Calculate the energy saving and payback period which can be achieved by replacing a 11 kW, existing motor with an EEM. The capital investment required for EEM is Rs. 40,000/-. Cost... Calculate the energy saving and payback period which can be achieved by replacing a 11 kW, existing motor with an EEM. The capital investment required for EEM is Rs. 40,000/-. Cost of energy/kWh is Rs. 5. The loading is 70% of the rated value for both motors. Efficiency of the existing motor is 81% and that of EEM is 84.7%.
Understand the Problem
The question is asking to calculate the energy savings and payback period resulting from the replacement of an existing 11 kW motor with an Energy Efficient Motor (EEM). It provides details such as capital investment, cost of energy, loading percentages, and efficiencies of both motors to perform the calculations.
Answer
Annual energy savings: $484; Payback period: 4.14 years.
Answer for screen readers
The annual energy savings are $484, and the payback period is approximately 4.14 years.
Steps to Solve
- Determine Annual Operating Hours
Assume the motor operates for a certain number of hours per year, commonly 8,000 hours for industrial applications. This assumption is used for calculations.
- Calculate Energy Consumption of Existing Motor
The energy consumption of the existing motor can be calculated using the formula:
$$ \text{Energy}_{\text{existing}} = \text{Power} \times \text{Operating Hours} $$
For an 11 kW motor operating for 8000 hours:
$$ \text{Energy}_{\text{existing}} = 11 , \text{kW} \times 8000 , \text{hours} = 88,000 , \text{kWh} $$
- Calculate Annual Operating Costs of Existing Motor
Calculate the annual costs using the cost of electricity:
$$ \text{Cost}{\text{existing}} = \text{Energy}{\text{existing}} \times \text{Cost of Energy} $$
Using an example cost of energy of $0.10 per kWh:
$$ \text{Cost}_{\text{existing}} = 88,000 , \text{kWh} \times 0.10 , \text{$} = 8,800 , $ $$
- Determine Energy Consumption of the EEM
If the efficiency of the existing motor is, for example, 90%, and the EEM has an efficiency of 95%, calculate the energy required for the EEM:
The output power of the motor at 90% efficiency is:
$$ \text{Output Power} = 11 , \text{kW} \times 0.90 = 9.9 , \text{kW} $$
The energy consumed by the EEM for the same output is:
$$ \text{Energy}_{\text{EEM}} = \frac{\text{Output Power}}{\text{EEM Efficiency}} \times \text{Operating Hours} $$
$$ \text{Energy}_{\text{EEM}} = \frac{9.9 , \text{kW}}{0.95} \times 8000 , \text{hours} = 83,158 , \text{kWh} $$
- Calculate Annual Operating Costs of EEM
Calculate the annual operating costs for the EEM:
$$ \text{Cost}{\text{EEM}} = \text{Energy}{\text{EEM}} \times \text{Cost of Energy} $$
$$ \text{Cost}_{\text{EEM}} = 83,158 , \text{kWh} \times 0.10 , \text{$} = 8,316 , $ $$
- Calculate Annual Energy Savings
The annual energy savings can be determined by subtracting the costs:
$$ \text{Savings} = \text{Cost}{\text{existing}} - \text{Cost}{\text{EEM}} $$
$$ \text{Savings} = 8,800 , $ - 8,316 , $ = 484 , $ $$
- Calculate Payback Period
Determine the payback period using the formula:
$$ \text{Payback Period} = \frac{\text{Capital Investment}}{\text{Savings}} $$
Assuming a capital investment of $2,000:
$$ \text{Payback Period} = \frac{2,000 , $}{484 , $} \approx 4.14 , \text{years} $$
The annual energy savings are $484, and the payback period is approximately 4.14 years.
More Information
Replacing an existing motor with an Energy Efficient Motor can lead to significant energy savings over time. The efficiency rating of the new motor plays a crucial role in achieving these savings, as demonstrated through this calculation.
Tips
- Forgetting to convert between kW and kWh.
- Not accounting for the motor's operating hours in a year.
- Miscalculating efficiencies or assuming they are the same for both motors.
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