As the global push towards environmentally friendly solutions continues, the HVAC industry has been experiencing a shift in refrigerant technology. A2L refrigerants, categorized as "mildly flammable,” have been a hot conversation topic in the construction community. The push towards eliminating A1 refrigerants, which have a higher Global Warming Potential (GWP), has coincided with additional design requirements for A2L refrigerants that have been challenging for many architects and engineers. In this article, we'll provide a detailed overview of A2L refrigerants, touching on everything from their fundamental characteristics to the critical code requirements surrounding their installation and use. What are A2L Refrigerants?A2L refrigerants are a class of mildly flammable refrigerants, developed as part of the HVAC industry’s transition to more environmentally friendly alternatives. These refrigerants fall under the A2L classification according to ASHRAE Standard 34, where “A” indicates low toxicity, and “2L” signifies low flammability with limited flame propagation. The adoption of A2L refrigerants, such as R-32 and R-454b, is driven by their significantly lower Global Warming Potential (GWP) compared to traditional refrigerants like R-410a and R-134a. What Federal Regulations are Driving A2L Refrigerants The federal regulation driving the use of A2L refrigerants in the United States is the American Innovation and Manufacturing (AIM) Act, signed into law in December 2020. The AIM Act gives the Environmental Protection Agency (EPA) authority to phase down the production and consumption of hydrofluorocarbons (HFCs), which are high Global Warming Potential (GWP) refrigerants widely used in air conditioning, refrigeration, and other cooling systems. The AIM Act aligns the U.S. with the Kigali Amendment to the Montreal Protocol, a global agreement aimed at reducing the environmental impact of HFCs, which are potent greenhouse gases. The Kigali Amendment sets a timeline for the phasedown of HFCs over the next few decades to help limit global warming. A2L refrigerants, which have significantly lower GWP compared to traditional HFCs like R-410A and R-134a, are part of the solution for transitioning to more sustainable alternatives. Under the AIM Act, the EPA has implemented a schedule for reducing HFC consumption by 85% over the next 15 years. This creates a regulatory push for HVAC manufacturers, contractors, and building owners to adopt low-GWP alternatives, such as A2L refrigerants. Additionally, the EPA is working on updating safety standards, building codes, and certification requirements to ensure that the adoption of A2L refrigerants is done in a safe and compliant manner. There have been a number of published rules and rule updates, but the most recent regulations for residential and light commercial HVAC systems have the following requirements:
For Variable Refrigerant Flow (VRF) systems, the regulations prohibit the manufacture and import of HVAC products with GWPs > 700 on or after January 1, 2026. A2L Refrigerant Codes and StandardPrior to the 2024 IMC, A2L refrigerants are not recognized for human comfort use. Starting with the 2024 IMC, numerous requirements were added that govern the design and installation of systems using A2L refrigerants including refrigerant charge limits, ventilation requirements, leak detection requirements, and shaft enclosures. For jurisdictions that have not yet adopted the 2024 I-codes, the ICC has released proposed amendments to the 2021, 2018, 2015 or 2012 I-codes that a jurisdiction could adopt. If your jurisdiction does not adopt these amendments, you may need a code modification to use A2L refrigerants for human comfort. The 2024 IMC references the 2022 Editions of ASHRAE 15 and 34, both of which provide additional requirements for A2L refrigerants. ASHRAE 34 is the referenced standard for classifying refrigerants. ASHRAE 15 provides a wide range of requirements and is applicable to all A2L refrigerants per IMC 1101.1.1. In the following sections, we'll review some of the key requirements for A2L refrigerants that could impact your designs. Shaft Enclosures for A2L Refrigerant Pipes Perhaps the biggest impact that A2L refrigerants will have on building design is the requirement for shaft enclosures when refrigerant piping penetrates two or more floor/ceiling assembles (IMC 1109.2.5). This code section has had an exception for shaft enclosures for A1 refrigerants where the Refrigerant Concertation Limit (RCL) is not exceeded, but this exception was not extended to include A2L refrigerants. (See below for a potential solution to this challenge based on future code cycles.) So for most buildings that are three or more stories, rated shafts will be required to protect the pipe risers containing A2L