The North American Sustainable Refrigeration Council (NASRC), under a grant from the California Air Resources Board (CARB), is soliciting proposals from qualified third-party subcontractors to conduct a full risk assessment of residential monobloc air-to-water heat pumps (ATWHPs) using higher charges of A3 (flammable) refrigerants, including propane (R290), isobutane (R600a) and other hydrocarbon refrigerants.
The proposal solicitation was announced by CARB on September 4. Proposals must be submitted to info@fripfunding.com by 5 pm Pacific Time on October 3. For questions or clarifications regarding this solicitation, contact info@fripfunding.com no later than September 19. Responses to questions will be publicly posted by September 25.
The grant to cover the cost of the project is provided by California’s F-Gas Reduction Incentive Program (FRIP), which is administered by NASRC and has funded a number of natural refrigerant projects in the state. The total proposed cost for this project “should not exceed $1.5 million,” said the solicitation document, authored by NASRC, CARB and California Climate Investments. In addition, match or in-kind funding of at least 25% must be provided by respondents. The agreement is expected to be executed in October 2025 and the work completed by March 2027.
The project would include performing a complete flammability risk assessment under different residential installation configurations and lifecycle events for monobloc ATWHPs. Notably, monobloc ATWHPs restrict the propane refrigerant to the outside equipment, reducing the risk to end users.
According to the solicitation, the primary objective of this project is to support stakeholder groups responsible for developing product and application safety standards and building codes for the safe use of A3 refrigerants, justifying higher charge amounts. These groups include the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Standing Standard Project Committee (SSPC) 15 and Subcommittee 15.2, Underwriters Laboratories (UL) and the International Electrotechnical Commission (IEC) 60335-2-40 Standard committee.
“The awardee will be required to establish an advisory panel that will include representatives of relevant codes and standards bodies.”
Danielle Wright, Executive Director for NASRC
Through the course of the project, “the awardee will be required to establish an advisory panel that will include representatives of relevant codes and standards bodies such as UL and ASHRAE, fire service professionals and other stakeholders to facilitate direct input and information exchange to guide the research project,” said Danielle Wright, Executive Director for NASRC.
“Upon publication of the final report, the awardee is required to submit the report to codes and standards bodies to inform and help facilitate updates to the relevant codes,” she added.
The project will also “help support California’s climate and decarbonization goals by completing risk assessments for residential installation configurations of ATWHPs using ultra-low-GWP A3 refrigerants, which are currently being deployed in Europe,” the solicitation said.. It also “directly supports the legislative directive in [Senate Bill] 1206 to increase the availability of ultra-low-GWP refrigerant technologies available internationally in California.”
The California-funded research “is a great step forward and I hope it moves as quickly as possible with strong input from standard and code experts that need timely and useful data for to finalize proposals to enable R290 and other A3 refrigerants in AC and heat pumps in the key safety standards and the development of 2030 building codes,” said Christina Starr, Senior Manager, Climate Campaign for the Environmental Investigation Agency (EIA) US.
ASHRAE considers charge increase
In 2023 ASHRAE’s SPCC Subcommittee 15.2 began considering a change to the ASHRAE 15 standard that would allow the use of up to 4.9kg of A3 refrigerants in outdoor (indirect) heat pumps and air conditioners (such as ATWHPs) in the U.S. Existing regulation in the U.S. only permits 114g of propane in fixed or non-fixed heat pump and AC units (including outdoors).
This change would be dependent on research confirming the safety of the higher charge limit; to that end, in 2024 SPCC Subcommittee 15.2 formed a working group, which developed a “work statement” to do computational fluid dynamics (CFD) and verification testing under the direction of Xudong Wang, Vice President of Research at the Air-Conditioning, Heating and Refrigeration Institute (AHRI).
If approved by ASHRAE, the higher charge would also need to be endorsed by UL under its 60335-2-40 standard and then by the U.S. Environmental Protection Agency (EPA); it would also be incorporated in the next model and state building codes. Twenty-three states have already passed legislation that would enable this use of hydrocarbons (in addition to A2Ls), once UL 60335-2-40 and ASHRAE 15 are updated and EPA SNAP (Significant New Alternatives Program) approved.
Other research
The California-funded project is not the only initiative aimed at doing a risk assessment of A3 residential heat pumps. Last year the U.S. Department of Energy convened a working group with industry and other stakeholders that prioritized the need to fully understand the risks of A3 refrigerants in residential monobloc air-to-water heat pumps.
To that end, two other research and testing projects on A3 refrigerant safety are underway at Oak Ridge National Laboratory (ORNL). One project looks at self-contained heat pump and air-conditioning equipment including heat pump water heaters; a second project examines small- to medium-size commercial chillers.
In addition, UL recently announced the formation of a new Technical Harmonization Committee (THC) to develop the 5th Edition of UL 60335-2-40. The committee will hold its first meeting at the end of September and is anticipated to consider proposals related to A3 refrigerants.
Overall, the research projects “are designed to look at the IEC 60335-3-40 [global] standard and conduct modelling and testing to validate the safety requirements for using larger charge sizes than UL and ASHRAE standards currently permit, or to determine if any additional effective mitigation is needed in those standards in the U.S. context,” said EIA’s Starr.
“My only concern,” Starr added, “is that so far the research projects being funded are for a relatively narrow scope of equipment types. This is great progress but we need more research covering all the most commonly used air-conditioning and heat pump equipment types, such as residential ducted systems, mini-split ACs and commercial packaged and rooftop units.”
