Engineering notes
Chilled-water flow switches: a tank float is not an AHU pipe
An AHU needs proof of flow before the chilled valve opens. A paddle switch matches the pipe size. A tank float is a different article.
AHU interlocks often ask: the pump is running, and the pipe has flow. The take-off issues a roof-tank float because it is a “water sensor”. A float does not know whether DN65 is moving. The chiller drops on interlock for a missing flow switch — not for “bad software”.
Pick the paddle by DN, flow direction, NO/NC to match the logic (no flow = fault). A vertical pipe or a tight elbow makes the paddle stick or lie. If the file writes a 4–20 mA flow meter, that is a different price — do not swap a switch and call it “still a water signal”.