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Multifamily Domestic Hot Water

Measure Description

This CASE Report for multifamily domestic water heating will include four submeasures: central heat pump water heating, hot water distribution, solar thermal water heating, and multifamily drainwater heat recovery.

Central Heat Pump Water Heating

This submeasure will develop a prescriptive compliance pathway for domestic central heat pump water heating systems to encourage implementation in multifamily buildings by leveraging existing software algorithm development, lab testing, and design guide development. The CASE Team will perform additional market readiness research across a broad group of stakeholders and develop code and compliance manual language.

Hot Water Distribution

The 2013 Multifamily Central DHW and Solar Water Heating CASE Report estimated that 33 percent of hot water generated at the water heater is lost in the recirculation loop to ambient space. As a result of the 2013 CASE Report, currently Title 24 prescriptively requires demand control recirculation, as well as a minimum of two recirculation loops in multifamily buildings that have nine or more dwelling units.

The current requirement for 2 loop recirculation systems has faced adoption challenges including inconsistent interpretations of meaning of the requirement and challenges establishing appropriate baseline and proposed systems in the California Compliance Simulation Engine (CSE).  In addition, the 2 loop requirement was developed based on research on low-rise multifamily that is not directly applicable across all multifamily buildings types (low-rise, mid-rise, and high-rise).

The 2022 multifamily hot water distribution CASE measure will replace the current 2 loop requirement while reducing the performance budget for multifamily DHW recirculation systems with the following prescriptive requirements.

  • Increased Insulation: This measure involves increasing pipe insulation requirements in Table 120.3-A.  Three options to increase pipe insulation requirements are being evaluated: (a) increase insulation on all pipes including recirculation loop and runout pipes, (b) increase insulation only on recirculation loop pipes, (c) or increase insulation on specific portions of recirculation loop pipes such as large supply headers.
  • Pipe Insulation Verification: This measure involves adding a requirement for field verification of pipe insulation quality. Field verification would confirm installation of code minimum pipe insulation meeting California Plumbing Code (CPC) and Title 24 Part 6, including insulation on all fittings and valves, and thermal isolation at pipe hangers.

The 2022 multifamily hot water distribution CASE measure will also add the following alternative compliance options or alternate prescriptive paths:

  • CPC Appendix M pipe sizing: This measure will add at least one alterative prescriptive compliance path that includes pipe sizing based on CPC Appendix M (CPC 2019, UPC 2018). CPC appendix M is a performance-based pipe sizing calculation procedure that typically results in smaller pipe sizes than standard practice sizing that reduce first costs and distribution system heat loss.
  • Clustered Design without Recirculation: This measure will support use of clustered design without recirculation as a compliance option in the performance approach. The California Simulation Engine currently has the capability of modeling clustered systems without recirculation, but there is no mention of the option in Title 24 Part 6 and limited guidance in the Alternative Calculation Method (ACM) Reference Manual. This measure will add code language and clarify and align code and ACM requirements for clustered design without recirculation.

Solar Thermal Water Heating

This submeasure will investigate ways to expand solar thermal water heating requirements for new
high-rise and low-rise multifamily buildings for individual/central gas water heaters and
individual/central heat pump water heaters. The Statewide CASE Team will evaluate energy savings and
cost-effectiveness of the following solar water heating measures.

  • Increase the prescriptive solar savings fraction (SSF) requirement of solar thermal water heating for central gas water heating systems. Add requirement of solar thermal water heating for individual gas water heaters, if feasible and cost-effective.
  • Develop prescriptive solar water heating (SWH) requirement for central heat pump water heaters. Evaluate option for installing an energy-equivalent PV system if solar water heating is not cost effective for this system type.
  • Evaluate an option to combine solar thermal system with individual heat pump water heater, if feasible and cost effective.
  • Revise performance approach to include an hourly model of solar thermal energy production, for improved accuracy.

Multifamily Drainwater Heat Recovery

This CASE Report will look at drainwater heat recovery for both multifamily and nonresidential buildings. This CASE topic builds on a drainwater heat recovery measure added for low-rise residential in the 2019 code cycle as a compliance credit and a prescriptive alternative path for gas storage water heaters, heat pump water heaters, and solar water-heating systems. The 2019 CASE Report introduced drainwater heat recovery as a compliance credit and prescriptive alternative path and found that drainwater heat recovery was cost-effective for low-rise, multifamily buildings in all climate zones (assuming four residential units share one drainwater heat recovery unit) and would likely be cost-effective for high-rise multifamily buildings in a similar configuration.

In multifamily buildings, the proposed code change would prescriptively require drainwater heat recovery in all multifamily buildings for all hot water system types. The CASE measure may allow for exceptions for dwelling units that are slab-on-grade and may also allow for tradeoffs with other hot water compliance credits, such as compact hot water distribution. This measure would also update the prescriptive pathways in Section 150.1(c)8, refine the HERS test procedure, and update the Residential and Nonresidential Alternative Calculation Method Reference Manual calculations.

For nonresidential buildings, the features would be added to the compliance software to allow designers to receive compliance credit if they choose to install drainwater heat recovery units. The credit would be available for limited applications such as drain lines for showers in recreation centers, dishwashing stations in commercial kitchens, and clothes washers in laundry facilities. The Statewide CASE Team will evaluate appropriate verification requirements for nonresidential drainwater heat recovery units.

Provide Feedback

Participate in the Utility-Sponsored Stakeholder meeting for this topic on October 3rd, 2019! View the event here.

This measure description will be updated as research is developed to support the 2022 code cycle. For questions or suggestions, email Include the measure name in the subject line.


Relevant Documents

Measure proposals, supporting documents, and other outside references will be made public as they become available.


Give Us Your Feedback

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.

  • Use the form above to provide feedback on this measure.