Seminar on Natural Refrigerants focus on R744

Experts from leading European and Asian universities have gathered at the HVAC&R Japan to discuss latest research and development activities regarding natural working fluids in heat pumps, air-conditioning and refrigeration.

For the third time, the Japan Refrigeration and Air Conditioning Industry Association (JRAIA) and the “Heat Pump and Thermal Storage Center of Japan” (HPTCJ) have invited experts in the field of natural refrigerants to discuss present technologies, market trends, standards, and future prospects of natural working fluids. The seminar, held on 15 February, thus provided a global overview of the present status of CO₂ and other working fluids in heating and cooling applications around the world.

Presentations

Europe: The seminar started off with a presentation by Björn Palm, Royal Institute of Technology Sweden, who gave an update on “Natural Refrigerants in Europe: Research, development & use”. The next speaker, Felix Ziegler from the Technical University Berlin, spoke about the “Status of natural working fluids for heat pumping devices in Germany”. According to Ziegler, the main political driver for the use of CO₂will be the German Ministry for Environment which supports CO₂ as the most natural and efficient alternative for HFCs in new HVAC&R appliances (see attached presentation Lahl, 2007). Given that cooling accounts for nearly two third of the total electricity consumption in the food retail sector, Ziegler presented case studies involving CO₂in commercial and industrial applications as an energy-saving solution. He also referred to current research efforts to apply the natural refrigerant in domestic heating and hot water supply.

Korea: Min Soo Kim, Seoul National University, provided a comprehensive overview of R&D activities with natural refrigerants in Korea, focusing on the optimization of CO2 components, especially compressors. Elaborating on R744 twin rotary compressors, Kim presented results on vapor injection leading to a 5-14% higher performance of the compressor. Concerning CO₂ heat exchange, the scientist compared heat transfer coefficients and pressure drops in horizontal, helically coiled and vertical tubes for gas cooling, and in smooth tube and micro fin tubes with vertical flow for evaporation processes. Kim presented latest experimental studies about the correlation between the length of the internal heat exchanger and the system performance. His lecture also covered CO₂-oil miscibility research, multi-stage compression, expander cycles, and ejector system characteristics.

Japan: Mitsuhiro Fukuta from the Shizuoka University, referred to CO₂ compressor types, covering reciprocating, scroll (low- and high pressure shell, horizontal), screw, swing, rotary (two-stage), wobble plate, swash-ring, swash plate and rotary vane compressors. Any kind of compressor is now available for CO₂ with pressure-proof design, Fukuta concluded, suggesting that the development of R744 compressors will now move into the more advanced stage of improvement, noise and vibration reduction. The second part of his presentation was dedicated to CO₂ expanders, covering three-stage, free piston type, scroll, swing, rotary, swash plate type, reciprocating, screw, hinge-vane, and turbine type models.

Japan - NEDO: Eiji Hihara, The University of Tokyo, focused on the activities of NEDO – the New Energy and Industrial Technology Development Organization - founded in 1980, and a key driver to support the Japanese industry in the development and commercialization of energy-saving products. The promotion of CO₂heat pump water heaters is a top priority under NEDO’s consumer-oriented programme which has helped the leading manufacturers Sanyo, Matsushita, Daikin, Denso, Hitachi, Corona, and Mitsubishi Electric to downsize their models, and develop efficient solutions for cold climates. At present, NEDO is promoting the following projects involving CO₂ in different applications:

Transportation:

waste heat system using the R744-based Mobile Air Conditioning system (Honda R&D)

Commercial:

air-conditioning system using super-critical CO₂ as a secondary refrigerant (Mitsubishi Heavy Industries)
non-fluorinated refrigeration with hydrocarbon & CO2 (Mac)
high-efficiency technology for CO₂ refrigeration cycle (Sanyo)
propane/CO₂cascade system for freezing, refrigeration, and cold air conditioning (Mitsubishi Heavy Industries)
air-conditioning system capable of simultaneous heating and cooling (Mitsubishi Electric)

Residential: