Find the motor which is recommended to purchase based on the given information.
Answer to Problem 14P
Bases on the given information, the Motor – Y is recommended to purchase.
Explanation of Solution
Given data:
The power of the Motor – X
The pump is expected to run
Average electricity cost of the motor is
The number of years for the life of Motor – X
Initial cost for Motor – X and Motor – Y is
Operating point efficiency of the Motor – X
Maintenance cost of Motor – X and Motor – Y is
Calculation:
Assume the interest rate as
Case (i): For Motor - X
Initially calculate the operating cost for the Motor- X using the power, efficiency at the operating point, electricity cost and pump life time.
Convert the electricity cost from cent per kWh to dollar per kWh using the following relationship.
Therefore,
The average electricity cost of the motor is
Formula to calculate the operating cost of the Motor – X is,
Here,
Substitute
Therefore, the present worth of the Motor – X can be calculated using the following expression:
Here,
Substitute
Refer to the Table 20.9 in the textbook, the value for
Substitute
Hence, the present worth of the Motor – X is
Case (ii): For Motor - Y
Initially calculate the operating cost for the Motor- Y using the power, efficiency at the operating point, electricity cost and pump life time.
Convert the electricity cost from cent to dollar using the following relationship.
Therefore,
The average electricity cost of the motor is
Formula to calculate the operating cost of the Motor – Y is,
Here,
Substitute
Therefore, the present worth of the Motor – Y can be calculated using the following expression:
Here,
Substitute
Refer to the Table 20.9 in the textbook, the value for
Substitute
Hence, the present worth of the Motor – Y is
Compare the equations (4) and (8), from the analysis it is clear that the Motor – Y provides the least present value than the Motor – X.
Therefore, the Motor – Y should be recommended to purchase.
Conclusion:
Thus, the Motor – Y should be recommended to purchase.
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