In search of greener refrigeration
The 1989 Montreal Protocol calls for a phasing out of chlorofluorocarbons (CFCs) – implicated in ozone depletion – which are used in various industrial, commercial and household applications, including as coolant in refrigerators. Danish and German researchers set up several ‘demo’ units to test naturally occurring coolants for smaller-scale commercial and industrial uses.
The discovery of polar ozone depletion in the Earth’s stratosphere over Antarctica, in 1985, prompted further investigation into ozone depletion processes, and calls to reduce or stop production of CFCs – first in aerosols and gradually in other applications, such as in refrigeration plants.
|CFCs in aerosol cans are a thing of the past –snapshot taken from Ex Nihilo’s documentary Pollution de l’air.|
© EX Nihilo production
A complex cocktail of atmospheric dynamics, chemical reactions and solar radiation was found to explain this ozone depletion during polar springtime. Recent research on the Arctic regions shows similar processes can occur in the northern hemisphere.
The EU-funded project looking into innovative small-capacity ammonia refrigeration plants (OSCAR) has recently published the results of its 27-month investigation. While several of their ammonia-based designs and innovations scored a high ‘green’ profile, others were less successful, but provide valuable technical know-how for future use.
In its final report, the Fifth Research Framework Programmes (FP5) OSCAR project acknowledges that manufacturers would only take up its designs if there is a potential market for them. But while CFCs are banned in the EU and gradually being removed from circulation, restrictions on the use of hydrofluorocarbon (HFC) coolants are less clear-cut.
“As long as there is uncertainty about… this matter, companies are still allowed to use HFC-refrigerants and do not have to use resources on new HFC-free alternatives,” notes the report. To reduce the greenhouse effect of refrigeration systems, innovative new systems are needed. Currently, ammonia is used effectively in large-scale facilities. But for the new designs using natural refrigerants to work on a smaller-scale, they have to be competitive compared with conventional units, say the report’s authors from Dresdner Kuehlanlagenbau and the Danish Technological Institute.
Freezing use of CFCs
Three demonstration, or ‘demo’, plants were developed in Denmark to test two heat pump chiller systems – one for cooling milk and another for marine applications – and an ice flake machine. A further three were set up in Germany to analyse refrigeration systems for cooling cells – one for normal cooling conditions and one for deep-freezing – and a brine chiller.
In its report, entitled Innovation in small capacity ammonia refrigeration plants, OSCAR present a summary of the findings and recommendations for further research. Briefly, the researchers admit, to date, the use of natural refrigerants, either ammonia or a mix of ammonia and dimethylether, is limited. Savings in energy costs (of around 7%) by using these alternatives – indirectly lowering the ‘global warming potential’ (GWP) of these sorts of refrigeration plants – were recorded.
The ammonia-based milk chilling system, for instance, performed between 5% and 7% more efficiently than CFC- and HFC-cooled systems. The marine chiller and flake machine demos also proved it is possible to produce competitive, efficient systems with low initial investment costs. But while it is still legal to use HFCs, the authors suggest these applications are not likely to be developed.
The research team are confident – from a technical point of view – that specifications for reliable and energy-efficient refrigeration systems using ammonia can be made based on the experiences and data gathered in the project. But further development is necessary in, for example, “designs for wet operation and oil return systems”.
ILK Dresden, Danish Technological Institute, EU sources
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