WE HAVE SELECTED the most appropriate air purification device for our school/office building. It is a NuShield-R, which is a compact unit—smaller than a cigar box. It uses needlepoint bipolar ionization (NBPI) technology.
It appears that we can count on the impending air scrubber to significantly reduce the airborne transmission of disease inside our school building — as long as the hallway doors are kept ajar, so that the air can keep circulating throughout the building.
Below the jump, this post explains this unit’s benefits and features.
What is NBPI?
Needlepoint bipolar ionization (NBPI) technology is not new. As described here and here, the device generates a nearby field that creates positive and negative ions in the air. As the supply air flows past the unit inside the HVAC system, those ions then form chemical bonds with particles floating in the air, including aerosols with (many kinds of) bacteria and viruses. That action induces the particles to cluster together with other particles, growing in size until they get trapped in the HVAC filter. Meanwhile, those ions also neutralize the pathogens.
How well does it work?
Unfortunately, this technology has not been well tested in real-world conditions. Hence some expert organizations such as ASHRAE, the EPA, and the CDC have cautioned that laboratory tests of NBPI effectiveness (which employ a small test chamber under idealized conditions), as are touted by manufacturers of the devices, should not be taken at face value.
Happily, some real-world results are available—and they were encouraging enough to convince me to rely upon such a device. The best example I found came from late 2020: Trane, a major manufacturer of HVAC systems, sponsored and supervised a series of tests of the effectiveness of an off-the-shelf NBPI device that is similar to what we are ordering. I will summarize their report below.…
A test of effectiveness
The experiments were conducted in a chamber whose dimensions (1007 cu ft) were like the size of a normal room (10′ wide x 12.5′ long x 8′ high). The ionization device was the same type and size rating as we are considering, albeit made by a competitor. It was installed in the ductwork of the HVAC system per the manufacturer’s guidelines. The HVAC system included a standard MERV-8 filter upstream of the BPI device, and its blower created 6 air changes per hour, which is what a properly sized HVAC system should be achieving. In other words, these were normal real-world conditions.
The virus used for testing was a non-infectious kind that is often used as a surrogate for a coronavirus, in part because it is a variety that is thought to be actually harder to disable.
In the control case (with the ionizer off), a known amount of the virus was injected into the air for 14 minutes (not stated whether aerosolized). After 30 minutes from the start of that test, the amount of the virus had decayed naturally by 60%; after 1 hour, by 70%. (I.e., 30% of it still lingered in the air after an hour.)
Happily, the BPI device did demonstrate apparent efficacy for inactivating airborne viruses and bacteria. In one of the test runs, the device was first turned on for one hour prior to the same 14-minute injection of the virus, thus resembling a real-world situation where the HVAC would have been running already for a while when someone contagious walks in to the room. Then the device was kept on throughout the test period. The concentration of ions in the chamber dropped quickly when injection began, which shows that ions were interacting with the contaminant. The same 60% reduction of virus was achieved much faster than in the control case—after only 10 minutes. After 30 minutes, there was 90% reduction of the virus; after 1 hour, 99% reduction.
Similar results were obtained for the bacterium used for testing, which was Staphylococcus aureus, taken as representative of bacteria; it can be found resident on healthy humans yet it can cause respiratory and skin infections.
(In the Trane tests, the ionization device did not demonstrate improvements with regard either to contaminated surfaces, or to the amount of VOCs—volatile organic compounds—even though manufacturers say that it did so in its laboratory tests. Those lackluster results may be a matter of managing to achieve a sufficient concentration of ions near the surfaces in question, and where the VOCs have their source. Another encouraging case study by an engineering company can be found here, which found a big drop in the level of VOCs but by using a large-scale commercial system.)
No ozone involved
Where there are ions, there can also be ozone (a highly reactive gas that can damage lungs). Happily, the NuShield-R is a newer version of the model that our committee member Motz had helped to get installed at Santa Monica Synagogue a few years ago. The difference is that the newer model produces no ozone, whereas the older model produces a small amount, yet at a level that is said to be safe for normal healthy adults. However, I learned from a bit of research that the so-called standard level for safety was actually arbitrary, and that there is good evidence that even tiny amounts of ozone can cause harm in vulnerable populations. Well, in our case we are dealing with preschool children, and at least one adult staff member with compromised lungs. Therefore it seemed important that we get a zero-ozone device. The added cost: a mere $50.
Other characteristics
During installation, the device will be wired so as to run only when the HVAC blower is on. Its power draw is less than 10 watts, which suggests that its use will add less than $10/yr to our electric bill.
It has no moving parts, and it needs no maintenance. It comes with a 3-yr warranty and is expected to last for 10–15 years.
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