Is CO2 the Natural Refrigerant Choice?

Food Retail & Cold Chain Sectors Turn to Natural Refrigerant Options

With an increased interest in using natural refrigerants, typically ones having a Global Warming Potential (GWP) no greater than 150 and with a drive to protect our environment, what would make carbon dioxide the “natural” refrigerant choice for food retail, food manufacturing, food processing plants, and cold chain? There are several important considerations to make when questioning the use of CO₂ (R-744) as a refrigerant gas for these sectors, such as: environmental benefits, refrigeration system technology, regulations and compliance, safety requirements, maintenance and operating conditions and refrigerant leak detection technology.

Environmental Benefits of CO₂

Natural refrigerants like carbon dioxide, ammonia and hydrocarbons (Propane, Isobutane and Propylene), are often used because of their inherent environmental benefits. With zero ozone depletion potential (ODP) and very low to zero GWP, natural refrigerants are seen as a great alternative to synthetic refrigerants as they are less polluting to our atmosphere. For the food retailer or manufacturer, using a natural refrigerant, like CO₂ carries with it a positive environmental message, which in the case of a grocery store or food chain, often coincides with the “natural” foods, or “farm to table” branding messages that customers find appealing.

Refrigeration System Technology

CO₂ refrigeration systems are now an established technology, and the hurdles with early adoption of commercial CO₂ systems have now been overcome over the past 15 years. OEMs and gas suppliers have increased the support base for these systems, and the engineering base for maintenance has increased to enable quick responses to call-outs. There have also been improvements made to the CO₂ systems when it comes to CO₂’s energy efficiency, especially regarding the transcritical stage with injector technology and parallel compressors.

Regulations and Compliance

It is easy to see why a food retailer or manufacturer would now seriously consider using CO₂ as a refrigerant. Depending on where you live in the world, there are also strict regulations in place to reduce the use of high GWP refrigerant gases, like F-Gas (EU Regulation No. 517/2014), the US EPA Clean Air Act Section 608 and CARB thus making it obligatory to report information and ensure compliance.

Using a natural refrigerant like CO₂, also mitigates a company having to comply with local regulations targeting high GWP refrigerants like HFCs, meaning the commercial user or facility using the CO₂ as a refrigerant are not required to report the information to regulatory bodies. This could potentially mean not having to pay for costly fines for refrigerant leaks and non-compliance, while also eliminating any corresponding negative press coverage for the user.

Health and Safety Requirements

All of these factors mean CO₂ is an increasingly attractive option for use as a refrigerant. However, regardless of the equipment in place, the systems used for leak detection, legislation, maintenance, support and the environmental messaging, CO₂ can pose a huge potential health hazard to humans when seen in high concentrations.

CO₂ concentrations play an important function as part of the Occupational Safety and Health Administration (OSHA) exposure limits if there were to be a leak event. Typical figures stipulated for CO₂ exposure by OSHA are:

• 5,000 ppm – Occupational Exposure Limit (OEL)
• 40,000 ppm – Immediately Dangerous to Life or Health (IDLH)

Since CO₂ is part of the air we breathe (around 0.04% or 400 parts per million), it can be challenging to measure leaking CO₂ refrigerant in low concentrations, due to its natural background level. When measuring for background CO₂ in parts per million (PPM) for example in a retail supermarket, the levels vary depending on how many customers are in the area of the sample. It also depends if dry ice is being used in the area, as that too, could add to the overall concentration. Similarly, if a bakery section was sited in a food retail where yeast proofing took place or if the food manufacturing or processing function involved fermentation or carbonating, carbon dioxide levels may well fluctuate considerably. Typically the concentrations found in this type of application would range from 600 – 1400 ppm CO₂.

Since CO₂ systems operate at much higher pressures than systems used with other types of refrigerants, such as HFC DX systems, when a CO₂ refrigerant leak occurs, it tends to fill the space more rapidly and become more catastrophic quicker. This means the amount of refrigerant lost is much higher and can cause more disruption to trade, higher inventory or stock losses and be dangerous to life and health. Leakage rate for CO₂ when compared with their HFC refrigerants, is typically much higher.

Maintenance and operating conditions

Although CO₂ refrigeration systems are designed to operate at pressures much higher than the HFC DX systems, it is always good to consider a maintenance program for the continued use and wear of the equipment. These high pressures and relative performance through the heat rejection and expansion process, pose inherent challenges to its efficiency as a refrigerant at these high operating and pressure conditions. As an additional consideration, CO₂ systems are more expensive than their HFC / HCFC DX equivalents due to the use of the electronics controls at all the fixtures and the extra elements required to operate and control CO₂ systems. They may carry more upfront costs than a traditional type of system, therefore, financial justification from a retailer’s perspective is an important consideration for the initial capital expenditure.

Refrigerant leak detection technology

The technology and equipment used in CO₂ refrigerant detection is either an aspirated system, which pulls air from sample points in various zones located at distances of up to 1200 feet or four football fields, or a local / point sensing head, which uses diffusion to detect the presence of a gas. Whichever technology is adopted; non-dispersive infrared (NDIR) sensing is the choice for sensing CO₂. The choice between aspirated and point sensing is an end-user preference, as both are suitable technologies to use, and aspirated will always be the better solution over the long term / life cycle of the system.

CO₂ users must have leak detection for health and safety reasons, to protect operations and personnel, especially in confined spaces i.e. walk-in coolers / freezers and confined rack rooms from exposure to high CO₂, typically 5,000 ppm. Regardless of the CO₂ sensing technology alarming for CO₂ is the same and tends to follow:

1. Additional alarms/sirens for confined areas to alert people in those spaces:
   • Inside the walk-in / cooler freezer
   • Outside the CO₂ rack rooms
2. Additional signage in the confined areas to alert people in those spaces:
   • Inside the walk-in / cooler freezer
   • Outside the CO₂ rack rooms

Is CO₂ the “Natural” Refrigerant Choice for You?

The environmental benefits of using CO₂ as a refrigerant far outweighs the risk of using synthetic refrigerants, the potential harm through refrigerant emissions, and the risks involved. With zero ozone depletion potential and very low global warming potential, CO₂ can be a great asset for food retail, food production and processing and cold chain applications. The principles of a comprehensive refrigerant management strategy remains the same. They are simply tweaked on the local leak detection deployment based on the refrigerant’s toxicity and flammability properties.

With an effective refrigerant management strategy coupled with leak detection systems, CO₂ can provide any forward-thinking refrigeration manager or food retailer with reduced operating costs, improved system uptime, protection for their employees and responsibility for their environmental footprint. ∎

Do you have questions about CO₂ or other natural refrigerants? Let us know in the comments below or by emailing us at news@mybacharach.com.