To turn fans on/off, we used time clocks. The main drawback was the amount of time it took to go around to all of the various time clocks to prepare for holidays and whenever occupancy schedule changes occurred, and so many times clocks were placed in the “always on” mode. Therefore time clocks are seldom used at the University of Michigan today.

    For temperature control, we used pneumatic controllers. Their principal drawback is that they tend to drift out of calibration, and the vast majority suffers from "offset", which is the inability to keep the desired conditions at set-point under changing load conditions. They are still in use today in some smaller systems, but most have been replaced with DDC, and more are being replaced when there is a reasonable payback for doing so. The majority of individual room controls are still pneumatic, but in time these will also be converted to DDC where it makes good economic sense.

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