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Nonresidential Daylighting

Measure Description

This CASE Report will use a comprehensive approach to daylighting design and control strategies that maximize the use of natural light while minimizing glare and solar heat gain. Specifically, this CASE Report comprises several submeasures to promote more efficient use of daylight and to generate more energy savings.

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. There are no changes to the threshold daylight illuminance level triggers. This measure 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.

The proposed code change does not recommend revisions to the existing definition or applicability of the prescriptive power adjustment factor (PAF) for daylight dimming plus OFF controls in Section 140.6(a)2H. However, the factor itself needs to be updated to account for the PAF applying to dim from 10 percent to OFF instead of dim from 35% to OFF.

Mandatory Controls in Secondary Sidelit Daylit Zones

This submeasure 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 the Title 24, Part 6. Currently, the requirement for automatic daylighting controls in SDZs is the only prescriptive lighting control requirement, which means that users who choose the performance approach can trade off other high efficiency features in the building against SDZ controls; i.e. users can install the SDZ controls and then install another building system (such as HVAC) at a lower efficacy. Since this is the only prescriptive control requirement, there is confusion and uncertainty during code compliance inspection about whether the controls in SDZs were traded off, or if they were required and installed. Converting the SDZ controls requirements into mandatory requirements would simplify the daylighting code and the compliance enforcement process and align the daylighting requirements in Title 24, Part 6 with daylighting requirements in ASHRAE 90.1. The proposed changes would also provide certainty about when daylighting controls in SDZs are required, which would make it more likely that lighting in SDZs are controlled with photocontrols.

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

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.

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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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