Economizer Fault Detection Diagnostics (FDD) Requirements

Nonresidential HVAC

Codes and Standards Enhancement (CASE) Report

The Statewide CASE Team 2019 Title 24, Part 6 Final CASE Report is available below. The Final CASE Report incorporates feedback received during utility-sponsored stakeholder meetings, Energy Commission Pre-Rulemaking workshops, and personal communication with stakeholders. We encourage stakeholders to email feedback on the Final CASE Report to You can also participate in the 2019 Title 24, Part 6 Standards updated by attending the Energy Commission workshops and submitting written comments to the rulemaking docket. Refer to the Pre-Rulemaking and Rulemaking Workshop Notices for instructions on how to submit comments to the Energy Commission’s docket (available here).

Measure Description

This CASE Report proposes expanding the existing mandatory code language in Section 120.2(i), which
requires economizer fault detection and diagnostics (FDD) for nonresidential packaged and split air
handling HVAC (heating, ventilation, and air-conditioning) systems greater than 54,000 Btu/hr (4.5
tons) in size with an air-side economizer, to also cover built-up handlers with these characteristics. As a
result, the proposal will expand the requirement to cover all air handlers, both packaged and built-up,
that are greater than 54,000 Btu/hr in size and equipped with an air-side economizer.

FDD systems are automated systems designed to detect, diagnose, and report faults to improve
economizer longevity and occupant comfort. Economizer FDD systems can be standalone, such as those
onboard many packaged systems, or they can be integrated into a building direct digital control (DDC)
systems via sequences of operations (SOO). This code change would require the detection and reporting
of the following economizer faults listed in 120.2(i)7 for built-up systems as well as packaged systems:

  • Air temperature sensor failure/fault
  • Not economizing when it should
  • Economizing when it should not
  • Damper not modulating
  • Excess outdoor air