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Roller optimises fin options for CO2

GERMANY: Walter Roller claims to have developed an optimised heat exchanger fin system for CO2 deep-freeze applications, with fin spacings up to 12mm.

While CO2 has become a most important refrigerant in the grocery market. However, CO2 alone does not make a system energy efficient. To support the energy-efficient characteristics of CO2 in the system technology, Roller says it has developed a fin system for evaporators that optimises the energy-intensive defrosting costs in deep-freezing.

The fin spacing of an evaporator has a significant influence on the resulting heat exchanger surface, with a closer fin spacing allowing more heat to be transferred. If the fin spacing is too narrow, however, there is a risk of heavy, disruptive icing, which results in frequent defrosting processes and thus reduces efficiency. 

While 6-8 mm fin spacing is generally used in deep-freezing, even this spacing can be too narrow if the deep-freeze room is affected by increased humidity. Frequent defrosting intervals are the result.

For defrosting, both the direct and indirect costs must be included in the energy cost calculation, Roller argues. These are the direct costs in terms of the electrical defrosting of the ice from the evaporator and the indirect costs of the defrosting heat generated in the room, which must be reabsorbed by the refrigeration system when it restarts.

The high-performance, in-line tube system developed by Roller, with the optimum tube diameter of 9.52mm (3/8in) for CO2 applications, is available with up to 12mm fin spacing and thus contributes significantly to the requirements of a modern, operationally reliable and efficient deep-freeze system.

Another advantage is the use of 0.3 mm thick aluminium strips for the fin package, which partially compensates for the slight loss of performance of evaporators with a high heat transfer density compared to evaporators with a smaller surface area (due to smaller fin spacing or staggered tube systems). The robust fin thickness also offers the advantage of a high mechanical load capacity, necessary for cleaning work.

The 12mm fin system is already available in Roller’s DLK and FHV evaporator series and will be extended to other series in the coming months. 

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