Clean room wind speed requirements and air changes

Sufficient ventilation volume is to dilute and eliminate indoor polluted air, according to different cleanliness requirements, when the clean room net height is higher, the appropriate increase in the number of air changes. Among them, the ventilation volume of 1 million clean rooms is considered according to the high efficiency purification system [7], and the rest are considered according to the high efficiency purification system. When the 100,000-class clean room HEPA filter is centrally arranged in the machine room or the end of the system, the number of air changes can be appropriately increased by 10-20%.

For the above recommended value of ventilation volume, the author believes that the wind speed through the room section of the unidirectional flow clean room is low, and the turbulence clean room is the recommended value with a fuller safety factor. Vertical unidirectional flow ≥0.25m/s, horizontal unidirectional flow ≥0.35m/s, in the empty state or static detection of cleanliness, although can meet the requirements, but the anti-pollution ability is poor, once the indoor into the working state, cleanliness may not meet the requirements, such examples are not individual; At the same time, China's ventilator series has not yet been more suitable for the purification system of the fan, the general designer often does not accurately calculate the air resistance of the system, or does not pay attention to whether the selected fan is in the characteristic curve of the more favorable working point, so that the system is put into operation soon after, the air volume or wind speed can not reach the design value. The United States Federal standard (FS209A~B) has been so stipulated before October 27, 1987: The airflow speed of unidirectional clean room through the clean room section is usually maintained at 9Oft/min(0.45m/s), and under the condition of no interference in the whole room, the speed uniformity is within ±20%. Any significant decrease in airflow velocity increases the likelihood of contamination effects between the self-cleaning time and the working position (all parameters other than dust concentration are not specified after the promulgation of FS209C in October 1987).

To this end, the author thinks that it is appropriate to appropriately increase the current domestic design value of unidirectional flow speed, our unit in the actual project to do so, the effect is better. The turbulence type clean room is a recommended value with a fuller safety factor, but many designers are still not assured that when doing the specific design, the 100,000 level clean room ventilation volume is increased to 20~25 times /h, the 10,000 level is increased to 30~40 times /h, and the 1000 level is increased to 60~70 times /h, which not only increases the equipment capacity and increases the initial investment. It also increases the cost of future maintenance and management, and it is not necessary to do so. When preparing China's air cleaning technical measures [7], more than 100 domestic clean rooms were investigated and measured, and many clean rooms were still tested under dynamic conditions, and the results showed that the ventilation volume of 100,000 grade ≥10 times /h, 10,000 grade ≥20 times /h, and 1000 grade ≥50 times /h could meet the requirements. The United States federal standard (FS2O9A~B) stipulates that non-unidirectional flow clean room (100,000 class, 10,000 class), room height 8~l2ft(2.44~3.66m), usually consider the whole room at least once every 3 minutes (that is, 20 times /h). Therefore, the provisions of the design specification [6] have taken into account the larger affluence coefficient, and the designer can safely choose according to the recommended value of ventilation volume.