ASHRAE Journal - June 2019 - 17

INDUSTRY NEWS

While the authors highlighted
several good technical points on
the speciﬁc technology utilized in
the testing, it does not provide sufﬁcient detail on the differences
between corona discharge and NPBI
technologies. The technology and
subsequent product used in the
tests in the New York study are listed
as a known ozone generator by the
State of California. Furthermore,
the same product was removed
from the FEMA Trailer Study for
Formaldehyde Reduction due to
their high ozone output. Publishing
a study from 2013 based on a known
ozone producing technology does
not reﬂect the current state of the
art. The column fails to detail the
differences between the technologies which has caused a lot of confusion, skepticism and concerns in
the market. The column has done a
great disservice to all that are dedicated to promoting the use of proven
new technologies to deliver clean
indoor air while delivering energy
and cost savings.
Corona discharge systems have
been operating since the late
1800s and were developed by Sir
William Crooks. At the time they
were called the "Crooks Tube," as
well as cathode ray tubes. Around
1928 William Langmuir changed
the name to "plasma tube." They
are marketed as corona discharge
tubes (CDT), or dielectric barrier
discharge (DBD) systems. Many
companies use CDT/DBD to generate ozone for odor control in unoccupied spaces. In short, there will
be ozone when using corona CDT/
DBD technology.`
Figure 1 shows an example of a
CDT. There is an inner ﬁlament, a
glass tube, and an outer ﬁlament,

Figure 3. NPBI electrode.

Figure 2. A sample of eV potential for several
compounds.

very similar to the product used in
the New York classroom study. The
glass is the "dielectric," or resistance
to the voltage path to ground. The
dielectric can be glass, quartz, mica,
ceramic, or any material that has a
high insulating value. For a corona
discharge system to operate, the
voltage and current must be high
enough to breakdown the dielectric
material to complete the electrical
path to ground. When the power
output is high enough, and the
path to ground is achieved due to
the dielectric breakdown, a corona
discharge is formed. The corona
discharge is easiest seen in darkness.
It appears as a purple glow down the
entire tube.
The power required to breakdown
most dielectrics exceeds 12.07eV
(electron volts). Every gas has an
electron volt potential. Figure 2
shows a sample of eV potential for
several compounds. Oxygen has
a potential of 12.07eV. When the
power input is greater than 12.07eV,
ozone is created as oxygen is ionized. Understanding the relationship of power to eV is critical when
designing air puriﬁcation systems
to produce the desired effect, while
avoiding the formation of ozone and

other by-products. NPBI is uniquely
different from corona discharge
systems. NPBI does not use a dielectric. It does not produce ozone. The
power output is controlled to less
than 12.07eV.
NPBI electrodes, or "needles,"
are made from carbon fiber
(Figure 3), titanium, silver,
gold, stainless steel, and other
corrosion resistant conductive
materials. As you can see from
the Figure 3, the electrodes are
attached to the flexible circuit
and there is no dielectric.
NPBI has been used for particle
reduction, odor control, pathogen
control and static electricity control
for more than 10 years. The production of unwanted by-products,
including ozone, associated with
corona discharge air cleaners are
avoided when using NPBI. The
newer NPBI technology should NOT
be associated with corona discharge.
This should be made clear to all,
especially the readers of the ASHRAE
Journal.
Charlie Waddell, Associate Member
ASHRAE, Chief Technology Ofﬁcer,
Global Plasma Solutions, Savannah,
Ga.
Editor's Note: The authors of the column
were contacted for a response, but none
had been received by press time.

J U N E 2 0 19

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ASHRAE Journal - June 2019

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