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Water treatment in AC systems

By Selele Mashilo

Water is sometimes used as a secondary refrigerant in air conditioning, or it may be used in cooling towers for cooling purposes.

For cooling, water is mainly used in evaporative cooling systems. It plays a very important role in air conditioning, but it does not always come in a perfect condition as expected. It is water that contributes to corrosion of metals and can also react with other elements.

Water in air conditioning installations must be suitably treated to avoid calcium deposits on the surface of metals. The calcium deposits reduce heat transfer by cooling towers which may create system-tripping at high pressures. Material selection is therefore very important when being applied in air conditioning systems, and in various locations.

We are going to come across various terms in the field which define water treatment – knowledge of these makes it easier for one to understand the scientific approach required for water treatment. It is thus beneficial to look at the theory in application to realise the need for water treatment in these systems.

The result of poor water quality in water circuits is that metals used in most plants may be destroyed and thus shorten the lifespan of the plant. Water may be alkaline; which is the sum of dissolved chemical bicarbonate, carbonate and hydroxide salts.

The amount of dissolved calcium and magnesium in water determines its hardness. There might also be biological deposits in water like algae and slimes.

The pH value, or the logarithm of the reciprocal of the hydrogen ion concentration, which determines the acidity or alkalinity of water, may be too high or too low.

Water sludge formations, which are sedimentary water formed deposits, should be prevented. Water-formed deposits are also always found in the system where water is in contact with surfaces.

It can thus be deduced, that because of the various affecting factors that water in air conditioning systems can produce, treatment is required for both interior effects on the metals in a system, as well as corrosion which attacks the metal’s external surfaces.

References: ASHRAE