HVAC Automatic Control System for Cleanrooms
I. Controlled Objects of Cleanroom HVAC Automation
- Temperature Temperature control of cleanrooms is primarily determined by production processes, with requirements for temperature set-points and precision defined accordingly. Generally, temperature set-points are relatively low. For example, the temperature in cleanrooms of electronic factories is much lower than that in comfort air - conditioning systems. Therefore, the cooling load in summer is also relatively large. In addition, the heat generated by process equipment is substantial, meaning that temperature disturbances are significant and subject to great variations. The utilization rate of process equipment changes with production volume and product types, while product mix itself fluctuates according to market demands.
Summary of characteristics: Low temperature set-points and large load variations.
- Humidity: Humidity control of cleanrooms is also based on process requirements. For instance, in electronics and pharmaceutical factories, the relative humidity setpoints are relatively low but not excessively so. Excessively low humidity tends to induce static electricity, which must be avoided.
- Positive/Negative Pressure: During production, process equipment in cleanrooms may generate toxic, harmful, and waste heat - containing gases that need to be exhausted outdoors. To maintain indoor cleanliness, cleanrooms are generally required to maintain a positive pressure (negative pressure may be required for special processes). The required positive pressure values vary depending on different cleanliness classes.
- Cleanliness Level: Since the cleanliness of the production environment is closely related to product qualification rates, comprehensive and regular testing of cleanrooms is mandatory. If the cleanliness level fails to meet process requirements, an alarm should be triggered promptly.
Detection of Flammable, Explosive, Toxic and Harmful Gas Concentrations. When the concentration of flammable, explosive, toxic, or harmful gases reaches the specified limit values, the emergency exhaust system must be activated, and an alarm issued simultaneously.
II. Differences Between Cleanroom HVAC Automation and General HVAC Automation
All automatic control methods applicable to general HVAC systems can be utilized in cleanroom HVAC automation projects. However, production processes requiring controlled cleanliness levels typically impose more stringent requirements on temperature and humidity control. For example, maintaining a low temperature set-point with high precision poses certain challenges; these challenges are further compounded when coupled with the need to maintain a low humidity set-point with high precision. Consequently, higher technical standards are demanded for the automatic control system.
The cleanliness level of cleanrooms is achieved by replacing contaminated air with a specified volume of conditioned air from the cleanroom HVAC system. Therefore, the supply air volume is a fixed parameter, making the variable air volume (VAV) control method with fixed air supply conditions unsuitable. Instead, the constant air volume (CAV) with variable dew point control method is generally adopted to meet indoor temperature and humidity requirements, which represents a key difference from general HVAC control strategies.
In cleanrooms adopting the dry coil + FFU (Fan Filter Unit) air - conditioning configuration, if indoor cooling/heating loads change, the indoor temperature is generally controlled by adjusting the flow rate of chilled/hot water through the dry coils. Meanwhile, the indoor humidity is typically regulated by adjusting the air supply conditions of the fresh air handling system to meet design requirements.
Indoor positive pressure maintenance is achieved by balancing the supply air volume, return air volume, exhaust air volume, and fresh air volume. The automatic control system must be equipped with regulatory means to re - establish and maintain this balance when any of the aforementioned air volumes change, ensuring that the required indoor positive pressure is consistently maintained.
Suzhou Pharma Machinery Co.,Ltd.
2026/04/13
Gino
