(Image courtesy of NürnbergMesse / Thomas Geiger)

CO₂ Heat Pumps: Retrofits and New Installs

While many technologies and innovations were discussed, few received as much attention as CO₂ heat pumps. A CO₂ heat pump is much like a traditional heat pump except it utilizes CO₂ refrigeration (R-744), a natural refrigerant with a global warming potential of 1. R-744’s environmental benefits make it an attractive option for those seeking to meet strict environmental and efficiency regulations.

Many presenters heralded the technology’s reliability, and versatility, including Federico Ferrari, senior offer manager at Schneider Electric – Eliwell, who deemed CO₂ heat pumps a forward-thinking solution in the transition toward a more sustainable heating and cooling future.

“CO₂ heat pumps stand out because of their ability to deliver multiple benefits simultaneously: They provide a convenient way to switch from burning gasses to using electricity to produce three to five times the heat from one unit of electric energy,” said Ferrari in a presentation titled, HVAC Sustainable Transition: R-744 Heat Pumps for Both Retrofits and New Installations. “CO₂ has proven to be a reliable technology and a very sustainable refrigerant. It’s nontoxic and offers an efficient way to recover heat.”

The European Union's climate plans prioritize electrification to minimize dependency on fossil fuels, like propane and methane. Traditional heating systems that rely on combustion are increasingly being replaced with heat pumps that use natural refrigerants like CO₂. This shift supports the dual goals of carbon reduction and enhanced efficiency — goals crucial for achieving Europe’s climate objectives.

“By 2030, all new buildings must be zero emission buildings and, by 2050, all buildings must be zero emissions,” said Ferrari. “National building renovation plans shall include measures to phase out fossil fuels in heating and cooling with a view to phasing out all fossil fuel boilers by 2040.”

In response, the demand for heat pumps has surged across Europe, with technologies like air-to-air, air-to-water, and water-to-water systems growing rapidly. Despite a minor slowdown in recent years due to fluctuating gas prices and regulatory adjustments in countries like Italy and Germany, the market for heat pumps is projected to continue booming through 2030 as carbon reduction and electrification goals intensify.

GLOBAL CERTIFICATION: The European Heat Pump Association (EHPA) invited attendees to discover the infinite potential of heat pumps at the event. The organization touted its Keymark certification, which it hopes will provide a uniform certification for heat pumps all around the world. (Image courtesy of NürnbergMesse / Thomas Geiger)

CO₂ Heat Pumps in Extreme Weather

As weather patterns continue to become increasingly unpredictable, facility managers are seeking reliable, efficient energy solutions. CO₂ heat pumps are formidable options, and are continually improving with new technology on the horizon such as pressure exchangers.

“A remarkable feature of the latest CO₂ heat pumps is their efficiency at extreme temperatures,” said Darren Lacroix, account manager, Energy Recovery, during a presentation titled Retrofitting R-744 Systems for Heatwave Resilience with the PX G1300 Pressure Exchanger. “In the commercial refrigeration market, we are seeing PX G1300 pressure exchangers provide a significant lift in coefficient of performance [COP] of up to 30% when outdoor temperatures soar to 40°C. As we look towards future applications, we are excited about the potential of increasing heat pump performance and adaptability in extreme weather."  

Extreme weather conditions, such as high heat or sudden cold, can increase stress on cooling and heating systems, often leading to pressure fluctuations that cause system failures. CO₂ heat pumps. However, when equipped with advanced components — like the ceramic-based rotors in Energy Recovery’s PXG model that stabilize internal pressure — early laboratory testing shows the system can maintain smooth and efficient operation, even at higher ambient temperatures.

“What we have seen in the commercial refrigeration market is this stability prevents issues like flash gas formation and mitigates risks of high-pressure valve failure,” said Lacroix. “Less pressure means less stress. When you reduce the pressure, the full functionality capacity of the system is reduced. In summary, there is significant potential to further develop pressure exchanger technology to make CO₂ heat pumps a resilient choice for businesses that rely on uninterrupted cooling and heating.”

A Major Role in the Decarbonization Equation

Industrial heat pumps, particularly high-temperature models utilizing natural refrigerants, like R-744, are becoming vital elements in the global decarbonization effort. Research and advances in optimization methods now make it feasible to integrate these heat pumps into various industrial energy supply systems efficiently.

Sophie Knottner, research engineer, sustainable thermal energy systems, center for energy, Austrian Institute of Technology, said her organization has created mathematical optimization methods that support the integration of CO₂ heat pumps in industrial applications.

Mathematical optimization, or mathematical programming, is a method of finding the best values for various variables within defined constraints. In the context of industrial energy systems, these variables might include the capacities of different energy units, their operating schedules, and the target criteria for minimizing cost and emissions. This approach provides decision-makers with insights into how industrial energy systems could look in the future and which components, such as heat pumps, would best fit their specific setup.

The process of designing an industrial energy system begins by examining the core production requirements; on-site energy supply technologies, like combined heat and power plants, gas boilers, and chillers; and connections to external energy grids.

“All sectors are facing sustainability challenges, and this is especially true in the industrial sector,” said Knottner. “Finding clean, affordable, and green energy is really a key criterion to remain competitive. Optimization models can help design an energy system that balances these elements, integrating heat pumps where they add the most value for efficiency and sustainability.”

The mathematical optimization process consists of finding an optimal solution, optimal values and optimal variables. These calculations take into consideration many factors, including when a unit is online or offline, a project’s budget, efficiency goals, decarbonization efforts, maximum output, etc.

“A really big advantage of mathematical optimization is that you can consider technical, economical, and ecological aspects at the same time and answer several questions within one model,” said Knottner. “When heat pumps are integrated, they’re typically substituting CHP plants in the industrial sector, which brings forth a problem regarding the energy provision on-site, so the electricity and heat provision is switched to electricity consumption from the outside. This often results in many organizational and cultural changes when it comes to heat pump integration. Economic feasibility, process parameters, and the ratio between fossil fuels used now and future electricity usage are the drivers.”

The results speak for themselves, though. In the pulp and paper industry, integrating heat pumps could yield significant reductions in CO₂ emissions of up to 100% and primary energy use reductions of up to 60%, said Knottner.

“Other sectors, such as food processing and textiles, benefit similarly from the use of heat pumps,” she said. “For example, in the food sector, models showed up to 50% CO₂ reduction and payback periods as low as seven years, while the textile industry could see reductions in both CO₂ emissions and operational costs by as much as 70%. While economics are still an issue, heat pumps are among the top technologies when it comes to pursuing efficient decarbonization solutions.”

Conclusion

Chillventa 2024 demonstrated that CO₂ heat pumps are not just a technological advancement — they represent a powerful solution for businesses and industries committed to sustainability, energy efficiency, and resilience in an era of climate change. With the capacity to reduce greenhouse gas emissions, operate efficiently under extreme weather, and integrate seamlessly into both new and retrofit applications, CO₂ heat pumps offer a tangible solution to meet the dual goals of economic feasibility and sustainability, paving the way for a cleaner industrial future. For companies looking to take the next step, exploring the benefits of CO₂ heat pumps and the opportunities they provide could be a game-changer.