Applying direct digital control

One particular aspect of a wide range of HVAC research at the US Center for Building Technology concerned interfacing DDC with the pneumatic system for one of the existing air handling units at the CBT building itself. Using solenoid air valves induced both positive and negative air leaks in the pneumatic system; this did not occur with motorised pressure regulators, though these produced a time delay whenever the regulator's direction of rotation was reversed. Details are given of an adaptive PI algorithm with a self‐tuning regulator approach, developed at CBT and implemented on the air handler in question. From the experience, it is strongly recommended that such an algorithm should be implemented on a positional basis.