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  • Lisa Troller

CO₂ as a better refrigerant option

Is CO a better refrigerant?

From an environmental perspective, the natural refrigerant CO offers a significant advantage over currently-used HFC refrigerantsand CO has been proved as an alternative refrigerant for many years. Still, higher costs associated with the equipment, installation, and operation have prevented CO from being widely adopted in the U.S. up until now. This is changing, however, as greater familiarity and economies of scale are bringing initial costs down and as regulatory restrictions on traditional refrigerants continue to increase.

Section 608 of the Clean Air Act

The EPA’s Clean Air Act (CAA) Section 608: Regulatory Requirements for Stationary Refrigeration and Air Conditioning limits the allowable refrigerant leak rate on systems with more than 50 lbs. of refrigerant to 20% annually on commercial refrigeration and 30% for industrial process refrigeration.

The CAA also specifies leak repair requirements and establishes guidelines for refrigerant reclamation, sales restrictions, technician certification, service practices, appliance disposal, equipment recycling, and recordkeeping. This rule was modified on February 26, 2020, so that some of these requirements, such as the leak repair requirements and associated recordkeeping and reporting provisions will only apply to ozone-depleting refrigerants as of April 10, 2020.

What to expect next

Nevertheless, these requirements are a bellwether for what can be expected at a state level in the coming years. The California Air Resources Board (CARB) already has a refrigerant management program that requires facilities with refrigeration systems containing more than 50 lbs. of a high climate-impact refrigerant to conduct and report periodic leak inspections, promptly repair leaks, and keep service records on site.

The synthetic problem

Hydrofluorocarbons (HFCs) are greenhouse gases that trap thousands of times more heat than carbon dioxide. HFCs are used in refrigeration and cooling, and their use is increasing rapidly to match the global demand for cooling. HFCs are short-lived climate pollutants (SLCPs), which are exponentially more impactful in the near term than other greenhouse gases. Their elimination could avoid up to 0.5°C of warming by the end of the century; this would help us avoid catastrophic tipping points that are only 1.5°C away.

CO is the better refrigerant

Since emissions are usually characterized in terms of "carbon dioxide equivalent," it might feel counter-intuitive to brand CO as the better refrigerant. Here's the short version: Carbon dioxide's impact on the environment is the baseline for measuring the impact of all other greenhouse gases. Carbon dioxide's impact is considered one. The HFCs most commonly used in refrigerant and cooling average 2,440 times the climate impact of carbon dioxide. (Check out our Global Warming Potential series for more information.)

Climate impact

The Ozone Depletion Potential (ODP) of CO is 0 and the Global Warming Potential (GWP) is 1, which is far less than that of synthetic refrigerants. Since most of the CO used for refrigeration is chemical and an industrial by-product emitted from factories, using CO as a refrigerant is like recycling or delaying the emission of this exhaust gas. This, in turn, is quite beneficial to the environment. This translates as an average climate impact of 2,400 times less than the most commonly used HFCs.

Cost and efficiency

The thermophysical properties of CO are perfectly suitable for refrigeration cycles and equipment. The heat transfer characteristics of CO are more attractive than synthetic refrigerants, increasing energy efficiency in systems. CO must operate at high-pressure, which can increase system efficiency, reduce the size of components and piping and enable the design of more compact systems.

The chemical properties of CO are stable. It’s non-toxic, harmless, noncombustible, and will not decompose into toxic gases at high temperatures. At 12 times more economical than traditional HFCs, CO is a natural, safe, and inexpensive refrigerant.

What's the hang-up?

So why doesn’t everyone make the switch to CO systems? Ultimately, it all comes down to cost. We'll talk through it step by step, but here's the punchline: as demand for these systems increases the cost will come down.

Component and equipment costs

Carbon dioxide operates at a far higher pressure than typical HFC refrigerants, therefore the leak potential increases, and the component cost also rises. Carbon dioxide packs and condensing units need special components, more controls, and safety features than an equivalent HFC unit, therefore the component and equipment costs become higher.

When the requirement for gas leak detection is considered, we need to compare the room volume with the refrigerant “practical limit” value to establish the maximum gas charge of the system. Carbon dioxide has a “practical limit” of approximately 25% when compared to other HFC refrigerants, therefore leak detection equipment is 4 times more likely to be required.

Training and personnel costs

Carbon dioxide can change from a gas directly to a solid (triple point) at 4.2bar, therefore the commissioning engineer must take more care when charging the system with refrigerant. Also, the design of PRV vent lines must allow for the possible freezing of carbon dioxide as it approaches atmospheric pressure.

Carbon dioxide is very sensitive to water contamination and can form unusual compounds when there is a leak in a water heat exchanger. It is also important to ensure that no moisture is allowed into the system when charging refrigerant or oil.

Strength in numbers

To accomplish the successful phase-out of synthetic refrigerants, we need to eliminate the barriers of cost and training associated with natural systems. Several organizations are tackling this issue, including the North American Sustainable Refrigeration Council (NASRC). Organizations and alliances like the NASRC bring together like-minded companies and provide the scale needed to drive down training and equipment costs.

Refrigerant Carbon Credits (RCCs) are Therm's contribution to the solution. We help you monetize your positive environmental impact and reduce the financial burden associated with natural system upgrades.

Call us optimists

We believe that we are right around the corner from large-scale natural refrigeration and cooling systems. With the solutions available on the market today, we can help smaller grocers and operations upgrade their systems to CO.


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