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A 75-hp (shaft output) motor that has an efficiency of 91% is worn out and is replaced by a high efficiency 75-hp motor that has an efficiency of 95.4%. Determine the reduction in the heat gain of the room due to higher efficiency under full-load conditions.

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Answer:

The heat gain of the room due to higher efficiency is 2.84 kW.

Step-by-step explanation:

Given that,

Output power of shaft = 75 hp

Efficiency = 91%

High efficiency = 95.4%

We need to calculate the electric input given to motor

Using formula of efficiency


\eta=(Work\ Output)/(Work\ input)


Work\ Input =(Work\ output)/(\eta)


Work\ Input =(75*746)/(0.91)


Work\ Input =61483.51\ W


Work\ Input = 61.48 kW

We need to calculate the electric input

For, heigh efficiency


Work\ Input_(inc) =(75*746)/(0.954)


Work\ Input_(int) =58647.7\ W


Work\ Input_(int) = 58.64\ kW

The reduction of the heat gain of the room due to higher efficiency is


Q=Work\ Input-Work\ Input_(int)

Put the value into the formula


Q=61.48 -58.64


Q=2.84\ kW

Hence, The heat gain of the room due to higher efficiency is 2.84 kW.

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