The HVAC industry has gone through refrigerant transitions before. Some may remember the move from R-11 to R-123, R-12 to R-134a, or, more recently, R-22 to R-410A. These progressions largely occurred to meet requirements designed to remove ozone-depleting refrigerants from HVAC systems. Future refrigerant conversions will likely be driven by global standards focused on reducing global warming. To meet these requirements, manufacturers will be expected to utilize refrigerants with low global warming potentials (GWPs).
The Kigali Amendment to the Montreal Protocol is an international agreement designed to phase down the use of hydrofluorocarbons (HFC) with higher GWPs, such as R-410A. While the current U.S. administration has failed to ratify the amendment, North American legislators and regulators continue to draft future GWP-driven phasedowns. However, the upcoming low-GWP refrigerant transition is poised to be much different than its predecessors. In previous refrigerant transitions, all HVAC manufacturers transitioned to the same refrigerant, such as R-22 and R-410A. But, this time, not all HVAC manufacturers have announced which lower GWP refrigerant they intend to use.
Two potential low-GWP R-410A replacements are R-32 and R-454B.
R-32 is a pure, single-component refrigerant with zero ozone-depletion potential (ODP) and a GWP of 675. It’s a nonproprietary (commodity) refrigerant with proven performance that’s available globally from multiple suppliers and is known to facilitate the development of new HVAC systems with less refrigerant charge.
R-454B is 68.9% R-32 and 31.1% R-1234yf, a hydoflouroolefin (HFO).
Both of these refrigerants are commercially available and classified by ASHRAE 34 as A2Ls, or lower flammability refrigerants.
Consequently, HVAC systems need to be safety listed in compliance with UL 60335-2-40-2019 third edition and installed in compliance with ASHRAE 15-2019. Several manufacturers are focused on developing equipment and components for R-32 and R-454B.
Several manufacturers are conducting system and component evaluations to prove chemical stability and resulting system reliability, compatibility, and economics. One such option is R-466A, an A1-classified, three-component, proprietary blend refrigerant, but it isn’t currently commercially available. In June 2019, Midea, a Chinese electrical appliance manufacturer, headquartered in Beijiao, announced its decision to validate R-466A. Midea’s declaration is the only of its kind regarding R-466A to date.
CODES AND STANDARDS
Now that the common safety standards have been updated to address the design and application requirements of equipment with lower flammability refrigerants, model building codes also need to be updated before A2L equipment is finally allowed to be more broadly installed in the market. Model building codes for mechanical systems include the International Code Council’s (ICC’s) International Mechanical Code (IMC) and International Residential Code (IRC) and the International Association of Plumbing and Mechanical Officials’ (IAPMOs’) Uniform Mechanical Codes (UMCs.) All of these have three-year revision cycles, and the industry and policymakers are working diligently to update these codes to ensure safe installation and application of HVAC systems using A2L refrigerants. But, sometimes, updating model building codes can take significant time. As a result, the current 2021 editions of the IMC, IRC, and UMC don’t include provisions to allow use of A2Ls in most high-probability direct systems. Nonetheless, IMC and UMC continue to permit up to 6.6 pounds of A2L refrigerants in certain high-probability direct systems. That’s why window air conditioners (WRAC) using R-32 are readily available across North America. Also, both IMC and UMC permit use of A2Ls in outdoor indirect systems (e.g., air-cooled chillers). But this leaves the vast majority of HVAC systems unable to take advantage of the benefits of these new refrigerants and sets the Americas several years behind much of Europe, Asia, and Australia.
What can engineers do now to help their clients prepare for transitions that may occur at different times for different locales?
Every state and locality generally adopts these model codes into their respective building codes at their own pace, and some localities have already started making appropriate changes to allow for the optional use of A2L refrigerants. Engineers should review the upcoming standards and engage with those who update building codes in their areas. UL 1995 is to be replaced by 60335-2-40 third edition on Jan. 1, 2024. Listing to 60335-2-40 third edition is required for HVAC equipment using A2L refrigerants. Considering HFC phasedowns will likely happen at different times, manufacturers may choose to continue to list their legacy R-410A products to 1995 fifth edition beyond January 2024.
