Updated Requirements for Refrigerant Detection Systems

To address growing concerns about climate change and environmental sustainability, regulatory bodies, consumers and other stakeholders have placed an increased focus on the reduction of potent greenhouse gas emissions, such as traditional hydrofluorocarbon (HFC) refrigerants, to the atmosphere. In the U.S., several states have introduced measures curtailing use of these products, including the California Air Resources Board's (CARB's) global warming potential (GWP) limit of 750, effective Jan. 1, 2023, for HVAC/R products and Jan. 1, 2024, for chillers, as well as additional requirements for refrigeration systems that went into effect in 2021. In response to these state regulations, manufacturers have been developing systems to use lower-GWP refrigerant alternatives. However, the alternatives to traditional HVAC/R refrigerants typically exhibit more flammable properties than refrigerants designated by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) as A1.

The air conditioning and refrigeration industry has developed the A2L classification of refrigerants to overcome the challenges of using lower-GWP refrigerants. While having slightly higher flammability characteristics as compared to traditional A1 refrigerants, A2Ls are much more difficult to ignite and less flammable than A3 hydrocarbon refrigerants, such as propane. A binational (U.S. and Canada) consensus group formed to update the product safety and application standards to allow for the safe use of these more environmentally friendly refrigerants within HVAC/R systems.

Safety requirements for household electrical heat pumps, air conditioners and dehumidifiers

UL 60335-2-40, the Standard for Household and Similar Electrical Appliances - Safety - Part 2-40: Particular Requirements for Electrical Heat Pumps, Air-Conditioners and Dehumidifiers, is a binational (U.S. and Canada) Standard based on the international IEC 60335-2-40 standard. UL 60335-2-40 establishes more conservative safety requirements than the IEC standard to reflect product usage in the North American market.

One of the risks associated with household electrical heat pumps, air conditioners and dehumidifiers is refrigerant leakage. A refrigerant leak detection system that senses a loss of refrigerant pressure, a critical component in mitigating this risk, is required for all systems in the occupied space exceeding a prescribed refrigerant charge limit. Refrigerant leak detection systems are required to have both sensors and control logic electronics that activate the evaporator fan and use circulated air to quickly disperse and dilute refrigerant in the event of a leak to prevent the formation of refrigerant concentrations.

UL 60335-2-40 also requires that refrigerant charge limits 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 4 to help ensure any leaked refrigerant is diluted to well below the lower flammability limit (LFL) based on room size. In addition, UL 60335-2-40 requires appliances to be free of potential internal ignition sources to mitigate the risk of fire due to a leak.

UL 60335-2-40, fourth edition, updates

On Dec. 15, 2022, UL Standards & Engagement published the fourth edition of UL 60335-2-40. Among other updates, the fourth edition refined requirements for leak detection systems to accommodate various methods, increase robustness and reliability, and account for deviation and drift over the system life cycle.

Key updates for refrigeration detection systems

Annex LL

Annex LL is a normative element in UL 60335-2-40, pertinent to refrigerant detection systems for flammable refrigerants. The fourth edition contains a rewritten Annex LL that no longer references IEC 66079-29-1 for the conformity of flammable gas detectors. It clearly establishes that when the refrigerant detection system senses a concentration of refrigerant gas that is 25% of the lower flammability limit (LFL) for that gas, the refrigerant detection system must initiate a system response to mitigate the potential hazard, as required by Clause 22 and Annex GG. When the refrigerant detection system incorporates a group controller, it must also comply with the requirements of Annex 101.DVN for informational technology equipment (ITE) cooling appliances.

The fourth edition Annex LL also contains rewritten test methods based on current North American carbon monoxide detector sensor requirements, as specified in UL 2075, the Standard for Gas and Vapor Detectors and Sensors.

Annex 101.DVM

An informative Annex 101.DVM, a supplement to Annex LL, was revised to include requirements for deviation and drift over the lifetime of the refrigerant sensor. Annex 101.DVM now describes examples of acceptable paths of compliance for providing data and evidence substantiating the claimed life of a refrigerant sensor, as required by Clauses LL.7.2.DV of Annex LL.DV.

Further updates to UL 60335-2-40

Requirements specified in the fourth edition of UL 60335-2-40 needed to be published by the end of 2022 in order to be included in the 2024 building code. At that time, however, discussions about refrigerant detection system requirements were not yet complete.

Annex 101.DVM was added as informative to the fourth edition, but requirements were agreed upon as part of the review for Amendment 1 to the fourth edition of UL 60335-2-40.

UL 60335-2-40, fourth edition, Certification Requirement Decisions

The following requirements were published for Public Review on Feb. 24, 2023, and incorporated in the Certification Requirement Decisions (CRDs) published in early March 2023 for:

• UL 60335-2-40 as a replacement for Annex LL (dated March 8, 2023)
• UL 60335-2-89 as a replacement for Annex 101.DVP (dated Feb. 28, 2023)

Additional clarification provided in CRDs was published in October 2023 for:

• UL 60335-2-40 as a replacement for Annex LL (dated Oct. 1, 2023)
• UL 60335-2-89 as a replacement for Annex 101.DVP (dated Oct. 9, 2023)

The following updates were made between March and October 2023:

• Clarification that all sequential tests do not need to be repeated for any alternate constructions or additional models (LL.1.3DV/101.DVP.1.3DV)
• Specification that a longer time (60 minutes instead of five minutes) is allowed for the reaction to occur during specific tests:
  • LL.7.2.1.2DV, item b
  • LL.7.2.1.3DV, item b/101.DVP.7.2.1.2DV, item b
  • 101.DVP.7.2.1.3DV, item b

Comparing UL 60335-2-40 third edition with fourth edition CRDs

The following table compares the requirements applicable to refrigerant leak sensors and detection systems in the third edition and the CRDs for the fourth edition. The right column lists the reasons the revisions were needed to help ensure refrigerant leak sensor reliability.

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