As the U.S. Environmental Protection Agency (EPA) continues to phase out hydrofluorocarbon (HFC) refrigerants, HVAC/R equipment manufacturers must make design changes to ensure their products are compatible with low-global warming potential (low-GWP) refrigerants. Because A2L refrigerants are considered mildly flammable, compliance often requires the integration of a refrigerant leak detection system (RLDS) and mitigation protocol as part of the equipment design.

1. The EPA, as well as some states, have mandated several hydrofluorocarbon (HFC) phase-down requirements. How are these regulations evolving, and how are they impacting the design and engineering of HVAC/R systems?

Under the AIM (American Innovation and Manufacturing) Act, the EPA is phasing down the production and consumption of hydrofluorocarbons (HFCs) in the United States. The EPA’s main objective is to facilitate the transition to low-GWP refrigerants and next-generation technologies through sector-based restrictions.

Equipment manufacturers will be required to redesign their air conditioning and refrigeration equipment to meet the required GWP requirements, specifically to consider using A2L refrigerants such as R-32 and R-454B. A full list of the equipment and application types can be found online here: Restrictions on the Use of Certain HFCs under Subsection (i) of the AIM Act (epa.gov).

Due to the U.S. EPA’s imposed GWP limits, residential and light commercial air conditioner and heat pump manufacturers must consider using A2L (mildly flammable) refrigerants such as R-32 or R-454B.

Manufacturers of self-contained commercial refrigeration equipment have the option of using either natural (e.g., R-600a/isobutane and/or R-290/propane) or A2L (e.g., R-454A, R-454C and/or R-455A) refrigerants.

Retail food equipment manufacturers, depending on the refrigerant charge, must consider either natural (e.g., R-744/CO2 or R-290/propane) or A2L (e.g., R-454A, R-454C and/or R-455A) refrigerants.

2. As refrigerated systems shift to low-GWP A2L and A3 refrigerants, what measures must be in place to ensure manufacturers are compliant with new regulations?

According to the EPA, to ensure compliance for HVAC/R systems using A2L refrigerants where the refrigerant charge is greater than 4 pounds, equipment manufacturers must incorporate both A2L refrigerant leak sensors and control logic that activate evaporator fan(s) and use circulated air to quickly disperse and dilute refrigerant in the event of a leak. This is intended to prevent the formation of refrigerant concentrations. The other requirement is that refrigerant charge limits must be based on the minimum occupied volume of the room where the equipment is expected to be used. This charge limit requirement also includes a safety factor of four to ensure any leaked refrigerant is diluted to well below the lower flammability limit (LFL), based on room size.

For HVAC/R systems using A3 (highly flammable) refrigerants, the U.S. EPA has imposed refrigerant charge limits. The current charge limit is 150 grams of R-290 refrigerant per refrigeration circuit. The U.S. EPA via SNAP (Significant New Alternatives Program) Rule 26, published on May 31, will allow charge limits for R-290 to increase to 300 grams for closed (with doors) and 500 grams for open (without doors) refrigerated cabinets.

3. What elements make up A2L refrigerant leak detection and mitigation components? Explain how these are critical requirements and how they work within the refrigeration system design.

According to the EPA’s requirements, refrigerant leak detection systems must have both sensor(s) and a controller with the necessary logic to activate evaporator fan(s) and use circulated air to quickly disperse and dilute refrigerant in the event of a leak. This is intended to prevent the formation of refrigerant concentrations.

A2L refrigerant sensor(s) must be calibrated to the specific A2L refrigerant with the LFL mitigation trigger point being factory-set and sealed with no field adjustment. Self-test protocols embedded in the refrigerant leak sensor run periodically, ensuring proper operation. In the event of a sensor failure, the system will go into mitigation and stay in mitigation until such time that the failed refrigerant leak sensor is replaced.

The refrigerant leak sensor and its firmware are considered part of a protective electronic circuit. RLDSs are required to pass testing designed to address long-term stability, vibration, range and set point verification. Refrigerant leak sensors that have a defined life must provide notice of replacement after reaching end-of-life.

