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Dew Point Measurement How Accurate Dew Point Measurement Saves cost

Editor: Dominik Stephan

In a refrigerant-based compressed air dryer system, the dew point sensor installed at the dryer outlet helps monitoring the dryer’s performance most accurately.

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Common cyclic and non-cyclic refrigerated air dryers (Picture: Vaisala)
Common cyclic and non-cyclic refrigerated air dryers (Picture: Vaisala)

Compressed air is vital for virtually any manufacturing industry, from operating pneumatic tools to spray painting, blowmoulding, and chemical mixing. Whatever be the application, the compressed air needs to be dry to avoid risk of corrosion, malfunctions and poor end-product quality, all o fwhich can result in unnecessary costs. Today, roughly 80 per cent of compressed air systems use refrigerant dryers to maintain dryness. Unfortunately, many of them lack accurate dew point measurement, leading to unnecessary operating costs and lower endproduct quality.

Depending on the desired pressure dew point, the choice in dryer selection will vary. Generally, the two most common types of industrial dryers used in compressed air Common cyclic and non-cyclic refrigerated air dryers systems are desiccant and refrigerant. Desiccant dryers use adsorbing materials – such as silica gel or activated aluminium to remove moisture from the air, whereas refrigeration dryers remove moisture by cooling it in a heat exchanger and purging the condensed water. Separate refrigerant compressor and heat exchanger are used to handle this cooling function. Refrigeration dryers can produce the dew point levels required for compressed air of class 4 quality or above, whereas desiccant dryers are needed for class 3 and below (based on ISO Standard 8570.1, see table 1).

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Measuring temperature – A Valid Equivalent for Dew Point Measurement

Traditionally, refrigeration dryers have been equipped with only a temperature sensor – which is mostly considered to be equivalent to a dew point measurement. Yet there are several potential reasons why the temperature measurement may not indicate the true dew point of the air. A few of such reasons are cited below:

● Drain valves can fail.

● Drain points can become blocked, leading to improper removal of water — and consequent contamination of the compressed air with micro droplets.

● The condensate can overload the drain system. This clearly means — that even a steady condensate flow is no guarantee of normal operation.

● Temperature measurement can also be misleading in cases of high flow rates, as the whole air mass is not cooled to the heat exchanger temperature.

As these factors indicate, the only way to accurately measure moisture and monitor correct dryer operation is to use a dew point sensor installed at the dryer outlet.

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