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What kind of control methods do the Laboratory Fume Hoods use?
May 22, 2018

Laboratory Fume Hoods are an integral part of laboratory ventilation design. In order to prevent laboratory workers from inhaling or swallowing toxic, pathogenic, or toxic chemicals and organisms, the laboratory should have good ventilation. The main function of the Laboratory Fume Hood is the exhaust function. In the chemical laboratory, various harmful gases, odors, moisture, and flammable, explosive and corrosive substances are generated during the experimental operation to protect the user's safety. To prevent the spread of pollutants from the laboratory to the laboratory, use a Laboratory Fume Hood near the source of the pollution. Taking into account the improvement of the experimental environment, the experiments carried out on the experimental bench were gradually transferred to the Laboratory Fume Hood, which required the most suitable function for the equipment in the Laboratory Fume Hood. In particular, most newly-built laboratories require air conditioning. Therefore, the number of Laboratory Fume Hoods to be used must be included in the air conditioning system plan during the preliminary design phase of the building. Because the Laboratory Fume Hood occupies a very important position in the biochemical laboratory, considering the improvement of the laboratory environment, improvement of labor hygiene conditions, and improvement of work efficiency, the use of Laboratory Fume Hoods has dramatically increased. Followed by the ventilation ducts, piping, wiring, exhaust, etc. have become an important task of laboratory construction.

The air flow control in the laboratory mainly refers to the control of the lab pressure commonly used in laboratory laboratories such as Laboratory Fume Hoods, universal exhaust hoods, atomic absorption hoods, etc. In order to ensure the safety of the pre-fume cabinet testers, all countries have strict requirements on the surface wind speed entering the Laboratory Fume Hood. China's industry standards also specify that the surface wind speed should be kept at 0.5m/s. Therefore, under normal circumstances, it is required that the air speed of the ventilation counter be strictly limited to about 0.5 m/s. The strong "suppression force (control ability for toxic and hazardous substances)" of the Laboratory Fume Hoods for the toxic and harmful substances produced in the experiment mainly comes from the dynamic balance and stability of the wind speed of the hood. Because if the air velocity of the Laboratory Fume Hood is too low, the Laboratory Fume Hood gas is likely to overflow. If the air velocity of the Laboratory Fume Hood is too high, turbulence will form in the cabinet and the gas in the cabinet will overflow. After nearly 40 years of development, the laboratory control system has evolved from the original fixed air volume system to the more commonly used adaptive control system.

1. Constant air volume control (CV)

In the 40s of the last century, regardless of the degree of opening of the window of the Laboratory Fume Hood, the air volume remained constant. The advantage of this method is that the control is simple, but the disadvantages are also very obvious. The wind speed of the Laboratory Fume Hood will constantly change with the position of the adjustment window, resulting in poor safety performance and surprising energy consumption.

2. Bistable control (2-state)

As people gradually realized the defects in the safety and energy consumption of the air volume system, bistable control came into being. This type of control system has only two conditions: high air volume and low air volume. Its typical application is to reduce the system to low air volume operation when there is no operator at night or in the laboratory. The energy consumption can be reduced to a certain extent, but as with the constant air volume system, its ability to resist external disturbances is still poor, and at the same time, the pressure fluctuations in the room are large when the operating conditions are changed.

3. Variable Air Volume Control (VAV)

After entering the 1980s, with the continuous development of control technology, a more reasonable laboratory air flow control method, namely variable air volume control, has emerged. VAV control is to adjust the system's air supply and exhaust volume through the change of the door opening degree in the laboratory Laboratory Fume Hood or the change of the air speed of the Laboratory Fume Hood, so as to ensure that no matter how the opening of the adjustment window, the air speed of the Laboratory Fume Hood can always be accurately controlled to 0.5 m/s. The system has strong adaptability and can reduce energy consumption on the premise of fully guaranteeing safety. However, it requires high control precision and reaction speed of the valve, and it has been widely used in laboratories of major pharmaceuticals, scientific research institutions, and the like.

4. Adaptive Control (UBC)

At the end of the 20th century, the Occupation Based Control system was based on the VAV system. By installing detectors on Laboratory Fume Hoods and biosafety cabinets, it was monitored whether there was any activity in front of the Laboratory Fume Hoods or biosafety cabinets. When someone is operating, the surface wind speed is kept constant at 0.5m/s to protect the operator's safety. If no one is operating before the Laboratory Fume Hood, the inlet wind speed is reduced to 0.3m/s. With this control method, energy consumption can be significantly reduced again on the basis of using the VAV system.

In today's increasingly tense energy issues, on the basis of ensuring the safety and comfort of the laboratory, intelligence and energy conservation have become a topic of great concern to laboratory managers. For laboratories, 100% brand-new air is used. It operates 24 hours a day, seven days a week, and it consumes a lot of energy. Using a more intelligent variable air volume system can minimize energy consumption on the premise of ensuring safety.

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