Laboratory exhaust system: the ventilation design requirements of the laboratory and the comfortable air-conditioning system are different. The main purpose of laboratory ventilation is to provide a safe and comfortable experimental environment and reduce the exposure of experimental personnel to the harmful air environment. Solve the problem of the experimental environment for the physical health and labor protection of the experimental personnel.
The laboratory exhaust system consists of ventilation equipment, ventilation ducts and ventilation terminals, and a ventilation control system.
①The fume hood has the ability to capture and collect dust to achieve a constant wind speed of 0.5m/s on the surface of the fume hood, reaching international standards.
②Laboratory pressure difference control, implement negative pressure with adjacent rooms, the reference value (-5~10Pa).
③Control the fan frequency to achieve the energy-saving effect.
④Precise temperature and humidity control, control range: +1.5°C, humidity is 60%, and the range of change is +5%.
⑤Remote control, which closely connects the laboratory control system with the building.
⑥ Exhaust gas purification treatment.
The laboratory selects a certain number of fume hoods according to process requirements and functional layout, and some also have partial exhaust hoods. Usually, the number of air changes is far greater than 10 times,–generally, more than 20-30 times, which meets the requirement of air changes. But the number of air changes is in accordance with the ventilation.
According to the calculation of the maximum opening area of the cabinet, the data and experience show that 100 ventilation cabinets are used by only 18 people or less 99% of the time. Therefore, the ventilation volume and the number of air changes should also be checked when the minimum opening area of the fume hood is
The laboratory exhaust system adopts a fresh air system, and the exhaust of the fume hood does not circulate indoors. Because the laboratory requires the room to be negative pressure relative to other auxiliary areas. Therefore, the fresh air volume in the laboratory is designed to be 70% -80% of the exhaust air volume. Another 20% -30% of fresh air is sent to laboratory auxiliary rooms, offices, management rooms, internal walkways, etc., and then supplemented to the room by the gaps between doors and windows.
The air volume balance of the fume hood can adopt a constant air volume control system, that is, the exhaust air volume is constant, and the air supply volume and the supplementary air volume of 1 door and window gap are constant. This method is suitable for laboratories where the maximum exhaust air volume meets the minimum air change requirements.
For rooms where the exhaust air volume is much greater than the minimum ventilation volume requirement, a two-stage ventilation control system can also be used to ensure the air volume balance. In order to maintain the minimum number of air changes, save.
About energy consumption. In this case, the drug testing institute adopted a variable laboratory exhaust system. When the air volume of the fume hood changes, the exhaust air volume will be relatively small.
At this time, the exhaust fan placed on the roof is required to change the frequency with the position of the fume hood cabinet, reduce the air volume, and ensure the constant wind speed of the fume hood. At the same time, the automatic control system changes the frequency of the fresh air fan, reduces the air volume, and maintains the negative pressure balance. A variable air volume system can reduce system energy consumption. If the system’s maximum and minimum air changes are close to each other, a constant air volume system is considered, which makes the system simple and reduces the initial investment.
In addition to the special requirements for fume hoods mentioned above, the laboratory exhaust system also has certain requirements and standards for other equipment and control systems. The choice of fume hood not only satisfies the exhaust and capture ability but also pays attention to the need to change the air volume immediately according to the movement of the adjusting door to maintain a constant surface wind speed.
Shandong Kedilang recommends that the measurement and control of the air volume of the system take the displacement of the cabinet door as a signal instead of measuring the surface wind speed. Laboratory pressure control and minimum ventilation control In addition to equipment selection factors, ventilation system design and control system are key factors, and the system’s response must be ensured
The time should be short enough (<1 second). The unbalanced exhaust system will cause the exhaust and capture capacity of the fume hood to lose, the airflow will flow out of the laboratory, and the pressure in the building will be unstable.
