The environment to be conditioned is controlled at a targeted dew point temperature and then reheated to a specified air temperature. Maintaining a constant dew point and air temperature will produce a very constant relative humidity.
(A) Air introduced to water spray
A portion of the air returning from the conditioned area is directed through a water spray area with a closely controlled temperature. The water spray is adjusted to maintain the dew point temperature of the targeted condition. As the air passes through the water spray, it is cooled down to the temperature of the water and approaches saturation.
(B) Air leaves spray chamber
The air then leaves the spray chamber through a mist eliminator, and is next mixed with air that has by-passed the spray area.
(C) Air is returned to conditioned space
After passing over an electric heater, to warm the air back to the desired dry bulb temperature, the air is returned to the conditioned space.
Utilizing the above method, a very precise humidity control is achieved. The system does not distinguish between humidifying and dehumidifying; it is always setting a dew point and reheating.
The temperature of the water spray is automatically adjusted by the feedback from a RH sensor in the controlled space. If the set point is lower than the actual condition, the temperature of the water spray will gradually decrease until the RH set point is achieved. On the other hand, when the relative humidity set point is above the actual condition, the water spray temperature is incrementally increased until the RH set point is achieved.
For conditions that require a below freezing dew point, a desiccant dryer is utilized.