Time clocks are a simple and inexpensive way to reduce space-conditioning costs. The equipment can be turned off at the close of business every day so that cleaning crews or late-working tenants don’t keep the equipment running late. Even if only a single air handler in a large building operates extra hours, the main chiller or boiler must stay on-line, and both systems end up operating at very inefficient, low loading conditions. Packaged systems can be controlled by a timer. A school, for example, may have individual units for the classrooms, kitchen, and gymnasium. These can all be controlled by a single timer set for the regular school schedule. The timer can even be set to activate the units an hour early, so conditions are favorable when everyone arrives. A local override switch in each space might be installed to permit operation of the unit for a few hours when the rest of the units in the building are off.
Several units can be operated by a single electromagnetic time clock. All that’s required at each remote location is a relay activated by low-voltage control wiring from the central timer. Timers are available that establish a 7-day, 24-hour schedule with 20 or more on/off set-points. Some people prefer mechanical units, although electronic devices have many more features. The latter should be located out of harm’s way or in a locked cabinet.
One final requirement with time clock systems is to check on a routine basis to be sure the clocks are calibrated correctly. This includes correct time of day (especially after changing to and from daylight savings time) and programming of all on/off setpoints. Unauthorized adjustment should be prevented by installing the system in a locked box, and locked room too if necessary.
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Excerpt from Energy Conservation Projects.