A2L Refrigerant Transition: Understanding Leak Mitigation Sensors

The shift to A2L refrigerants is reshaping HVAC systems across the United States. Starting January 1, 2025, the EPA will ban manufacturing systems using refrigerants with a Global Warming Potential (GWP) above 700, such as R-410A. This change aims to reduce environmental impact but raises concerns about the flammability of new refrigerants like R-454B and R-32. Understanding how leak mitigation sensors work in these systems is crucial for safety and compliance.

Why A2L Refrigerants Matter

A2L refrigerants are classified as mildly flammable, which means they pose a lower fire risk than highly flammable gases but still require careful handling. Their lower GWP makes them more environmentally friendly, aligning with global efforts to reduce greenhouse gas emissions. However, their mild flammability means HVAC systems must include safety features to detect and respond to leaks quickly.

How Refrigerant Detection Systems Work

Refrigerant Detection Systems (RDS) are designed to identify leaks of A2L refrigerants and activate safety measures immediately. These systems use specialized sensors placed in strategic locations within HVAC units. When a sensor detects a refrigerant leak, it triggers a sequence of operations to reduce the risk of fire or explosion.

Sequence of Operations for Leak Detection

1. Leak Detection

   The sensor continuously monitors the air for refrigerant concentrations. Once it detects a level above a preset threshold, it signals the control system.

   
   

2. Indoor Blower Activation

   The system responds by running the indoor blower at 100% capacity. This action dilutes the refrigerant concentration in the air, lowering it below the Lower Flammability Limit (LFL). The LFL is the minimum concentration of gas in air that can ignite.

   
   

3. System Shutdown

   If the leak persists or reaches a dangerous level, the system may shut down the compressor and other components to prevent further refrigerant release.

   
   

4. Alarm Notification

   The system alerts building occupants or maintenance personnel through alarms or notifications, prompting immediate inspection and repair.

   
   

Leak sensors and components - (credit: Johnstone Supply)

Importance of Dilution Below the Lower Flammability Limit

Diluting the refrigerant concentration below the LFL is the key safety step in preventing ignition. The indoor blower’s role is critical here. By increasing airflow, it disperses the refrigerant quickly, reducing the chance that the gas will reach a flammable concentration. This approach allows the system to continue operating safely while technicians address the leak.

Practical Example: Leak Mitigation in a Residential HVAC System

Imagine a home using an HVAC system with R-454B refrigerant. A small leak occurs near the evaporator coil. The A2L sensor detects the leak and immediately signals the control board. The indoor blower ramps up to full speed, pushing fresh air through the ducts and diluting the refrigerant concentration. Meanwhile, the system alerts the homeowner via a smart thermostat notification. The homeowner calls a technician who arrives promptly to fix the leak before it becomes a hazard.

This example shows how leak mitigation sensors protect both property and people by combining early detection with active dilution.

What HVAC Professionals Should Know

Technicians installing or servicing A2L refrigerant systems must understand the role of leak mitigation sensors and their sequence of operations. Proper sensor placement is essential to ensure early detection. Sensors should be installed near potential leak points such as compressor compartments, evaporator coils, and refrigerant lines.

Regular maintenance and testing of these sensors are also critical. Sensors can degrade over time or become obstructed, reducing their effectiveness. HVAC professionals should follow manufacturer guidelines for calibration and replacement intervals.

Addressing Common Concerns About Flammability

Many questions arise about the safety of A2L refrigerants due to their mild flammability. It is important to recognize that these refrigerants are not highly flammable like propane or natural gas. The risk of ignition is low when systems include proper leak detection and mitigation measures.

The combination of early leak detection, blower dilution, and system shutdown creates multiple layers of protection. This approach significantly reduces the chance of fire or explosion compared to older systems without these features.

Preparing for the Transition

Building owners and facility managers should prepare for the A2L refrigerant transition by:

• Reviewing existing HVAC systems to identify those using high-GWP refrigerants.

• Planning upgrades or replacements with A2L-compatible equipment.

• Ensuring new systems include refrigerant detection sensors and follow safety protocols.

• Training maintenance staff on the operation and servicing of A2L systems.

  
  

Taking these steps will help ensure compliance with EPA regulations and maintain safe, efficient HVAC operation.