EAOC is used to identify the pilot-plant equipment option with the lowest equivalent annual financial burden. It converts each alternative’s fixed capital investment into an annual capital charge and adds the expected yearly operating cost. This allows engineers to compare equipment with different purchase prices, service lives, and operating expenses on a consistent annual basis.
The equipment with the lowest feasible EAOC is generally the most economical choice, provided all alternatives meet the required capacity, performance, safety, and reliability criteria.
Why Pilot Plants Need an Annualized Cost Measure
Different equipment options have different cost profiles
One pilot-plant unit may require a low initial investment but consume more energy, labor, or consumables. Another may cost more initially but operate more efficiently and remain useful for longer.
Comparing purchase prices alone ignores these lifecycle differences. Comparing only annual operating costs ignores the financial burden of the initial investment.
Unequal service lives make direct comparisons difficult
Pilot-plant equipment may have expected operating lives of three, five, seven, or more years. A standard NPV comparison can be misleading when alternatives generate costs over different time periods unless the analysis uses an appropriate common comparison horizon.
EAOC addresses this issue by converting each investment into an equivalent annual cost over its expected service life.
How EAOC Is Calculated
Use the capital recovery factor
The standard equation is:
[ EAOC = FCI \left[\frac{i(1+i)^n}{(1+i)^n-1}\right] + YOC ]
The bracketed term is the capital recovery factor, also written as ((A/P,i,n)).
Define the economic inputs
- FCI: Fixed capital investment, including the equipment purchase and relevant installed costs.
- YOC: Yearly operating cost, including energy, maintenance, labor, consumables, and other recurring expenses.
- i: Interest rate, discount rate, or cost of capital.
- n: Expected equipment service life in years.
The first term annualizes the capital investment. Adding YOC produces the total equivalent annual cost.
Include savings where appropriate
If an equipment option produces annual savings or additional annual financial benefits, those benefits can be subtracted from the annualized cost:
[ EAOC_{\text{net}} = FCI \left[\frac{i(1+i)^n}{(1+i)^n-1}\right]
- YOC - YS ]
Here, YS represents yearly savings. The alternative with the lowest net annualized cost is preferred after technical screening.
Applying EAOC to Equipment Selection
Establish a consistent calculation basis
Before comparing equipment, define the process basis. This may be a specified mass flow rate, molar flow rate, batch size, throughput, or quantity of material processed.
If the design specifies a flow rate, use it. If compositions are given as mass fractions, a mass or mass-flow basis is appropriate; if they are given as mole fractions, use a molar basis.
A consistent basis ensures that equipment capacity, energy use, labor requirements, and operating costs are compared for the same process duty.
Estimate the full fixed capital investment
The relevant capital value is not always the vendor’s bare purchase price. FCI should include the costs required to install and operate the unit, such as:
- Piping
- Structural supports
- Electrical work
- Instrumentation and controls
- Insulation and painting
- Installation labor
Lang factors or equipment-specific installation multipliers may be used during preliminary design when detailed estimates are unavailable. The same estimation method should be applied consistently to every alternative.
Estimate annual operating costs
YOC should reflect the pilot plant’s actual operating pattern. Typical components include:
- Electricity, steam, cooling water, and other utilities
- Maintenance and replacement parts
- Filter media, solvents, membranes, or other consumables
- Operator or technician labor
- Waste handling
- Routine calibration and testing
For pilot plants, utilization can be substantially lower than in a commercial facility. Annual costs should therefore be based on expected pilot-plant operating hours and campaign frequency, rather than assuming continuous operation.
Calculate and rank the alternatives
For each technically acceptable equipment option:
- Determine FCI.
- Estimate the service life (n).
- Select the common discount rate (i).
- Calculate the capital recovery factor.
- Add YOC, or subtract annual savings where applicable.
- Rank the alternatives by EAOC.
The lowest EAOC identifies the lowest annualized financial burden.
Example: Comparing Separation Equipment
Consider three solid-liquid separation alternatives evaluated at an 11% interest rate:
| Alternative | FCI | YOC | Service life | EAOC |
|---|---|---|---|---|
| Rotary vacuum filter | $15,000 | $3,000/year | 6 years | $6,550/year |
| Filter press | $10,000 | $5,000/year | 8 years | $6,940/year |
| Hydrocyclone and centrifuge combination | $25,000 | $2,000/year | 10 years | $6,250/year |
Interpret the ranking
The filter press has the lowest initial investment, but its higher yearly operating cost produces the highest EAOC of the three options.
