long-term investment ahead of the inevitable phasing out of F-gas.

“The new [EU] rules are going to make it difficult and expensive to get F-gases,” he says. “When you invest in a cooling system you want to keep for 15-20 years, but the reality is those gases might not be available at all in ten years, and then you have to replace your whole system.

“So natural refrigerants is a safer choice, and we’re seeing that more and more from end users because they don’t want a system that immediately becomes outdated.”

Moensted adds: “Big changes like this take time of course, and it will not happen overnight, but we have shown over the last few years in Denmark that it is possible to phase out these gases.”