What does the CDU CO2 controller do?

Unlike a traditional condenser unit (CDU), CO2 CDU’s require an electronic controller to control the process as well as variable capacity control of the system to ensure optimal efficiency under all conditions. Modern compressors are typically made with high efficiency permanent magnet motors. These motor types requires an inverter (also called variable frequency drive (VFD) or variable speed drive (VSD)) to operate.

The optimum choice for CO2 refrigeration control

The Reftronix CDU electronic controller is the heart of a CO2 refrigeration system. It maintains precise, energy efficient control of the complete process by:

  • Measuring temperatures and pressures
  • Calculating optimal performance
  • Adjusting the speed of the compressor (by using the variable frequency drive)
  • Adjusting opening degree of the electronic valves
  • Adjusting the speed of the fan(s)

CO2 Cooling
How to keep it simple and cost effective!

Most refrigeration systems around the world are small condensing units, serving just a few cabinets or a single cold room. With climate change and legislation reducing the use of F-gases, the industry is moving towards natural refrigerants, and CO2 (R744) has taken over as the refrigerant of choice in medium-sized applications. However, due to the complex design of CO2 systems, they become too expensive to produce when the cooling need is small.

That is the conventional thinking at least, but this is not necessarily true!

By simplifying the design, small CO2 condensing units require only one more valve than a traditional HFC unit, and they can be built at a similar cost. Simplified CO2 designs also have efficiencies comparable to R404A units. These designs are not only less costly to build - the units are also stable and cheaper to maintain with fewer moving parts that can break down.

Condensing Unit Control graph

Ways to simplify the design (and reduce the cost) of a CO2 condensing unit:

Two-stage Compressor

Using a two-stage compressor - instead of separate LT and MT compressors - simplifies the design and eliminates the complex receiver control. Two-stage CO2 compressors have proven performance and are commercially available from several manufacturers. They act as an economiser and improve system COP up to 30%.


Active oil management systems

Active oil management systems are complex and expensive, but CO2 refrigerant gas is much denser than HFC and a better solvent, meaning that with some clever piping it is possible to bring the oil back to the compressor without them. Granted, up to 30% oil in the refrigerant will have a negative effect on the evaporator heat-transfer efficiency, but this is also the case in traditional HFC systems, meaning the COP is still similar. Due to the high pressure in CO2 systems, the piping can also be designed with a larger absolute pressure drop than HFC systems, as the relative drop will be much smaller.


Electronic valves

The availability of electronic valves has increased dramatically the last couple of the years as Asian manufactures have entered the market. These valves are very reliable and offered at a very competitive price point.


Compressor & room controls

A CO2 refrigeration system requires an electronic controller but by combining the compressor and room controls in the same controller, the overall cost is greatly reduced.


Reftronix offers a CO2 condensing unit controller with built-in control of up to two cold rooms. The controller includes a Google-hosted cloud solution. This remote connection can provide significant savings, reducing the need for on-site service and aid in troubleshooting.

Condensing Unit Control graph

Integrated Inverters

Maintaining energy efficiency as cooling demand varies

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ECO & Compact

Maximise refrigeration performance

Optimum food preservation with high energy efficiency

The Reftronix CDU controller constantly adjusts cooling output to meet the precise demand of each display case. This minimises heat and cool cycles, ensuring food items are always maintained around the target temperature and maximises energy efficiency.

EU Flag

Comply with
F-Gas regulation and ECO-Design directives