Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
From Enhancements to ASHRAE Standard 90.1 Prototype Building Models
Section 2.4.2 Fan Motor Efficiency
Addendum aj to Standard 90.1-2010 requires motors from 1/12 hp to under 1 hp to be electronically commutated (EC) motors or have a minimum efficiency of 70%. The intent is to replace standard permanent-split capacitor (PSC) motors with more-efficient EC motors. Intended applications include toilet and elevator exhaust fans, series fan-powered VAV boxes, and fan-coil units. Exemptions to this requirement include motors in an airstream where only heating is provided, motors in packaged equipment, and capacitor-start capacitor-run, capacitor-start induction-run, and polyphase motors.
To capture savings from this addendum, changes to the baseline assumptions were required. Baseline motors were assumed to be PSC motors. Sources give a range with peak efficiencies as high as 65%, but this is very sensitive to the design load, and operating off the design load gives efficiencies in the range of 12% to 45% (Taylor Engineering 2011). Research presented to the California Energy Commission, considering EC motors for California Title 24, used 29% efficiency for PSC motors (Taylor Engineering 2011). The ENERGY STAR program uses a criterion for small exhaust fans of a minimum of 2.8 cfm/W tested at 0.25 in w.g., and requires a 60% efficient fan for rated airflow under 90 cfm, and 70% efficient fan for rated airflow from 90-500 cfm. This implies a motor efficiency as low as 12%. A motor efficiency of 29% was used as an intermediate value between highest potential efficiency and lowest efficiency. The minimum required for EC motors as per the addendum is 70%. This is close to the average typical EC motor efficiency, and therefore this was the value used for the analysis.
