Airflow control is the core of the entire laboratory. For the laboratory, in order to fully ensure that pollution is impossible to leak from the contaminated area of the laboratory to the clean area or even the surrounding environment, to ensure the safety of the outdoor environment and the safety of the experimental operator, it is necessary to establish a stable and reliable air flow organization and a negative pressure gradient to ensure the stability of the laboratory air flow. Thus, a safe, reliable and effective protective barrier is established.

The variable air volume ventilation system adopts the pipe static pressure control method, which is complicated to control and debug, and is suitable for laboratory projects with large ventilation volume and large number of fume hoods. Install a pipe pressure sensor 1/3 of the way between the system fan and the last branch duct. Used to detect the wind pressure value in the pipeline. The opening of the electric air valve of the exhaust equipment in the laboratory area makes the actual pressure detected at the top pressure sensor less than the set pressure value. The control system increases the starting frequency of the roof fan through the frequency converter, and maintains the pressure at the pressure sensor to the set value. When an emergency occurs, turn on the emergency exhaust mode.

Butterfly valve VAV control

1) Surface wind speed control system continuously monitors the actual surface wind speed. When any factor affects the surface wind speed change, the system will automatically adjust the electric wind valve on the pipeline to a constant setting

Surface wind speed value. Variable air volume butterfly valve using high-quality brand products, with rapid response ability, high air tightness without whistling, with a high degree of anti-corrosion, fire prevention and many other characteristics. Straight molding to ensure high strength and durability, with water collection ring to prevent pipe condensate back into the cabinet:

· The valve body adopts PP molding and is highly anticorrosive, specially designed for exhaust air of laboratory fume hood, resistant to all kinds of organic/inorganic steam corrosion; · Actuator drive mode: full travel of high-speed electric actuator ≤2.5 seconds, using the original imported brand actuator;

· Actuator control module comes with feedback microprocessor to achieve high stability;

· Low damping material self-lubricating connection is adopted at the connection between shaft rod and valve body to minimize actuator resistance; · In order to improve the anti-corrosion ability, no metal parts are allowed in the part in contact with the exhaust gas;

· The shaft rod and butterfly leaf are designed by PP molding to ensure high corrosion resistance;

· Meet laboratory fire prevention requirements;

· Excellent sealing ring to ensure high air tightness and aging resistance;

· Controlled by fume hood monitor, surface wind speed control accuracy: current surface wind speed set value ±10%; · Noise: less than 55dB;

· Operating pressure 50-1000Pa, operating temperature -18-55℃;

2) Different parameters can be set on the panel for different experimental conditions.

3) The system realizes through the infrared monitor that when there is an operator working in front of the fume hood, the wind speed is controlled at a certain setting value (such as 0.5m/s). When there is no one operating in front of the fume hood, the system automatically switches to another setting value (such as 0.3m/s) to save operating costs.

4) When the fume hood door is closed, the air volume valve should maintain the minimum exhaust air volume of the fume hood, and the 1500MM fume hood is 300CMH.

5) Sound alarm when the fume hood door is too high.

6) Sound and light alarm when the wind speed of the fault surface is too high or too low.

7) When there is an abnormal situation, turn on the emergency discharge mode control, the system will open all the air valve, the maximum air volume of the fume hood, not controlled by the surface wind speed value.

Venturi valve VAV control

During the operation of the fume hood, the biggest factor affecting the wind speed of the fume hood surface is the pressure of the ventilation system pipe network. Due to the opening and closing of other fume hoods or ventilation equipment, or other changes in the pipe network, the pressure of the fume hood pipe will change, and this change will often occur.

If the hood system uses ordinary butterfly valves, it will lead to frequent changes in the wind speed on the hood surface, which is very unfavorable to the safety of the laboratory. Even if the wind speed control system is used, it will only be adjusted after the surface wind speed changes, which will go through a series of sensing, calculation, adjustment and oscillation processes, and then the unsafe situation has occurred. Because the pressure change of the pipe network can occur at any time, relying solely on the wind speed control system will lead to slow and frequent surface wind speed control.

The fume hood control system using Venturi valve can solve the problem of the pressure change of the system pipe network, and the Venturi valve can automatically adjust according to the pressure change of the pipe network. This process is accompanied by pipe network pressure changes at the same time, so as to avoid the wind speed control system to adjust the process, to achieve rapid and stable air volume control, it has two different working modes, namely variable air volume and constant air volume.

Variable air volume means that the valve can react quickly through the signal to realize the rapid response of the automatic pressure balancing device of the ventilation system (response time <1 second), so as to meet the requirements of VAV variable air volume. The fixed air volume means that the valve can set an air volume value, so that the air volume inside the pipeline through the valve is certain, the control is accurate (±5%), and the adjustable rate is high (20:1).