Turndown ratio describes how far a variable speed compressor can reduce its output below full load while remaining efficient. A wide turndown lets one machine follow a variable demand without excessive start-stop cycles or blow-off.
Definition
- Ratio of maximum to minimum stable output
- Typical VSD screw range around 25 to 100 percent
- Wider turndown covers more demand variation
- Below minimum, the machine cycles on and off
Why it matters
Compressed air demand usually varies across the day. A compressor with wide turndown throttles smoothly and keeps efficiency high over more of the range, reducing the need for a second machine or a large storage buffer.
System design
Match the turndown range to your real demand profile, not just the peak. Combine a VSD base machine with fixed-speed trim machines and adequate storage, so the system covers both deep partial load and the peak.