Carter Synergy was approached by key client The Co-operative Group (TCG) to adapt our integrated CO₂ solution for trial in their estate. Working with Green & Cool Refrigeration (G&C) we tailored our already successful system for the Hulme store.

The key drivers for TCG were:

  • Natural refrigerant-based system
  • Reduce energy use
  • No impact on customer experience
  • Financially sustainable technology

Our system has and/or will meet all of the above criteria.

The Solution

The solution implemented was the Carter Group Integrated Transcritical CO₂ system, there are a number of key aspects of the system:


At the heart of the solution is a Green & Cool Sirocco Transcritical pack, this is a standard part of the G&C range however it was adapted to suit the specific needs of the Hulme store namely:

  • MT Refrigeration (-7°C SST)
  • LT Refrigeration (-32°C SST)
  • Heat Recovery to water for store heating
  • Integrated Heat Pump compressor for heating boost in low load
  • Internal Gas Cooler with integrated heat pump evaporator
  • Green CO₂ntrol PLC with interface to RDM system and HVAC control
  • High resilience 120/80/60 bar design

The plant was designed to provide all refrigeration (LT & MT) to the store and all space heating.
The Co-operative Group – Hulme Store
Integrated Transcritical CO₂ Solution

Cabinets & Evaporators

The cabinets and cold store evaporators used are standard TCG fixtures however the coils and valves have been selected so as to be suitable for the operating pressures of the CO₂ system.

Heating System

The heating system employed is a Low-Pressure Hot Water (LPHW) solution, the source of heat for the water is a plate heat exchanger (PHE) in the MT discharge on the pack which is recovering heat from the refrigeration system that is typically rejected to the atmosphere in traditional HFC systems.

A purpose-built controller was provided that interfaces with the refrigeration pack so it can be a reactive source of heat, the controller sends a 0-10V signal to the pack depending on the amount of heat required.

Should the heat available from the refrigeration process be insufficient to heat space then the heat pump stage is engaged to “boost” the heating until the space temperature is satisfied.


The installation of the refrigeration services is in k65 copper to support the system operating pressures, the installation process is the same as with conventional systems so there was no effect on the programme.

Expectations & Benefits

With a number of these systems now installed Carter Synergy are confident in predicting a reduction in energy use when compared with a similar store using conventional heating and refrigeration systems of 50% plus, this expectation is in line with actual results we are seeing elsewhere.