It is common for vessels with chiller systems to not treat their chilled water; this can easily turn out to be a costly mistake. The chilled water is plumbed through-out a ship going to all the air handlers and can easily incorporate hundreds of feet of piping and a similar number of connections. There is one obvious problem when a non-operational system is exposed to below freezing temperatures. You can easily imagine the carnage that would result once the water starts expanding due to freezing. The other less understood phenomenon is deposit build-up in the closed loop. Just like the deposits that prevent heat exchange on the raw water side, the chill water loop can have the same problem. The common symptoms include proper loop temperature with not enough heat being removed by the air handlers and possible spot freezing of plate heat exchangers.
This build-up can occur for many reasons; one common reason is the use of materials that slowly break down with time, such as galvanized steel and certain glues. A system that is leaking and/or where the chill water is replaced multiple times can also contribute to the problem with the galvanic action of the new water. This is due to the loop not being able to Ph balance itself. The final common reason for sludge build-up is air inside the system. This can be the case if your chiller is not equipped with air elimination devices such as a Spirovent. The non-dissolved air bubbles will cause pitting through-out the loop and especially at the circulating pump’s impeller, as the air bubbles strike the surfaces. The air that is dissolved in the chill water will cause something called oxygen pitting which can also contribute to material build-up in the loop.
Dometic Corporation who is the maker of Marine Air and Cruisair chillers recommends the use of a glycol solution with the percentage of glycol determined by the climate the vessel cruises in. The percentage of glycol should be the minimum necessary for the expected temperature range as the glycol negatively affects heat transfer (more run time for your chillers). Do not use automotive antifreeze, as it contains silicates which cause pump seal wear and fluid gelation. The glycol solution should also contain a nitrite inhibitor which would counter act the caustic qualities of the glycol. If the vessel only cruises in the tropics it is acceptable to only use a nitrite inhibitor which protects the inner surfaces from mineral build-up and suspends existing particles in the fluid. By treating the chilled water the operator can look for a more trouble-free experience with their chiller system.