Measure to Replace Standard Motor with Electronically Commutated Motor in Fan Coil

I am writing a measure to replace the standard motor in a fan coil unit with an electronically commutated motor (ECM) and am looking for suggestions on the best way to model this. The standard motor is of type openstudio::model::FanOnOff in an openstudio::model::ZoneHVACFourPipeFanCoil object. My first thought was to change the fan to openstudio::model::FanVariableVolume and increase the motor efficiency, but I'm not sure this is the best way to model it. Alternatively, I considered just increasing the motor efficiency of the openstudio::model::FanOnOff object. What is the best way to model an ECM?

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May want to look at this thread about the relationship between fan and motor efficiency in EnergyPlus and OpenStudio.

David Goldwasser (2015-09-03 11:18:26 -0500) edit

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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.