When asked to specify low-GWP equipment, engineers should look at their refrigerant options holistically. For example, engineers may be asked to specify a GWP value for the refrigerant used in their systems. That may prove difficult to do because certain manufacturers may transition to different A2L refrigerants across their product portfolios. Daikin has announced R-32 as the ideal choice to replace R-410A in the Americas and around the world for many of its key products. Carrier has announced its intention to use R-32 for scroll chillers and R-454B for other residential and commercial products.
When a GWP value is going to be specified, an engineer should consider providing a 750 GWP value for the R-410A replacement. Around the world, 750 GWP seems to be a common limit. Currently enacted legislative and regulatory standards in North American, European, and Japanese jurisdictions pinpoint this number. The Kigali Amendment doesn’t explicitly call out specific GWP values; instead, it functions on a quota allocation scheme.
GWP is just one metric to use when making a future refrigerant choice. Direct GWP may be a straightforward metric for regulators, but it does not tell the whole story about a refrigerant’s ability to limit climate change. In the U.S., about 85% of climate impact over an HVAC system’s product life cycle is from the carbon dioxide generated when fossil fuels are burned to produce electrical power — the usage of which is strongly influenced by an HVAC system’s efficiency. Moving to a low-GWP refrigerant that reduces system efficiency and consumes more electricity is heading in the wrong direction in terms of life cycle operating costs and total equivalent warming impact.
Does this mean a specifying engineer should specify efficiency? Yes. An engineer should always understand owner preferences and specify systems to meet those needs. With R-32, the refrigerant itself has a greater thermodynamic capacity and efficiency than R-410A and R-454B. And in tests of a Daikin inverter compressor rooftop unit with identical hardware, the use of R-32 improved IEER at nominal capacity by up to 8% and 11% as compared to R-410A and R-454B, respectively. Legislators are chasing environmental impact and carbon neutrality goals. One can’t get to carbon neutrality without converting to renewable sources of electricity and, therefore, effective load management. Consequently, the efficiency of building systems will continue as a theme.
Depending upon specific customer needs, OEMs will have the opportunity to leverage the additional thermodynamic performance of R-32 for potentially smaller and lighter equipment at baseline efficiency levels and/or for novel higher efficiencies in similarly sized products.
Another factor to consider is reclamation, which is strongly expected to become a more regulated aspect of new and used HVAC systems. To address this, engineers should consider specifying refrigerants that meet the quality and purity requirements of Air-Conditioning, Heating, and Refrigeration Institute (AHRI) Standard 700. Being a pure, single-component refrigerant, used and recovered R-32 can be brought to AHRI 700 quality standards relatively easily, using more straightforward and less energy-intensive reclamation processes when compared to alternative blends that require distillation and then re-blending to achieve their correct composition ratios and meet AHRI Standard 700.
Equipment owners and users should consider reclamation, reuse, and recycling of refrigerants to lessen refrigerant emissions to the atmosphere. Single component and azeotropic blends can be beneficial because they don’t change composition over time, which otherwise can negatively impact system performance. Indeed, because R-32 is a single-component refrigerant — rather than a zeotropic blend with glide — it can be charged in both liquid and gas phases, while some blends must be charged in only the liquid phase and with the refrigerant cylinder deployed upside down.
In summary, an engineer specifying replacement refrigerants for R-410A should specify commercially available, single-component, or azeotrope refrigerants meeting AHRI Standard 700 with zero ODP and a maximum 750 GWP. HVAC products and systems should be listed to the latest edition of UL 60335-2-40 and designed to the latest editions of ASHRAE 15 with an efficiency specification that serves owner-operator needs considering operating costs and environmental concerns.