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Single Family Variable Capacity HVAC Compliance Software Revisions

Measure Description

This measure will de-rate the performance of variable speed HVAC systems unless ducts are located inside conditioned space, or are installed with qualified zone controls. Variable capacity split system air conditioners and heat pumps (as distinguished from mini-split heat pumps) typically have significantly higher SEER and EER ratings than single speed equipment. However, research conducted at the UC Davis Western Cooling Efficiency Center (WCEC) has shown that the low air velocity in ducting significantly degrades cooling performance when ducts are located in hot attics, exposing a significant loophole in compliance methods. WCEC laboratory test data and modeling will be used to improve modeling methods for ducts in attic zones so that reduced airflow rate, as well as the currently modeled duct surface area and attic and duct temperature, is accounted for.

Provide Feedback

Participate in the Utility-Sponsored Stakeholder meeting for this topic on October 10th, 2019! View the event here.

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.


Relevant Documents

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


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.

  • Use the form above to provide feedback on this measure.