The desiccant process was selected for both efficiency
and simplicity. Engineers concluded that boilers, z-ducts, heat pipes, and other methods did not compare to the 85 percent efficiency the heat wheels provide. There were many problems with the original 1-HP AC motor and gearbox equipment in each of the energy wheel systems. At the time of installation, this was a fairly common equipment configuration. 

However, it was discovered that mechanical gearboxes
used for The RainForest were failing at an alarming
rate. Once a year, one of the gearboxes had to be replaced. There was no discernable pattern pointing

to a particular wheel-and-gearbox arrangement. It was random. The only constant element in the problem was the routine failure of a gearbox. Finally, it was evident that something was wrong with speed of the unit. The pace was apparently too slow for the gearboxes’ splash lubricating systems to properly engage. As a result, parts were not being properly oiled and prematurely wore out. Direct Air Systems replaced the drives and gearboxes with ABB 5-HP induction motor/AC low-voltage drive combinations, which allowed the motor to be connected directly to the motor/load without the need for a gearbox or pulse encoder. The ABB solution also allowed full motor torque down to zero speed.

Through the use of an algorithm, the ABB drives, in this case variable speed ACS models, can run without an encoder to provide speed feedback. The algorithm enables the drive to calculate the state of the motor’s torque and flux 40,000 times per second. Elimination of the encoder further reduces maintenance and decreases downtime. In the event of a control failure, the ABB ACS drives are designed to go, automatically, to a pre-set rpm rate, to ensure heat transfer is maintained.