How much is the positive and negative pressure difference in the clean room?



The problem of positive and negative pressure difference in clean room has always been a headache for purification engineering designers. How much is the pressure difference? The following is a partial description of the iwuchen summary:



Maintaining a certain positive pressure in a clean room is one of the essential conditions to ensure that the clean room is free or less polluted to maintain the design cleanliness level. Even in a vacuum-free workshop, it must have a positive pressure in adjacent rooms or suites that are not below its cleanliness level, and the cleanliness of a vacuum-free workshop can be maintained.



The positive pressure value of the clean room is the value of the indoor static pressure greater than the outdoor static pressure when the doors and windows are all closed. It is achieved by the method that the air supply volume of the purification system is greater than the amount of return air and the amount of exhaust air. In order to ensure the positive pressure value of the clean room, the air supply, return air and exhaust fan are preferably interlocked. When the system is turned on, the blower is started first, then the return fan and the exhaust fan are started. When the system is shut down, the exhaust fan is turned off first, then the fan is turned off. The blower is installed to prevent the dust-free workshop from being contaminated when the system is turned on and off.




The amount of air required to maintain a positive pressure in a clean room is determined primarily by the tightness of the maintenance structure. In the early stage of dust-free workshop construction in China, due to the poor airtightness of the envelope structure, it is necessary to maintain the air supply volume of 2~6 times/h to maintain the positive pressure of ≥5Pa. At present, the airtightness of the maintenance structure has been greatly improved, and the same positive pressure is maintained. 1~2 times/h air supply volume; maintain ≥1OPa as long as 2~3 times/h air supply.





China's design code [6] stipulates: the static pressure difference between different levels of clean room and clean and non-clean areas should be no less than 0.5mmH2O (~5Pa), and the static pressure difference between clean area and outdoor should be no less than 1. OmmH2O (~l0Pa). The author believes that the value seems to be low for three reasons:



1. Positive pressure means that the dust-free workshop suppresses the ability to pollute the indoor air through the gap between the door and window, or to reduce the pollutants infiltrated into the room when the door and window are opened for a short time. The positive pressure indicates the strength of the pollution suppression. Of course, the bigger the positive pressure, the better (more on this later).



2. The air volume required for positive pressure is limited. The air volume required for positive pressure of 5Pa and positive pressure of 10Pa is only about 1 time/h. Why not do it? Obviously, the positive pressure value is lower than l0Pa.



3. US Federal Standard (FS209A~B) stipulates that when all entrances and exits are closed, the minimum positive pressure difference between the clean room and any adjacent low-cleanness areas is 0.05 inches of water (12.5Pa), which has been Adopted by many countries.



However, the positive pressure value of the clean room is not as large as possible. According to the actual engineering test of the unit for more than 30 years, when the positive pressure value is ≥30Pa, it is more difficult to open the door. Close the door and pay attention to it, scream! Scary! When the pressure value is ≥50~70Pa, the gap between the door and window will be whistle, and the infirm or the person with some incompatibility will feel uncomfortable. However, the relevant norms or standards of many countries in China and abroad do not specify the upper limit of positive pressure. As a result, many units only seek the lower limit to meet the requirements, regardless of the upper limit, which is the actual number encountered by the author. The positive pressure value in the dust workshop is as high as 100Pa or more, which causes very bad results. In fact, adjusting positive pressure is not a difficult thing. It is entirely possible to control it within a certain range.




Quote some links:
Air shower: http://
High efficiency air filter: http://
High efficiency filter leak detection: http://
Operating room purification project: http://
Clean room level standard: http://
Cleanroom testing standards: http://
Cleanroom design specification: http://
Cleanroom management system: http://
Clean room ventilation frequency standard: http://


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