Energy Cert Exam · Free practical tool

Energy saving comparison

Compare an energy-audit baseline with a proposed equipment input at equivalent service. Keep assumed operating hours visible so an estimate is not mistaken for measured and verified savings.

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The method

Energy before = Pbaseline × baseline time; energy after = Pproposed × proposed time; savings = energy before − energy after. Cost difference = kWh difference × tariff.

Before using the result

  • Tariffs, operating hours and costs are user assumptions. Results exclude financing, taxes, demand charges and changes in equipment performance.
  • Baseline and proposed systems provide comparable service. This is an input comparison, not verified savings.

Worked examples

These original training examples illustrate the method for Certified Energy Manager (CEM). Use the matching “Load example” button above to explore a variation; example values are not equipment settings or prescribed criteria.

1. Worked example

Compare an energy-audit baseline with a proposed equipment input at equivalent service. Keep assumed operating hours visible so an estimate is not mistaken for measured and verified savings.

Baseline input power
10 kW
Proposed input power
7 kW
Annual operating time
2,000 h
Operating schedules
Same hours
Energy tariff (currency units/kWh)
0.15
  1. Power difference = 3000 W.
  2. Baseline = 10000 × 7200000 = 72000000000 J; proposed = 7000 × 7200000 = 50400000000 J.
  3. Energy difference = 72000000000 − 50400000000 = 6000 kWh.
  4. Cost difference = 6000 × 0.15.
  • Baseline annual energy: 72,000,000,000 J
  • Proposed annual energy: 50,400,000,000 J
  • Annual energy difference: 21,600,000,000 J
  • Annual cost difference: 900 currency units

2. Comparison example

Compare a different supplied condition using the same method. For Energy Cert Exam, the important check is that the input meaning, units and method assumptions still match the problem.

Baseline input power
10 kW
Proposed input power
6 kW
Annual operating time
2,000 h
Operating schedules
Same hours
Energy tariff (currency units/kWh)
0.15
  1. Power difference = 4000 W.
  2. Baseline = 10000 × 7200000 = 72000000000 J; proposed = 6000 × 7200000 = 43200000000 J.
  3. Energy difference = 72000000000 − 43200000000 = 8000 kWh.
  4. Cost difference = 8000 × 0.15.
  • Baseline annual energy: 72,000,000,000 J
  • Proposed annual energy: 43,200,000,000 J
  • Annual energy difference: 28,800,000,000 J
  • Annual cost difference: 1,200 currency units

Check your understanding

1. Which relationship is used?

Energy before = Pbaseline × baseline time; energy after = Pproposed × proposed time; savings = energy before − energy after. Cost difference = kWh difference × tariff.

2. Which assumption should you check first?

Tariffs, operating hours and costs are user assumptions. Results exclude financing, taxes, demand charges and changes in equipment performance.

3. How should you verify a different unit system?

Convert every input to the displayed calculation units first. Equivalent physical inputs must give equivalent results; a unit label alone does not convert a number.

Continue with the matching exam topic

This tool connects to Certified Energy Manager (CEM) free practice. Work through a question independently, then use the calculation steps to identify where your method differs. The tool stays free whether or not you choose paid preparation.

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