Nothing saves more energy than turning equipment off when it does not need to run. Occupancy schedule controls for the HVAC system could be an effective way to save the energy use. The equipment will run when it is needed and at appropriate temperatures. Adjusting building temperatures up or down during unoccupied periods is another strategy if the major system can not be turned off. In addition, using real people occupancy, such as people counters, occupancy sensors or CO2 sensors to adjust temperatures or turn off equipment when there is low occupancy, significantly adds to savings.
If a major HVAC unit such as an air handling unit is serving a simple or single area, such as administration offices, classrooms, etc. the unit could be turned off when the schedule is unoccupied. Areas like auditorium, gymnasium in schools or other educational buildings could go a further step. An occupancy sensor can be installed in the space. The unit can be placed into standby mode if the sensor senses no occupancy in the space during the occupied mode. In standby mode, the fan can be turned off or run at a lower speed. The system will resume normal operations when the space condition cannot satisfy the predetermined condition.
With a regular 10 hours schedule on weekdays, the unit could reduce the operational hours from 168 hours per week to 50 hours. This will save about 70% of the energy use!
If the major unit is serving multiple zone and some zones cannot be closed, a site survey might be required and system can be optimized based on the findings of the space usage. E.g. if some spaces have terminal units installed such as VAV boxes, we can reduce the flow or even close the box when the schedule is unoccupied. If there are no VAV boxes, we can use a zone damper to shut down the area. On the supply fan side, fan speeds could slow down as the flow requirement are reduced.
Overall, schedule setup for HVAC equipment is an effective way to reduce the energy usage. It is a low cost or even no cost solution if the control system is running.