Planning guide / energy-cost
Introduction
The data-center energy-cost calculator estimates monthly and annual energy charges, demand charges, combined totals, and an annual energy-cost comparison from a per-rack IT load, rack count, electricity rate, power usage effectiveness, and demand-charge input. Use it to compare planning cases with a consistent set of assumptions or to make the effect of PUE and rack count visible before using a utility bill or tariff model.
The calculator fixes its monthly window at 730 hours and uses 12 months for annual totals. Enter the electricity rate in dollars per kWh and a demand charge in dollars per kW per month; the demand charge starts at zero. PUE must be at least 1. The page applies PUE to each rack’s IT energy and demand as a simplified planning allocation.
The example rate is only an editable input, not an offer or a claim about any utility price. Real bills can contain time-of-use rates, taxes, riders, minimums, power-factor terms, ratchets, seasonal demand, and billing windows that this tool does not represent. Use actual tariff documents and interval data for a financial analysis.
Method / Calculation
How it works
IT energy per rack is entered IT kW multiplied by 730 hours. Facility energy per rack multiplies that result by PUE. This turns a rack IT-energy estimate into a simplified facility-energy allocation; the calculator explicitly notes that overhead may not scale linearly with rack count.
Energy cost multiplies facility kWh by the entered rate. Annual energy cost is monthly energy cost multiplied by 12. The all-rack totals multiply the per-rack amounts by rack count. With a fixed rate and identical rack loads, this is a straightforward scaled scenario rather than a measured facility bill.
Demand cost per rack uses IT kW times PUE times the entered flat monthly demand charge. The tool adds that amount to energy cost for total cost. Actual utility demand billing may be calculated at a site or account peak and may not allocate linearly by rack, so the per-rack presentation is an assumption in this model.
The annual savings metric applies a PUE reduction of exactly 0.1 to IT load, 730 hours per month, 12 months, and the electricity rate. It includes the modeled energy charge only. It does not subtract demand charge savings or estimate a retrofit outcome.
IT kWh/month = IT kW per rack × 730 h
Facility kWh/month = IT kWh/month × PUE
Energy charge = facility kWh × rate; annual energy = monthly charge × 12
Demand charge = IT kW × PUE × entered $/kW/month
Annual 0.1-PUE energy comparison = IT kW × 0.1 × 730 × 12 × electricity rate
- Choose an IT kW per rack value and a positive whole rack count that represent one scenario. Keep the rack count and load basis consistent across comparisons.
- Enter a per-kWh rate from the tariff or planning assumption being evaluated. The tool accepts a nonnegative rate; retain the source and effective date outside the calculation.
- Enter PUE at or above 1.0. The model multiplies IT energy and power by PUE; it does not calculate PUE from facility meter data.
- Enter the flat monthly demand charge if you want it included. The default of zero is a valid scenario and leaves energy cost as the only modeled charge.
- Multiply IT kW by 730 to get monthly IT kWh, then apply PUE and the rate. Multiply per-rack amounts by rack count and by 12 for annual totals.
- Read the 0.1-PUE comparison as an annual energy-cost calculation only. Compare the inputs with a bill, tariff, and measured facility profile before using the output in a budget.
The page cites The Green Grid, White Paper #49, PUE: A Comprehensive Examination of the Metric (2012). Its 730-hour month, demand allocation, and fixed 0.1-PUE comparison are stated calculator assumptions, not utility pricing or an expected savings claim.
For a more detailed financial model, reconcile the meter boundary, billing period, tariff schedule, demand determinant, taxes and riders, seasonal changes, actual rack utilization, and PUE measurement method. This page does not import or verify any of those records.
The per-rack view is a normalization aid: it can help compare scenarios with a common rack basis, but it does not mean the utility bills each rack separately. The rack count scales the displayed scenario linearly, so an entered facility average may conceal unequal loading, reserved capacity, or changes over time. For a month-to-month comparison, use a consistent time window and meter boundary, and distinguish billed demand from an energy charge. Preserve the rate source and effective date with the calculation; a sample rate is only an editable example. The page’s energy-only PUE comparison intentionally does not include demand-charge changes or establish an achievable efficiency improvement.
