What are the methods for adjusting the wind speed during the operation of a fume hood?

The adjustment of air velocity during the operation of a fume hood is a key operation to ensure experimental safety and maintain good ventilation effects. The following is an introduction from several aspects including the basis for adjustment, manual adjustment methods, automatic adjustment methods, and adjustment precautions:

Adjustment basis

The air velocity adjustment of a fume hood needs to take into account multiple factors comprehensively. The type of experiment is an important basis. For example, experiments involving volatile organic solvents produce high concentrations of harmful gases that diffuse quickly, and a relatively high wind speed is required to ensure the timely discharge of harmful gases. For some experiments that produce trace amounts of gas, excessively high wind speeds may interfere with the experimental operations. In such cases, the wind speed can be appropriately reduced. The size and structure of the fume hood also affect the air velocity requirement. For larger fume hoods, a higher air velocity may be needed to ensure the effective air exchange throughout the cabinet. For fume hoods with complex structures, there are dead zones for air flow, and it is also necessary to adjust the wind speed reasonably to reduce the dead zone areas. In addition, the environmental conditions of the laboratory, such as indoor temperature, humidity, and air flow, also have an impact on the wind speed regulation of the fume hood.

Manual adjustment method

Adjust the fan speed: The fan of the fume hood is the core component that generates wind force. By adjusting the fan speed, the air velocity of the fume hood can be directly changed. Generally speaking, the higher the rotational speed of a fan, the greater the wind speed it generates. On the control panel of a fume hood, there is usually a knob or button for adjusting the fan speed. Laboratory personnel can rotate the knob clockwise or counterclockwise according to actual needs, or press the corresponding button to increase or decrease the fan speed. For example, when conducting experiments with highly toxic gases, the fan speed can be adjusted to a higher gear to quickly discharge harmful gases. After the experiment is completed, if only some routine operations are carried out, the rotational speed can be reduced to save energy.

Adjust the opening degree of the air valve: The air valve is a device that controls the air flow in the ventilation duct. By changing the opening degree of the air valve, the air volume entering the fume hood can be regulated, thereby affecting the air velocity. Air dampers are generally installed on ventilation ducts. Laboratory personnel can manually operate the handle of the air damper to change its opening degree. When it is necessary to increase the wind speed, turn the handle of the air valve towards the opening direction to increase the opening degree of the air valve and allow more air to enter the fume hood. Conversely, when it is necessary to reduce the wind speed, turn the handle of the air valve towards the closing position to decrease the air volume entering the fume hood.

Automatic adjustment method

Wind speed sensor feedback regulation: The fume hood is equipped with a wind speed sensor, which can monitor the wind speed inside the fume hood in real time and feed the signal back to the control system. The control system compares the preset wind speed value with the actual wind speed value. When the actual wind speed is lower than the preset value, the control system will automatically issue instructions to increase the fan speed or open the opening degree of the large air valve to increase the wind speed. When the actual wind speed is higher than the preset value, the control system will reduce the fan speed or close the air valve opening slightly to restore the wind speed to the set range. For instance, during an experiment, if the wind speed inside the fume hood suddenly drops due to the experimental operation, the wind speed sensor will immediately detect this change and promptly feed it back to the control system. The control system will promptly adjust to ensure that the fume hood is always in a good ventilation state.

Interlocking regulation with the laboratory ventilation system: The fume hood is connected to the overall ventilation system of the laboratory. Through interlocking regulation, more intelligent wind speed control can be achieved. The laboratory ventilation system will automatically adjust the ventilation volume based on factors such as indoor air quality and the number of personnel, and the air velocity of the fume hood will also be adjusted accordingly. When the number of people indoors increases or experimental activities intensify, leading to a rise in the concentration of harmful gases indoors, the ventilation system will increase the ventilation volume, and the wind speed of the fume hood will also be raised accordingly to better expel the harmful gases. Conversely, when the indoor environment is relatively stable, the wind speed of the fume hood will automatically decrease to save energy.

Adjustment precautions

Avoid excessively high or low wind speed: Excessively high wind speed may interfere with experimental operations, such as blowing away experimental samples or affecting the normal operation of experimental instruments. Meanwhile, it will also increase energy consumption and noise. If the wind speed is too low, harmful gases cannot be effectively discharged, exposing the laboratory personnel to a dangerous environment. Generally speaking, the face velocity of a fume hood should be controlled between 0.3 and 0.6m/s, but the specific value needs to be adjusted according to the type of experiment and the design requirements of the fume hood.

Regularly calibrate the wind speed measurement equipment: To ensure the accuracy of wind speed regulation, it is necessary to calibrate the wind speed measurement equipment inside the fume hood regularly. If there is an error in the wind speed measurement equipment, it may lead to inaccurate wind speed adjustment and affect the ventilation effect. The calibration cycle can be determined based on the usage frequency and precision requirements of the equipment. Generally, it is recommended to conduct calibration every six months to one year.

Pay attention to the stability during the adjustment process: When adjusting the wind speed, ensure that the adjustment process is smooth and avoid significant fluctuations in the wind speed. Sudden changes in wind speed may affect the accuracy of the experimental results and even cause safety accidents. When adjusting the wind speed, the experimenters should operate the regulating device slowly and closely observe the changes in the wind speed until a stable state is reached.