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Free Air
When you use an air compressor, free air refers to atmospheric air at a given location. It is the air unaffected by the compressor, or the air available to the compressor for intake. Free air is the baseline measurement from which all compressed airflow is calculated. Understanding free air is critical for understanding compressor performance, sizing systems and ensuring your operations run reliably.
Air enters the air compressor intake from the surrounding environment, and its characteristics — such as pressure, temperature and humidity — affect performance. By measuring free air, operators can:
- Accurately calculate airflow requirements for tools and processes.
- Compare compressor displacement to actual usable air.
- Ensure proper air compressor sizing to meet current and future demand.
Understanding air at standard conditions, such as 14.7 pounds per square inch (PSI) at 68°F with 0% relative humidity, allows engineers and technicians to standardize measurements across locations and applications.
If you need more information, Quincy Compressor has put together online resources to help you learn more about FAD and related concepts. You can also contact us at any time to connect with our network of experienced air experts who can help you choose or optimize your system.
FAQs
Free Air Delivery (FAD), sometimes called standard free air, measures the volume of atmospheric air the compressor can deliver after compression. This value accounts for system pressure, temperature and losses, providing a consistent reference point for comparing compressors or sizing equipment.
FAD expresses the volume of atmospheric air delivered at the compressor intake, converted to standard conditions. For instance, a compressor may have a displacement of 100 CFM, but due to losses in the compression process, the FAD might be slightly lower. This distinction helps operators know exactly how much usable air is available for their end-use equipment.
Monitoring FAD is particularly important in demanding environments like automotive workshops, food and beverage production, or agricultural operations. Systems with insufficient free air can experience pressure drops, inefficiencies and excessive wear on components.
Proper air compressor sizing begins with understanding your free air requirements. Begin by calculating the total air demand for all machinery and processes that might run simultaneously. Compare this to the FAD rating of potential compressors to ensure continuous, stable operation.
Standard conditions provide a consistent reference for FAD measurement, allowing accurate comparison across compressors and locations.
Yes. Temperature, pressure, humidity and altitude affect atmospheric air characteristics, influencing the volume delivered after compression.
You may not be able to change the environment where your facility is located, but you can change the intake temperature. For example, you can cool the intake air, which makes it denser and improves FAD. Using proper filtration or dryers also ensures the compressor receives clean air, which can help improve FAD.