Control of cleanroom humidity is critical to FDA mandated CGMP manufacturing as well as numerous industries such as semiconductor, lithium battery and composites manufacturing. Methods to control humidity include air conditioning, humidifiers and dehumidifiers.
Figure 1. Humidity source
Too high cleanroom humidity can lead to condensation. Condensation can result in undesirable things in cleanroom like bacteria growth, mold growth and metal corrosion. Too low humidity in cleanroom can result in static buildup and ESD damage to electronics. FDA CGMP requires a controlled environment – including particle count, temperature control, humidity control, limits on bacteria counts, limits on mold counts. The FDA requires some cleanrooms to be sterile facilities.
Figure 2. AC Chiller system
Cleanroom air conditioning systems provide natural dehumidification when they cool the cleanroom. When the warm air hits the AC systems cooling coils the air drops in temperature causing moisture to leave the air forming condensate. This why air conditioners require condensate pans and drains. Since cleanrooms are net heat generators the dedicated cleanroom AC typically runs continuously providing dehumidification to the cleanroom.
Figure 3. Electric steam humidifier
Cleanroom Humidifiers Raise Humidity
Cleanrooms use industrial steam humidifiers to add moisture to the air. The humidifier converts water to steam which is injected into the HVAC ducting of the cleanroom. The humidifier can be gas or electric powered. It is recommended that distilled or filtered water be used to feed the humidifier to prevent mineral scale build up on heating coils.
Figure 4. Electric tube heater used for reheat dehumidification
Tighter Humidity Control
When tighter control of cleanroom humidity is required , reheat and humidifiers can be added in tandem to cleanroom AC systems. The reheat electric heater is turned on when you want to lower humidity. By raising the temperature of the cleanroom, the reheat causes the AC system to cool the air more, removing moisture from the cleanroom and lowering the cleanroom humidity. The humidifier is turned on when we want raise humidity.
Figure 5. Industrial Dehumidifier Process
When reheat systems are not sufficient, cleanrooms use industrial dehumidifiers remove humidity from the air. The cleanroom air enters the dehumidifier and passes through a slowly rotating desiccant wheel. The desiccant absorbs moisture from the air, leaving dry air to exit the dehumidifier. The wheel rotates and hot air is used to remove the moisture from the desiccant. The hot air absorbs the moisture from the desiccant. The system vents the hot moist air outside the building. The dehumidifier can be gas or electric.
Other parameters that affect cleanroom humidity:
Quantity of cleanroom exhaust cfm and make up air
Number of cleanroom workers
# of entries/exits to cleanroom per day.
If the quantity of exhaust cfm and make up air is large then a dedicated AC/heater unit may have to be added to the cleanroom to precondition outside air before it enters the cleanroom. A large of cleanroom workers and corresponding large number of daily entries/exits to cleanroom will introduce more humidity into cleanroom. This can be reduced by use of double airlocks.
Industries that are particularly sensitive to humidity:
Pharmaceutical – High humidity affects bacteria and mold growth
Food and powder – High humidity can cause clumping and bacteria growth
Summary: Cleanroom humidity control can be very important for CGMP medical and pharmaceutical cleanrooms as well as semiconductor, electronic, and battery manufacturing cleanrooms. Air conditioning, reheat, and industrial dehumidifiers are all used to lower cleanroom humidity. Industrial humidifiers are used to increase cleanroom humidity. These systems can be used in tandem to control cleanroom humidity minimum and maximum.
Author: The author Anthony Chien has worked at American Cleanroom Systems for past 12 years. He has more than 40 years of cleanroom experience. Anthony has a BS and MS in Electrical Engineering specializing in semiconductor manufacturing from the University of Illinois. American Cleanroom Systems is a design build modular cleanroom manufacturer based in Rancho Santa Margarita CA. It is expert in ISO-5 through ISO-8 (class 100 to class 100k) modular cleanrooms for pharmaceutical cleanrooms, medical device cleanrooms, and industrial cleanrooms.
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