Testing the future: CO2 unit cooler and gas cooler technology

Date: 29 May 2023

The use of R-744 (CO2) as a working fluid is well-established in the refrigeration industry, and the number of new plants is continuously increasing. There is no doubt that CO2 unit coolers and CO2 gas coolers are the future of heat exchanger technology. R-744 is a natural refrigerant, which makes an excellent replacement for HFCs due to its non-flammable and non-explosive qualities, along with its low environmental impact (GWP=1).

Nonetheless, for R-744 to take its place confidently as a true replacement to HFCs, and not be seen as a green gimmick, CO2 unit coolers and CO2 gas coolers have to ensure high and reliable performances. The reliable cooling capacities of CO2 unit coolers and CO2 gas coolers are essential to reach the refrigeration plants' expected performances, and keep the overall power consumption at the predicted values. Third-party certification offers both this reassurance and reliable product data. In fact, the third-party certification verifies manufacturers’ claims impartially, to ensure designed capacity is in line with real performance. This means that specifiers, designers, buyers, installers, and end users can be sure that certified products work as expected and offer reliable system efficiencies. However, due to the peculiar properties of R-744, Eurovent Certita Certification has had to establish a dedicated performance evaluation process for CO2, with a new state-of-the-art test rig developed at the Center of Competence for Refrigeration and Air-Conditioning of TÜV SÜD.

Eurovent Certified Performance (ECP)

The Eurovent Certified Performance programme for Heat Exchangers (HE) involves the major manufacturers on the market. The programme, based on a voluntary approach, certifies the performance of the product impartially, through selection software validation and product testing in an independent laboratory, with dedicated performance items for both CO2 evaporators and CO2 gas coolers respectively.

CO2 evaporator certified performances include:

  • Standard capacity [kW]

  • Fan power input [W]

  • Energy Ratio R [-]

  • Energy class [-]

  • Air volume flow [m3/h].

With the cooling capacity declared within four (4) standard conditions:

Standards Conditions for refrigerants

Air inlet temperature (oC)

Evaporating temperature (oC)













While certified performance items for CO2 gas coolers include:

  • Standard capacity [kW]

  • Fan power input [W]

  • Air volume flow [m3/h]

  • A-weighted sound pressure level [dB(A)]

  • A-weighted sound power level [dB(A)].

With the cooling capacity declared within two (2) standard conditions:

Transcritical mode:

Standard condition

Air inlet temperature

[± 1 K]

Gas cooler inlet pressure

[± 1 bar]

Gas cooler inlet temperature

[± 5 K]

Gas cooler outlet temperature

[± 1 K]



90 bar



Subcritical mode:

Standard condition

Air inlet temperature

Condensing temperature

Refrigeration inlet temperature






<3 K

In addition, certified performances include correction factors according to the market condition, with all factors applied accordingly before certifying products.

State-of-the-art test rig

For the testing of CO2 units to DIN EN 327 and DIN EN 328, an innovative test rig was developed at the Center of Competence for Refrigeration and Air-Conditioning of TÜV SÜD Industrie Service GmbH. The test rig records high-precision measurements of capacities in standard conditions as well as outside the usually required conditions.

The new CO2 test

With the new test rig, it is possible to measure CO2 evaporators with capacities up to 40 kW and gas coolers up to 100 kW. Units of various sizes and capacities can be tested due to the use of four compressors with different performance levels.

Because of the high-pressure strength of the used refrigerant-bearing components, measurements are possible in trans-critical and sub-critical operations. The incorporated components include pipes, safety valves, connections, and flexible hoses to meet the requirements of a wide range of applications and test units. In addition, the test rig can withstand thermal stress in a temperature range down to -40°C in evaporating mode and up to 120°C in the gas cooling mode.

Of course, since carbon dioxide is odourless and displaces oxygen, the test chambers in the TÜV SÜD laboratory are equipped with the appropriate sensors and warning systems to guarantee a safe operation.

Accessing certified data

With the number of new CO2 plants constantly growing, it is extremely important that specifiers and system designers have access to reliable data on real-life system capabilities. The new state-of-the-art test rig puts CO2 unit coolers and CO2 gas coolers through their paces under a dedicated performance evaluation process, with all the benefits of independent third-party certification. When it comes to reliability, the Eurovent Certified Performance mark acts as a warranty, certifying the performance of the CO2 unit coolers and gas coolers.

The good news is that it’s easy to download product data and compare certified products online. Simply visit www.eurovent-certification.com to access the certified product directory for free. Alternatively, to find out more about certifying CO2 unit coolers and CO2 gas coolers, or the ECP Heat Exchangers programme, please contact Japhet HABIMANA at e-mail.

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