Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
Fan objects (Fan:ConstantVolume, Fan:VariableVolume, Fan:OnOff) in EnergyPlus/OpenStudio have two inputs related to fan motor efficiency: Fan Total Efficiency and Motor Efficiency.
From the EnergyPlus Input/Output reference...
Fan Total Efficiency represents the product of motor efficiency and the fan efficiency. The motor efficiency is the power delivered to the shaft divided by the electrical power input to the motor. The fan efficiency is power delivered to the fluid (air) divided by the shaft power.
Motor Efficiency is the shaft power divided by the electrical power consumed
To understand the impact of premium efficiency motors you will need to adjust both input fields. The Motor Efficiency field is used in conjunction with the Motor In Airstream Fraction field to determine the amount of motor heat loss that goes into the airstream as heat. The Motor Efficiency field will not impact the amount of fan power directly but it will impact the amount of heating or cooling used by your HVAC system.
The Fan Total Efficiency field (simply 'Fan Efficiency' in OpenStudio) will need to be adjusted to represent the change in motor efficiency and fan power consumed. Fan Total Efficiency = Motor Efficiency * Fan Efficiency, so you can adjust your fan total efficiency accordingly if you know the change in motor efficiency.
