CO2 Series: Best Practices to Service CO2 Refrigeration Systems

Refrigeration Guide

Sep 25, 2024

CO2 transcritical booster system installations are expected to increase significantly in the next few years. It's only a matter of time before technicians will be asked to perform service on them. Technicians should be aware of the following basic best practices when servicing these systems.

Best Practices When Storing CO2

R-744 tank storage and/or refrigerant cylinder best practices are similar to those of legacy HFCs, including stacking procedures, safety precautions and assigning designated storage areas. To handle its high pressures, CO2 tanks are reinforced and weigh significantly more than HFC tanks. Empty CO2 tanks can weigh close to 123 lbs and can reach nearly 180 lbs when fully charged.

Supermarkets that prefer to have an entire system charge in reserve could potentially require 2,000 lbs of refrigerant. Storing that amount would require 40 cylinders weighing 7,200 lbs — or 3.6 tons. Contractors need to understand where to store the reserve refrigerant, and if the sheer volume and weight could affect building codes and/or a building's structural integrity.

Charging a CO2 Refrigeration System

When charging a CO2 refrigeration system, the most important consideration a technician should keep in mind is the refrigerant's triple point pressure (60.4 psi) and how to guard against turning the charge to dry ice. Instead of charging with liquid CO2 when the system is below 60.4 psi, contractors should charge with vapor until the system reaches CO2’s triple point. Failure to do so is likely to result in the formation of dry ice in the charging line, a common (and potentially costly) mistake for those unfamiliar with CO2 installations.

Most equipment manufacturers recommend charging the system with vapor until it reaches at least 100 psi. After achieving 100 psi with vapor, which has equalised throughout the entire system, technicians can switch charging with liquid to speed up the process.

Dealing with Trapped Liquid

Because CO2’s coefficient of expansion (COE) is higher than a typical HFC refrigerant, it has a higher probability of refrigerant pressure increasing rapidly between two valves. If this occurs, the pressure can increase by 145 psi for every 1.8 °F increase in temperature. As a result, sections of a system need to be fitted with appropriate check valves or pressure-relief valves for safe system operation and service.

Detecting Leaks in CO2 Systems

Because R-744 refrigerant is colorless, odorless and heavier than air, it can be difficult for building occupants to detect leaks. CO2 transcritical booster systems must utilise integrated leak detection systems with detection devices mounted 18 inches off the ground. Like HFC systems, it's important to immediately detect and mitigate CO2 leaks as they occur.

Safe Handling Best Practices

Technicians should take proper precautions when handling high-pressure CO2 refrigeration systems. Even when a system is shut off, standstill pressures are still likely to remain high and should be handled accordingly. Because it is heavier than air, CO2 can quickly displace O2 when it is released in excessive amounts. Thus, technicians should avoid handling it in confined spaces and ensure they use proper leak detection procedures and equipment.

In addition, CO2 vapor temperature at atmospheric pressure is -109.3°F; technicians should follow proper service procedures and always wear personal protective equipment (PPE) to limit the potential for skin burns. With proper training, tools and equipment design – and when maintained and operated properly – CO2 is a safe and natural refrigerant alternative.

Contact Us

If you have any further questions about the best practices to service CO2 refrigeration systems, or if you have any other questions regarding refrigeration, you can contact the Refrigeration Support Team for further advice. Alternatively, you can contact your local branch for support.