Variable Air Volume (VAV) Fume Hood

What is the Variable Air Volume (VAV) Fume Hood?

A VAV fume hood adjusts exhaust volume as the sash is raised or lowered so face velocity stays constant. It cuts exhaust and conditioning energy in laboratories with multiple hoods where occupancy varies.

Overview

A sash position sensor and face velocity sensor send signals to a controller that modulates an exhaust damper or fan, reducing volume from around 1200 m3/h at full open to 300–400 m3/h when closed, while holding face velocity at 0.4–0.5 m/s. Response time is under 3 seconds. The hood body is similar to a bypass hood, with reduced or no bypass. A digital monitor displays face velocity, sash position and alarms. VAV systems integrate with the building management system via BACnet or Modbus, and require matched supply air control to keep room pressure negative relative to corridors. Energy savings of 30–60 % relative to constant volume hoods are common when sashes are kept low.

How does it work?

A ducted fume hood creates a controlled inward airflow through the sash opening so contaminants generated inside are carried to the exhaust rather than into the room. Face velocity, typically 0.4–0.6 m/s at the sash, is produced by an exhaust fan located on the roof or in the duct. A baffle system at the rear distributes air across slots at the top, middle and bottom to avoid dead zones. A bypass airfoil keeps flow smooth as the sash moves. Variable air volume (VAV) hoods modulate exhaust as the sash opens or closes, saving energy while holding face velocity. The work surface, liner and sash are chemical resistant. Airflow monitors, alarms and lighting complete the hood, and the building make-up air system replaces exhausted air.

What are the key features?

• Sash and face-velocity sensors modulate exhaust
• Exhaust reduced from 1200 to 300–400 m3/h when closed
• Response time under 3 seconds
• Digital monitor with alarms
• BACnet or Modbus building integration
• Energy savings of 30–60 % with low sash use

What are the technical specifications?

A typical variable air volume (vav) fume hood configuration offers face velocity (held) of 0.4–0.5 m/s, exhaust volume range of 300–1500 m3/h, response time of < 3 s, width of 1200 / 1500 / 1800 mm, controller of Digital, PID and communication of BACnet or Modbus. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Variable Air Volume (VAV) Fume Hood is used in multi-hood laboratories, pharmaceutical research, university chemistry buildings and energy-efficient laboratory design. Across the wider Ducted Fume Hoods class, laboratories also deploy it for chemistry laboratories, pharmaceutical research and materials testing.

Which standards and certifications apply?

Relevant standards and methods include EN 14175-2 (fume cupboards, safety and performance), EN 14175-3 (type test methods), EN 14175-4 (on-site test methods), ASHRAE 110 (method of testing performance of laboratory fume hoods), GB/T 34269 and ISO 14644-1. Certification candidates for this model are CE and ISO 9001 manufacturing; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Commission each hood with a face velocity survey and, where required, a containment test such as EN 14175-3 or ASHRAE 110. Place it away from doors, walkways and supply diffusers, since cross-drafts above 0.15 m/s degrade containment. Keep the sash at or below the marked working height, and avoid blocking baffles with equipment. Check airflow monitors, alarms and exhaust fans at least every 6–12 months, and clean the liner regularly. Plan make-up air so the room does not become negatively pressured. Train users and label the hood with its tested face velocity and date, and do not use it for storage of chemicals beyond what the work requires.

How do I select the right Variable Air Volume (VAV) Fume Hood?

Choose VAV hoods when several hoods share an exhaust system and energy cost is a priority. They need matched supply control and commissioning. RFQ: width, controller protocol, response time, alarm requirements and integration with the building management system.

How does it compare with other Ducted Fume Hoods variants?

Select the hood by the chemicals and process. Choose width, commonly 1200, 1500 or 1800 mm, to match equipment and operators, and check that depth and height suit tall apparatus. Decide between constant volume, bypass and VAV designs, taking the building's exhaust capacity and energy costs into account. Specify liner material: fibre-reinforced cement or epoxy for general use, stainless steel or polypropylene for acids. Consider sash type, vertical or combination, face velocity monitoring, service fittings and base cabinet for storage. Confirm whether perchloric acid or radioisotope work requires a specialised hood instead. Coordinate duct size, fan capacity and make-up air with the building engineer, and plan for containment testing.