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Single Family Fault Detection Diagnostics

Measure Description

The focus of the Residential Fault Detection and Diagnostics (FDD) measure is to provide credit for use of advanced technologies that detect when residential HVAC systems are installed and operated optimally. The Statewide CASE Team is proposing a compliance credit that will be granted for installation of FDD devices that can identify over time when an HVAC system’s performance is not optimal (due to installation faults or faults that emerge over time) and alert the owners or service providers.  Credit may be provided in a way similar to the refrigerant and airflow verification credit—Section 2.4 of the 2016 Title 24, Part 6 Residential ACM Reference Manual describes credit given to systems for which the charge is verified as correct by establishing a “compressor efficiency multiplier,” which is used in calculations to degrade the efficiency of a compressor by a factor of 10 percent when charge is not verified as correct, but only by 4 percent when it is verified as correct.  In this case, an efficiency multiplier may be used to provide credit for installation and proper configuration of an FDD device or FDD-enabled HVAC system.  In this effort, the Statewide CASE Team is conducting field research to identify the appropriate efficiency multiplier for systems with and without an FDD device, and also providing performance-based specifications for manufacturer certification of FDD effectiveness and field verification of proper FDD installation.

Relevant Documents

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

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This measure description will be updated as research is developed to support the 2022 code cycle. For questions or suggestions, email 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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