How to Size an Oil-Free Screw Air Compressor
A shortlist is defensible only when the operating point and system losses are documented.
1. Measure or calculate demand
Separate average, normal, peak and minimum demand. Include production growth only when tied to a real project plan. For an existing plant, log flow and pressure over representative shifts. For a new plant, build an equipment schedule with load factors and simultaneous-use assumptions.
2. Calculate required compressor pressure
Add the process inlet pressure to pressure losses through treatment, receivers, valves and piping. Check clean and dirty-filter conditions. Avoid raising compressor set pressure to compensate for an avoidable piping restriction; excess pressure increases energy use and may reduce FAD at the required row.
3. Match control strategy
Variable-frequency models publish an FAD range and can follow changing demand within the offered control envelope. Fixed-speed models publish one FAD per row and are suited to stable load or sequenced base load. Compare minimum demand, starts per hour, receiver volume and redundancy.
4. Correct for site and verify
Altitude, inlet temperature, humidity, cooling conditions and electrical frequency can change capacity or limits. Request a performance statement at the stated site conditions. Confirm reference conditions, tolerances and acceptance test method before placing the order.
Selection worksheet
- Normal/peak/minimum FAD
- Pressure at process inlet
- Pressure losses
- Ambient temperature and altitude
- Cooling utility
- Air quality class
- Operating hours
- Redundancy
- Power supply
- Local compliance