efficiency motor instead of the standard motor. Also, determine the simple payba
ID: 703179 • Letter: E
Question
efficiency motor instead of the standard motor. Also, determine the simple payback period if the purchase prices of the standard and high-efficiency motors are $5449 and $5520, respectively 3-56 Consider an electric motor with a shaft power output of 20 kW and an efficiency of 88 percent. Determine the rate at which the motor dissipates heat to the room it is in when the motor operates at full load. In winter, this room is normally heated by a 2-kW resistance heater. Determine if it is neces- sary to turn the heater on when the motor runs at full load.Explanation / Answer
Ans 3-56
power output = 20 kW
efficiency = 0.88 = power output / power input
Power input (operates at full load) = 20/0.88 = 22.72 kW
Power dissipated into the room at full load = excess power
= Power input - power output
= 22.72 - 20 = 2.72 kW
Heated by resistance heater = 2 kW
Therefore no requirement to turn the heater on when the motor runs at full load because it dissipates 2.72 kW.
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