The hydrocyclone and centrifuge combination has the highest FCI, but its lower YOC and longer service life result in the lowest EAOC. Subject to technical feasibility, it is therefore the preferred economic alternative.
Understand what the result means
The result does not mean that the hydrocyclone and centrifuge combination has the lowest cash expenditure in every year. It means that, after annualizing the capital investment and combining it with yearly operating costs, its lifecycle burden is lowest on an equivalent annual basis.
EAOC Must Follow Technical Screening
Confirm that every option meets the process duty
EAOC should be calculated only for alternatives capable of meeting the required separation, heat-transfer, reaction, mixing, pressure, throughput, or residence-time specifications.
An inexpensive unit that cannot deliver the required process performance is not a valid economic alternative.
Check pilot-plant flexibility
Pilot facilities often support multiple experiments, materials, and operating conditions. A technically more flexible unit may justify a higher EAOC if it avoids purchasing additional equipment or enables a broader research program.
This benefit should be represented explicitly through avoided capital costs, operating savings, additional usable capacity, or another documented economic value.
Consider capacity and utilization
An option with a low EAOC at one throughput may become less attractive if it is undersized or requires extensive operator attention. Equipment comparisons should use the same process basis and realistic utilization assumptions.
For capacity expansions, incremental analysis can be more informative than comparing total plant costs. Incremental NPV can determine whether the additional investment creates sufficient savings or revenue relative to the baseline.
Understanding the Trade-offs
EAOC depends on assumptions
Service life, discount rate, energy prices, labor costs, maintenance requirements, and utilization are estimates. A small change in one of these inputs can change the ranking, particularly when alternatives have similar EAOCs.
Sensitivity analysis should test the effect of plausible changes in the most uncertain inputs.
Salvage value and replacement timing may matter
The basic EAOC equation provided assumes no explicit salvage value. If an asset has a meaningful salvage value, it should be included in the annualized capital calculation; otherwise, the capital charge may be overstated.
Replacement timing, refurbishment, and downtime should also be considered when they materially affect lifecycle cost.
The lowest EAOC is not always the best overall decision
EAOC does not by itself measure safety, operability, data quality, environmental performance, schedule risk, or compatibility with existing laboratory infrastructure.
A sound selection process first eliminates technically unacceptable options, then uses EAOC alongside these nonfinancial criteria.
Do not mix inconsistent cost estimates
Comparisons become unreliable when one option uses bare equipment cost while another includes installation, or when one YOC estimate includes labor and the other does not.
All alternatives should use the same cost boundary, process basis, currency year, discount-rate convention, and operating assumptions.
Making the Right Choice for Your Goal
EAOC is most useful when it is treated as the economic ranking within a broader engineering decision.
- If your primary focus is minimizing lifecycle cost: Select the technically feasible option with the lowest EAOC after using consistent installed-cost and operating-cost estimates.
- If your primary focus is comparing equipment with unequal lives: Use the capital recovery factor to annualize each investment over its own service life, and apply the same discount rate to all alternatives.
- If your primary focus is pilot-plant flexibility: Include the economic value of avoided future purchases, additional usable capacity, or yearly savings before comparing net EAOC.
- If your primary focus is a capacity upgrade: Compare the incremental capital and operating costs against the baseline and supplement EAOC with incremental NPV or another profitability measure.
- If your primary focus is decision reliability: Perform sensitivity analysis on service life, discount rate, utilization, energy, maintenance, and consumable costs.
Used with technical screening and transparent assumptions, EAOC turns competing pilot-plant equipment options into a consistent, defensible annual economic comparison.
Summary Table:
| Decision factor | What to evaluate | Why it matters |
|---|---|---|
| EAOC formula | Annualized capital cost + yearly operating cost - annual savings | Converts lifecycle costs into a comparable annual figure |
| Fixed capital investment | Equipment, installation, piping, controls, electrical work, and supports | Reflects the true installed investment |
| Yearly operating cost | Utilities, labor, maintenance, consumables, calibration, and waste handling | Captures the ongoing financial burden |
| Economic assumptions | Discount rate, service life, salvage value, utilization, and replacement timing | Determines the reliability of the comparison |
| Technical screening | Capacity, process performance, safety, flexibility, reliability, and compatibility | Ensures only feasible equipment is economically ranked |
| Selection rule | Choose the technically acceptable option with the lowest EAOC | Identifies the lowest annualized lifecycle cost |
| Example result | Hydrocyclone and centrifuge combination: $6,250/year EAOC | Lowest EAOC among the three separation alternatives |
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