# Thread: 60 HP Electric Motor Heat Rejection

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Six NEW pump motors are located in a small building at a water teratment facility.

The BTUh load seems Quite significant along with the heating due to 93'F DB / 77'F WB in this area.

Thanks in advance for "the Check".

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Unless you know the efficiency ratings of each motor you can't figure out the waste heat they produce. If they were "zero" percent efficient (not realistic but just giving you the numbers), they would produce 3.42 btu of heat per watt. In other words they would be heaters rather than motors.

If they were 100% efficient, they would not produce any waste heat at all. Instead, they would be putting all the input watts into mechanical rotational work out the motor shaft. This is also not possible.

So, you need to know the motor efficiency in order to figure out the waste heat.

Norm

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BTW, the pumps the motors drive also produce additional heat due to friction. Yet another calculation.

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## Efficiency of 60 HP

Right !

Efficiency is likely > 90% ...
But How Much more?

Only Experienced writers need apply ( write ).

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If the motor efficiency is not listed on the motor data plate you can figure it out if the data plate lists the following information"

voltage
amperage
power factor

From there you can figure the waste motor heat.

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%EFF = HP X 746 / V X A X PF X 1.73

Use motor name plate data in the above equation and you will get the efficiency rating that the motor manufacturer did not list on the data plate.

Don't bother using some average efficiency that you can find in some books. This equation gives you EXACTLY the right efficiency.

Norm

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## Thanks

Originally posted by NormChris
%EFF = HP * 746 / V * A * PF * 1.73

Use motor name plate data in the above equation and you will get the Efficiency rating that the motor manufacturer did not list on the data plate.
T H A N K S for the REALity Check.

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