Operating Cost Comparison Calculator

The Operating Cost Comparison Calculator estimates the annual cost difference between an existing electrical option and a proposed option. It produces five planning values:

• Existing annual cost
• Proposed annual cost
• Annual cost saved
• Simple payback
• Cost difference

The calculation is commonly used to screen electrical upgrades such as LED lighting retrofits, motor replacements, VFD applications, HVAC electrical improvements, transformer replacements, process-equipment changes, or controls projects. It does not determine AWG or kcmil conductor size, ampacity, voltage drop, raceway fill, overcurrent protection, branch-circuit loading, feeder capacity, or NEC compliance. Those electrical design decisions remain separate from the operating-cost comparison.

An upgrade may reduce annual kWh through lower connected load, fewer operating hours, improved motor efficiency, reduced losses, or better controls. The calculator converts that energy change into annual dollars using the entered utility rate and fixed annual costs.

Annual Energy and Rate Inputs

The existing arrangement is entered with three values:

Input	Purpose
Existing annual energy (kWh/year)	Annual electrical energy used by the existing equipment or system
Existing rate ($/kWh)	Energy rate applied to the existing annual kWh
Existing fixed cost ($/year)	Annual non-energy cost assigned to the existing option

The proposed arrangement uses the matching fields:

Input	Purpose
Proposed annual energy (kWh/year)	Expected annual electrical energy use after the upgrade
Proposed rate ($/kWh)	Energy rate applied to proposed annual kWh
Proposed fixed cost ($/year)	Annual non-energy cost assigned to the proposed option
Incremental project cost ($)	Added first cost used to calculate simple payback

Annual kWh should represent energy consumption, not connected load alone. A motor rated at 20 hp, for example, does not automatically consume a fixed annual kWh value. Its annual energy depends on loading, operating hours, motor efficiency, control method, and actual input power. Likewise, a lighting retrofit estimate should reflect fixture wattage, operating schedule, control behavior, and any expected changes in connected lighting load.

The entered rate should match the intended comparison basis. If the existing and proposed options are billed under the same energy rate, the same value may be used in both rate fields. Different rates can be useful when comparing separate meters, service accounts, tariff structures, or operating locations.

Annual Operating Cost Formula

The calculator calculates each annual operating cost from annual energy, energy rate, and fixed annual cost:

\(\displaystyle \text{existing annual cost} = \text{existing annual kWh} \times \text{existing rate} + \text{existing fixed annual cost}\)

\(\displaystyle \text{proposed annual cost} = \text{proposed annual kWh} \times \text{proposed rate} + \text{proposed fixed annual cost}\)

It then calculates savings as:

\(\displaystyle \text{annual cost saved} = \text{existing annual cost} - \text{proposed annual cost}\)

The Cost difference is the proposed annual cost less the existing annual cost. A negative Cost difference indicates that the proposed option costs less to operate. Its magnitude matches Annual cost saved when the proposed option is less expensive.

Simple payback is calculated only when annual savings are positive:

\(\displaystyle \text{simple payback years} = \frac{\text{incremental project cost}} {\text{annual cost saved}}\)

Simple payback shows the number of years required for annual operating savings to equal the entered Incremental project cost. It does not calculate discounted cash flow, net present value, internal rate of return, financing cost, or lifetime project economics.

Calculation Example

Assume an electrical upgrade has the following annual operating inputs:

Field	Entered value
Existing annual energy (kWh/year)	20,000
Existing rate ($/kWh)	$0.18
Existing fixed cost ($/year)	$200
Proposed annual energy (kWh/year)	15,000
Proposed rate ($/kWh)	$0.16
Proposed fixed cost ($/year)	$150
Incremental project cost ($)	$5,000

Existing annual cost:

\(\displaystyle 20{,}000 \text{ kWh/year} \times \$0.18/\text{kWh} + \$200/\text{year} = \$3,800/year\)

Proposed annual cost:

\(\displaystyle 15{,}000 \text{ kWh/year} \times \$0.16/\text{kWh} + \$150/\text{year} = \$2,550/year\)

Annual cost saved:

\(\displaystyle \$3{,}800/\text{year} – \$2{,}550/\text{year} = \$1,250/year\)

Simple payback:

\(\displaystyle \$5{,}000 \div \$1{,}250/\text{year} = \text{4 years}\)

The result shows that the proposed option reduces the modeled annual operating cost by $1,250 per year. With a $5,000 Incremental project cost, the simple payback is 4 years.

Electrical Project Use

Operating-cost comparison belongs early in electrical project screening, after enough information exists to estimate annual kWh and before final capital approval. It helps compare alternatives that may have different electrical operating characteristics:

• Replacing existing lighting with lower-wattage fixtures and controls.
• Comparing across-the-line motor operation with a VFD-driven motor application.
• Evaluating a higher-efficiency motor, transformer, or power-conversion system.
• Comparing electrical equipment with different standby, control, or auxiliary power requirements.
• Reviewing alternatives that change run hours, duty cycle, or process energy consumption.

The result should be considered alongside electrical design requirements. A lower-energy option may still require a separate review of branch-circuit and feeder loading, conductor ampacity, terminal rating, adjustment factor, correction factor, current-carrying conductors, voltage drop, raceway fill, overcurrent protective devices, available fault current, equipment listing, and manufacturer installation requirements.

For example, a VFD may reduce motor energy use under variable-torque loading, but it can also affect feeder and branch-circuit design, harmonic considerations, motor insulation suitability, grounding and bonding requirements, conductor termination details, and the installation instructions for the drive and motor. The annual cost result does not resolve those items.

Field Verification

Use measured or supportable operating data whenever practical. Annual kWh estimates based solely on nameplate horsepower, breaker size, or panel schedule load are often unsuitable for project economics because those values do not establish actual annual energy consumption.

Verify the comparison basis against available records and project conditions:

• Utility bills, interval data, submeters, or logged kWh where available.
• Operating hours, production schedules, seasonal operation, and control schedules.
• Existing equipment load profile rather than nominal connected load only.
• Proposed equipment input power and expected duty cycle.
• Whether fixed annual costs are truly attributable to the compared options.
• Whether the proposed work changes demand charges, maintenance costs, rebates, taxes, financing, degradation, or replacement timing.

The calculator’s boundary is limited to annual kWh multiplied by the entered rate, plus the entered fixed annual cost, with simple payback based on positive annual savings. It does not include inflation, maintenance, escalation, degradation, financing, rebates, taxes, or demand-charge results. Formal project approval should use the applicable utility tariff, equipment data, measured load information, project scope, and the electrical and code review required by the AHJ and the installation.