Control systems for adsorption dryers with heat generation are somewhat more complex, having to fulfil the needs of the overall system. For switching over from adsorption to regeneration and back again, as well as for pressure buildup, individual valves are actuated within a time cycle. Adsorption dryers with heat regeneration are often fitted with a programmable logic controller. Beyond the basic functions, valve switching and heating, pressure build-up and a fault signal are integrated into the control system. A rigidly fixed time cycle with adsorption dryers using heat regeneration is exceptional and can be justified only if the throughput performance of the compressor is equal to the compressed air consumption, i.e. during continuous operation. More and more control systems for adsorption dryers using heat regeneration operate as a function of load. The concentration of residual humidity at the outlet is used as a signal for switching over from adsorption to regeneration. The conditions applying to a load dependent cycle are the same for adsorption dryers using heat regeneration as for other adsorption drying systems. For this reason, this subject will only be briefly described. Control systems operating as a function of load make sense when the moisture load is subject to wide variation. Modern controllers linked to a humidity measuring device, can register every part load level of an adsorption dryer. Based on this, they make the adsorption period longer while maintaining regeneration time constant. Beyond this, limiting values describing the internal state of the dryer can be utilised or be made visible in signal form. Functions relevant for monitoring are:
- Heating temperature
- Main valve
- Exhaust valve
- Pressure build-up
- Pressure dewpoint
