Cleanroom relative humidity
Cleanroom relative humidity (=RH) is adjusted to the activities in the room. For example, plastics are sensitive to static electricity and a low RH, i.e. below 43%, is undesirable. Electronic equipment can be damaged by static electricity so here too, RH plays an important role in maintaining correct cleanroom humidity.
Moisture can be produced in various ways in air handling units. It is essential to control clean room humidity in sensitive environments where microorganisms pose a risk, therefore steam humidification is generally used. In adiabatic humidification, adiabats atomize moisture at a temperature level where microorganisms can grow. This poses a potential risk for companies in the food, healthcare and pharmaceutical industries. So the steam humidifier is preferred here.
Dehumidification of air is realized via a cooling battery or with an absorber. This depends on the desired RH. A cooling coil can reduce the cleanroom relative humidity to 35%, a lower percentage can be achieved with an absorber.
The water for the cooling coil in the air handling unit usually comes from a cooling machine or chiller. This heat exchanger is located outside and supplies enough cold water to condense moisture from the air at the correct air speed.
It is important to meet cleanroom temperature and humidity requirements. A commonly used RH in cleanrooms is 55% +/- 5%. In environments that need lower percentages, such as in the production of effervescent tablets or strips of paper in Corona test strips, the RH must be much lower, < 30%.
Cleanroom relative humidity in winter
It’s been a long time since we’ve experienced outside temperatures below -15 ºC. This is when then the air is extremely dry and the humidifier has to convert liters of water into steam. The cleanroom must be designed to compensate for such exceptional conditions or, in the case of critical production processes, production must be stopped.
Sometimes anti-static floors are used in conjunction with an adjusted RH to prevent sudden discharges. Cleanrooms are critical areas where arrangements must be made for both extreme heat and frost to meet all clean room humidity control requirements and sometimes you have to accept that production might need to be interrupted for a few hours every few y