c-dig Meeting: Focus on R744 Refrigeration

By R744.com team, Feb 29, 2008, 00:00 4 minute reading

The Carbon Dioxide Interest Group (c-dig) met this week in Stockholm to explore and discuss latest advancements in R744 (CO2) systems for supermarkets, food processing, fishing vessels and ice rinks, amongst others.

On 26-27 February, refrigeration experts gathered in Stockholm to discuss technical and financial aspects of sub- and transcritical refrigeration systems working with CO2 (R744). The programme included theoretical and experimental test results from various application areas, including supermarket and transport refrigeration, food processing or the winter. The Royal Institute of Sweden, host of this c-dig meeting that mostly focused on commercial and industrial refrigeration, had chosen Stockholm as the event venue as Scandinavian countries are among the frontrunners in operating CO2 systems.

While the first day held presentations about complete system installations and single components, the second day was reserved for a site visit to an ice rink powered by a subcritical CO2 system. 

First day - Industrial & Commercial Refrigeration

Green & Cool: Founded only one year ago, the Swedish manufacturer of CO2 systems has already installed 20-30 racks powering supermarket cabinets across Europe, thus accounting for a significant proportion of all transcritical installations in Europe. Their units, comprising of 1-4 compressors with a swept volume of 0.4 – 50.4 m3/h, comply with all EU pressure and electrical legislation, leading to substantial energy savings (see presentation attached).

SINTEF: Havard Rekstad from the leading Scandinavian research institute presented a prototype liquid chiller to be used on fishing boats and the fish processing industry. As CFC-22 will be phased out soon, and R-404a will be subject to heavy taxes in Norway, the use of CO2 refrigeration is part of a project financed by the Norwegian Research Council to explore sustainable alternatives. After the first period of operation has proved a good system performance and cooling capacity, SINTEF is now looking for commercial partners to develop this project further, and improve single components, such as the evaporator design.

Frigo Consulting: The Swiss consultancy specialized on planning and optimizing CO2 systems and ice slurries, presented its cascade system leading to 10-20% reduced energy consumption. The system includes a transcritical unit for medium and a subcritical unit for low temperature applications, as well as a heat recovery function to provide for additional space heating. The company confirmed that R744 is thus more energy efficient than R134a with cost efficiency of new CO2 installations largely depending on local climatic conditions and cooling capacities. Frigo Consulting’s systems have already been installed in supermarkets of the leading retail group Coop, among others.

KTH: Yang Chen from the host organization Royal Institute of Technology (KTH) presented the EffSYS 2 project which includes testing of a commercial heat pump sold in Sweden, and the creation of a permanent testing center at the KTH for CO2 heat pump system research. He then focused on other R744 novel systems, such as a power system in low-grade heat source utilization and a CO2 double loop system. A reverse CO2 refrigeration cycle can thus be used to generate power, while a solar panel will provide the compressor with energy to keep the system operating. KTH estimates that once the energy gained from the cycle will be transferred to the compressor, the new Coefficient of Performance (COP) could be at 4.45, which translates to a 40% COP improvement for a CO2 cooling and power combined system. (see presentation attached)

KAVConsult: R744 systems can save up to 40% of the total energy in the pork, chicken and beef industry. This was estimated by Klaas Visser who presented a two-stage transcritical CO2 refrigeration system in Australian food processing plants that combined floor and storage cooling with hot water supply, leading to a 16% less energy consumption.

OBRIST Engineering: The Austrian engineering company focused on compressor developments, stressing that successful developments in Mobile Air Conditioning will influence compressor designs in stationary applications, too. Obrist stressed the need to further improve the ejector and compressor expander.

Danish Technological Institute (DTI): The research institute presented results about the leakage risks in cascade NH3/R744 systems. DTI has found that a mixture of CO2 and ammonia will form Ammonium Carbonate (NH2CO2NH4) which can be removed by heat splits or cold water.

Second day – Site visit Ice Rink

Based on the experience of the Swedish organization IUC in putting in place a CO2 ice rink, the second day was dedicated to a visit to the IUC laboratory where the CO2-ammonia system was developed. The use of R744, according to UIC, can save about 150,000 kW, or 15% of energy, per year, and will improve the ice quality at more even temperatures and better control. Due to the use of copper tubes design, CO2 requires 90% less pump power. During a subsequent visit to the CO2 ice rink in Katrineholm, participants could get a first-hand experience of the reliable operation of the system.


The carbon dioxide interest group (c-dig) promotes CO2 as a refrigerant in cost-effective and energy-efficient systems through a regular exchange of information, technical presentations, and research support. At present, it counts 138 members from the academia, manufacturers, contractors, and the media from all around the world.



By R744.com team (@r744)

Feb 29, 2008, 00:00

Related stories

Sign up to our Newsletter

Fill in the details below