The A2L mitigation controller must have firmware and hardware necessary to receive A2L sensor inputs and outputs to provide the required mitigation functionality. Functionality includes closing/opening relays that turn off system components (potential sources of ignition) and turn on components such as evaporator fans, which reduce the concentration of A2L refrigerant. Once a refrigerant leak or a faulty sensor is detected, the controller must lock out the system for a minimum of 5 minutes. The controller must be manually reset, and the system can’t be restarted until the refrigerant leak and/or sensor fault has been resolved. Another requirement is that, once the original equipment manufacturer (OEM) has set and locked the controller’s mitigation configuration, the configuration can’t be changed in the field. This ensures that the required A2L leak sensing and mitigation protocols remain intact.

4. Accuracy and false positives are two major concerns around A2L refrigerant sensing. What technological advancements are enhancing reliability?

There are three (3) primary technologies used to sense A2L refrigerants. These are speed-of-sound, NDIR (nondispersive infrared) and thermal conductivity. The main trade-offs with A2L refrigerant leak sensing technologies are cost, response time and reliability. Speed-of-sound technology, which is what we use at Johnson Controls, appears to be the front-runner when it comes to response time. However, all three technologies meet safety agency requirements. A2L sensors are required by the EPA to be immune from poisoning, damage or false alarms as a result of common household and workplace contaminants (which have not been approved by the safety listing agency).

5. Have there been any advancements in controls to support or enhance leak detection and mitigation performance?

Having data available to quickly and adequately get an HVACR system up and running is critical. At PENN we have chosen to use Modbus communications and cloud-based remote connectivity. These technologies assist with system alerts, troubleshooting and diagnostics. In the case where an OEM uses more than one A2L refrigerant sensor, Modbus communications allow the controller to identify which sensor detected the refrigerant leak and provide warnings/alerts. The same is true if an A2L sensor drifts out of calibration. Modbus can also provide an early warning and alerts when an A2L sensor is approaching end-of-life. Additional sensor information is available via Modbus registers, such as A2L refrigerant type, LFL level and remaining sensor life.

6. Cloud-based remote connectivity allows service technicians and facility managers to constantly monitor HVAC/R equipment. With the advent of A2L refrigerants, remote monitoring is even more important, as refrigerant leaks need to be addressed immediately. In addition to remote monitoring, most cloud platforms allow service technicians to receive SMS text and/or email messages notifying them of HVAC/R system-related issues so that they can respond quickly. What are the most important factors systems engineers should understand when specifying refrigerant leak detection and mitigation components?

The three most important factors are: 1) A2L sensor technology and controller response time if a leak is detected; 2) the trade-off between A2L sensors equipped with relays vs. Modbus communications, where the later identifies the sensor that detected a refrigerant leak along with alerts for end-of-life; and 3) that monitoring HVAC/R equipment health and receiving alerts/alarms for system-related issues will require some form of remote connectivity. Cloud-based platforms enable HVAC/R systems to be monitored by responsible parties, from any place and at any time.

7. Are there any safeguards equipment manufacturers can take to be certain the sensing controls they specify are compliant with the latest regulations?

A2L sensors and controllers must be approved by authorized safety agencies, such as U.L., CSA, Intertek and others. Per the EPA, OEMs should request that component manufacturers provide the appropriate safety agency reports and file numbers confirming that the devices conform to the latest regulations.

8. What does the future of refrigerant leak detection and mitigation look like, and how can manufacturers prepare?

Refrigerant leak detection is not only needed for safety reasons, but it’s also important in protecting the environment, reducing product loss and maintaining the required temperature and humidity levels for indoor comfort.

With the continued transition to low-GWP refrigerants, leak detection will be needed for a high percentage of HVAC/R equipment and applications. Johnson Controls/PENN aims to do our part by determining the best location for refrigerant sensors and methodologies for minimizing refrigerant leaks.