Strategies for Heatwave-Resilient Transcritical CO2 Refrigeration

By Darren Lacroix

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Strategies for Heatwave-Resilient Transcritical CO2 Refrigeration

February 2024 marked one of the warmest Februaries globally, with an average surface temperature of 13.54°C (0.81°C above 1991-2020’s average temperatures).1 

For supermarkets across Europe, the rise in more prolonged and intense heat waves can cause serious operational difficulties, as thermally overloaded refrigeration systems struggle to keep inventory cold when hot weather strikes. 

With refrigeration systems designed to operate within specific temperature parameters, longer and more intense heat waves have left supermarkets grappling with how to design and retrofit CO2 refrigeration systems to accommodate extreme stress.

CO2 refrigeration systems are particularly vulnerable to heat waves as they lose efficiency and experience a reduced coefficient of performance (COP) at higher ambient temperatures. 

CO2 is a natural refrigerant regulated by F-Gas regulations and therefore is future-proof against regulation2, non-toxic, non-flammable, and has ideal thermodynamic properties for compact system designs. However, due to CO2’s constraints with higher temperature energy efficiency, adoption in Europe is still at roughly 23% across all food retail3. 


Nordic European countries with average temperatures of 15° C or below were early adopters, while nations with warmer temperatures averaging 20°C or above have been historically slower to adopt CO2 refrigeration3.

With the latest innovations in CO2 refrigeration, there are now simple, commercially available solutions to mitigate warm weather inefficiency. These innovations can offset or eliminate the risks of heatwave-induced shutdowns to protect supermarkets against HACCP violations, food loss, and escalating electricity costs.

Supermarkets can now acquire or retrofit transcritical CO2 refrigeration systems to operate efficiently and reliably, regardless of climate or region. 

What Happens When Refrigeration Systems Break Down In High Heat?

Refrigeration systems are engineered to operate efficiently within the specific climate zone of their installation region, known as the 'design temperature'.


Extended runtime beyond design temperature forces systems to work harder to maintain cool temperatures and increases production of excess waste (or flash gas) in the system, which results in reduced efficiency or, in severe cases, shutdowns due to high-pressure discharge failure. 

CO2 is unique among refrigerants because of its low critical point of 31° C, over which it behaves both as a liquid and as a gas. Above 31° C, the system operates in the transcritical state. This transcritical state is where the first generation of CO2 systems struggled with increased energy costs and elevated pressures. 

Designing Resilient CO2 Refrigeration Systems

When designing a new transcritical CO2 system, refrigeration engineers can now use several mitigation strategies to drive efficiency in hot weather. 

Mechanical subcooling, gas ejectors, or parallel compression are all established strategies across Europe, but also tend to require extensive engineering integration or multiple parts working in tandem before the system can reach optimal functionality.


Recently, pressure exchangers4 have been introduced into transcritical CO2, enabling energy efficiency over a wide operating range and protecting against heat waves all within a single component. Pressure exchangers were invented for the desalination industry over 30 years ago, where this game-changing technology enabled seawater reverse osmosis plants to reduce their energy consumption by as much as 60%.5

Pressure exchangers drive energy efficiency in CO2 refrigeration by leveraging the latent pressure energy in a system to recover 'lost' energy. 

Pressure exchangers can offer both expansion and compression within a simple, mechanical device. When high ambient temperatures cause increased compressor power demand, pressure exchangers offer 'free' compression to alleviate the workload on the system. This increases system efficiency, cooling capacity and design temperature, allowing supermarkets to save on high energy bills and safeguard their systems during heat waves. 

Most importantly, pressure exchangers can integrate into new and existing systems through a few simple tie-in points.


Safeguarding Your Transcritical CO2 Refrigeration System Against Heat Waves

Prior to the invention of energy efficiency technologies, CO2 refrigeration systems did not have a robust solution for dealing with heat waves. This left stores to deal with high-stress operational complexities of constantly monitoring their equipment, utilising water-spray technology or alternative solutions to cool their systems, or by purchasing temporary refrigeration when the situation called for it.6 

Pressure exchangers are a simple solution for rising temperatures by increasing transcritical CO2 refrigeration efficiencies. The PX G1300 pressure exchanger from Energy Recovery has been shown to improve efficiency by over 30% at temperatures above 40°C, compared to a standard CO2 booster system.7 

If you are looking for a proactive solution to rising temperatures, please visit to learn more about how pressure exchanger technology can help.  

About the Author

Darren Lacroix has nearly two decades of expertise in state-of-the-art CO2refrigeration technologies and currently oversees European sales for Energy Recovery, Inc.


This article was written in partnership with Energy Recovery.

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