Cooling tower fall shutdown: what to inspect, treat, and document before the system goes offline for the season.
Cooling towers and boilers share a seasonal rhythm. As the cooling season winds down and the heating season approaches, both systems need attention before the transition. The boiler that did not get a pre-season inspection becomes an emergency service call in January. The cooling tower that did not get a proper fall shutdown becomes a water treatment problem, a mechanical failure, or a Legionella risk the following spring when the system is brought back online.
The good news is that a thorough cooling tower fall shutdown takes a few hours and the findings are almost always manageable when they are addressed in the fall rather than discovered during the spring startup. What follows is what a proper cooling tower fall shutdown covers.
Water treatment and blowdown
The water treatment step happens before anything else. The cooling tower basin contains water that has been circulating through the system all season, concentrating minerals, biocides, corrosion inhibitors, and biological matter with every cycle of evaporation. Before the system goes offline, the water chemistry needs to be assessed and the basin needs to be treated.
A full water analysis at the end of the season confirms the current chemistry and identifies whether any constituents have concentrated to levels that could cause corrosion or scale during the shutdown period. Conductivity, pH, hardness, biological activity, and inhibitor concentrations should all be measured and documented.
Blowdown to reduce the cycles of concentration before shutdown reduces the mineral load in the basin water during the idle period. A basin that is left at high cycles of concentration over the winter is more aggressive toward metal surfaces than one that was bled down before shutdown.
A biocide treatment before shutdown addresses biological matter in the basin, the fill media, and the distribution system. Biological growth that is present at shutdown will continue to develop in the standing water during the idle period if it is not addressed. For systems that are subject to Legionella risk management programs under ASHRAE 188, the shutdown treatment should be documented as part of the water management program record.
Basin inspection and cleaning
With the water chemistry addressed, the basin should be drained and inspected. A full basin cleanout removes sediment, biological matter, and scale deposits that accumulate on the basin floor and walls over the course of the season. Sediment that is left in the basin over the winter provides nutrients for biological growth and can clog strainers and distribution nozzles when the system is restarted in the spring.
Inspect the basin for corrosion, cracks, and damage to the liner or coating. A basin with active corrosion or a damaged liner will continue to deteriorate over the winter and may require repair before the system can be safely restarted. Catching this in the fall gives time to plan and schedule the repair before the cooling season resumes. Discovering it during spring startup means the system may not be available when it is needed.
Check the makeup water connection and the float valve for correct operation. The float valve controls the water level in the basin during operation. A float valve that is sticking or leaking will cause the system to overfill or run low during the next operating season.
Fan, motor, and drive inspection
The fan, motor, and drive components should be inspected before the system goes offline for the season. Inspect the fan blade condition for erosion, cracking, or debris damage. A fan blade that has lost material or developed a crack during the season will continue to deteriorate over the winter and may fail during the spring startup when the system is brought back to full speed.
Check the fan shaft bearings for play, noise, and lubrication condition. Bearings that were running warm or making noise at the end of the season should be replaced during the shutdown rather than left to fail during the next operating season. Repacking or replacing bearings during a planned shutdown is a fraction of the cost of an emergency replacement when the cooling system is needed.
For belt-driven cooling towers, inspect the belt for wear, cracking, and proper tension. A belt that is worn or cracked at the end of the cooling season should be replaced during shutdown. For direct-drive towers, inspect the motor coupling for wear and proper alignment.
The motor should be checked for moisture ingress, particularly in outdoor towers where the motor has been exposed to weather throughout the season. Moisture in the motor windings can cause insulation degradation that leads to motor failure. If the motor shows signs of moisture or if the insulation resistance is below acceptable limits, the motor should be dried out or replaced before shutdown.
Fill media, drift eliminators, and nozzles
Inspect the fill media for biological fouling, scale deposits, and physical damage. Fill media that is heavily fouled reduces heat transfer efficiency and provides a surface for biological growth during the shutdown period. Heavily fouled fill may need to be replaced rather than cleaned if the deposits cannot be removed without damaging the media.
Drift eliminators should be inspected for damage and debris accumulation. Drift eliminators that are missing sections or that have collapsed allow excessive drift discharge, which wastes water during operation and can create Legionella exposure risk.
Distribution nozzles should be inspected and cleaned. Plugged nozzles create uneven water distribution across the fill media, reducing heat transfer efficiency and creating dry spots that are prone to biological growth. Cleaning nozzles during shutdown is significantly easier than cleaning them during operation.
Freeze protection for cold climates
For cooling towers in climates where freezing temperatures occur during the shutdown period, freeze protection is required to prevent damage to the basin, the piping, and any water-containing components that are not drained.
The basin should be drained completely or, where the basin cannot be fully drained, protected with basin heaters sized for the expected ambient temperatures at the site. Basin heaters that are left without a functioning thermostat or that are undersized for the site conditions will not prevent freeze damage.
All exposed piping that contains water should be drained or heat-traced. The makeup water connection, the blowdown line, and any instrumentation connections that contain water are freeze risks if not addressed.
Documentation
The shutdown documentation should record the water chemistry at shutdown, the blowdown and biocide treatment performed, the basin inspection findings, the fan and motor inspection results, and any deficiencies identified along with the corrective action taken or planned. For systems under an ASHRAE 188 water management program, the shutdown documentation is a required record that should be maintained with the program file.
This documentation becomes the baseline for the spring startup. A cooling tower that was properly documented at shutdown can be restarted with confidence that the system is in known condition. One that was shut down without documentation requires a full inspection at startup to establish the baseline that should already exist.
For facilities coordinating cooling tower shutdown with boiler pre-season startup, the GP Energy Products team handles commercial boiler inspections across Pennsylvania, New Jersey, Delaware, and Maryland. The same window that allows a proper cooling tower shutdown also allows a boiler pre-season inspection before heating season begins. Visit gpenergyproducts.com for more on GP Energy’s pre-season boiler inspection capabilities. For condenser water heat exchangers and coils that should be inspected on the same schedule, the HX Coils team handles custom coil fabrication and replacement across the Mid-Atlantic. Visit hxcoils.com for more.
References
1. Cooling Technology Institute. CTI Legionella Position Statement and Water Treatment Guidelines. Covers biological risk management for cooling tower systems including seasonal shutdown treatment. cti.org
2. ASHRAE Standard 188. Legionellosis Risk Management for Building Water Systems. Covers water management program requirements for cooling tower systems including shutdown documentation. ashrae.org
3. ASHRAE Guideline 12. Minimizing the Risk of Legionellosis Associated with Building Water Systems. Covers cooling tower inspection, treatment, and shutdown procedures. ashrae.org
4. Cooling Technology Institute. CTI Standard STD-201. Governs cooling tower performance testing and maintenance standards. cti.org