ASHRAE Journal - June 2022 - 34

TECHNICAL FEATURE
FIGURE 2 Background schematic of testing apparatuses
inside of the fume hood: (from top) the
glass tube rotameter, (b) the thermostatic heaters,
(c) the large clutter, (d) the small clutter.
A
equipment configuration,10 and
Figure 2 presents more details of the
testing apparatuses placed inside
the fume hood with the large and
small clutter.
B
Testing Procedure
The fume hood opening was
divided into multiple equal-sized
rectangular zones to form an imaginary
testing grid pattern, as shown
in Figure 3. The grid spaces (318
mm × 145 mm [12.52 in. × 5.71 in.])
were less than 0.09 m2 (0.1 ft2), and
the larger side of the grid rectangle
did not exceed 330 mm (13 in.), as
recommended by ASHRAE Standard
110-2016.11
C
D
The airflow velocity perpendicular
to the sash was recorded at the
center of each grid box using the
thermal anemometer mounted on
a moveable stand. The sensor of the
anemometer was held at an angle
parallel to the opening of the hood
to avoid misalignment, which might
cause erroneous readings.
The anemometer recorded 20
The tracer gas ejector (diameter
90 mm [3.5 in.], height 400 mm
[15.7 in.]) was constructed at the
center of the fume hood inner
desktop. The tracer gas, SF6 (≥99.9%
pure), was used as a surrogate for
the potential contaminant and was
constantly supplied from one gas
cylinder close to the fume hood
during the field test. The figures in
the research by Chen, et al., give
a general picture of the overall
34
ASHRAE JOURNAL ashrae.o rg
velocity readings per grid rectangle,
at the rate of one per second, starting
at the center of the top left rectangle
grid (point 1). This procedure
was repeated for each grid rectangle
from left to right and top to bottom
until the entire sash opening area
had been surveyed. The 20 readings
for each grid rectangle were averaged
to yield their respective zone
face velocities, and then all of the
zone face velocities were averaged to
give the average face velocity of the
fume hood.
The face velocity values were tested
in scenarios with different inside
clutters (small and large), thermal
loads (without thermal challenge,
100°C and 200°C [212°F and 392°F])
J U N E 2022
and tracer gas emission rates (4 and
8 L/m [0.14 and 0.28 cfm] emission
rates). The higher releasing rate (8
L/m [0.28 cfm]) was designed to
simulate the worst-case condition
under which volatile materials are
heated to evaporate continuously or
pure gases leak out directly.1
Although the releasing rate can
exceed 8 L/m (0.28 cfm) at some
extreme conditions like projectiles
from a grinder or gases from an orifice
on a high-pressure pipeline,21
these scenarios are not considered
in this research because using a
typical chemical fume hood for such
operations or under such conditions
may not be appropriate.11
Instantaneous tracer gas concentrations
were continuously
monitored at the bottom center of
the sash under the same condition
of the face velocity testing. Apart
from the on-site testing, multiple
samples were selectively collected
with sample bags connected to air
sampling pumps and analyzed using
a gas chromatograph-discharge
ionization detector and a gas
FIGURE 3 Demonstration of the fume hood face
velocity measurement in the laboratory.
http://ashrae.org http://ashrae.org
ASHRAE Journal - June 2022

Table of Contents for the Digital Edition of ASHRAE Journal - June 2022
