An induction system has a central air-handling unit that supplies heated or cooled primary air at high pressure to the zone induction unit, typically located on an outside wall. The supply air under pressure goes through nozzles and draws air from the room into the unit. This mixed air then passes through the cooling or heating coil and into the occupied space. Outside air is introduced at the central air handler, and not at the individual induction units. There are several things that can be done to save energy in this system:
1. Over time, any mechanical system gets out of adjustment. Whenever any adjusting and balancing work is done, the primary air volume should be modified to conform with the original design values, for optimum system performance.
2. The metal nozzles on older induction units can become enlarged after being cleaned many times. This affects the volume and pressure balance of the entire system. The only remedy is to recalculate the HVAC space loads (which have likely changed considerably over time anyway) and the air needed to be supplied to each zone. Then rebalance the primary air system to match the nozzle pressures and rebalance the induction units to maintain enough airflow to reach the space temperature setpoint.
3. Each unit goes out of balance—if to a lesser extent—whenever the nozzles get dirty: There is higher resistance through the unit, diminished airflow, and increased fan energy used. Thus, it’s essential to keep the nozzles clean.
4. Adjust the heating and cooling schedules to closely match the space- use schedules.
5. During the heating season, the secondary water temperature can be reduced so that most of the heating is done at the air handler, where it can be accomplished most efficiently.
6. The secondary water flow to the induction units can be reduced during the peak heating and cooling periods by turning a pump off or by adjusting the pump’s variable-frequency drive to a lower operating speed, to reduce energy use.
7. Hot-water reset of the primary air temperature for heating can reduce energy use by lowering the temperature of the supply air as the temperature outside gets warmer.
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Excerpt from Energy Conservation Projects.