What are the three fan laws?

1) Flow Q ∝ N (speed); 2) Pressure ΔP ∝ N²; 3) Power P ∝ N³. For impeller diameter D changes: Q ∝ D³, ΔP ∝ D², P ∝ D⁵. These laws (per ASHRAE and AMCA standards) allow performance prediction at new operating conditions without retesting.

Why does a 10% speed reduction save so much energy?

Because power scales with the cube of speed (fan law 3), a 10% speed reduction gives approximately 0.9³ = 0.729, i.e., ~27% power savings. This makes variable-speed drives (VSDs) extremely effective for fan energy management.

Fan Law Speed Ratio Calculator

Apply the affinity laws (fan laws) to predict airflow, pressure, and power changes when fan speed or impeller diameter changes.

2D stress state at a point. All stresses in MPa.

σx — Normal Stress X (MPa)

σy — Normal Stress Y (MPa)

τxy — Shear Stress (MPa)

⚙ Mechanical Note: Results are based on standard textbook formulas and ISO/AASHTO references. Always verify critical designs with applicable codes (ISO 898, AASHTO 1993, AISC, Eurocode 3) and a qualified engineer.

How to Use

Enter the values for the patient or scenario you are assessing. Apply the affinity laws (fan laws) to predict airflow, pressure, and power changes when fan speed or impeller diameter changes. Use the fan laws result to inform your clinical assessment.

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Fan Law Speed Ratio Calculator

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Frequently Asked Questions

What are the three fan laws?

Why does a 10% speed reduction save so much energy?