ASHRAE Journal - December 2023 - 48

TECHNICAL FEATURE
FIGURE 5 Particle count measurements versus time for the smoke test. Note
that the data point at t = 5 min for the 0.5 µm - 1.0 µm diameter particles was
removed because it was deemed as unreliable.
1010
108
0.3 µm-0.5 µm
0.5 µm-1.0 µm
1.0 µm-3.0 µm
3.0 µm-5.0 µm
5.0 µm-10.0 µm
>10.0 µm
106
104
102
5
10
Time, t (min)
FIGURE 6 Particle removal efficiency versus time for the smoke test. Note that the
data point at t = 5 min for the 0.5 µm - 1.0 µm diameter particles was removed
because it was deemed as an outlier. The inset is a zoomed-in view of the main
figure, focusing only on the 0.3 µm to 3.0 µm particles.
0.3 µm-0.5 µm
120
100
80
60
40
20
5
0.5 µm-1.0 µm
1.0 µm-3.0 µm
15
20
slightly to 99.72%. Where a post-filter is not used, the
minimum efficiency further decreases to 76.98%, with
an efficiency of 82.2% for particles in the 0.3 µm to
1.0 µm range (approximately equivalent to a MERV 14
filter). The results here therefore highlight that while a
non-thermal plasma system can operate as an efficient
particle removal device in itself, its performance can be
raised to a HEPA-like filter when used in combination
with an appropriate porous media post-filter.
Results from a smoke test have also shown that the PFS
is able to remove 99.8% of smoke particles introduced
into the room (i.e., greater than a 2 log10 reduction)
within 15 minutes of operating in a room at a flow rate
equivalent to 30 air changes per hour.
While the results show that non-thermal plasma
air purification systems are capable of removing PM
at HEPA-like levels with significantly less pressure
drop, further research and development is currently
underway to further optimize these systems under a
broader range of operating conditions.
References
102
100
98
96
10
10
Time, t (min)
is likely due to outdoor air leakage into the room.
Conclusions
Experiments of PM count have revealed a nonthermal
plasma air purification system can achieve
single-pass particle collection efficiencies in excess
of 99.95% (similar to a H13 HEPA filter) across all
measured particle sizes between 0.3 µm and 10 µm
where filter face velocities are <1 m/s (<197 fpm) and a
MERV 13 post-filter is used. At greater face velocities
(1.6 m/s [315 fpm]), the minimum efficiency decreases
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15
Time, t (min)
15
20
20
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Particle Removal Efficiency, ρ (%)
Particle Count
ρ (%)
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