Delivering Excellence in Climate Control Solutions

CO2 / Transcritical

Some Background

CO2(R744) was one of the first refrigerants used back in the mid 1800s through until the 1920-1930s. It was then phased out in favour of the newly developed CFC refrigerants.


Due to the discovery of the damaging effects of CFC & HCFC refrigerants on the Ozone layer, the New Zealand Government signed the Montréal Protocol in 1987 to phase out all CFC & HCFCs ( i.e. R12, R22, & R502).  

HFC refrigerants were then adopted as the new norm in the mid 1990s (i.e. R134a, R404A etc.), however HFC refrigerants have since been found to have high Global Warming Potential (GWP).

refrigeration systems image

So, CO2has recently returned to vogue due to it being natural, efficient, and having a very very low GWP. With the introduction of the Emissions Trading Scheme (ETS) and levies on HFCs, interest in CO2 as now being a viable alternate refrigerant is growing rapidly. Some European countries have banned the use of HFC refrigerants already.

Other natural refrigerants used in refrigeration are Ammonia NH3 (R717) and Propane HC (R290), but they are not favoured in Supermarket use due to high Health and Safety risks (with Propane being Flammable, and Ammonia being Toxic) especially with most supermarkets being located in populated areas.

Pros for CO2

  1. As more and more systems are installed, component suppliers are enabling economies-of-scale and introducing better components and controls, as well as maximising the energy potential of operating a CO2 system.
  2. A Transcritical system is 100% CO2, so only one gas is required on site and it operates on a Direct Expansion cycle for both LT and MT applications.
  3. Typically a CO2 system has some energy saving advantages in cooler climates, combined with excellent heat recovery properties. Total store energy savings can be obtained in winter months  in HVAC and year round via water heating.
  4. Green image!  It's non-toxic, natural and non-flammable so there are no adverse effects on the environment.
  5. It's future is secure and it won't be phased out as other refrigerants have been in the past.  It is the environmental choice for many refrigeration system applications.
  6. High volumetric cooling capacity, so smaller piping, evaporators and compressors can be employed, however in summer months it operates at higher pressures.
  7. It's a high density gas so all heat exchangers become very efficient.
  8. As more and more systems are installed and equipment supplier technology increases, the perception CO2 is only viable for large stores decreases. CO2 is now being used in domestic HVAC and Heat-pump DHW applications so is becoming more viable for all store sizes.

Cons for CO2

  1. In summer ambient conditions the efficiency gains are reduced and, in some instances negated, compared to traditional HFC systems. Special care in design needs to be made by experienced designers to avoid high energy costs, predominantly through smart control algorithms and additional control componentry. Transcritical CO2 is currently not recommended for warmer climates in the sub-tropical regions because of this.
  2. Requires specific training in the maintenance of systems. Incorrect service and maintenance can lead to  loss of refrigerant and wasted energy. Only use CO2 trained service technicians.
  3. Operates at higher pressures so thicker wall  piping and stronger components are required.  This offsets the reduction in pipe and compressor size so capital cost can be more
  4. A subcritical system(Hybrid) still requires two gases on site with typically R134a (HFC) as the secondary gas which attracts an ETS levy. (Although due to the use of CO2 it requires a smaller total charge than traditional 100% HFC systems offsetting some of the ETS levies.)

What do I do if .....?

I currently have CO2 in my store?

Contact your nearest McAlpine Hussmann Service Branch to ensure that you are getting the best efficiencies out of your system.

I'm looking to upgrade my store?

Contact your nearest McAlpine Hussmann representative to discuss options and guide you through the best solution for your current and future needs.

I want to see Transcritical CO2store system?

Contact your local McAlpine Hussmann representative.