The carbon dioxide interest group’s (c-dig) meeting on 3-4 November comprised technical tours to French research organisations, as well as numerous presentations about latest developments and future challenges in the field of R744 cooling and heating.
Meeting in Lyon this week, around 40 experts from around the world discussed latest advances in the development of CO
2 Technology for cooling, refrigeration, and heating. Presentations covered a wide range of areas with relevant technical progress and challenges, including leak measurement, compressors, next-generation Environmental Control Units, suction receivers, or energy savings in R744 heat pumps.
The first day was dedicated to technical tours to two French laboratories. Starting at CETIAT – the Technical Centre for the Heating, Ventilation and Air Conditioning Industries – participants could gain an insight into the structure of the organisation active in the HVAC&R sector, among others. Robert Tetrel, the independent laboratory’s Director General, introduced c-dig members to CETIAT’s work with alternative refrigerants since the early 1990s. At the moment, CETIAT is preparing training modules on R744 to support its activities in the field of transcritical and subcritical CO
2.
The second technical tour went to CETHIL, the Centre of Heat Transfer of Lyon, where participants were familiarized with several test facilities for the analysis of the dynamic behaviour of refrigerating systems and for the study of heat and mass transfer phenomena in refrigerants, including CO
2. CETHIL operates a joint laboratory with French energy provider EDF to study and optimize high performance buildings.
The presentations
The second day was reserved for technical presentations by key players in the CO
2 world, including Star Refrigeration, Bitzer, Grasso and Birton:
Star Refrigeration: Elaborating on the “Challenges of using CO
2”, Andy Pearson explained the vocabulary of importance when operating with R744. Talking about the level of R744 necessary to cause risks to human health, Pearson concluded: “With a suitable training, CO
2 is not less safe than other refrigerants, it is just different.”
CETIM: The French Industrial and Mechanical Technical Centre has been actively involved in the development of several leak test procedures on F-gases now part of the French legislation and proposed as EU-wide standards. CETIM developed a test procedure for CO
2 leakage, using an infra-red spectrophotometer and an accumulation method. The concentration of CO
2 is measured over time, both in subcritical and transcritical systems. Its test procedures are suitable for testing prototypes and detecting low leakages. Identifying 50 different sources in a supermarket with a leakage potential of more than 2 g/year, CETIM summarized: “It is always important to go from A to Z through the test procedure, just tightening a leak may not be enough.”
Nestlé: Paul Homsy, representing the world’s largest food group, talked about the early commitment to CO
2 refrigeration in the company’s production and distribution facilities. Since 2001, Nestlé’s official policy prescribes the use of natural refrigerants wherever it is technically feasible. As the end user with the highest number of natural refrigerant plants, Nestlé operates R744 cold stores in France. It is now testing 100 CO
2 freezers in comparison to HFC units, connected with a GSM data logger to obtain continuous monitoring results.
Grundfos: The Danish group has worked together with Johnson Controls to test CO
2 pumps in supermarket refrigeration systems. Using a new pump design and variable speed capacity control, an 8% saving in the energy consumption of the cascade system have been obtained. Cavitation – the forming and subsequent implosion of vapor bubbles in the pump inlet section – occurs often in CO
2 pumps due to the special properties of CO
2. However, unlike cavitation in liquids like ammonia and water, cavitation in CO
2 doesn’t have a damaging effect on the pump parts. Grundfos identified the issue of low required NPSH and pump performance robustness to vapor bubbles in the inlet to be the major issues in the further optimization of CO
2 pumps.
GEA / Grasso: Part of the GEA group, Grasso has developed a CO
2 transcritical screw compressor with a bare shaft oil injected twin screw, a flanged motor of 160 kW, and a variable speed of up to 6000 rpm. Test results have been promising, allowing for a further development of the technology.
CTS: Together with Modine, CTS developed a next-generation Environmental Control Unit (ECU) used by the army. Using micro channel gas coolers and internal heat exchangers, the unit is lighter and uses less material. Compared to a baseline R134a system, the R744 unit with a 10 ton cooling capacity leads to a 30% higher COP at 52°C. The cooling output capacity per weight is increased by 55%.
About c-dig
The carbon dioxide interest group (c-dig) is an affiliation of scientists and engineers who are working on the development of refrigerating systems using CO
2. It's aim is to assist the dissemination of technical information and operational experience of these systems. c-dig today comprises around 140 members.
