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

asked 9 years ago

Alec
139 ●3

updated 9 years ago

__AmirRoth__

4446 ●5 ●17 http://bleedinggreenna...

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?

Comments

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

David Goldwasser ( 9 years ago )

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answered 9 years ago

aparker

8187 ●4 ●18 http://www.openstudio.net/

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.