Servicing the Next Generation of Lower-GWP Refrigerants

As the phasedown of hydrofluorocarbon (HFC) refrigerants ramps up over the next several years, technicians can expect to see a wider variety of refrigeration architectures that use lower-global warming potential (GWP) alternatives.

As I detailed in a recent article for Engineered Systems, these emerging refrigerant substitutes have unique properties and characteristics compared to legacy HFCs, which impact system design and servicing considerations.

To navigate this evolving landscape, service technicians should educate themselves on the fundamentals of working with the next generation of lower-GWP refrigerants. Despite critical differences and refrigerant-specific nuances, most long-held and widely adopted servicing best practices still apply.

Working with the next generation of lower-GWP refrigerants will require familiarity with already approved substitutes — namely, CO₂ (R-744) and R-290 (propane) — and a new class of A2L alternatives.

As each refrigerant is poised to play unique and specific roles within commercial refrigeration, it’s important to understand their respective potential impacts on system servicing and adhere to the UL 60335-2-89, 2^nd edition requirements, if applicable.

Expanded potential for R-290

In most stand-alone equipment, R-290 systems are critically charged and hermetically sealed at the manufacturer’s facility. Malfunctioning units are typically refurbished by a qualified technician and/or reconditioning company. If servicing is required, it’s important to follow R-290 servicing procedures.

Before entering a service area, use a portable gas monitor that can alert you to the presence of R-290 in the air. Always wear the required personal protective equipment (PPE) to ensure safety. Brazing should be performed only by qualified personnel and under specific precautionary conditions. Check all brazing and silver soldering equipment for leaks and proper pressure settings.

Refrigerant must first be evacuated with a vacuum pump and purged from system lines with an inert gas (e.g., nitrogen). Before working on a stand-alone, R-290 system, it should be moved to an unconfined, unoccupied and well-ventilated area. If possible, place a fan in the room to ensure active ventilation.

Understanding A2L systems and safety standards

Lower-flammability A2Ls are well on the path to regulatory approval and poised to fill expanded roles across a broad spectrum of commercial refrigeration systems. From both servicing and safety perspectives, A2Ls follow guidelines established in the UL 60335-2-89, 2nd edition safety standard.

Each A2L refrigerant has a unique lower flammability limit (LFL) rating, which is used to calculate charge limits. For example: the LFL of R-454C is 0.293 grams per cubic meter (g/m³). LFL is based on the worst-case formulation (WCF), as defined in ASHRAE 34.

When servicing an A2L system, the first step is to identify which A2L refrigerant is being used. Look for refrigerant labels on the system and red markings on all service fittings; and clearly mark fittings for future servicing. Use only A2L-certified gauges, vacuum pumps, and leak detection and refrigerant recovery machines.

Servicing A2Ls requires additional steps that are already considered industry-accepted best practices: evacuate, purge and test for leaks. If possible, try to work in a well-ventilated area using a continuous leak monitoring and detection system.

Braze all connections before embarking on higher-risk activities and be aware of your servicing space, including the presence of other people or potential hazards. For the most part, typical A1 system best practices are required on A2L systems.

Note: it’s important to use only A2L-qualified components and controls, and only charge systems according to their designed charge limits.

CO₂ characteristics and considerations

Compared to traditional HFC-based systems, CO₂ (R-744) has unique servicing considerations — high system pressures, a low critical point and high triple point — impacting refrigerant storage, system charging and other key servicing requirements.

Because CO₂ tanks are designed to handle its high pressures, they weigh significantly more than standard HFC tanks — potentially up to nearly 200 lbs. A full charge of a 2,000-lb. system may require 40 cylinders weighing 8,000 lbs. (i.e., 4 tons). Technicians will need to plan for storing reserve refrigerant and be aware that storing high quantities of CO₂ will affect building codes.

System charging is an especially important consideration with CO₂ systems, primarily because liquid R-744 will turn to dry ice if the system reaches the triple point pressure of 60.4 psig. To avoid this, charge with vapor until system pressures exceed the triple point pressure — typically beyond 100 lbs. psig — then finish charging with liquid.

CO₂’s coefficient of expansion (COE) is higher than a typical HFC, which can cause pressure to rise rapidly when liquid refrigerant gets trapped in between two valves. Pressure can increase 145 psig for every 1.8 °F increase in temperature. Many systems are fitted with appropriate pressure-relief valves at the location of the trapped liquid to prevent pressure rise and assist with system servicing.

Leak detection is also an important consideration for maximizing the performance and safety of CO₂ systems. R-744 is colorless, odorless and heavier than air — and can be potentially toxic in high concentrations. Leak detectors should be mounted 18 inches off the ground and below the breathing level. Early detection can prevent CO₂ system performance issues and protect food quality.

To learn more about servicing best practices for A3, A2L, and CO₂ refrigerants, please visit the contractor training section of our content hub.