A2L Refrigerants and the Growing Challenge of Thermal Drift

The HVAC industry is undergoing a major transformation as it shifts to A2L refrigerants to comply with new environmental regulations. Alongside this, A3-driven heat pumps are also expanding across Europe and beyond.

While the focus has largely been on refrigerant leak detection systems to meet safety standards such as UL 60335-2-40, the transition to these new refrigerants brings another important consideration — thermal drift. This phenomenon, caused by changes in system temperature ratings, is pushing manufacturers to adopt more accurate and stable designs.

From the Montreal Protocol to A2L Adoption

The move to A2L refrigerants began with the Montreal Protocol (1989), which aimed to eliminate ozone-depleting substances like CFCs. HFCs replaced CFCs due to their ozone safety, but their high Global Warming Potential (GWP) led to the Kigali Amendment, which targets an 80–85% reduction in HFC use by the 2040s in developed nations.

A2L refrigerants offer much lower GWP but are mildly flammable. This classification means OEMs must address two safety conditions:

1. Concentration above a critical threshold

2. Presence of an ignition source

UL 60335-2-40 sets strict limits: refrigerant concentration must remain below 25% of the Lower Flammability Limit (LFL). For example:

• R454A LFL: 0.278 kg/m³

• R290 (A3) LFL: ≤ 0.10 kg/m³

Leak detection systems—often using acoustic resonance technology—monitor critical areas, such as near condenser coils, with lifespans exceeding 15 years to minimize maintenance costs.

Thermal Drift: A New Engineering Challenge

A2L systems often require higher operating temperatures, which can cause drift in pressure readings—especially on the high-pressure side. This impacts the reliability of high-pressure cutoff switches, essential for system safety.

Excessive thermal drift can:

• Reduce reliability of protective cutoffs

• Cause incorrect system responses

• Prevent compressors, pumps, and fans from running at peak efficiency

• Increase energy consumption and maintenance costs

For sensitive applications, low thermal drift ensures accurate data and better performance for smart control systems—critical in high-efficiency HVAC designs.

Ongoing Optimization in a Changing Market

The shift to A2L and A3 refrigerants is not a one-time transition. As energy efficiency targets tighten—especially with HVAC systems accounting for 40–60% of a commercial building’s energy use—manufacturers must continually refine their designs.

Future HVAC systems will need components that:

• Maintain accuracy across changing temperature profiles

• Ensure compliance with evolving safety standards

• Deliver maximum efficiency without increasing lifecycle costs

Our best choice and suggested solution? Resonix RGD by Sensata Technologies