California Title 24

California updates the Title 24 Building Energy Efficiency Standards commonly known as Title 24, every three years. The 2022 version covers all types of buildings and includes the following major sections:

Building Energy Efficiency Standards for Residential and Nonresidential Buildings

• Article 1 - Regulations 10-xxx
• Subchapter 1 - Scope and definitions - Section 100
• Subchapter 2 - Building components - Section 110
• Subchapter 3 – Nonresidential and hotel/motel mandatory – Section 120
• Subchapter 4 – Nonresidential and hotel/motel lighting – Section 130
• Subchapter 5 – Nonresidential and hotel/motel performance and prescriptive – Section 140
• Subchapter 6 – Nonresidential and hotel/motel additions, alterations, repairs – Section 141
• Subchapter 7 – Single family residential mandatory – Section 150.0
• Subchapter 8 – Single family residential performance and prescriptive – Section 150.1
• Subchapter 9 – Single family residential additions, alterations, repairs – Section 150.2
• Subchapter 10 – Multifamily residential mandatory – Section 160.0
• Subchapter 11 – Multifamily residential performance and prescriptive – Section 170
• Subchapter 12 – Multifamily residential additions, alterations, repairs – Section 180

Many other related documents, including appendices, manuals, and compliance forms, are available.

The building energy modeler is probably most interested in the Alternative Calculation Method (ACM), which is the performance approach. Sections 140.1 and 170.1 refer to the Nonresidential ACM Reference Manual and ACM Approval Manual. For single-family residences, Section 150.1 refers to the Residential ACM Reference Manual.

The metric used for calculation is called the Time Dependence Valuation (TDV), which varies for each hour of the year, for each energy type, climate zone, and building type and is described in Joint Appendix JA3. In general, TDV accounts for the cost of providing energy, which varies by time of year, time of day, geography, and energy source.

Unlike ASHRAE Standard 90.1 or the IECC, the ACM method for California requires the software itself to comply by passing a long list of tests specifically about how the building energy model is modified by the rules in the ACM. Since only certified software can be used with the ACM, only a short list of software is available. Similar to other tradeoff methods, the ACM uses a model of the design building and compares it to a reference building, which generally represents a building that is similar to the design building, but each component complies with the prescriptive requirements of the standard. For nonresidential buildings, HVAC systems are mapped following Table 2 in the ACM reference manual, which uses Space Type, size of the building, number of above-grade floors, climate zone, and cooling capacity to select which HVAC system to use for the standard design.

Nonres ACM Manual

• System 1 – RAC Residential air conditioner
• System 2 – RESERVED
• System 3a – SZAC Packaged single-zone air conditioner
• System 3b – SZHP Packaged single zone heat pump
• System 3c – SZDFHP Packaged single-zone dual-fuel heat pump
• System 4 – Reserved
• System 5 – PVAV Packaged VAV
• System 6 – VAV Built-up VAV
• System 7a – SZVAVAC Packaged single zone variable-air volume air conditioner
• System 7b – SZVAVHP Packaged single zone variable-air volume heat pump
• System 7c – SZVAVDFHP Packaged single zone variable-air volume dual-fuel heat pump
• System 8 – RESERVED
• System 9 – HEATVENT Heating and ventilation only
• System 10 – CRAH Computer room air handler
• System 11 – CRAC Computer room air conditioner
• System 12 – Reserved
• System 13a – BKITCHMAU Built-up kitchen makeup air unit
• System 13b – PKITCHMAU Packaged kitchen makeup air unit

Calculation Process for Title 24 Compliance

Much of the ACM manual describes hundreds of “building descriptors,” each roughly corresponding to individual simulation inputs. These building descriptors must be populated by software that is certified to be used in California. The groupings of descriptors include:

• Project Data
• Thermal Zones
• Space Uses
• Building Envelope Data
• HVAC Zone Level Systems
• HVAC Secondary Systems
• HVAC Primary Systems
• Miscellaneous Energy Uses
• Onsite Energy Generation and Storage
• Common Data Structures
• Exterior Surface Properties
• Two Dimensional Curves

These high-level groupings are further divided into groups that contain the specific building descriptors. For example, for Building Envelope Data, the groups of building descriptors include:

• Materials
• Construction Assemblies
• Roofs
• Exterior Walls
• Exterior Floors
• Doors
• Fenestration
• Below-grade Walls
• Slab Floors in Contact with Ground
• Heat Transfer Between Thermal Zones

As an example, for Roofs, the building descriptors include:

• Roof Name
• Root Type
• Roof Geometry
• Roof Solar Reflectance
• Roof Thermal Emittance
• Roof Construction

Each building descriptor shows:

• Applicability
• Definition
• Units
• Input Restrictions
• Standard Design
• Standard Design: Existing Building

These building descriptors both capture the building features but also, since they are fixed, can prevent novel energy efficiency measures from being characterized by the software.

Information Flow

Resources

California Building Energy Efficiency Standards

Non Residential ACM Reference Manual

Energy Code Ace

California Association of Building Energy Consultants

California Energy Code Stakeholders

California Energy Commission Energy Code Support Center

California Utility Allowance Calculator (CUAC)