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Fan Affinity Law Scenario Calculator

Let r be new speed divided by positive reference speed.

196 / FAN AFFINITY LAW SCENARIO

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Starting values are illustrative. Use your own costs, rates and assumptions.

INPUT GROUP 01

Entered quantities and model assumptions

Illustrative defaults are examples. Replace them with matching measurements, reviewed properties and actual quote terms.

Check the assumptions before acting on a result.

Read the method and example

YOUR CALCULATION

Apply ideal fixed-geometry speed-ratio similarity.

New / reference rotational speed

0.8

Ideal scaled flow · entered flow units

8

Ideal scaled pressure · Pa

320

Ideal scaled shaft power · kW

5.12

Keep the calculation

Saving is optional and stays on this device. Unsaved edits are not kept when you leave. CSV includes every input and the current results.

Illustrative inputs loaded. Replace them with your own assumptions.

How the fan affinity law scenario calculator works

Let r be new speed divided by positive reference speed. Ideal flow scales by r, matching pressure by r² and shaft power by r³. The reference and new cases assume the same fan geometry, compatible density and applicable operating similarity.

These are ideal laws, not an actual system-curve intersection. Shaft power is not automatically electrical input. No safe speed, available motor power, ventilation adequacy, permitted modification or real energy-saving guarantee is established. Do not use this speed-only model for impeller trimming or density changes.

Quantities use the stated units and finite bounded inputs. Whole purchases round up under the documented model; cost components round half-up to cents before totals are summed. Undefined ratios stay unavailable. π and logarithms use normal numeric precision. Display rounding does not alter the entered assumptions.

Worked example

At a speed ratio of 800/1,000 = 0.8, 10 m³/s becomes 8, 500 Pa becomes 320 and 10 kW shaft power becomes 5.12. Restoring new speed to 1,000 rpm returns the ideal shaft power to 10 kW.

Sources and assumptions

The source material explains the underlying calculation or pricing structure. Entered prices, costs, schedules and scenario choices are your assumptions; this tool does not obtain supplier quotes or predict actual results.

  • Fan Air Power

    Air power in kW = actual cubic metres per second × pressure rise in Pa ÷ 1,000.

  • Planar Thermal Conduction

    Area-normalized resistance in m²·K/W is the sum of each layer’s thickness in metres divided by conductivity in W/(m·K).

  • Cooling Energy Cost

    Convert entered useful cooling energy through a matching COP or EER convention to an electrical-energy cost.

  • Equipment Electricity Cost

    Estimate electricity use from input power, equipment count and operating time. Apply your energy rate and a separately entered monthly charge.

Calculation methods, testing and sources · Practical calculation guides