VFDs contribute to CO2 refrigeration efficiency

UK/NORWAY: Variable frequency drives from Welshpool-based Invertek Drives have been retrofitted to a CO2 based HVACR system at a hospital in Trondheim, Norway.

A total of 10 400V Optidrive Eco VFDs were supplied for the system at St Olavs Hospital in Trondheim to reduce its carbon footprint, as well as creating significant energy savings.

Sinop Technoblock, a specialist refrigeration company in Norway, was appointed to undertake the work from design to implementation. It includes a laboratory, an on-site hotel and a canteen which all have numerous cold rooms.

They incorporated Reftronix CO2 controllers for packs and cold rooms and Invertek’s Optidrive Eco VFDs for the compressors. The combination of controllers and VFDs ensures the precise control of the complete refrigeration process as well as remote access to live data, alarms and settings.

The Optidrive VFDs control the speed of the compressors depending on the temperature required and other conditions. This data is picked up by the controller which communicates with each of the drives. Optimising the speed of each of the compressors motors makes them more energy efficient than the conventional start/stop used in HFC refrigerant systems.

The VFDs – four 2.2kW, four 1.2KW, one 5.5kW and one 11kW – are connected via a Modbus communication link to the controllers. This means configuration of the drives can be undertaken through the Reftronix controller online portal. The page also allows the status and live data to be available remotely via the cloud.

The controller is capable of measuring temperatures and pressure, calculating optimal performance, adjusting the speed of the compressor through the Optidrive VF and adjusting the opening of electronic valves and the speed of the fan.

“The controller user interface is a web page which makes it easy to commission and provides a good graphical overview of the run-time conditions. All the controllers are on the same ethernet network,” explained Kjell Robert Overlev, the founder of Sinop Technoblock.

“This means you can link the controller webpages, making it possible to look at a pack and with the press of a button you can view the cold room controller. There is no need for a system manager or front end which saves a lot of upfront cost.”

Any alarm or trip warnings are also highlighted via the web page.

Henrik Christensen, general manager at Reftronix, said the combination of their controller and the VFD ensured the refrigeration system was as accurate and efficient as it possibly could be.