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Venturi Air Flow Meter: Low Pressure Drop Sensing for HVAC Duct Ventilation
Quick Answer
A Venturi air flow meter measures air flow in HVAC ducts with very low pressure drop. It suits duct sizes from DN100 to DN2000 and provides a 4-20 mA signal for building control systems. Silver Instruments supplies these meters with local display and Modbus RTU as standard.
Why Low Pressure Drop Matters in HVAC Duct Ventilation
Most HVAC air flow meters create a restriction in the duct. That restriction adds pressure drop. Fan power increases to overcome the drop. In large ventilation systems, a small pressure loss per meter can add up to thousands of dollars in annual energy cost.
A Venturi air flow meter avoids this problem. The design uses a gradual contraction and a gradual recovery section. The air accelerates through a narrow throat and then slows back down. The pressure loss stays under 60 Pa at 10 m/s in many installations. In practice, this is less than 1 percent of the fan static pressure in medium pressure ducts.
How the Venturi Air Flow Meter Senses Duct Air Flow
The meter senses differential pressure between the inlet section and the throat section. A differential pressure transmitter converts this pressure into a flow signal. The flow rate follows the square root of the differential pressure. A 4-20 mA output sends the compensated air flow value to the BMS or HVAC controller.
Silver Instruments supplies the VFM-DV series for duct ventilation. The series includes meters for round ducts from DN100 to DN2000. Rectangular duct versions are available on request. Each meter arrives with a local LCD display, 4-20 mA output, and Modbus RTU. HART is optional for users who need remote configuration.
Typical HVAC Duct Ventilation Applications
We see these meters in office towers, hospitals, data centers, and pharmaceutical cleanrooms. A facilities team in Singapore installed VFM-DV units in a hospital air handling unit to balance fresh air intake across 14 zones. The duct sizes ranged from DN150 to DN600. Low pressure drop was the main reason for selection because the existing fans had limited spare capacity.
A food processing plant in Saudi Arabia used the same series for exhaust air monitoring in a packaging hall. The air contained light dust. We supplied a version with stainless steel wetted parts and an IP65 enclosure. The plant connected the 4-20 mA signal to a central PLC with no extra signal conditioner.
Recommended Model and Key Specifications
For most HVAC duct ventilation jobs, use the Silver Instruments VFM
Key specifications for the VFM-DV series:
Duct sizes: DN100 to DN2000 round duct, rectangular on request
Air velocity range: 0.5 to 40 m/s
Accuracy: plus or minus 1.5 percent of reading
Pressure drop: typically below 60 Pa at 10 m/s
Output: 4-20 mA with HART option, Modbus RTU, pulse
Power supply: 24 V DC
Process temperature: -20 to 80 degrees C
Protection class: IP65
Wetted materials: carbon steel or 304 stainless steel
Most engineers skip the HART option for basic HVAC jobs. 4-20 mA plus Modbus RTU covers most control needs. Use stainless steel if the air contains moisture or light dust. Use carbon steel for clean indoor ducts to reduce cost.
What to Send for a Quote
Send us your duct diameter in DN, your air velocity or volume flow range, your required output signal, and your installation length. We will verify the meter size and pressure drop for your duct layout. A typical quote covers the meter, a differential pressure transmitter, and a local display. Delivery to Southeast Asia, Oceania, Latin America, Africa, and the Middle East is available.
Contact Silver Automation Instruments.
Tel: +86-135-1213-1526
Whatsapp: 86-135-12131526
WeChat: +86 13512131526
FAQ: Venturi Air Flow Meter for HVAC Ducts
Q1. What duct sizes can the Venturi air flow meter cover?
A: Standard VFM-DV units cover round ducts from DN100 to DN2000. Rectangular duct versions are available on request. Tell us the duct width and height for a custom fit.
Q2. What output signals are available for building management systems?
A: The meter provides 4-20 mA and Modbus RTU as standard. HART is optional. Pulse output is available for totalized air flow.
Q3. What is the typical accuracy for HVAC air flow measurement?
A: The VFM-DV series has an accuracy of plus or minus 1.5 percent of reading. This is enough for ventilation balance, energy monitoring, and filter loading checks.
Q4. How much straight pipe run is required?
A: For most HVAC ducts, install the meter with 5D of straight duct upstream and 2D downstream. If space is tight, a flow straightener can reduce the upstream run to 3D.
Q5. Can the meter handle dust or condensation in air ducts?
A: Yes, choose 304 stainless steel wetted parts and an IP65 enclosure. For heavy condensation, add a drain port on the low pressure tap. We will confirm the best option based on your air conditions.