Air Purification – UV-C vs Plasma
Two air purification technologies are regaining popularity amid the COVID-19 pandemic, Ultra Violet Germicidal Irradiation in the ‘C’ spectrum (UV-C) by Sanuvox, and ion generating plasma using Global Plasma Solution’s company Needle Point Bipolar Ionization (NPBI) technology. Both have claims to kill viruses. This tech memo will show that both of these technologies have merit and when applied properly, can improve air quality, reduce maintenance, improve occupant health, and save energy.
Let us begin first with a short description and application of each technology.
Of all the spectrums of ultraviolet light, only the ‘C’ spectrum is used for killing bacteria and viruses. The ‘A’ & ‘B’ spectrums are the reasons we wear sunglasses and sunscreen at the beach to protect our retina and our skin from harmful sunburns. The ‘V’ spectrum does not reach us since our ozone layer absorbs these rays. The ‘C’ spectrum breaks down the DNA/RNA structure of viruses and bacteria, rendering them incapable of infecting our lungs. UV-C lamps emit UV radiation towards an object in the airstream and are effective at killing viruses and bacteria that are present in that location. When applied on the leaving air side of
the cooling coil and aimed at the coil and drain pans, UV-C is effective at reducing and even eliminating algae growth thus maintaining a cleaner coil and reducing air pressure drop. This in turn saves fan energy, reduces coil cleaning maintenance, and provides cleaner air to the occupants reducing the chance that someone will become sick in the workplace. Since all the system airflow must pass through the coil section, the benefits of killing viruses and bacteria are felt throughout the system. However, some viruses have such a small particle diameter that they can linger in the space and rarely can be driven by the ventilation system passed the UV lamps. The COVID-19 virus particle diameter has recently been found to be approximately 0.12-micron diameter. Very small when comparing to a human hair that is about 80 micron in diameter! And still very small when comparing to the tuberculosis (TB) bacteria at 3 to 5 micron in size. Some other drawbacks to UV-C technology are the cost of replacing lamps at the frequency that they fail to deliver adequate irradiation. Since it is difficult to determine if the blue light is still effective, one of our clients has adopted lamp replacement at regular filter changeout intervals, which is quarterly (every 3 months) for them. The lamps are also harmful for human eyes and skin contact, so a shut off switch and viewing window is necessary to disable power to the lamps and verify lamp is out prior to entry into the cooling coil section of an air handler. The manufacturer, Sanuvox, does claim to build their lamps with seal tight wiring connectors so the lamps will last longer than the conventional life when used in the moist airstream downstream of the cooling coil. They also make parabolic reflectors for their lamps making them more effective at concentrating the rays on objects and particles in the airstream. There is a wide range of product offerings using germicidal UV-C technology including portable room units, duct mounted units, and units configured special for coil mounting in specific MFG A/C units such as Bard. A good place to begin is the cooling coil of your existing house air handling system and take advantage of the existing duct distribution already in place.
PLASMA (Needle Point Bipolar Ionization - NPBI)
Much like UVC, plasma kills viruses by breaking down the DNA/RNA, thus making the virus ineffective at infecting people’s respiratory system. Plasma technology has the added benefit of agglomerating particles. As particles pass through the plasma field, they become ionized into positive and negatively charged particles, they circulate through the space, they are attracted to and attach to other particles, like a snowball effect. Each time through, the particles get larger until the filters can effectively trap them, making the filters more effective. The plasma technology basically ionizes particles or breaks down molecules into their elemental constituents. For instance, the air pollutant ammonia or NH3 will be ionized into N and H which will later combine in the air to become harmless N2 (nitrogen molecules) and H2O (water molecules). This technology is also UL Listed as having “zero ozone emission’s”, when tested in accordance with UL-2998 does not exceed 0.005 ppm ozone. Unlike electronic air cleaners for instance that can produce ozone above allowable limits.
The best place to apply the NPBI ionization device is down stream of the filters and upstream of the cooling coil. The plasma field is not as effective in the moist air environment downstream of the cooling coil. If there are final filters in the system, it is recommended to place the ionization device downstream of the last filter bank. If there are high efficiency filters downstream of the ionization device, most of the ionized particles can be trapped by the filter and greatly reduce the effectiveness of this technology since it depends on those ionized particles continuing their circulation through the space to agglomerate (snowball) and return pollutants into their harmless elemental constituents. A hospital operating room air handling system for instance would not be a good application for ionization since the last filter bank is a HEPA filter diffuser located in the operating room. UVC would be better applied for hospital operating rooms. Ionization has the same effect as UVC at keeping the cooling coil clean and free of algae even when located on the upstream side of the coil. The ionization passes through the coil and is effective on both sides thus keeping the coil clean. A great benefit of the NPBI plasma technology is it is virtually maintenance free. Only annual cleaning of the carbon fiber brushes is recommended, and the carbon fiber material never needs replacement. The cleaning process is as simple as using a nylon (wire free) brush for gently cleaning the needles (carbon fiber tips) and a cloth using isopropyl alcohol for between the brushes and outer bar.
NPBI technology is not available in a portable room unit. The only options are in the air stream using coil or duct mounting types. There are a wide range of types for air stream mounting including a ribbon type that is suitable for mounting in small PTAC style A/C units. The company, GPS, also manufacture’s ion detectors in both room mounted or duct mounted versions. These are intended to be used downstream of the ionization device for verification of ion levels and reporting ion levels in real time to a BMS using hardwired analog outputs or communication interfaces such as BACnet or MODBUS. This provides positive feedback to the facility manager verifying the ionization device is operating effectively. Also offered is a detection device installed with the ionization device. The detection unit senses output and the “Plasma On” indicator light at the ionization device power supply unit will illuminate. Alarm contacts are also included to indicate when the unit is not operating properly.
Both technologies have their application and place in the field. For reasons stated above we would recommend UVGI for hospital operating room air handling systems. Because of the maintenance (lamp replacements) associated with UVGI, we would recommend NPBI plasma technology for air handling systems that do not use HEPA filter diffusers. Although we do not have any clients with NPBI plasma technology installed, the GPS manufacturer does have a long reputable client list of existing installations indicated on their website.