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Updated Requirements for Refrigerant Detection Systems

UL 60335-2-40, fourth edition, Certification Requirement Decisions (CRDs) refine refrigerant detection systems requirements to help mitigate fire hazards and evaluate system reliability.

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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., item b
    • LL., item b/101.DVP., item b
    • 101.DVP., 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.

  Third edition Fourth edition updates Reason for CRDs
LL1 Refers to IEC 60079-29-1 and ISO 817 Clearly defines the number of samples needed for the testing. No clear way to determine what samples are needed.
LL2 Refrigerant detection systems shall be capable of detecting a preset concentration level of the refrigerant marked on the appliance nameplate and initiating the operation as defined in Annex GG. It in no way defines the clean air test gas concentration parameters for all testing. Clearly defines the clean air test gas concentration parameters for all testing. Requires the testing technician to reference Annex GG for the response time; CRD eliminates this need.
LL3 Refrigerant detection system range, accuracy and response time: Including the worst-case combined effects of declared manufacturing tolerances and drift, the preset level shall be selected such that the refrigerant detection system shall provide an output according to applicable clauses of Annex GG of this standard within 10 seconds or less when the sensor is put into refrigerant concentration of 100% LFL or lower. These requirements shall apply after the refrigerant detection system power is turned on and the warm-up time period has elapsed. Clearly defines the response time that the sensor has to detect a concentration of 25% of the LFL. 100% LFL is too high to mitigate risk of fire due to refrigerant leak.
LL4 Refrigerant detection system calibration: Refrigerant detection systems shall be preset and calibrated from the factory for the refrigerant used. The preset level shall not be adjustable. Recalibration other than zero-point self-recalibration shall not be allowed.
The requirements for long-term stability Group II for indicating fixed sensor in IEC 60079-29-1 shall apply. The test gas shall be 100% refrigerant.
Clearly defines the refrigerant detection system calibration and short-term stability.
LL5 Selectivity test and poisoning test: Refrigerant sensors shall not have false or nuisance trips and not subject to poisoning. Clearly defines selectivity test and establishes that the poisoning test shall not have false or nuisance trips or poisoning damage under typical environmental conditions. Very similar test
LL6 DV electrical outputs for refrigerant detection system Clearly defines refrigerant poisoning and oil spray test, shall not be damaged or deteriorated by release of the refrigerant(s) marked on the appliance and oil (if any) contained within the appliance. CRD LL5 and LL6 of the CRD are combined in one section in third edition.
LL7 No comparable section Sensor drift: Over the refrigerant sensor life, the refrigerant detection system shall consistently initiate a system response within 60 seconds when the refrigerant sensor is directly exposed to a refrigerant gas concentration of 25% of LFL. IEC 60079-29-1 has removed an annual recalibration requirement meeting the third edition’s requirements does not help ensure reliability over system lifetime.
LL8 No comparable section Humidity test: Over the humidity range of the appliance, the refrigerant detection system shall consistently initiate a system response.
LL9 No comparable section Temperature test: Over the temperature range of the appliance, the refrigerant detection system shall consistently initiate a system response.
LL10 No comparable section Pressure test: Over the air pressure range of the appliance, the refrigerant detection system shall consistently initiate a system response.
LL11 LL7 Vibration requirements: Vibration requirements of IEC 60079-29-1 for fixed gas detection sensors. Vibration test: The refrigerant detection system shall withstand vibration without breakage or damage of parts and shall continue to function. Similar test
LL12 No comparable section Electromagnetic compatibility test: The refrigerant detection system shall consistently initiate a system response.
LL13 No comparable section Refrigerant sensors shall not be a source of ignition for leaked refrigerant.
LL14 LL8 refrigerant detection system self-test routine: The refrigerant detection system shall include a means for self-testing to determine if a refrigerant sensor or sensing element malfunction has occurred. Refrigerant detection system self-test routine: Refrigerant detection systems, by design, shall employ electrical or electronic circuitry that is intended to fail-safe and engage an appropriate system response. Similar test

Importance of CRDs to system safety and reliability

The CRDs are crucial to enhancing the safety and reliability of refrigerant leak detection systems. Because the third edition referenced IEC 60070-29-1, there were several points that did not alight with the UL 60335 appliance Standard. Clearly defining the clean air test gas concentration parameters for all testing in LL2 without needing to reference Annex G improves the Standard’s usability. Defining the requirement that a sensor must be able to test a concentration of 25% of the LFL helps reduce the fire risk due to refrigerant leaks. Introducing drift and deviation allowances in LL7 helps evaluate the system’s reliability over its lifetime. Moreover, the CRDs incorporate what the working group and manufacturers have learned about this new technology to make UL 60335-2-40 a more robust and reliable Standard.

Jim Dominik, managing member of Polaris Public Safety Solutions, shared his perspective about the CRDs’ importance:

“The fire service has been concerned about A2L usage, and we worked hard to be part of the team and implement a safe solution. Since the beginning, the fire service has asked for detection, mitigation, identification and training. Lessening anything that could cause a reduction in detection and mitigation would decrease the overall safe operation of the equipment. To date, we have no installed equipment, and I feel reducing any of the safety features would be concerning. The current requirements proposed by UL Standards & Engagement in the latest Certification Requirement Decision following current UL Standards that have been proven to be safe is critical to the long-term safety of the equipment and potentially the people and environment.”
- Jim Dominik, managing member of Polaris Public Safety Solutions.

Paving a pathway to compliance with UL 60335-2-40

The updated requirements are mandatory for all new certifications of these products by UL Solutions, effective Jan. 1, 2025. Because the previous Standard for these products, UL 1995, the Standard for Heating and Cooling Equipment, does not address refrigerants other than class A1, UL 1995 is no longer being maintained and will not be used for new certifications after Jan. 1, 2025. Products certified to UL 1995 before this date may be allowed to have continuing certification until Jan. 1, 2028, in alignment with the Environmental Protection Agency’s (EPA’s) allowed sell-through date.

UL Solutions leverages our deep industry expertise and active participation in the standards development process to help you understand and navigate compliance with UL 60335-2-40 for your products.

Watch our complimentary on-demand webinar for more detailed information about the updates to the fourth edition of UL 60335-2-40.

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