Corrosion and Bacterial Problems in Off-line Chillers

Many large commercial and healthcare facilities are designed with multiple chillers that get their condenser water from a single large tower water system. During the summer months, when the comfort cooling demand is high, there is a regular flow of tower water through all of the chillers. The tower system is treated with a corrosion inhibitor, an oxidizing biocide and a non-oxidizing biocide that are designed to control corrosion and bacterial growth in the system.

During the cooler months, it is often the case, that only a single chiller is needed to provide comfort cooling to the building. This may leave one or more chillers idle for long periods of time. In most cases, there is a motorized valve, on the inlet side of the chillers that interrupts the flow of tower water to the chillers that are not running.

The chillers that are offline, see no flow, and become a large dead leg. Because there is no regular flow of water through these chillers, no inhibitor or biocide will be introduced. The lack of chemicals will accelerate corrosion and bacterial growth inside the tube bundles of these machines. A secondary problem associated with this condition is the potential for bacterial growth (Legionella) inside the idle chillers that may migrate into the bulk tower water.

The solution to this problem is your Energy Management System. Biocides are added by a specific timed program. Simply program your computer system to open the valves that control the flow of water through the idle chillers when a biocide addition is happening. This will allow treated tower water to enter the chiller bundle thus eliminating the biological and corrosion problem.

Brian R. Cusick CWT

The Metro Group, Inc.