Condensing Drying
The two methods of condensing drying are high-pressure drying and refrigerant drying.
High-Pressure Drying
High-pressure drying may be used when main air piping is kept away from outside walls and chilling equipment. During compression and cooling to ambient temperatures, air gives up moisture which then collects in the bottom of the storage tank. The higher the tank pressure, the greater the amount of moisture that condenses. Maintaining a high pressure removes the maximum amount of moisture. The compressor should have a higher operating pressure than is required for air supply purposes only. However, higher air pressure requires more energy to run the compressor. The tank must include a manual drain valve or an automatic trap to continually drain off accumulated moisture. With tank pressures of 70 to 90 psi, a dew point of approximately 70F at 20 psi can be obtained.
Refrigerant Drying
Lowering air temperature reduces the ability of air to hold water. The refrigerated dryer (Fig. 13) is the most common means of obtaining dry, compressed air and is available in several capacities. It provides the greatest system reliability and requires minimal maintenance.