Heat gain from electrical motors for continuous operation (kW). Source: engineeringtoolbox.com
Shaft Output(kW)	Motor Efficiency(%)	Electrical Input(kW)	Config. 1(kW)	Config. 2(kW)	Config. 3(kW)
0.05	40	0.13	0.13	0.05	0.08
0.07	46	0.15	0.15	0.07	0.08
0.1	55	0.18	0.18	0.1	0.08
0.14	60	0.23	0.23	0.14	0.09
0.2	64	0.31	0.31	0.2	0.11
0.28	66	0.42	0.42	0.28	0.14
0.4	70	0.6	0.6	0.4	0.2
0.56	72	0.78	0.78	0.56	0.22
0.8	76	1.05	1.05	0.8	0.25
1.1	80	1.38	1.38	1.1	0.28
1.6	80	2	2	1.6	0.4
2.5	81	3.1	3.1	2.5	0.6
4	82	4.9	4.9	4	0.9
5.6	84	6.7	6.7	5.6	1.1
8	84	9.5	9.5	8	1.5
11.2	86	13	13	11.2	1.8
16	87	18.4	18.4	16	2.4
20	88	22.7	22.7	20	2.7
25	89	28	28	25	3
32	89	36	36	32	4
40	89	45	45	40	5
50	90	56	56	50	6
63	90	70	70	63	7
80	90	89	89	80	9
100	91	110	110	100	10

Source: engineeringtoolbox.com

Heat Gain Calculation Formulas

The electrical motor input power determines the potential heat load. The actual heat gain to the conditioned space depends on the installation configuration.

Electrical Motor Input:

P_{\text{input}} = \frac{P_{\text{shaft}}}{\eta}

where $P_{\text{shaft}}$ is the shaft output (kW) and $\eta$ is the motor efficiency (decimal).

Heat Gain Configurations:

Motor and Fan in Air Flow/Room:
$Q_{\text{gain}} = P_{\text{input}}$
All electrical input power is dissipated as heat into the conditioned space.
Motor Outside, Fan in Air Flow/Room:
$Q_{\text{gain}} = P_{\text{shaft}}$
Only the mechanical energy delivered to the fan is dissipated as heat within the space.
Motor in Room, Fan in Outlet Air Flow:
$Q_{\text{gain}} = P_{\text{input}} - P_{\text{shaft}}$
This represents the heat loss from the motor itself ( $I^2R$ losses, friction, etc.), as the fan's work is removed with the exhaust air.

Installation Configuration Definitions

Configuration 1: Motor and fan are both located within the inlet airstream or the conditioned room. All energy consumed by the motor is added to the space as heat.
Configuration 2: Motor is located outside the airstream or outside the conditioned room, but the fan is in the inlet airstream or room. Only the mechanical energy (shaft work) is added as heat to the space.
Configuration 3: Motor is located within the conditioned room, but the fan is in the outlet (exhaust) airstream. The motor's heat loss ( $P_{\text{input}} - P_{\text{shaft}}$ ) is added to the room, while the fan's shaft work is rejected with the exhaust air.

Unit Conversions

1 kW = 1000 W = 3412 Btu/h = 1.341 British hp = 737.6 ft·lbf/s

Interactive Charts

Heat gain from electric motors in fans

References

Original Source

Source: engineeringtoolbox.com