Priority #2: Manage the
After you have optimized the operation of your air handlers, move your focus to the thermostats.
Since off is the most efficient setpoint, scheduling thermostats for the minimum run time is the first step in an optimization effort. If your system can’t determine the minimum time to get room temperatures ready, then some testing and monitoring through the year is in order. Coming on one hour early is a good starting point.
Set minimum air flows based on occupancy and floor type. For rooms with a heat island, use a minimum circulation so the thermostat senses the room temperature. In my experience, the minimum air flow for a terminal box specified by the design engineer is just a percentage of the design cooling flow. When a room is occupied, it should be based on the ASHRAE standards.
When a room isn’t occupied, it might be set to zero depending on the requirements for off-hour air circulation. Carpets, humidity control, and other factors can easily require more than zero, but air flow should still be less than half the minimum found in the design plans. If in doubt, check with the design engineer for recommended minimum flows.
Determine the allowable room temperature setpoints for each thermostat. For example, until a hallway temperature is above 76 degrees, don’t lower the AHU setpoints. For an executive office, the upper limit might be 72 degrees. The following logic can be written for each thermostat: If the temperature is above 75 degrees, the setpoint is below 75 degrees, and the cold deck damper is above 95% open, then calculate an adjustment factor for the AHU to maintain 75 degrees. Each thermostat is checked and the worst case is used to control the AHU. Do the same programming for the heating season.
If a room has two thermostats, set the one nearer to the entrance as the master and the other as the slave. This minimizes the time when one unit delivers hot air and the other cool air. Most people will never see the second thermostat much less remember to keep the setpoints the same.
My program monitors all override buttons. If someone pushes a button off schedule, the air handler changes from night settings to day settings.