Add the measured energy in each state
Annual electrical energy in kWh = loaded kW × loaded hours + unloaded kW × unloaded hours. Multiply by your tariff in £/kWh for annual electricity cost. The selected loaded/unloaded model assumes zero air delivery while unloaded and no energy outside the entered operating hours.
For electric compressors only, use measured whole-machine package electrical input, including the components within that measurement boundary. Motor nameplate or shaft power is not a measurement of consumed power. Variable-speed operation and varying load profiles are not modelled by these two states; use representative measurements and a suitable separate assessment for those systems.
Add delivered flow only when measured
Loaded specific electrical input = loaded electrical kW ÷ loaded FAD in m³/min. This ratio describes the measured operating point; it does not predict CFM from a motor kW rating. Flow and input must be measured together at the same working pressure and reference conditions.
Annual delivered reference air = loaded FAD × 60 × loaded hours. Divide total annual energy, including unloading, by that volume for kWh/m³; divide the electricity cost by it for £/m³. With no loaded hours, those per-volume figures are unavailable. Leave optional flow blank if it is unknown; the energy calculation still works.
Worked example: loaded and idle energy
30 kW × 3,000 h + 8 kW × 1,000 h = 98,000 kWh/year. At an example £0.25/kWh, electricity costs £24,500/year. With measured loaded FAD of 5 m³/min, loaded specific power is 6 kW/(m³/min), and annual delivered air is 900,000 m³. Including unloaded energy gives an annual average of 0.108888889 kWh/m³ and approximately £0.0272222/m³.
Use a consistent comparison
This is a whole-machine energy balance extending the energy-cost principle in the DOE leak guidance. It is not a DOE-certified calculator. It excludes hire charges, transport, treatment energy outside the measurement boundary, fuel, maintenance, standing and capacity charges, and VAT unless already included in your tariff. Diesel compressors are outside this electrical model. It does not promise savings from a different compressor or a leak repair.
Use the leak cost calculator for allocating measured leakage cost, and the hire cost guide for the complete quotation checklist.