R744 has great properties for many different applications and a GWP of one.
CO2 (R744) is a climate-friendly natural refrigerant. But how can CO2 refrigeration be climate friendly when everyone is talking about reducing CO2 emissions to address global warming?
Global warming potential (GWP) is a relative measure of heat-trapping impact. Carbon dioxide has a GWP of one. For example: Greenpeace states that the commonly used HFC R134a has a 20-year GWP of 3,830; thus one kilogram of R134a is as harmful to the environment as 3,830 kilograms of CO2-equivalent (CO2e) over 20 years.
“Yet the global warming potential of HFC-134a, the most widely used HFC, is 3,830 times greater than carbon dioxide over 20 years." — Greenpeace
R744 has great properties as a refrigerant. It has excellent heat transfer properties and a high volumetric cooling capacity and can thus be used in many different heating and cooling applications. CO2 refrigeration is efficient in small-, medium- and large-scale applications. It also shows great potential in mobile air conditioning (MAC). Refrigerant supplier Linde Gas summarises these advantages.
Thanks to the efficiency of the refrigerant and continuous technical development, energy consumption in systems using it is often less than that of alternatives. Less energy consumption decreases the running costs of the system, especially the energy costs. Gullo et al (2017) from the Norwegian University of Science and Technology and the Brunel University of London found that, with technological advantages, R744 is 3% to 37.1% more efficient than a R404A direct expansion (DX) unit and the running costs are lower in almost all settings.
“[A]dvanced commercial “CO2 only” configurations feature energy savings ranging from 3% to 37.1% across Europe over a R404A unit." — Gullo et al. (2017)
Currently, the prices for HFCs are rapidly increasing as a result of being phased out. Thus, the purchase price for systems that use synthetic refrigerants are increasing as well.
“Öko-Recherche forecasts HFC prices to increase further to 35€/tCO2e on average by 2030."
However, R744 has a low critical point at 31° C. This makes CO2 refrigeration less effective in hot climates. This issue will be addressed in the next part of this series. It also produces higher pressure in the system. Special equipment that is able to withstand higher pressures needs to be used. Systems using this refrigerant tend to be more complex than conventional systems as well. Emerson gives an overview of the advantages and disadvantages.
R744 is classified in the safety class A1. It is non-toxic, but very high concentrations can lead to asphyxiation. The refrigerant is not flammable. The International Institute of Refrigeration summarized the safety classifications for commonly used refrigerants. The GWP of the refrigerant is one. These properties keep it safe from many regulatory standards and a potential phase out. Thus, R744 is a safe investment in the future. Retail giant ALDI Süd uses this refrigerant and ammonia to reduce its carbon footprint and future-proof its stores.
If you want to read more about R744 in different settings, read the articles below:
Ritchies IGA supermarket installs Australia's first transcritical CO2 ejector
P&O Cruises opts for on-board CO2 transcritical technology
CP Foods targets sustainability with CO2 heat pumps
By shecco , published Oct 08, 2018 - 2 pages