The psychrometric process of the air passing through the system with four state points is shown on the psychrometric chart of Figure 2 as 1, 2, 3 and 4. The state points of the air are also depicted in Figure 1. In this application, the air returning from the space, typically around 50% relative humidity (RH), is presented to the desiccant wheel and dries the desiccant. The air picks up moisture and cools in process 1 to 2. The moist air is now presented to the cooling surface (cooling coil of the air conditioner), which cools it below its dew point and dries the air in process 2 to 3. This represents the work done by the cold coil. In the meantime, the dried desiccant from below is rotated to the upper air stream. The saturated air leaving the coil, typically 93–98% RH, is presented to the desiccant at 3, where the air is dried further in process 3 to 4, where it is presented to the space as supply air. The desiccant, now loaded with moisture, rotates to the return air, where the cycle repeats.