TL;DR
Reduced capacity is usually scaled fill blocking air-water contact, low water flow, or a fan running below design speed. Inspect fill, measure flow, and verify fan RPM.
What you might see
- leaving water temperature above design point
- condenser supply water warmer than normal
- reduced approach temperature to wet bulb
- process cooling inadequate under normal load
Likely causes
Scaled or fouled fill media blocking air-water contact surface
Low circulating water flow from a worn pump, throttled valve, or clogged strainer
Fan running below design speed from belt slip, worn sheaves, or motor underspeed
Clogged spray nozzles causing uneven water distribution over fill
Required tools
- Calibrated thermometer or thermocouple
- Wet-bulb thermometer or sling psychrometer
- Tachometer (contact or non-contact)
- LOTO kit
- Nozzle pick or small wire brush
- Flow meter or pump curve data
Safety first
- Lock out the fan motor before entering the tower plenum. Fan blades are not guarded inside the tower.
- Cooling tower basins may contain biological hazards including Legionella. Wear gloves and eye protection when working near basin water.
Procedure
- 1
Record the entering and leaving water temperatures and the ambient wet-bulb temperature. Compare them to the original tower design conditions.
- 2
Lock out the fan motor and circulating pump before any physical inspection.
Warning: Rotating fan blades cause severe injury. Lock out before entering the tower plenum. - 3
Inspect the fill media from above and below. Look for scale deposits, biological growth, or collapsed sections that restrict air flow.[1]
- 4
Measure the circulating water flow rate at the pump discharge. Compare to the design GPM on the Marley NC nameplate.
- 5
Check the inlet strainer on the pump suction for debris. Clean it if partially blocked.
- 6
Inspect each spray nozzle or distribution basin orifice for scale or debris. Clear blocked nozzles with a brush or nozzle pick.
- 7
Re-energize the fan and measure the fan RPM with a tachometer. Compare to the design RPM on the fan curve.
- 8
If fan speed is low, check belt tension and sheave wear. Adjust or replace belt as needed.[1]
- 9
If fill is heavily scaled, schedule a chemical descaling or fill replacement during the next planned shutdown.
Sources
Marley NC Cooling Tower User Manual, Marley Cooling (SPX Cooling Technologies)
Marley NC Cooling Tower Installation, Operation and Maintenance manual, performance and fill inspection procedures (general)
View source
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