Based on measuring its achieved dew point. Just like air compressors, most air dryers see average compressed air demands and moisture loads that are less than the nameplate rating; therefore, the internal desiccant does not get fully saturated during each cycle. If controls are installed to detect when the desiccant is fully saturated, the purge cycles can be delayed or reduced — if rated conditions are not being experienced.
A dew point controller stops expensive regeneration processes of the adsorption dryer bed until it is necessary (based on dew point set up point). The need to start or end regeneration results from continuous measurement of air humidity over time using a hygrometer (dew point meter) behind the dryer. If its humidity is within the nominal operating range of the dryer set point, then regeneration does not need to be initiated.
Dew Point Based Swing Controller reduces purge losses and saves energy.
It consists of a hygrometer that can reliably measure the dew point of the compressed air at outlet and displays at the control panel. As the exact quality of the output air is measured and displayed, the purge operation of the dryer is controlled based on the output of the air quality.
This results in energy saving because the switching of the towers is not based on the fixed timing and hence reduces loss of purge air especially during part-load operations.
Various measurement methods are used to measure the dew point, but in all cases these probes are quite sensitive to shock and contamination. When these probes become contaminated or damaged due to water or lubricant accidentally getting into the unit, the output signal can be permanently altered significantly, reducing the effectiveness of the control mode or causing it to fail altogether. Probes that are reading too high cause the control to never save energy. Errors showing too low may cause the purge to fail altogether, allowing wet air to enter sensitive areas of the plant. It is very important to ensure the accuracy of the sensors by testing them against a standard or regularly changing them out with recalibrated units.