Cooling Tower Systems may have periods of time when they are in low-to-no use. Reasons may include change of seasons, scheduled or unscheduled maintenance, and low load. During these standby or idle conditions, cooling systems should ideally be free of water. However, this is not always possible. If the cooling system must remain full of water during standby or idle conditions, the cooling system must continue to be properly maintained to minimize microbial growth and corrosion. Without proper maintenance, idle conditions can cause fouling and premature failure of the cooling components and microbiological health concerns. Taking the steps below will greatly reduce excess costs due to failed equipment, decreased efficiency during start up, and spread of waterborne illness.
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- Cooling tower corrosion and scale inhibitors need to be added and monitored during idle periods. Over time, the protective films formed by these inhibitors breakdown, leaving chiller condensers, piping, and heat exchangers vulnerable to pitting and general corrosion. Replenishing and monitoring levels will keep systems as protected as possible.
- Routine feed of biocides is essential during these idle periods. Idle cooling water systems can also provide ideal conditions for microbiological activity, including Legionella bacteria. The growth of anaerobic, sulfate reducing and iron related bacteria can cause corrosion and fouling concerns. These problems can lead to loss efficiency and premature failure of system components. Enhance heat exchanger tubes are more prone to these corrosion and fouling problems.
- We recommend that during these standby or idle periods of time the cooling tower water is circulated daily for 2-4 hours, making sure there is cooling water flow through all the equipment and heat exchangers. When the system is circulating, the oxidizing biocide should be feed into the system to maintain proper microbiological control. The non-oxidizing biocide should also be fed at least weekly during this standby period. The dosage of the biocides should be lower than what is typically used when the cooling tower is operating normally. Routine bacteria testing should still be performed to verify good microbiological control.
- During this period of time the cooling tower inhibitor needs to replenished and maintained at the recommend dosage in the cooling tower. In order to limit the retention time of the cooling tower inhibitor, the normal conductivity level of the tower should be reduced, to lower the tower cycles. The amount of the reduction will depend on the system and the makeup water quality. However, if you typically maintained 10 cycles in the tower, a 50% reduction in the conductivity level will be necessary.