The laboratory ventilation design adopts the following steps and schemes:

(1) According to the process requirements and functional layout, the laboratory selects a certain number of fume hoods, some of which also have partial exhaust hoods. Generally, the air change rate is far greater than 10 times, generally more than 20-30 times, meeting the requirements of air change rate. However, this ventilation rate is calculated according to the maximum open area of the fume hood. Data and experience show that only 18 or less people use 100 fume hoods 99% of the time. Therefore, it is also necessary to check the ventilation rate and air change rate when the minimum opening area of the fume hood is less than the requirement of the ventilation rate, then the comprehensive exhaust system shall be added.

(2) Laboratory ventilation adopts fresh air system, and the exhaust of fume hood is not circulated in the room. As the laboratory requires the room to be negative pressure relative to other auxiliary areas. Therefore, the fresh air volume of the laboratory is designed as 70% - 80% of the exhaust air volume. In addition, 20% - 30% of fresh air is sent to the laboratory auxiliary room, office, management room, internal corridor, etc., and then supplemented to the room by the gap between doors and windows.

(3) The air volume balance of the fume hood can adopt the constant air volume control system, that is, the exhaust air volume is constant, the supply air volume and the supplementary air volume of the door and window gap are constant. This method is suitable for the laboratory where the maximum exhaust air volume meets the minimum ventilation rate requirement.

(4) For rooms where the exhaust air volume is far greater than the minimum ventilation rate, the two-stage ventilation control system can also be used to ensure the air volume balance. That is, according to the displacement signal of the fume hood, the exhaust fan and the forced draft fan have two air supply conditions, and the low air volume condition is used to maintain the minimum air change frequency and save energy consumption. In this case, VAV control system is adopted in the Institute for drug control. When the air volume of the fume hood changes, the exhaust air volume will also be relatively small. At this time, the exhaust fan placed on the roof is required to change the frequency with the change of the position of the fume hood door, so as to reduce the air volume and ensure the constant wind speed on the ventilation cabinet surface. At the same time, the automatic control system changes the frequency of the new fan, reduces the air volume and maintains the negative pressure balance. VAV system can reduce energy consumption. When the maximum and minimum air change times of the system are close, the constant air volume system is considered to make the system simple and reduce the initial investment.

In addition to the special requirements for fume hood mentioned above, the ventilation system also has certain requirements and standards for other equipment and control systems. In addition to meeting the exhaust and capture capacity, the selection of fume hood should also pay attention to the need to change the air volume immediately according to the movement of the regulating door, so as to maintain the constant surface wind speed. The author suggests that the measurement and control of the air volume of the system should be based on the door displacement instead of the surface wind speed. In addition to equipment selection factors, the design and control system of ventilation system are the key factors in laboratory pressure control and minimum ventilation rate control. To ensure that the reaction time of the system should be short enough (< 1s), the imbalance of ventilation system will lead to the loss of exhaust and capture capacity of fume hood, the airflow will flow out of the laboratory, and the pressure in the building will be unstable.