The determination of airflow velocity under a certain cleanliness in a clean room varies with the specific situation such as the use of the clean room. It is not only affected by the amount of indoor dust and filter efficiency but also by other factors. In terms of industrial clean rooms, the factors affecting the cleanliness and selection of airflow velocity are mainly:

I. Indoor pollution sources: building components, the number of personnel and operation activities, process equipment, process materials and process processing itself are dust emission sources, which vary greatly according to the specific situation.

2. Indoor air flow pattern and distribution: unidirectional flow requires uniform and equal streamlines, but it will be affected by the changes of process equipment layout and position and personnel activities to form local eddy currents; For non-unidirectional flow, mixing is allowed to avoid dead corners and temperature stratification.

3. the control requirements of self-cleaning time (recovery time) : the interruption of pollutants or air flow released or brought into the clean room by accident or the movement of intermittent convective air flow or people and equipment during normal operation will cause the deterioration of cleanliness. The self-cleaning time to restore to the original cleanliness is determined by the airflow speed; The CONTROL REQUIREMENTS FOR SELF-CLEANING TIME DEPEND ON THE ABILITY TO WITHSTAND THE IMPACT ON THE QUALITY AND yield of product production within this time frame (under deteriorating cleanliness).

4. the efficiency of the final filter: in a certain amount of indoor dust, lower efficiency filter can be used to reduce the airflow speed; For energy saving should consider the use of a lower efficiency filter, and reduce the airflow speed, or the use of a lower efficiency filter and use a higher airflow speed, in order to minimize the product of flow and resistance.

5. economic considerations: excessive airflow velocity will cause the increase of investment and operating costs. The appropriate airflow velocity is a reasonable synthesis of the above factors. Excessive airflow velocity is often unnecessary and may not be effective.

6. For clean rooms with low cleanliness requirements, sometimes the number of air changes is determined by the requirements of indoor heat removal.