Freeze Damage To Water Coils

By far the most common cause for premature failure of coils is ruptures caused by water freezing within the tubes. Damage can occur on coils at moderate altitudes in unheated situations in Victoria, however is mostly due to the effects of heat removal by a nearby cooling coil. The water usually freezes first in the tubes and bends outside the fined area but expansion and cracking will occur in the finned area in extreme cases. Bulging of the tubes in these areas is a sure sign of freezing having taken pace.

The most important thing is to remedy the cause of the problem rather than just fixing the leak. Repairs are usually only effective a few times before the coils is rendered irreparable. People often blame the light wall construction of modern copper tubed coils as contributing but in fact when water freezers the forces involved will easily crack thick steel pipes. The bursting pressure of the light gauge copper tube is normally around 20Mpa or 3000 PSI. Heavier coil construction will only take slightly more damage before rupture and never solve freezing problems.

Possible causes of coils freezing include:

INCORRECTLY SET OR STICKING REFRIGERATION CONTROLS can result in freeze up at low load conditions. Evaporator temperatures should be set at least a few degrees above zero but even this will not guarantee that the air off the cooling coil will not be below zero under certain conditions.
LACK OF AIR FLOW caused by dirty coils or filters allows evaporators to produce air at below zero degrees. The installation of an interlocked dirty filter pressure differential switch may be a good answer. Broken fan belts are another common cause of freeze damage.
SYSTEM SHUTDOWN can leave evaporators full of liquid but no air flow which can cause local temperature below freezing. A fan run on circuit that operates for a few minutes at system shutdown will solve this but will not guard against power failure.
CONDUCTION BETWEEN FRAMES of evaporators and heating coils bolted together often result in damage. Sometimes just unbolting the two coils and separating them with some low conductivity material such as wood is sufficient to stop damage occuring.

Often the cause of the freezing cannot easily be identified. In these cases one possible cure would be the addition of antifreeze solution like ethylene glycol to the water circuit. This can be expensive on a large system and the danger is that somebody will drain and not replace the solution at a later date. Repositioning the coil downstream or upstream of the cooling coil where low temperatures cannot occur is always the best answer if space permits.

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