Measure Overview
This proposal seeks to introduce mandatory and prescriptive requirements in Section 120.5 and 140.4, respectively for AWHP. This measure includes three proposals. Improve quality installation and operation and reduce the gap between manufactured performance and field performance by requiring guidelines, require a buffer tank and sizing limitation to improve the temperature stability, limit the concentration of ethylene glycol in some situations, and mandate AWHP/Water-to-Water Heat Pump (WWHP) isolation.
Submeasure 1: Improve Quality Installation Improving quality installation and operation will require new acceptance test, commissioning requirements, and “best practice guidelines” for design, installation, control, management and operation of Air-to-Water Heat Pumps (AWHPs) to ensure that they meet at least the advertised performance. Include limitations on buffer tank size in small volume loops with single stage AWHPs, require stratified buffer tanks, establish requirements for combination DHW and space heating systems, and reference other manufacturer product requirements (found in their literature) to ensure equipment is installed and operated as intended. These requirements will be applied for all AWHP installations including new, additions and alterations (system replacements and new system installations only) irrespective of climate zones, building and space types, and construction types.
Submeasure 2: Glycol Concentration Limits Place limits on ethylene glycol concentrations, with adjustments based on climate zone and system type, reducing the negative impacts on heat exchanger performance and pump power associated with excessive glycol concentrations.
Submeasure 3: AWHP Alignment with Boiler and Chiller Requirements Similar to equipment isolation requirements for other hydronic plant equipment such as chillers and boilers, this measure would require preventing the pump flow to any AWHP/WWHP that is in off condition without impacting the flow to active units.
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This measure page will be updated as the 2028 code cycle progresses. For questions or suggestions, submit feedback to [email protected]. Please include the measure name in the subject line.
View the Energy Commission's proceedings and available proposed code language by visiting their CEC 2028 Proceedings Website page.
Scope of Proposed Code Change
| Building Type(s) | Construction Type(s) | Type of Change | Updates to Compliance Software | Third Party Verification |
| Nonresidential | New construction, alterations | Mandatory | No updates | No changes to third party verification |
Justification for Proposed Change
A recent PG&E code readiness report[1] and other similar studies have shown that AWHP equipment frequently realizes much lower efficiencies than advertised. Opportunities exist to establish requirements in the code (and potentially during acceptance and commissioning) to prevent poor design and installation practices from being scaled in the industry as the hydronic heat pump product category continues to grow.
There are also some code-related obstacles to the widespread adoption of AWHPs. While there is a compliance option for AWHPs implemented in the compliance software, the requirements to meet this credit are unclear, hindering adoption. It has been difficult to get projects approved, as designers, plans examiners, and inspectors struggle to discern which requirements and forms to apply.
This measure will improve the communication of “best practice guidelines” for installation, control, management and operation of AWHPs to help ensure that the advertised performance is achieved in practice. In addition, code language related to isolation of inactive units in multi-unit systems, which is already in place for chillers and boilers, will be adapted and applied to AWHPs. Finally, limits to glycol concentration will help improve heat exchanger and pump performance while protecting systems from freezing in colder climates. Additional verification tests will be required to demonstrate compliance.
The preliminary statewide energy savings for the first year from this measure are projected to be 4.24 GWh, which is likely underestimated since the savings were calculated for 4.5 million ft2 (new construction only) assuming 10% savings of HVAC and DHW end uses. The final savings will be recalculated based on a more thorough assessment of common installation mistakes and the resulting energy impacts. Final savings analysis will include all non-residential building types along with additions and alterations.
[1] Weitze, H., Stober, W., and Gantley, M., Nonresidential Hydronic Heat Pumps: System Operation Field Study and Analysis, PGNE Code Readiness Final Project Report ET21PGE7201-2, October 2024. https://etcc-ca.com/reports/code-readiness-final-project-report-nonresidential-hydronic-heat-pumps-system-operation
Relevant Documents
Round One Utility-Sponsored Stakeholder Meeting Materials
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The Statewide CASE Team values input from all stakeholders engaged in the Title 24, Part 6 code change process. We encourage the open exchange of code change comments and concerns.