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Nonresidential Daylighting

Measure Description

The Statewide CASE Team recommends two revisions to the daylighting controls requirements in Title 24, Part 6, as described below. 

Daylight Dimming to 10 Percent

This proposed code change would update the mandatory automatic daylight dimming controls provisions to require deeper reductions in lighting power when illuminance levels are met with daylight. Current code requires general lighting power in the daylit zone to be reduced to 35 percent or less when daylight illuminance is greater than 150 percent of design illuminance. The proposed requirements would require general lighting power to be reduced to 10 percent or less. This proposed code change leverages the proliferation of solid-state lighting and its dimming capability in the nonresidential sector and takes full advantage of the 10-100 percent dimming range that is already required for LED luminaires and sources found in Table 130.1-A of Title 24, Part 6.  

The existing mandatory requirements for automatic daylight dimming controls apply to new construction, additions, and alterations of nonresidential, high-rise residential, and hotel/motel buildings. The proposed changes would not apply to parking garages.  

Currently, automatic daylighting controls are only required in rooms where the combined installed general lighting power in the Skylight Daylit Zone and Primary Sidelit Daylit Zone is 120 Watts or higher. American Society of Heating, Refrigerating and Air-Conditioning Engineers Standard 90.1 – Energy Standards for Buildings Except Low-Rise Residential Buildings 2019 edition (ASHRAE 90.1-2019) includes a similar threshold requirement wherein automatic daylighting controls are only required if the combined general lighting power is 150 Watts or higher. At the time this Final CASE Report was published, there is a pending revision to ASHRAE 90.1-2019 that would reduce the wattage threshold in 90.1 from 150W to 75W. This revision is expected to be approved by the full ASHRAE 90.1 committee in November 2020.4 The Statewide CASE Team supports this revision and recommends that the Energy Commission align with the pending revision to ASHRAE 90.1 and require automatic daylighting controls when the combined general lighting power is 75W or higher. This proposed change would modify Exception 3 to Section 130.1(d). This report does not present supporting documentation for this proposed change, but the Statewide CASE Team is analyzing the cost effectiveness and energy savings associated with revising the wattage threshold requirement and will be provide results to the Energy Commission in advance of the Energy Commission’s pre-rulemaking workshop where the revisions to daylighting requirements will be discussed.  

The proposed code change does not update the prescriptive power adjustment factor (PAF) value for daylight dimming plus OFF controls in Section 140.6(a)2H. However, language has been updated to clarify that only continuous dimming systems qualify. Stepped dimming systems would not qualify for the daylight continuous dimming plus OFF credit. Language has also been updated so the PAF can now be applied to secondary sidelit daylit zones.  

Mandatory Controls in Secondary Sidelit Daylit Zones

This proposed code change would move the prescriptive requirements for automatic daylighting controls in secondary sidelit daylit zones (SDZs) to Section 130.1, the mandatory indoor lighting controls section of Title 24, Part 6. Currently, the requirement for automatic daylighting controls in SDZs is the only prescriptive lighting control requirement. Since this is the only prescriptive lighting control requirement, stakeholders have reported there is confusion and uncertainty during code compliance verification process whether controls in SDZs are required, particularly when the building complies using the performance approach where this is the only lighting control requirement that a designer could opt not to install as long as they achieve the required energy budget. Moving the requirements for controls in SDZs to the mandatory section would simplify the lighting control requirements and subsequently the compliance and enforcement process for lighting controls. This change would also align the daylighting requirements in Title 24, Part 6 with daylighting requirements in ASHRAE 90.1. Finally, the proposed change would provide certainty about when daylighting controls in SDZs are required, which would make it more likely that lighting in SDZs are controlled with photocontrols. 

Daylighting Controls Acceptance Test Cleanup

The proposed code change would update the Advanced Daylighting Controls Acceptance Tests to fix editorial errors and improve the technical feasibility of completing the test. The suggested revisions address stakeholders’ comments that the existing test procedure is unclear and difficult or impossible to execute as written. Specifically, the proposed changes would: 

  1. Adjust procedures to verify and document that the lighting power reduction of controlled luminaires is at least 90 percent instead of 65 percent.  
  2. Fix numbering errors. 
  3. Adjust language and formatting to clearly depict the step where the Reference Location is identified. This is helpful because the Reference Location is mentioned multiple times throughout the remainder of the test procedure. 
  4. Allow the full daylight condition to be simulated by shining a bright light into the photosensor, which makes it easier for the technicians to complete the test. 
  5. Clarification that the automatic daylighting controls acceptance test is intended to be applied to the secondary sidelit daylit zone. 
  6. Add an alternative partial daylight test to address stakeholder concerns with the feasibility of using the current partial daylight test in all conditions, particularly in daylit spaces with dark glazing or small window areas. 

Stakeholders have expressed similar concerns about the Advanced Daylighting Controls Acceptance Tests to the Energy Commission. In response the Energy Commission has developed suggested revisions to the tests. The Energy Commission stated their intent to update the tests during a public workshop held on March 10, 2020 (California Energy Commission 2020a) and released marked-up language for public review on August 13, 2020 (California Energy Commission 2020d). The Statewide CASE Team agrees with many of the improvements the Energy Commission has suggested, but suggests some additional clarifications that are discussed in the Final CASE Report.  

Submeasures Moved to Other Initiatives

Shading Power Adjustment Factor (PAF) Improvements

The shading power adjustment factor (PAF) improvements submeasure was largely comprised of code language changes to improve the clarity, consistency, terminology and syntax of the current code language and has therefore been moved to the Code Cleanup Initiative.

This submeasure would simplify and correct the existing language for the Daylighting Design Power Adjustment Factors (PAFs). Some features of the PAF are better placed in the mandatory sections of the code rather than the prescriptive sections so that those features are also required under the performance path. Requirements would also be reviewed to evaluate whether their modification or deletion can be justified so as to increase the opportunities for installation on projects and ease the burden of compliance.

While implementing the PAFs in the 2019 code cycle, various errors or ambiguities were uncovered that require correction. The set of savings calculations derived in the development of the PAFs in 2019 vary depending on spacing, tilt and reflectance. This set would replace the single PAF value in the performance path compliance software.

High Performance Envelope Submeasures

The following measures were initially presented as nonresidential daylighting submeasures, but have been grouped, more appropriately, under nonresidential high performance envelope.

  • Refine prescriptive exterior shading reflective solar heat gain coefficient requirements
  • Exterior shading thermal breaks

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

Provide Feedback

Final CASE Report now available.

Pre-Rulemaking Energy Commission Workshop Scheduled

This measure description will be updated as research is developed to support the 2022 code cycle. For questions or suggestions, email info@title24stakeholders.com. Include the measure name in the subject line.

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.

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