Electrical Motors - Heat Loss
Heat Loss from Electric Motors during Operation
Heat loss from electric motors due to inefficiency:
| Size of Motor (kW) | Efficiency (%) | Heat Loss (watts/kW) |
|---|---|---|
| 0 - 2 | 75 | 250 |
| 3 - 15 | 85 | 150 |
| 15 - 150 | 90 | 100 |
| 150 - | 92 | 80 |
- 1 kW = 1.34 hp
- 1 hp = 0.746 k W
Example - Heat Loss from an Electric Motor
The heat loss from an electric motor supplied with 10 kW can with the heat loss 150 watts/kW from the table above be calculated as
(10 kW) (150 watts/kW)
= 1500 watts
= 1.5 kW
The rest of the energy
(10 kW) - (1.5kW)
= 8.5 kW
is output mechanical energy.
If the motor and the mechanical equipment connected to the motor is in the same room - or enclosure - all electric energy supplied to the motor will convert to heat and temperature increase in the room.
Heat Loss from an Electric Driven Device to a Room
The heat transferred to a room or enclosure depends on the location of the motor and the driven device related to the room.
- motor and driven device in the room - all energy to the motor is at the end transferred to the room (heat loss from the motor and frictional energy from the driven device)
- motor in the room and device outside the room - only heat loss from the motor is transferred to the room - frictional energy from the driven device is lost outside the room
- motor outside the room and device inside the room - frictional loss from the driven device is transferred to the room - energy loss from the electric motor is lost outside the room
| Nameplate Rating (hp) | Motor Efficiency (%) | Heat Loss to Room Air (Btu/hr per rated hp) | ||
|---|---|---|---|---|
| Motor in Room Driven Device inside Room | Motor in Room Driven Devise Outside Room | Motor Outside Room Driven Device inside Room | ||
| 0 - 1.5 | 0.80 | 2542 | 508 | 2034 |
| 1.5 - 12.5 | 0.85 | 2542 | 381 | 2161 |
| 12.5 - | 0.90 | 2542 | 254 | 2289 |
- 1 Btu/h = 0.293 W
- 1 horsepower = 2542 Btu/hr
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