How To Switch The Ventilation Mode of The Fume Hood During The Experiment?

Common ventilation modes and their characteristics

Constant air volume mode

Principle: In this mode, the fan of the fume hood always operates at a constant air volume, and the stability of the air volume is maintained by adjusting the opening degree of the air valve. No matter how the opening height of the window and door of the fume hood changes, the system will strive to ensure that the exhaust volume remains constant.

Features: Simple operation, relatively easy system control to achieve, capable of maintaining a stable ventilation effect all the time, suitable for situations where the amount of harmful gases produced during the experiment is relatively stable. However, when the opening height of the window and door of the fume hood is relatively small, it will cause a certain amount of energy waste because a relatively large air volume is still being discharged at this time.

Variable air volume mode

Principle: By using sensors to monitor parameters such as the opening height of the window and door and the face velocity of the fume hood in real time, the speed of the fan or the opening degree of the air valve is automatically adjusted according to the changes in these parameters, thereby changing the exhaust volume.

Features: It can flexibly adjust the ventilation volume according to actual needs, effectively reducing energy consumption while ensuring ventilation effect. For instance, when the opening height of the window and door of the fume hood is relatively small, the exhaust air volume decreases accordingly. When the opening height of Windows and doors increases, the exhaust air volume also increases accordingly. However, this mode system is rather complex, and the equipment cost and maintenance cost are relatively high.

Supplementary air mode

Principle: While the fume hood is discharging air, a certain amount of fresh air is replenished into the room through the air supply device to maintain the balance of indoor pressure. The make-up air volume is usually adjusted according to the exhaust air volume to ensure that there is no excessive negative pressure in the room due to exhaust air.

Features: It helps maintain the stability of indoor air, reduces the disturbance of indoor air flow and fluctuations in temperature and humidity caused by exhaust, and improves the comfort of the experimental environment. At the same time, it can also reduce the risk of inhaling unclean air from outside through gaps in doors and Windows and other places due to excessive negative pressure indoors. However, special attention should be paid to the quality and temperature control of the make-up air to avoid affecting the experimental results.

Ventilation mode switching scenarios and operations

Switch from constant air volume to variable air volume mode

Switching scenarios: When the amount of harmful gases produced during an experiment varies significantly, such as during a chemical synthesis experiment, the intensity of the reaction at different stages is different, and the amount of gas produced will also fluctuate. At this time, it is more appropriate to switch from a constant air volume mode to a variable air volume mode.

Operation method: Generally speaking, the intelligent control system of the fume hood will provide a mode switching function. The experimenters can find the mode switch button or menu option on the control panel and select "Variable Air Volume Mode". The system will automatically activate the sensors to start real-time monitoring of the relevant parameters of the fume hood and automatically adjust the ventilation volume based on the monitoring results. During the switching process, pay attention to observing the operating status of the fume hood to ensure a stable ventilation effect.

Turn on the make-up air mode

When the exhaust volume of the fume hood is large and there is a significant negative pressure in the room, or when the experiment has high requirements for the stability of the indoor environment, such as conducting precision instrument analysis experiments, it is necessary to maintain the stability of indoor temperature, humidity and air flow. At this time, the supply air mode should be turned on.

Operation method: On the control panel of the fume hood, find the supply air mode switch or the relevant setting option and turn it on. At the same time, adjust the make-up air volume according to the actual situation, which can generally be achieved by regulating the opening degree of the air valve of the make-up air device or the make-up air parameters of the control system. After turning on the make-up air mode, it is necessary to check whether the indoor pressure has returned to normal and whether the quality of the make-up air meets the requirements.

Different mode combinations can be switched

Scene switching: In some complex experimental processes, it may be necessary to use multiple ventilation modes simultaneously. For example, in the early stage of the experiment, the amount of harmful gases produced is relatively small, and the constant air volume mode can be adopted. As the experiment progresses, the gas volume increases and switches to the variable air volume mode. When the exhaust air volume is large, causing a significant negative pressure indoors, then activate the supply air mode.

Operation method: According to the operation method for switching individual modes mentioned above, select the mode and set the parameters in sequence. During the process of combination switching, attention should be paid to the coordination and cooperation among various modes to ensure the stable operation of the fume hood and the safety of the experimental environment. For instance, when switching from a constant air volume mode to a variable air volume mode and then turning on the supply air mode, it is necessary to closely monitor the matching of ventilation volume and supply air volume to avoid problems such as insufficient ventilation or indoor pressure imbalance.

Precautions for mode switching

Safety inspection: Before switching the ventilation mode, ensure that the fume hood and its related equipment are operating normally without any potential faults. Check whether the ventilation ducts are unobstructed and whether the fans, air valves and other components are working properly. For instance, if the fan malfunctions and is switched to the variable air volume mode, it may not be able to adjust the ventilation volume normally, affecting the ventilation effect.

Parameter Settings: According to the specific requirements of the experiment and the performance parameters of the fume hood, set the operating parameters of each mode reasonably, such as the air volume value in the constant air volume mode, the face velocity range in the variable air volume mode, and the supply air volume in the supply air mode, etc. Improper parameter Settings may lead to poor ventilation or energy waste.

Personnel training: Laboratory personnel should receive relevant training to be familiar with the principles, operation methods and precautions of various ventilation modes of fume hoods. During the mode switching process, operations must be carried out strictly in accordance with the operating procedures to avoid safety accidents caused by misoperation. For instance, without understanding the operation method of the variable air volume mode, adjusting the parameters at will may cause the fume hood to lose its normal ventilation function.