The function of Dedicated Outdoor Air Systems (DOAS) is to remove the stale and/or contaminated air from the building space to allow for the replacement of the exhaust air with fresh air. The old exhaust, that which is leaving the building, has been acclimated to the indoor space conditions (i.e. heated or cooled as appropriate). Therefore, there is typically a substantial difference in the heat and humidity of the exhaust air and the fresh air. The new air must be altered in order to blend in with the air inside the building.
Energy wheels rotate through both the fresh air and the exhaust air streams. As the wheel rotates, it transfers energy between the two air streams. There are two types of energy wheels: sensible and total. Sensible energy wheels transfer heat energy only, while total energy wheels transfer heat energy and moisture.
Total energy wheels are used in various places throughout campus, including Fenwick Place and Kennedy Auditorium in the CLC.
If the fresh air stream is cooler than the exhaust air stream, heat will be transferred from the exhaust air to the incoming air, thus pretreating the ventilation air and reducing the energy load on the DOAS unit's heating system. If the outside air is warmer than the exhaust air, the opposite will be true and the entering air will be precooled, thus reducing the energy load on the DOAS unit's cooling system.
The transfer of moisture between the two air streams means the energy wheel can serve as a dehumidifying component of the system in the summer time and a humidification component in the winter.