Engineering notes
Soft starter or VFD: a pump does not always need a drive
A soft starter only cuts inrush, then runs full speed. A drive changes speed with load. A PID on a valve or fan needs a drive.
The schedule says “15 kW soft starter”. The mechanical note wants the pump to follow load — that is a drive, not a soft starter. A soft starter lowers the inrush, then the motor runs full speed, cleaner than a star-delta. No 0–10 V speed, no pipe-pressure PID.
Fire pumps, on/off boosters, fans that never modulate: a soft starter (or direct-on-line if the file allows). AHUs, primary/secondary chilled-water pumps on differential pressure, VAV fans: a drive. Same 15 kW, two prices, two ways to talk to the BMS.
Read the file: “variable speed” or “soft start”. Size the drive