Basic Documentation

Laboratory Ventilation Codes and Standards
Siemens Industry, Inc. 4
Term Definition Commentary
ASHRAE 110 Tests
• (6.1(6.1) Face
Velocity
Measurements
• (6.2) VAV Face
Velocity Control Test
• (6.3) VAV Response
Tests
• (7.1) Flow
Visualization
• (7.2) Airflow Patterns
An anemometer mounted on a stand is used to measure the air velocity at the mid point
of an imaginary grid across the plane of the fume hood’s design sash opening, The grid
spaces must consist of less than 1.0 square feet (0.9 square meters). The anemometer
must read and record 20 measurements at one per second at the mid point of each grid
space. An average air velocity is then calculated for each grid mid point. The average
face velocity for the fume hood will be the average of all grid point average face
velocities The highest and lowest grid space average face velocities are also to be
recorded.
This test is for VAV fume hoods. (VAV fume hoods are equipped with a VAV fume hood
controller to always maintain a constant face velocity regardless of the size of the Face
Opening). The test consists of measuring the average face velocity at the sash design
openings of 25%, 50% and also at the maximum sash design opening.
This test is for VAV fume hoods and consists of two parts. (VAV fume hoods are
equipped with a VAV fume hood controller to always maintain a constant face velocity
regardless of the size of the Face Opening).
1. VAV Speed of Response determines the time in seconds required to first restore
the average face velocity to within 90% of its required value from the time a fully
closed sash is repositioned (opened) to the sash design opening. The sash is to
be moved at a rate of 1.5 feet per second.
2. VAV time to Steady State determines the time in seconds required until the hood
maintains the average face velocity within 90% and 110 % of its required value
from the time a fully closed sash is repositioned (opened) to the sash design
opening. The sash is to be moved at a rate of 1.5 feet per second.
This test provides a visualization of a fume hood’s ability to contain vapors. Smoke is
released just outside of the plane of the sash and its flow pattern is observed. Under
ideal conditions the smoke will flow into the fume hood and flow toward and through the
fume hood’s baffle openings at the rear.
This is a description of the Flow Visualization smoke flow patterns that might be
observed. ‘Reverse Flow’ is when the smoke reverses direction and flows toward the
front of the fume hood. ‘Lazy’ is used to describe a smoke flow that remains on the work
surface without smoothly flowing to the rear baffle openings.
Since the air velocity readings are required to
be taken and then recorded at a rate of one
per second at each grid space an automatic
measurement and data logging system is
necessary.
The average face velocity at each sash
opening is to be obtained following the face
velocity measurement procedure described in
6.1.
The average face velocity measurements for
the VAV Response Tests can be made by
directly measuring the air velocity through the
fume hood slot (see Fume Hood Airfoil) or by
measuring the fume hood exhaust air
velocity. (This latter method requires first
determining the exhaust air velocity that
corresponds to the required average face
velocity.)
The person releasing the smoke at the front
of the fume hood must be careful not to make
any ‘abnormal’ movements that would
influence the smoke flow pattern.
Some minimal amount of reverse flow can
normally be expected at the places where
there is a pronounced change in the fume
hood interior surfaces such as at the work
surface recesses.