ASHRAE Journal - June 2024 - 52

TECHNICAL FEATURE
reduced from 30.7% to
19.4% (by about 37% percent
(Figure 5). These figures
show nonuniformity in the
distribution of contaminants
in the lab space for both
low and high levels of ach,
which contradicts the
traditional belief that high
ach can create " well-mixed "
uniform concentrations.
Despite the mixing airflow
patterns, the contaminant
distribution is not uniform.
In reality, such " well-mixed " conditions can probably
A
Time: 720 s
Concentration (ppm)
25.0
22.5
20.0
17.5
15.0
12.5
10.0
7.5
5.0
2.5
0.0
Without DCV
occur only in the exhaust ducts. Previous studies
indicate that the airflow patterns are independent of the
ach levels, and the layout of supply and return locations
can impact the flow path of contaminants.7,8 Therefore,
A
Time: 720 s
SIBZ = 30.7%
B
Average 23.5 ppm
FIGURE 4 Distribution of contaminant concentration at the breathing zone after 720 s of the release of contaminant, with and
without DCV. It shows about 30% reduction in the average concentration with DCV.
B
Time: 720 s
Average 16.4 ppm
With DCV
FIGURE 5 Cloud of 25 ppm concentration showing the spread after 720 s of the release of contaminant with and
without DCV. It shows about 37% reduction in the spread of contaminants with DCV.
Time: 720 s
SIBZ = 19.4%
Without DCV
With DCV
DCV can enhance the dilution levels but can't alter the
airflow patterns and flow path of contaminants.
As shown in Figures 4 and 5, in both cases the zone of
high concentration (25 ppm and higher) tends to drift
toward the exhaust grille located near the door undercut.
This grille is also closer to the source
of the contaminant than the other
grille in the opposite corner. As a
result, the concentration levels in the
first row of the benches are lowest
compared to those in the second and
third rows. However, in the case of
DCV, Figure 4 shows a slightly higher
concentration in the first row. It
should be noted that these results
are showing the impact of dilution
due to DCV at 720 seconds when the
generation of chemical vapor ceases.
FIGURE 6 Variation of Spread Index (SI)BZ25 with time showing impact of DCV in reducing the Spread Index and
the Purge Time.
35.0
30.0
25.0
20.0
15.0
10.0
5.0
0.0
2
4
6
8
10
12
14
16
Time (minutes)
52
ASHRAE JOURNAL ashrae.org J U N E 2024
420 s
Without DCV
With DCV
Analysis of Spread Index (SI)BZ25 and
Purge Time (PT)
25
18
20
22
24
26
28
30
Figure 6 shows the variation of
Spread Index (SI)BZ25 with time for
both the cases-with and without
demand-control ventilation. As
shown in this figure for the case
without DCV, the (SI)BZ25 (spread
of contaminants) increases with
the release of contaminants and
reaches the peak value of 31% after
13 minutes-one minute after the
release of the chemical vapors stops.
After this time the (SI)BZ25 value
Spread Index BZ25
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ASHRAE Journal - June 2024

Table of Contents for the Digital Edition of ASHRAE Journal - June 2024

Contents
ASHRAE Journal - June 2024 - Intro
ASHRAE Journal - June 2024 - CT1
ASHRAE Journal - June 2024 - CT2
ASHRAE Journal - June 2024 - Cover1
ASHRAE Journal - June 2024 - Cover2
ASHRAE Journal - June 2024 - 1
ASHRAE Journal - June 2024 - Contents
ASHRAE Journal - June 2024 - 3
ASHRAE Journal - June 2024 - 4
ASHRAE Journal - June 2024 - 5
ASHRAE Journal - June 2024 - 6
ASHRAE Journal - June 2024 - 7
ASHRAE Journal - June 2024 - 8
ASHRAE Journal - June 2024 - 9
ASHRAE Journal - June 2024 - 10
ASHRAE Journal - June 2024 - 11
ASHRAE Journal - June 2024 - 12
ASHRAE Journal - June 2024 - 13
ASHRAE Journal - June 2024 - 14
ASHRAE Journal - June 2024 - 15
ASHRAE Journal - June 2024 - 16
ASHRAE Journal - June 2024 - 17
ASHRAE Journal - June 2024 - 18
ASHRAE Journal - June 2024 - 19
ASHRAE Journal - June 2024 - 20
ASHRAE Journal - June 2024 - 21
ASHRAE Journal - June 2024 - 22
ASHRAE Journal - June 2024 - 23
ASHRAE Journal - June 2024 - 24
ASHRAE Journal - June 2024 - 25
ASHRAE Journal - June 2024 - 26
ASHRAE Journal - June 2024 - 27
ASHRAE Journal - June 2024 - 28
ASHRAE Journal - June 2024 - 29
ASHRAE Journal - June 2024 - 30
ASHRAE Journal - June 2024 - 31
ASHRAE Journal - June 2024 - 32
ASHRAE Journal - June 2024 - 33
ASHRAE Journal - June 2024 - 34
ASHRAE Journal - June 2024 - 35
ASHRAE Journal - June 2024 - 36
ASHRAE Journal - June 2024 - 37
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ASHRAE Journal - June 2024 - 40
ASHRAE Journal - June 2024 - 41
ASHRAE Journal - June 2024 - 42
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ASHRAE Journal - June 2024 - 46
ASHRAE Journal - June 2024 - 47
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ASHRAE Journal - June 2024 - 49
ASHRAE Journal - June 2024 - 50
ASHRAE Journal - June 2024 - 51
ASHRAE Journal - June 2024 - 52
ASHRAE Journal - June 2024 - 53
ASHRAE Journal - June 2024 - 54
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ASHRAE Journal - June 2024 - 72
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ASHRAE Journal - June 2024 - Cover4
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