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.
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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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