Temperature and humidity in a cleanroom are two independent targets, yet they are often treated as one: if the room is too warm, add cooling; if humidity is too high, add cooling too. More cooling does lower temperature and remove moisture, but overcooled air then has to be reheated, energy use multiplies, and humidity may still miss the target.
The real problem is the wrong criterion. Whether humidity can be held depends on whether the apparatus dew point of the supply air is below the dew point of the room air—which is a different question from the chilled-water supply temperature.
1. Capability limits of the three common routes
| Route | Typical indoor RH range | Principle | Main cost |
|---|---|---|---|
| Cooling coil + reheat | about 45%–65% | A chilled-water coil cools air below its dew point to condense moisture, then air is reheated to supply temperature | Reheat energy; chilled water must be colder than the target dew point |
| Coil + desiccant wheel | about 30%–45% | The coil pre-cools and pre-dries; the wheel provides deep dehumidification | Wheel regeneration energy; the regeneration heat source drives running cost |
| Desiccant-wheel-led | below about 30% | The wheel adsorbs moisture; the regeneration side heats it to desorb | High regeneration energy; needs a stable regeneration heat source |
The three routes do not replace each other; they divide the work by humidity range. Ordinary workshops usually use the first, low-humidity processes the second, and ultra-low humidity the third.
2. The criterion: apparatus dew point vs room dew point
To judge whether a route will work, make one comparison: is the apparatus dew point of the supply air below the dew point of the room air?
If the supply dew point is above the room dew point, the supply air itself is a m