Norwegian hospital upgrades to a CO2 natural refrigerant system with Optidrive controlled compressors

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A Norwegian hospital has upgraded to an environmentally friendly R744 ( CO2 ) natural refrigerant-based HVAC-R system using Invertek Drives Optidrive variable frequency drive (VFD) technology.

St Olav Hospital in Trondheim has retrofitted the system to reduce its carbon footprint and impact on the environment, 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 accurately 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.

More energy efficient through optimised speed control

Optimising the speed of each of the compressors motors makes them more energy efficient than the conventional start/stop used in HFC refrigerant systems.

Kjell Robert Overlev, the founder of Sinop Technoblock, said: “To go with Reftronix and Invertek Drives was really a very easy decision. Their solutions and full integration with the inverters set them miles ahead of the alternatives.”

A total of 10 400V Optidrive Eco VFDs have been used. These include four 2.2kW, four 1.2KW, one 5.5kW and one 11kW.

The VFDs are connected via a Modbus communication link to the controllers. This means the 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.

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“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,” added Mr Overlev.

“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.

CO2 HVAC-R systems are becoming more widespread in cooling and heating systems. This is due to the push globally to phase out synthetic HFC systems which are some of the world’s worst polluters.

CO2 (R744) refrigerant has no negative impact on the environment

It is a naturally occurring gas that is low cost, safe, and doesn’t impact on the environment, unlike fluorinated gases.

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.

“We’ve worked with Invertek for a number of years and this has proved the right decision for us. They have the right inverter for the global HVACR-R industry, a fact proven by the large number of global compressors manufacturers who have endorsed their products,” he said.

“The new refrigeration systems at St Olav Hospital are a great demonstration of how CO2 HVAC-R systems are not only helping reduce energy use and creating greater efficiencies but are supporting the work in reducing harmful emissions and climate change.”

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Invertek Drives has also developed a VFD dedicated for BLDC compressors, CDUs and heat pumps. Coolvert is aimed at OEMs who want a compact and highly efficient drive. It can work with any controller and can be incorporated in systems where there is limited space, such as fridges and refrigeration systems used in supermarkets.

Large-scale refrigeration users, such as retailers, are already converting to CO2 refrigerant systems to reduce energy consumption and meet tighter emission regulations.

More details about the Optidrive Eco and Coolvert products can be found at Details of the Reftronix controller can be found at

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