Catalogue

20 UV-PRC003-EN
Application Considerations
adjacent outdoor and exhaust air streams pass through the wheel in a counterflow arrangement
that transfers energy from one air stream to the other.
During the cooling season, the drier, sensible heat and moisture transfer from the outdoor air to
the cooler, drier exhaust air. Conversely, during the heating season, sensible heat and moisture
transfers from the exhaust air to preheat and humidify the entering outdoor air stream. Figure 16
psychrometric ally depicts the impact of a preconditioning total-energy wheel on a unit ventilator.
This approach can’t directly control humidity in the space, but it can significantly reduce the
capacity (and operating cost) of the cooling and heating equipment required to condition the
outdoor air. Capable of recovering 65 to 75 percent of the energy in the exhaust air stream, total-
energy wheels used in conjunction with unit ventilators can be an attractive alternative when
upgrading existing classroom to meet ASHRAE’s ventilation requirements; they reduce, perhaps
even eliminate, the extra capacity needed at the chiller plant or boiler.
The Trane ERS energy recovery unit ventilator is one example of a “cold coil” unit with outdoor
air preconditioning.
Note: Both preconditioning (energy recovery) and post conditioning (reheat) may be applied in
the same system.
For more information on outdoor-air preconditioning and energy recovery, refer to the Trane
application engineering manual, Air-to-Air Energy Recovery in HVAC Systems (SYS-APM003-EN).
Figure 16. Energy recover wheel
Figure 17. Cold coil with outdoor air preconditioning
Draft Barrier and OA Preconditioning
UV-PRC003-EN.book Page 20 Tuesday, June 4, 2013 8:59 PM