German manufacturer Walter Roller has developed an “optimized” heat exchanger for evaporators in deep-freezing CO2 applications that minimizes defrosting, thereby saving energy.

The evaporator meets the specific requirements of CO2 (R744) for small-tube diameters of 9.52mm (0.37in), coupled with a maximum fin spacing of up to 12mm (0.47in). The fin system, in particular, reduces the energy-intensive defrosting costs in deep-freezing, said Walter Roller in a statement on its website.

“The energy-efficient operation of CO2 deep-freeze applications always goes hand in hand with the evaluation of the fin spacing and necessary defrosting cycles for evaporators,” said Walter Roller.

The closer the fin spacing the more heat that can be transferred. However, if the fin spacing is too narrow, “there is a risk of heavy, disruptive icing, which results in frequent defrosting processes and thus reduces efficiency,” the company said.

Generally, 6-8mm (0.24-0.31in) fin spacing is used in deep-freezing. But even this spacing can be too narrow if the deep-freeze room is affected by increased humidity, resulting in “frequent defrosting intervals,” the company said.

Walter Roller also uses 0.3mm (0.01in)-thick aluminum strips for the fin package, partially compensating for “the slight loss of performance” with the wider fin spacing.  

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