PennState Lab Furnishings Catalog

Fume Hood Accessories

Auto Sash & VAV Principles & Advantages Properly used VAV (Variable Air Volume) systems provide a clear energy conservation advantage over CAV (Constant Air Volume systems) which consume a large volume of energy when the fume hoods are not in use. Switching to VAV can de- crease exhaust volumes by up to 85%, reducing energy costs and carbon emissions. This can equate to $2,000 to $6,000 in savings per hood annually. A VAV controller measures face velocity and automatically reduces the exhaust volume as the sash is lowered, thereby saving significant energy and costs. Current systems provide stable readings over many years of operation without recalibration, ensuring reliability and safety. However, experience has shown that many operators leave their hoods open most of the time. If the sashes are left open, even with a VAV system, no energy is saved. An auto sash controller is designed to close vertically rising sash fume hoods automatically when the operator is not present in front of the fume hood. A passive infrared sensor (PIR) constantly monitors the work area in front of the fume hood. If a person is not detected and the sash opening is clear, the sash will automatically close after a pre-determined time. When the operator is present the sash can be operated manually via a touch sensitive feature or a key pad. Although preliminary designed for operation on VAV fume hoods, auto sash control- lers can also be used on CAV fume hoods for increased safety.

Illustration of Basic Principles

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100%

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20%

Open Bypass

Open Bypass

Restricted Bypass

Restricted Bypass

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Sash Up

Sash Down

Sash Up

Sash Down

Constant Air Volume System

Variable Air Volume System

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