1.1 PRINCIPLE OF OPERATION The operation of a desiccant dehumidification system is driven by two counter current air streams flowing through the desiccant wheel. In the occupied mode, outdoor air (less than 25% of total air flow) and return air are drawn through the filter, the process fan, evaporator coil (where it is cooled and some moisture is removed by condensation on the coil), and the desiccant wheel (where additional moisture is adsorbed). The dehumidified air is provided to the conditioned space. Outdoor air passes through a filter, the condenser coil, the desiccant wheel (where moisture is desorbed), and then through the regeneration fan before being exhausted to the exterior of the building. The emergency return air damper can be used to modulate building pressure by opening to exhaust building air through the regeneration side of the unit to regeneration fan and exhaust. When in the unoccupied mode, the unit closes the outdoor air damper for the air intake. Return air is drawn into the dehumidification section of the unit, dehumidified and returned to the conditioned space. In the High Carbon Monoxide/Dioxide mode the unit dampers switch and the process section takes in 100% fresh, outdoor air and passes it through the evaporator coils and the desiccant wheel and delivers it to the space. The second refrigeration circuit will run when outdoor enthalpy is above 28 BTU per pound of air. The regeneration air inlet dampers will switch to using return air (with the capability of adding some outdoor air if condensing temperatures rise) and will exhaust the return air out of the building. The unit also has hot water heating coils for winter operation. 1.2 DESIGN The galvanized metal frame of the 4000 DES/DX and all of the components used in the design are of solid construction and selected to withstand rugged use in a wide variety of applications. The interior of the 4000 DES/DX is laid out to minimize pressure drop through the system and to reduce the overall unit size. The blowers have a backward inclined design for high pressure, high flow output. The blower motors are provided with variable frequency drives. Maximum fan speed settings can be adjusted to optimize unit for system in which it is installed. The desiccant wheel can be removed from the side of the unit after removing the drive belt and the bolts holding the shaft collar.
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