Cooling Tower Range

Range is what the load does, not what the tower does. It is set entirely by how much heat the plant dumps into the water and how fast the water circulates — a chiller condenser rejecting a fixed duty at a fixed gpm will show the same range in January as in July. The classic North American design point is 95 °F in, 85 °F out: a 10 °F range at 3 gpm per ton, which is exactly the 15,000 BTU/h of condenser heat a ton of refrigeration rejects.

Because range depends on flow, a falling range is a diagnostic, not a compliment. If the range on a constant-load condenser drifts from 10 °F down to 6 °F, the circulating flow has gone up — usually a fouled or bypassed control valve. If it climbs to 15 °F, flow has dropped: a plugged strainer, an air-bound pump, or a partially closed isolation valve. Watch the range and the approach together and you can separate a hydraulic problem from a heat-transfer problem without opening anything.