refrigerant. There is another exception to route the piping on the exterior of the building, however this is often undesirable to many building owners due to aesthetic concerns. Shaft Ventilation for A2L Refrigerant Pipe If you do elect to run your A2L refrigerant pipes inside the building and a shaft is required, the shaft is required to be naturally or mechanically ventilated (IMC 1109.3.2). If you choose the natural ventilation option, a minimum opening size of 4" in diameter is required at the lowest point of the shaft. If you choose the mechanical ventilation option, the code requires a minimum ventilation velocity based on the area of the shaft and also requires either continuous ventilation or provision of a refrigerant detector to activate the ventilation system. Refrigerant Detectors for A2L SystemsThere are several situations where the IMC requires refrigerant detectors for A2L systems. First, if you are providing A2L refrigerant risers within a shaft and do not want to run the mechanical ventilation system continuously, a refrigerant detector is required (see section above). If your design includes machinery rooms (see IMC 1104.2 for when required), a refrigerant detector is required per IMC 1105.3. Note that the provision of a refrigerant detector is also part of two code exceptions in IMC Chapter 11:
Potential Code Path to Avoid Rated Shafts Using ASHRAE 15 The new requirements described above can pose a challenge to architects and engineers who will have to design buildings with additional rated shafts or plan for the routing of refrigerant linesets on the outside of the building. Fortunately, there are two current (and future) code provisions that provide a strong basis for a code modification request to avoid the rated shaft requirement. The 2022 Edition of ASHRAE 15, which is referenced by the 2024 IMC, offers the following "Shaft Alternative" options in Section 9.12.15.1: A shaft enclosure shall not be required for the refrigerant piping for any of the following refrigerating systems: The key focus here is Item b, which allows for the elimination of the shaft for any refrigerant, including A2Ls, when the refrigerant concentration does not exceed the limits found in ASHRAE 34. The similar exception in the 2024 IMC only applies to A1 refrigerants. While the 2022 ASHRAE 15 is referenced by the 2024 IMC, in situations where the code has a stricter requirement than a referenced standard, the code take precedence. Fortunately, there is a second piece to this code path, a proposed change to the 2027 IMC. Changes Coming in the 2027 IMCThe 2027 IMC code development process is currently under way. During the 1st Committee Action Hearing (CAH), which took place in April 2024, a code change proposal was submitted for the 2027 IMC to incorporate the same shaft exception that is currently found in the 2022 Edition of ASHRAE 15 (code change proposal M75-24). This proposal was approved unanimously in a 14-0 vote by the IMC committee. The second CAH is scheduled for October 2024, but since there were no comments to the CAH1 ruling, this code change proposal will move directly to the consent agenda for the Public Comment Hearing (PCH). Long story short - the shaft allowance will likely appear in the 2027 IMC. Using the combination of the ASHRAE 15 allowance plus the coming code change in the 2027 IMC forms a strong technical basis for a code modification to eliminate the rated shaft requirement for A2L refrigerant systems, even if you are seeking permit under one of the older code editions. Ultimately, code modification requests are subject to approval by the AHJ. If you need assistance pursuing a code modification for this approach, please contact our partners at Campbell Code Consulting for assistance. ConclusionThe new EPA requirements limiting the manufacture and installation of A1 refrigerants are driving the use of A2L refrigerants in a variety of building types. The use of A2L refrigerants comes with several new code requirements, such as rated, ventilated shafts, which will have a substantial impact on building designs. The use of provisions in the 2022 Edition of ASHRAE 15 and proposed code changes in the 2027 IMC are a strong basis for a code modification request to eliminate the rated shaft requirement.
Need assistance on your specific project? Add Campbell Code Consulting to your team. They are a full-service code consulting and fire protection engineering firm that can help you navigate complex code challenges.
1 Comment
10/15/2024 10:58:23 am
Good information! This is something that mechanical engineers, and the entire industry, are currently grappling with. I have enjoyed this blog, even though it doesn't always relate directly to my specialty. Keep up the good work
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