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Nonresidential Air Distribution

Measure Description

Air distribution systems in nonresidential buildings use a significant amount of energy. According to the United States Department of Energy (U.S. DOE), ventilation systems in commercial buildings use roughly 1.54 quadrillion British thermal units (i.e., quads) of primary energy consumption nationally, or roughly 1.5 percent of energy nation-wide (including transportation, natural gas usage, etc.)

At a fundamental level, there are a few ways to reduce fan electrical input power in building air distribution systems as shown by the following equation:

Image is of an equation that reads "Fan electrical input power equals flow times pressure all over 6343 times fan efficiency times transmission efficiency times motor efficiency"

This Final CASE Report proposes three submeasures to target each of these variables. To reduce fan electrical input power a fan system must:

  1. Reduce the pressure the fan must overcome (Fan Power Budget)
  2. Improve fanfan), motor motor), and transmissiontran), efficiency (Fan Power Budget/Fan Energy Index)
  3. Minimize the flow (Duct Leakage)

Fan Power Budget

The fan power budget submeasure would update the current methodology used to calculate prescriptive fan power limitations for fan systems. The submeasure would expand the current scope from all space conditioning fan systems ≥ 5 nameplate HP to ≥ 1 kW (which is roughly 1 nameplate HP). The submeasure would create new, clear definitions for fan systems as the fan power budget would apply separately to supply fan systems and to return/relief/exhaust fan systems. Each fan system would be allocated a fan power budget (kW) as function of the airflow (cfm), system type, and components in the fan system. The fan power budget submeasure would apply to new construction, alterations and additions. As a prescriptive measure it would require changes to the Alternative Calculation Method (ACM) Reference Manual and the compliance software. It should be noted there is a similar proposal being proposed for consideration as an addendum to American Society of Heating, Refrigerating and Air-Conditioning Engineers Standard 90.1-2019 (ASHRAE 90.1-2019). At the time the Final CASE Report was posted for public review, the proposal is being discussed within the ASHRAE 90.1 mechanical subcommittee.

Fan Energy Index

Fan Energy Index (FEI) is a straightforward metric to encourage mechanical designers to make fan selections closer to a fan’s peak efficiency. The higher the FEI, the less power is consumed at a given duty point (airflow and pressure). FEI is a ratio of the input power of a reference fan and the actual fan at the same duty point. To learn more about FEI see the Air Movement and Controls Association’s (AMCA) webpage on FEI here:

The FEI submeasure would add a mandatory requirement that certain fans must be selected at an FEI of 1.0 or higher, similar to ASHRAE 90.1-2019, which includes FEI requirements in Section (Fan Efficiency).[1] This submeasure would be mandatory and apply to new construction, and alterations and additions but only when a new fan system is being installed. Importantly, FEI would apply to a broad scope of fans than the fan power budget submeasure, such as fans that move unconditioned air. Additionally, as a mandatory submeasure, it would not require changes to the ACM Reference Manual and the compliance software.

Duct Leakage Testing

This submeasure proposes three changes that would minimize air leakage in ducts, align requirements in the California Energy Code and the California Mechanical Code (CMC or Title 24, Part 4), and recommend specifications in support of the mandatory duct leakage testing requirements in the 2019 CMC. The third change could be incorporated into the CMC instead of Title 24, Part 6.

  1. Add a mandatory requirement that all ductwork in all nonresidential buildings comply with Seal Class A (the highest degree of sealing) as defined by the Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA) HVAC Duct Construction Standards – Metal and Flexible (ANSI/SMACNA 2006). This would require sealing of all transverse joints, longitudinal seams, and duct wall penetrations. The proposal would align duct sealing requirements in Title 24, Part 6 with requirements that have been in ASHRAE 90.1 since the 2010 edition.
  2. Move existing prescriptive duct leakage testing requirements for buildings under 5,000ft2 to the mandatory section of Title 24, Part 6.
  3. Clarify which sections of ductwork need to be tested, who should execute the testing, and what documentation is needed to demonstrate compliance with existing mandatory duct leakage testing requirements in the 2019 CMC. Clarify with existing mandatory duct leakage testing requirements in the 2019 CMC. The proposal would clarify and standardize which portions of the ductwork would be tested, ensuring that representative portions of all aspects of the system are tested. The following ductwork would be tested to verify the maximum leakage rates defined in the CMC and Title 24, Part 6 are not exceeded:
    • All ductwork that would become inaccessible, to avoid large potential mitigation costs if the system fails. This includes all vertical ductwork in shafts and all horizontal ductwork above hard ceilings.
    • Supply-air systems upstream and downstream of terminal boxes. For example, in VAV systems 10 percent of the ductwork upstream of VAV valves and 10 percent of the ductwork downstream shall be tested.
    • Exhaust systems, and when there are multiple exhaust systems at least two would be tested.
    • The Statewide CASE Team is proposing that qualified technicians, certified as Testing, Adjusting, and Balancing (TAB) Technicians by the Associated Air Balance Council (AABC), the National Environmental Balancing Bureau (NEBB), or the Testing, Adjusting and Balancing Bureau (TABB) or as Duct Air Leakage Technicians by the International Certification Board (ICB) perform the testing.

Supporting the duct leakage testing requirement in the 2019 CMC will require coordination with the California Building Standards Commission and potentially other state agencies. At the time this Final CASE Report was published for public review, it is not certain if the revisions to clarify the testing requirements in the 2019 CMC would appear in Nonresidential Appendix 7 (NA7) to Title 24, Part 6 or as revisions to the code language in Section 603.1.10 in the CMC.

Relevant Documents

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

Round Two Utility-Sponsored Stakeholder Meeting Materials

Round One Utility-Sponsored Stakeholder Meeting Materials

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Final CASE Report Now Available

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.


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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.

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