Calculation trace / Illustrative inputs
Fully worked example
Illustrative calculation using the calculator’s defaults: 10 kW IT load per rack, one rack, $0.12/kWh as a sample editable rate, PUE 1.5, and $0/kW/month demand charge. The rate is a demonstration input, not a statement about a real utility tariff.
- IT energy per rack = 10 kW × 730 h = 7,300 kWh/month.
- Facility energy = 7,300 kWh × 1.5 PUE = 10,950 kWh/month.
- Energy charge = 10,950 kWh × $0.12/kWh = $1,314/month. Annual energy charge = $1,314 × 12 = $15,768.
- Demand charge = 10 kW × 1.5 × $0/kW/month = $0/month. Total modeled cost therefore remains $1,314/month or $15,768/year for one rack.
- Annual energy-cost comparison for a 0.1 lower PUE = 10 kW × 0.1 × 730 × 12 × $0.12 = $1,051.20. This excludes demand-charge changes.
Illustrative calculator result: 10,950 facility kWh per rack per month, $1,314 monthly modeled energy cost, $15,768 annual energy cost, and a $1,051.20 annual energy-only comparison for 0.1 lower PUE.
The example uses a sample rate and a fixed 730-hour month. It excludes tariff structure and other bill components. Planning estimate only; use actual utility records and a consistent meter boundary for financial decisions.
Review / Input checks
Common mistakes
- Treating the sample electricity rate as a live tariff. The page starts at $0.12/kWh as an editable demonstration value. Replace it with a documented applicable rate and record the tariff period; the calculator does not look up current prices.
- Using calendar months against the 730-hour window. The calculation intentionally uses 730 hours for every month. It does not vary month length, include leap years, or model partial billing periods.
- Assuming PUE is calculated by the tool. PUE is an entered value. The page applies it to rack energy and facility power; it does not measure IT or facility meters or assess whether the entered PUE uses a particular boundary.
- Allocating a site demand charge per rack without checking the tariff. The model applies one flat charge to each rack’s IT kW times PUE. Actual billing determinants and coincident peaks may not scale in that way, so review the tariff and site load profile.
- Reading the PUE comparison as a forecast. The savings output assumes an exact 0.1 PUE decrease with the same load, rate, hours, and rack count. It is an arithmetic comparison and does not model an efficiency project or guarantee a result.
Questions / Planning use
Frequently asked questions
Why does the calculator use 730 hours per month?
It is the fixed monthly window stated by the calculator. Monthly kWh and charges use that value, and annual values multiply the monthly result by 12 instead of using calendar billing periods.
Does the entered PUE come from a meter calculation?
No. PUE is an input. The calculator multiplies IT energy and power by that value as a planning allocation; it does not calculate or validate PUE from facility and IT meter readings.
How is the optional demand charge applied?
The tool multiplies IT kW per rack by PUE and the flat entered dollars-per-kW-per-month charge. It then scales that per-rack value by rack count. Confirm the actual tariff determinant before using the result.
Does the 0.1 PUE savings figure include demand charges?
No. The formula uses IT kW, 0.1, 730 hours, 12 months, and the electricity rate. It estimates an energy-charge comparison only and leaves demand-charge changes out.
What source basis does this page cite?
The calculator cites The Green Grid, White Paper #49, PUE: A Comprehensive Examination of the Metric (2012). The rate, fixed monthly hours, demand allocation, and 0.1 comparison are separately identified as assumptions.
Continue / Related tools
Related calculators
- PUE calculator
Review a separate PUE calculation before entering a ratio into the energy-cost scenario.
- Generator fuel burn and runtime calculator
Estimate standby fuel requirements separately from utility energy charges.
- Rack power density and PDU planner
Compare rack-level power assumptions before multiplying a load by facility PUE.