1. Define the thermal requirement
Record the heat dissipated into the air, maximum ambient temperature, allowable component temperatures and available airflow path. Identify filters, guards, heat sinks and vents that restrict flow.
2. Estimate airflow from heat load
For sensible heat carried by air, an initial estimate follows Q = P / (ρ × cp × ΔT), where Q is volumetric flow, P is heat load, ρ is air density and cp is specific heat capacity. Using approximate room-temperature air properties gives:
Example: 100 W and 15 K give approximately 0.33 m³/min, or 11.8 CFM.
This estimate does not account for every heat path, local hot spot or installation loss. Air density changes with temperature and altitude.
3. Find the installed operating point
A fan’s maximum airflow is normally a free-air rating. Maximum static pressure is a different point on its curve. The installed airflow is determined by the intersection of the fan curve and system resistance curve.
Do not assume a fixed percentage of free-air flow will be delivered in every enclosure. Use measured or estimated system resistance and confirm the result by testing.
4. Check the complete configuration
- Frame dimensions, thickness, mounting holes and clearance
- Supply voltage, frequency where applicable and start-up conditions
- Noise, vibration and installation orientation
- Operating temperature, bearing and expected duty
- Connector, wiring, control and monitoring requirements
5. Validate in the equipment
Measure temperatures at the relevant components under the expected worst-case load. Include filter loading and the operating environment in the validation plan. Record the selected model, supply conditions and installation arrangement.
Useful unit conversions
| From | To |
|---|---|
| 1 CFM | 0.02832 m³/min · 1.699 m³/h |
| 1 m³/min | 35.31 CFM |
| 1 mmH₂O | 9.80665 Pa |
| 1 inH₂O | 249.09 Pa |
Engineering overview. Final selection requires model-specific documentation and validation in your application.