Chilled Water Treatment for Closed-Loop Systems

A closed loop does not lose water to evaporation, so it does not concentrate like a cooling tower. But it is never perfectly closed. Make-up water brings oxygen and dissolved salts, air enters through vents, joints and during maintenance, and mixed metals set up galvanic cells. Carbon steel pipework in a loop with copper coils and aluminium parts is a common case. Corrosion in a closed loop is slow, but the damage is hidden until a leak appears or deposits block a coil.

Nitrite promotes the formation of a thin, stable oxide layer on steel that slows further corrosion. Advanced Chemicals Industrial supplies a nitrite-based inhibitor for closed-loop chiller systems. The film only forms and holds when enough nitrite is present, so the level must be checked and kept, which is why the residual is the central control parameter. The treatment rate is set by our technical team from the system water analysis and operating conditions.

Yes, although less visible. Nitrite is itself a nutrient for some bacteria, and warm sections of a loop, dead legs and low-flow branches allow growth. Slime lowers heat transfer and can attack metal beneath the deposits. Where microbiological tests show growth, a biocide suitable for closed loops is used. We supply cooling system biocides based on isothiazolinone (CMIT/MIT) and on DBNPA, and our technical team advises which suits a given loop and how it interacts with the nitrite program.

Start with a mechanical clean: drain, flush to remove debris, welding residue and oil, and refill with water of known quality. Treat the loop before it operates, test the residual after circulation, and record the first results as the reference. A loop treated while still dirty will never hold its residual.

Take samples from a point of good circulation, not from a dead leg, and test promptly because some parameters change in the bottle. Sample from the same point each time so that the trend is meaningful. Check strainers and filters when you can, as they collect debris and show the condition of the loop.

Not as a habit. Each refill resets the protection and brings new oxygen. A drain is justified by water that cannot be brought back into range, heavy contamination, or major repair, and it should always be followed by the full start-up routine.

Send your operating data and a recent water analysis to our technical team for a technical review. Technical data and product samples are available through the team.