Compact two-stage CO2 compressor

ITALY: Frascold’s new range of two-stage CO2 piston compressors are said to aimed at the evolution of commercial refrigeration towards increasingly compact solutions. 

While in the past, the sector was the prerogative of medium and large systems, based on transcritical or subcritical compressor units, today mono-compressor units are mainly used.

Consisting of eleven models distributed across three sizes, the series builds on the improvements of the TK heavy duty transcritical CO2 models. The CO2 two-stage series is designed to meet the needs of heavy applications due to the high number of service hours. 

The technology is said to provide a correct balance between the first- and second-stage volumes and combines the with the use of steel, a very high-strength material, subjected to advanced surface treatments that drastically reduce friction and wear. 

More specifically, the pistons feature nitrided and brushed surfaces, while components, such as pins, bushings, cylinders and piston segments, have anti-friction finishes. A further distinctive element is the adoption of specific internal barriers between the oil sump and the motor in four-cylinder models, in order to reduce the mixing of the oil in the suction gas stream. 

In addition, the provision of multiple ports allow for the integration of flash tanks, desuperheaters and subcoolers. 

The compressors are sized for a nominal volumetric displacement from 1.5 m³/h and 12.6m³/h at 50Hz in the first stage, and from 1.8m³/h and 15.1m³/h at 60 Hz, with a maximum allowable pressure of up to 100bar in suction, LP/MP side and up to 155bar in delivery on the HP side. 

Finally, they are developed to operate with maximum operating temperatures at 160°C and minimum evaporation at -50°C.