Quick answer
How do you stop condensation on chilled-water pipework?
Chilled-water pipework is kept condensation-free by a continuous vapour barrier over the insulation. The insulation keeps the outer surface above dew point, and every joint, bend and fitting is sealed so moist air cannot reach the cold pipe. Gaps and unsealed terminations are where condensation starts.
Why does cold pipework sweat?
Air always contains moisture. When that air touches a surface colder than its dew point, the moisture condenses into water. A chilled-water pipe is exactly that kind of surface, so without insulation it will drip continuously and the water will damage ceilings, finishes and the pipe itself.
What is dew point?
Dew point is the temperature at which air can no longer hold its moisture and condensation begins. The warmer and more humid the space, the higher the dew point. Insulation thickness on cold services is chosen to keep the outer surface of the insulation just above the dew point of the surrounding air.
How does a vapour barrier work?
A vapour barrier is a sealed outer layer that stops moist air passing through the insulation to the cold pipe. It must be continuous along the full run, with sealed joints at every bend, tee, valve and termination. One unsealed joint lets moisture in, and condensation then forms inside the insulation where it cannot be seen.
Closed-cell vs mineral wool — what is the difference?
Foil-faced mineral wool sections rely on the foil facing and taped joints for the vapour seal, and are the common choice on commercial chilled-water systems. Closed-cell materials such as phenolic or elastomeric foams resist moisture through their structure as well as their facing. The project specification states which system each service requires.
Where do condensation problems usually start?
Almost always at fittings. Valves, flanges, supports and terminations are where vapour seals get cut, compressed or left incomplete. Pipe supports need insulated inserts so the insulation is not crushed to nothing. Regular inspection catches failed seals before the resulting hidden corrosion becomes a pipe failure.
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