Compare the cost of delivering the same workload and service level over one common, explicitly hypothetical future period—not the price of old equipment against the price of new equipment.
A two-option matrix helps separate equipment spending, operating energy, facility effects and lifecycle work. Without site-specific costs, loads and service-life assumptions, it cannot identify a cheaper option.
Data center deep-dive series
What must both options deliver?
The short answer is to hold the service and comparison period constant, then ask what each option would require to deliver them. The matrix below shows where to put the costs; the energy boundary and missing evidence determine whether those entries can eventually be compared.
Suppose, hypothetically, that an existing fleet and a proposed replacement must handle the same transactions and other work for the next three years. Three years is an example, not a recommended ownership period or an estimate of either fleet’s life.
Specify the work by time of day, including low-load operation, plus the required storage, network capacity and continuity. The fleets need not have identical utilization: the question is whether each can provide the same service. The U.S. Department of Energy (DOE) describes server efficiency in work per watt, but that measure alone does not establish the cost of delivering the service.
Set the start and end of the period and ask whether either option needs repair, an upgrade or another replacement before it ends. State how a purchase made before the start is treated rather than entering its old invoice as a new purchase.
DOE’s Best Practices Guide for Energy-Efficient Data Center Design raises first cost versus life-cycle cost; it does not prescribe an accounting rule for historical purchases, depreciation or residual value. Reliability is a requirement for both options, not a saving to assign to one without evidence about outages and their costs.
U.S. Department of Energy — Best Practices Guide for Energy-Efficient Data Center Design
IBM — What Is a Data Center? | IBM
IBM — What Is a Green Data Center? | IBM
What belongs in each column?
Use this as a question sheet for the hypothetical on-premises comparison, not as a published cost model or a quotation. Leave monetary entries blank until project information is available. For each row, mark what is common to both options, conditional on a real change, excluded with a stated reason, or unknown.
A common cost can appear consistently in both totals or be set aside when examining only their difference; it is not an option-specific saving.
Equipment and deployment
- Retain existing equipment
- State the treatment of the earlier purchase; identify necessary upgrades
- Replace equipment
- Separate acquisition from installation and deployment
- Boundary to record
- Record future expenditure and timing; leave unquoted amounts unknown
IT electricity
- Retain existing equipment
- Assess energy for the specified work and load profile
- Replace equipment
- Assess energy for that same work and profile
- Boundary to record
- Use the same period and measurement boundary
Storage and networking
- Retain existing equipment
- Identify required capacity, redundancy, equipment and energy
- Replace equipment
- Identify anything the refresh would change
- Boundary to record
- Mark genuinely unchanged shared items as common, not savings
Supporting facility
- Retain existing equipment
- Check affected cooling, fans, UPS and distribution
- Replace equipment
- Check load effects and any necessary power or cooling changes
- Boundary to record
- Include modifications or specialized cooling maintenance only if required
Maintenance and later work
- Retain existing equipment
- Check repairs, refurbishment, upgrades and component replacement
- Replace equipment
- Check maintenance and any further intervention within the period
- Boundary to record
- Record whether and when work is needed; do not assume either option needs none
Service and thermal fit
- Retain existing equipment
- Check continuity and operating conditions
- Replace equipment
- Check the same requirements and site cooling capacity
- Boundary to record
- Establish feasibility before assigning a cost or benefit
End-of-use treatment
- Retain existing equipment
- Consider continued use, refurbishment or eventual recycling
- Replace equipment
- Consider the removed equipment and the replacement’s status at period end
- Boundary to record
- Enter disposal costs or remaining value only with project evidence
A replacement does not automatically require a cooling rebuild, nor does retention mean maintenance-free operation. DOE advises checking initial, future and low-load cooling conditions.
It also distinguishes recommended operating conditions from manufacturers’ allowable functionality boundaries; being within an allowable boundary is not, by itself, a reliability guarantee. IBM’s equipment-lifecycle discussion identifies upgrades, refurbishment, reuse and responsible recycling as possibilities, but provides no prices or dates for this project.
How do you keep electricity costs from being counted twice?
Estimate IT electricity for the same work under each option’s plausible operating-load profile, including part- and low-load periods. Check storage and network energy where those systems change. DOE explains that an IT-load change can also affect cooling and electrical systems, but it does not establish a saving for this particular site.
Record affected facility energy—such as cooling, fans, UPS and distribution losses—without claiming that the shared facility’s entire bill changes with one equipment choice.
Label the meter boundary before adding energy rows. A total-facility electricity figure already includes IT and supporting loads; an IT-only figure does not. Adding cooling or UPS consumption again to the facility total would double-count it.
PUE relates facility energy to IT energy; it is performance context, not a monetary total or an extra multiplier for an already measured facility total. Water and carbon measures likewise need their own boundaries and cost evidence before they become cost entries.
Converting energy into charges requires this facility’s applicable prices and, where relevant, demand charges or contract terms. DOE’s illustrative electricity price is not a tariff for this comparison. Label each energy input measured, supported estimate or unavailable.
DOE recommends metering, including where electrical-chain losses matter, and discusses retaining measurements for at least one year to obtain annual energy totals. That monitoring guidance does not set the length of the hypothetical ownership-cost period.
When does this stop being an on-premises refresh comparison?
If one option moves the workload to cloud or colocation, redraw the cost boundary. The same delivered service and period still matter, but ownership and responsibility for equipment, space, power, cooling and operations differ.
In a traditional colocation arrangement, a customer can own and manage its IT equipment while renting facility services; management services may also be offered. A cloud arrangement assigns infrastructure operations differently. Compare the responsibilities and charges in the proposed contract rather than placing a service fee into the on-premises equipment column.
What would make a cost decision possible?
First confirm that both options meet the specified service and continuity requirements. Then fill the matrix with acquisition and deployment quotes, likely intervention dates and costs, credible remaining-life assumptions, load-based energy measurements or supported estimates, applicable electricity terms and the facility changes each option would actually cause. Keep unresolved entries visible rather than replacing them with assumed savings.
The general guidance cannot rank these options or establish a break-even point. Its useful implication is narrower: once common costs are separated from costs caused by each choice, the missing measurements and quotations become clear—and only then can a project-specific total-cost comparison support a decision.
Sources
- IBM — What Is a Data Center? | IBM
- IBM — What Is a Green Data Center? | IBM
- U.S. Department of Energy — Best Practices Guide for Energy-Efficient Data Center Design
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