1. How Is Fume Hood Exhaust Airflow Determined?
Fume hood exhaust airflow is directly related to the effective sash opening area and the design face velocity. It can be preliminarily calculated as follows:
Q = A × V × 3600
Where Q is the exhaust airflow (m³/h), A is the effective sash opening area (m²), and V is the face velocity (m/s).
For example, if the effective opening area is 1.2 m² and the design face velocity is 0.5 m/s, the theoretical exhaust airflow is approximately:
1.2 × 0.5 × 3600 = 2160 m³/h
For an actual project, the final airflow should also be determined according to the fume hood manufacturer’s data, experimental risks, and project design requirements. The valve must not be selected solely according to the duct size.
2. How Should the Venturi Valve Airflow Range Be Selected?
The Venturi Valve must cover the minimum and maximum operating airflow of the fume hood:
Qmin ≤ Actual Operating Airflow ≤ Qmax
Instead of providing only “2000 m³/h,” purchasers should provide:
Minimum Airflow: 500 m³/h
Normal Airflow: 1200 m³/h
Maximum Airflow: 2200 m³/h
An undersized valve may be unable to meet the maximum exhaust requirement. An oversized valve may cause the normal operating point to remain near the lower end of its calibrated range.
The valve size and control range should therefore be matched to the actual Qmin and Qmax. A larger valve is not necessarily better.
3. CAV or VAV Control?
A CAV system maintains a relatively constant exhaust airflow. It has a simple control method and is suitable for laboratories with a small number of fume hoods or without strict energy-saving requirements.
A VAV system dynamically changes the exhaust airflow according to the sash position or control demand:
Sash Raised → Opening Area Increases → Exhaust Airflow Increases
Sash Lowered → Opening Area Decreases → Exhaust Airflow Decreases
For laboratories where many fume hoods operate continuously, VAV control can reduce unnecessary exhaust airflow while meeting safety requirements. This helps reduce the energy consumption of the supply-air, exhaust-air, and air-conditioning systems.
4. Why Are Operating Differential Pressure and Response Time Important?
When several fume hoods operate simultaneously, system static pressure may change as other valves move. Therefore, a Venturi Valve must not only meet the design airflow but also provide suitable operating differential-pressure range and airflow-control performance.
The actuator response time is also important in VAV fume hood systems. When the sash is opened quickly, the control system must promptly increase the exhaust airflow. If the valve responds too slowly, the containment performance of the fume hood may be temporarily affected.
The following parameters should therefore be checked together:
Airflow Range + Operating Differential Pressure + Control Accuracy + Actuator Response Time
5. 0–10 V, 2–10 V, or Modbus?
Common Venturi Valve control options include 0–10 V, 2–10 V, and Modbus/RS-485.
0–10 V provides simple control and is suitable for PLC/DDC analog control. Depending on the controller design, 2–10 V can reserve part of the signal range for status identification. Modbus is more suitable when multiple Venturi Valves need to be connected to a BMS or centralized laboratory control system.
Purchasers should confirm:
Input Signal, Airflow Feedback, Valve-Position Feedback, Power Supply, and Fault Alarm
When Modbus is used, the device address, baud rate, communication format, and register map should also be confirmed to prevent integration problems after the equipment arrives on site.
6. How Should the Fume Hood and Room Ventilation Systems Work Together?
A typical VAV fume hood adjusts exhaust airflow through a sash sensor or controller:
Sash Movement → Controller Calculates Target Airflow → Venturi Valve Adjusts → Exhaust Airflow Changes
However, a laboratory cannot control only the fume hood exhaust. When several fume hoods simultaneously increase their exhaust airflow while the room supply airflow remains unchanged, the room negative pressure may increase excessively.
A complete system should coordinate:
Fume Hood Exhaust + General Room Exhaust + Room Supply Air + Room Pressure Differential
By maintaining a suitable offset between supply and exhaust airflow, the laboratory can maintain the designed pressure relationship with corridors and adjacent areas.
7. Which Parameters Should Be Confirmed for Engineering Procurement?
When purchasing Venturi Valves, provide at least:
Number and dimensions of fume hoods;
Qmin, normal airflow, and Qmax;
Duct dimensions;
Operating differential-pressure range;
CAV or VAV control mode;
0–10 V, 2–10 V, or Modbus interface;
Actuator response requirements;
Exhaust medium and corrosiveness;
Room supply, exhaust, and pressure-differential requirements;
BMS/DDC interface requirements.
If acidic or alkaline vapors or other corrosive gases are present in a chemical laboratory, the valve-body material, corrosion-resistant treatment, sealing materials, and operating temperature must also be confirmed.
8. Frequently Asked Questions
Is a larger Venturi Valve always better?
No. It should be selected according to Qmin, Qmax, and the actual control range. The valve should not operate continuously within an unsuitable part of its calibrated range.
How many Venturi Valves are required for one fume hood?
This depends on the maximum exhaust airflow, valve operating range, and duct design. If one valve cannot cover the required design airflow, a combined-valve solution should be evaluated.
Can a Venturi Valve be connected to a BMS?
Yes. Analog signals or digital communication can be used according to the controller configuration, but the interface and communication protocol must be confirmed in advance.
9. Yueboyang Venturi Valve Solutions
For laboratory fume hoods, clean laboratories, and room-pressure control systems, Yueboyang can select and configure Venturi Valves according to the exhaust airflow, Qmin/Qmax, operating differential pressure, control signal, response requirements, and corrosive environment.
The system can use 0–10 V, 2–10 V, or Modbus to coordinate fume hood exhaust with room supply and exhaust airflow.
The key to selection is not simply determining the valve diameter. The exhaust airflow, face velocity, valve operating range, response time, and room-pressure control must be properly matched as a complete system.
