In a new whitepaper, Danish component manufacturer Danfoss reported that its BOCK HGX series CO2 (R744) compressors experienced an average of 83% less vibration compared to legacy compressors in a test retrofit installation at a supermarket in Ohio.
The whitepaper – “Danfoss BOCK CO₂ Compressor Reduces Vibration for Optimal Transcritical Supermarket Refrigeration Performance” – is available here.
Using a calibrated vibration meter, Danfoss application engineers captured measurements at multiple locations on the rack and at various points on individual compressors and common piping lines.
Compared to existing CO2 compressors, the BOCK units achieved vibration reductions ranging from 48.3% to 97.7% at various points and capacities, the whitepaper said.
In addition, the BOCK lead compressor employing a variable frequency drive (VFD) achieved a wider frequency range – from 35–70Hz compared to the original compressor’s 40-60Hz range – resulting in a larger capacity range in the suction group without added vibration,” it said.
Abnormal vibration
The Ohio supermarket had been experiencing “abnormal, excessive compressor and rack vibration” in its legacy transcritical CO2 system, said the whitepaper. It added that excessive vibration is “one of the most persistent CO2 compressor reliability challenges,” causing damage to racks, piping and structural components and resulting in reduced compression cycle effectiveness and excess energy consumption.
“We are encouraged by the test results that affirmed the operational and sustainability benefits of BOCK compressors for transcritical CO2 refrigeration systems,” said Chris Brown, Application Engineering Manager at Danfoss, in a statement. “Danfoss BOCK HGX compressors can deliver the energy savings and environmental benefits of CO2 safely and reliably in a wide range of supermarket refrigeration sites, removing a critical barrier to increased adoption of CO2 across the industry.”
“We are encouraged by the test results that affirmed the operational and sustainability benefits of BOCK compressors for transcritical CO2 refrigeration systems.”
Chris Brown, Danfoss
In the test case, seven Danfoss BOCK HGX series compressors were employed in a transcritical system. All compressors were semi-hermetic and were charged with a synthetic refrigeration oil based on special polyolesters for use with CO2 in transcritical applications. The refrigeration rack supplied a total of 1,121kBTUh (93.4TR/328,5kW) of cooling.
“The vibration reductions also resulted in less noise and less shaking of the pipes and other rack components,” Danfoss said. “In addition to the improvements in safety and reliability of the operating components, the environment of the area was much more pleasant for maintenance personnel.”
Danfoss’s BOCK HGX56 CO2T six-cylinder semi-hermetic compressor was named the winner in the refrigeration category of the 2025 AHR Expo Innovation Award.
Danfoss finalized its acquisition of CO2 compressor manufacturer BOCK from NORD Holding in March 2023.
