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Nonresidential HVAC Controls

Measure Description

This CASE Report consists of three submeasures: adding prescriptive requirements for dedicated outside air systems (DOAS), and modifying existing prescriptive requirements for VAV zone controls, and expanding prescriptive requirements for air side economizer and integrated economizer operation.  Further details can be found below. 

Expanded Economizer Requirements

This submeasure aims to modify both economizer requirements and integrated economizer requirements. The measure will expand economizer requirements to include smaller-sized units and expand integrated economizer requirements by requiring lower compressor turndown. This submeasure was previously referred to as an “Air efficiency” measure. 

Improve VAV Zone Control

This measure would adjust prescriptive requirements for variable air volume (VAV) zone controls. Currently, when a zone is in the deadband operation, flow controls must meet mandatory requirements of Section 120.1 for ventilation requirements and an additional prescriptive requirements of fixed minimum rate flow rate of 20% from section 140.4(d). This measure would remove the 20 percent prescriptive requirement, allowing for lower airflow during deadband operation, while ensuring indoor air quality. The measure is based on research conducted for ASHRAE Research Project (RP)-1515, which was co-funded by the California Energy Commission PIER program and evaluated occupants’ thermal comfort and air quality satisfaction of reduced airflows using lab and field studies. Findings from RP-1515 resulted in the approval of Addendum AU to ASHRAE 90.1-2016, which reduced minimum airflow requirements. As a result, this measure proposes to align Title 24, Part 6 with ASHRAE Standard 90.1-2019 and simplify the existing code requirements.

Dedicated Outside Air Systems (DOAS)

This measure will add prescriptive requirements to dedicated outdoor air system units (DOASu) when used as the primary source of ventilation in nonresidential buildings to include a minimum level of efficiency criteria and an exception to economizing for space conditioning when combined with ventilation heat recovery. The combination of a separate DOAS unit and heating and cooling system as a package is referred to as a Dedicated Outdoor Air System (DOAS).  

This measure is based on research into low energy HVAC systems used in California nonresidential net zero energy buildings, field monitoring research conducted by PG&E’s Code Readiness project, and code change enhancements made in Washington State Building Energy Code, starting in 2015 and up to changes adopted in 2019. This strategy has been shown to cost effective to operate while reducing source energy by 30% compared with standard designs.  

The measure will add a prescriptive option to install a DOAS with a minimum set of efficiency criteria. This includes: 

  1. A minimum level of sensible energy recovery ratio with bypass capabilities. 
  2. Ability to modulate fan speed of the DOAS unit. 
  3. A total system fan power limit on DOAS units, including <5hp 
  4. Compliance with DCV and Occupancy Standby. 
  5. Zone terminal fans for cooling or heating cycle to off if no call for conditioning. 
  6. DX-DOAS or DOAS with active cooling must have a maximum reheat limit of 60F when in cooling model. 

DOAS units with a minimum level of ventilation heat recovery and free cooling controls would be required to achieve the exception to economizing.

Exhaust Air Heat Recovery

This measure will add prescriptive requirements to all nonresidential systems for exhaust air heat recovery depending on climate zone, hours of operation, and fraction of outside air. 

Guest Room Controls

The 2019 code requires guest rooms in hotels and motels to have occupancy sensing zone controls. These controls must be programed to implement the following after all rooms in the zone have been unoccupied for 5 minutes: 1) shut off ventilation to every room in the unoccupied zone if there is no call for heating or cooling, and 2) adjust the temperature setpoints by 5°.  After 30 minutes, guestrooms are required to further setback/setup setpoints by 5°F.

This measure proposes to require ventilation to be shut off to the guest room within 5 minutes of all occupants leaving the room, and require temperature setpoints of at least 60°F for heating and 80°F for cooling for unrented and unoccupied guest rooms. These requirements will align Title 24 Part 6 with the guest room ventilation control requirements in ASHRAE Standard 90.1 (2016) and guestroom purge requirements of 189.1 (2017). Thresholds for number of guest rooms in the hotel or networked control of guest rooms may be included in the requirements upon further research. ASHRAE 90.1 (2016) requires the measure for >50 guest rooms, so this may be the appropriate starting point to consider. This measure will also attempt to clarify and clean-up the ventilation and setback requirements that are currently spread over multiple sections of Title 24 Part 6: 120.1(d)5, 120.2(e)3, and 130.1(c)8.

Opportunities for Discussion

Currently the requirements for occupant sensing and resulting control are somewhat spread out in various sections and somewhat disparate.  We propose to not only include the guest room control requirements from ASHRAE 90.1, but also consolidate the sensor system requirements into Chapter 110 and adjust the references in Chapters 120.1, 120.2 and 130.1 such that ‘inoccupancy’ is consistently defined in all spaces for HVAC and lighting.   The current draft lists time requirements in each section, however we also propose to define when and how a space is determined to be unoccupied, specifically by motion and IR based systems, in section 110.13

Relevant Documents

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

Submeasure Summaries

Utility-Sponsored Stakeholder Meeting Presentations

Utility-Sponsored Stakeholder Meeting Notes

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.

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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