Basic Documentation

Table Of Contents
Laboratory Ventilation Codes and Standards
Siemens Industry, Inc. 26
Topic Requirement(s) Commentary
VAV (Variable
Air Volume)
American National Standard for Laboratory Ventilation ANSI/AIHA Z9.5-2003
3.2.6 A variable air volume hood is a laboratory hood that shall meet the
requirements in 3.2.1 and 3.3 and is designed so the exhaust volume is varied in
proportion to the opening of the hood face. (3.2.1 requires hood construction be
adequate and 3.3 requires adequate face velocity, periodic face velocity
measurement and an airflow measuring device on the hood.)
The (laboratory) supply and exhaust systems shall be balanced. If the laboratory
uses variable air volume, the supply and exhaust shall modulate together to
maintain this balance In addition, modification of the hood exhaust shall not
compromise the total laboratory exhaust. Any modification of the hood exhaust
shall not compromise other fundamental concerns.
6.5.3.3 The VAV hood controls shall provide stable control of flow in the exhaust
and supply ducts and variation of flow must not exceed 10% from design at each
sash configuration or operating mode.
VAV fume hoods are termed ‘restricted
bypass’ hoods by certain manufacturers
since the bypass area is only required to
allow the required minimum airflow through
the fume hood when the sash is completely
closed. VAV fume hoods require automatic
exhaust air controls that adjust the hood
exhaust in conjunction with the VAV fume
hood’s sash position and the exhaust
system’s static pressure. These controls must
also be integrated with the overall laboratory
room ventilation control system to maintain
the ‘balance‘ referred to in the AIHA/Z9.5
3.2.6 text.
VAV type fume hoods offer the following
advantages over non-VAV fume hoods:
Positive face velocity control.
Less laboratory room supply makeup air
is required when VAV hood sashes are
not fully open thus yielding an energy
savings.
Less fume hood exhaust and a
correspondingly less room supply
makeup airflow often reduce the room
sound level.
Less overall ventilation air requirements
in the building can reduce the size of
HVAC system components including the
boilers, chillers, fans, ducts, etc. which
yields a lower installed system cost.
(Also see Diversity on the pages that
follow.)