Managing water in high-temperature heat transfer systems is not only important for smooth operations, but also for safety. Taking steps to prevent water from entering your system can help avoid unnecessary complications.

Precautions

To keep your system running reliably, never use water for pressure testing. Regularly inspect water-side heat exchangers and monitor them for leaks. When storing heat transfer fluid, especially in drums, make sure they’re sealed and sheltered. If outdoor storage is unavoidable, position drums on their side to prevent water from collecting on top. Dedicated pumps and hoses for heat transfer fluid help prevent cross-contamination from water or other liquids.

Keep in mind that systems operating in humid environments can draw in moisture. Also, if fluid in the expansion tank drops below the dew point, condensation can form and gradually accumulate water.

Detection Prior to Start-up

The good news is that most heat transfer fluids don’t mix with water, so if a significant amount is present, it will form a visible layer. Drawing a sample from the system’s lowest point while it’s off makes detection easier. While large amounts of water are obvious, smaller amounts—just a few hundred ppm—are harder to spot but can still cause operational problems.

Detection at Start-up

During system start-up, if things go smoothly until the fluid temperature approaches 104°C (220°F), trapped water may be the culprit behind any issues. As the fluid warms, it becomes thinner, and you might notice a gradual drop in pump pressure—that’s normal. However, if you see a sudden pressure drop at around 93°C (200°F) accompanied by pump vibrations or cavitation, water is likely present. Sometimes, these problems can occur at higher temperatures if water is deeply trapped within the system.

Detection During Operation

Small traces of water, even just a few hundred ppm, can appear as fluctuations in pump pressure or brief episodes of pump cavitation. Take these warning signs seriously. Water can remain hidden in low points or dead legs of the system and may escape unexpectedly, even if your operating temperature is above water’s boiling point (100°C/212°F). Persistent small leaks—such as from a heat exchanger—can also introduce water gradually.

Protection Measures

Always exercise caution when dealing with water in your system. Water expands dramatically—over 1,000 times—when it turns to steam. If water contacts hot fluid, it vaporizes rapidly, and the steam expansion can push hot fluid out of the loop, potentially through the expansion tank or out of the vent.

Removal of Water

Remove larger amounts of water from the system’s low points whenever possible. During start-up, you can gently heat the system to between 93°C and 104°C (200°F to 220°F), letting small amounts of water vaporize as steam. If steam continues to escape, raising the fluid temperature in the expansion tank above 104°C can help prevent it from condensing back into water.