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6 TROUBLESHOOTING
The HCU has state-of-the-art design, with a sophisticated control system using a microprocessor with
solid-state electronics. This unit has proven to be very reliable in a wide variety of installations. Features
exist that facilitate troubleshooting on the occasion that a problem occurs.
6.1 DEHUMIDIFIER Operating Principle
Figure 6-1 shows how the HCU removes moisture from the air. The “heart” of the system is the
HoneyCombe® wheel. The wheel has a series of air passages or channels arranged in a honeycomb
pattern. Air can be forced through these channels in either direction.
The passages inside the wheel are impregnated with a desiccant material. When the desiccant contacts
damp air, it soaks up moisture. When the desiccant is heated, it releases the moisture. The HCU
operates with two separate air streams. The supply air stream is the air supplied to the space being
conditioned. The reactivation air stream is part of the condenser air stream and is used to remove the
heat from the condenser coil and reactivate (dry out) the desiccant wheel. Supply air is pulled from
outdoors into the HCU unit. This air is first drawn through the DX cooling coil. The cooling coil cools and
removes moisture from the air through condensation. The air is then drawn through the desiccant wheel.
The desiccant picks up additional moisture in the air. At this point, the moisture has been taken out of the
air from outdoors, and stored in the HoneyCombe® wheel. Once it has been dried, the supply air is
ducted into the conditioned space.
The next job is to remove this moisture from the wheel. The desiccant will give up moisture when it is
heated. Hot air can hold a large amount of moisture. When hot air reaches the desiccant, and the
moisture is released, we say the desiccant is “reactivated”.
Figure 6-1
In the HCU, a stream of ambient air is taken from the outdoors through the condenser coil. This heated
condenser air, which would normally go immediately back to the atmosphere, is recycled for reactivation
heat. This heated air is pulled through the desiccant wheel. The desiccant releases the moisture into the
heated condenser air stream, where it is vented outside again. This is the reactivation process. This is a
continuous process as the desiccant wheel rotates.
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