Electrical Motors - Heat Loss

Heat Loss from Electric Motors during Operation

Heat loss from electric motors due to inefficiency:  

• 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. 

1. 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)
2. 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
3. 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

• 1 Btu/h = 0.293 W 
• 1 horsepower = 2542 Btu/hr

Temperature ^oC
K
^oF

Length m
km
in
ft
yards
miles
naut miles

Area m²
km²
in²
ft²
miles²
acres

Volume m³
liters
in³
ft³
us gal

Weight kg_f
N
lbf

Velocity m/s
km/h
ft/min
ft/s
mph
knots

Pressure Pa
bar
mm H₂O
kg/cm²
psi
inches H₂O

Flow m³/s
m³/h
US gpm
cfm