There are a number of alternative commercial air purifiers available. Each one is unique. You need to choose one to suit your own requirements. Here's what to look for in an HVAC air purifier.
One of the key things to understand is the difference between an active purification method and a passive method. Active methods get far better results.
IMPORTANT
Passive vs. Active air cleaning
Passive air purifying systems rely on the contaminant to be brought to the device to affect a change. Active systems go to the affected space to interact with the contaminant at it’s source. For example a filter or UV can only impact on those contaminants that arrive close to it. Ionisation creates ions which spread widely into the whole contaminated space to eliminate contaminants in the indoor environment.
How to choose the best commercial air purifier for the job
Media Filtration
Filters are used to trap particles from the air passing through the filter.
Increasing the surface area or thickness of the filter will increase efficiency of the filter to trap more and smaller particles.
Filters are highly reliant on airflow and air exchange to drive contaminants to the filter.
Higher efficiency air purification filters will increase static pressure and restrict airflow, using more fan horsepower to saturate the space with conditioned air. AC systems cycle more often and for longer duration to satisfy the thermostat and use more energy.
This is a passive technology
Sorbent Filtration
These devices are designed to absorb gases from the air passing through the device.
It is very airflow restrictive so will use significant HVAC energy to allow for operation.
This method is highly reliant on airflow and air exchange to bring the contaminant to the device.
It needs frequent maintenance as sorbent gets spent and can no longer absorb.
Maintenance can be cumbersome as spent filters or cartridges need careful disposal.
Intended only for VOCs removal.
This is a passive air cleaning method.
Dielectric Barrier Discharge -Bi-Polar Ionisation
Not all BPI Ionisers are the same
There are multiple ways to generate the energy needed to create air ions. The most effective technology uses dielectric barrier discharge (DBD).It is the most comprehensive & powerful Form of HVAC Air Purification.
Ions are generated when voltage is applied to a cathode tube, where the inner metal is a cathode, and a stainless-steel outer screen is an anode. The voltage causes a non-thermal plasma discharge on the surface of the tube, which then produces ions in an alternating fashion, negative, positive, switching polarities 60 times per second.
DBD operates at 12.6 ev or higher. This is done because at 12.08 ev ozone can be generated but at greater than 12.53 ev ozone is destroyed and converted back to oxygen, which allows for sanitization of microbes & breakdown of complex VOCs.
DBD tubes are sealed, they are protected from fouling by contaminated air = reliable performance.
DBD BPI has proven effectiveness on particle reduction, VOC reduction and microbial reduction.
The technology has been in use and studied worldwide for over 50 years.
The BPI air purifier is located on the supply side of a HVAC system. Airflow passes over patented ion generating tubes which are energized creating Dielectric barrier Discharge + and – air ions. The ions are attracted to oppositely charged contaminants removing them from the air and surfaces.
A properly designed HVAC air purifier increases bipolar ions in indoor environments to concentrations of 500 – 1,500 ions/cm3. Replicating ion levels found in pristine natural environments.
This is an Active air cleaning method of air purification - the charged Ions actively seek out contaminants to eliminate them regardless of people or objects in the occupied space.
Electrostatic Precipitation (EP)
Very commonly used technology for in-duct HVAC air purification and standalone air cleaning units as an air purification method.
EP can be a very effective & efficient filter: it can trap very small particles with very low airflow restriction as compared to media filters.
However, maintenance is critical to performance as the collector cell must be regularly cleaned to allow it the trap particles.
EP will not affect VOC’s and can only trap micro-organism sized particles and not neutralize them.
Single polarity ionizing wires or grids or needles use high DC voltage up to 15,000 VDC and can generate ozone as a by-product especially when systems are not maintained.
EP is a Passive air cleaning method
NeedlePoint Bi-Polar Ionisation
This technology uses a corona discharge.
Whilst it is a more affordable form of BPI Air Purification, it has limitations.
Discharge occurs when voltage is applied to rows of nickel coated steel pins recessed in electronic modules. Each module has two pins, one will produce a positive charge or form a positive ion and the other a negative charge or negative ion.
The technology produces bi-polar ions by applying voltage to rows of needles or carbon fiber brushes. The needles alternate in polarity one positive, one negative.
NBPI will cause particle agglomeration and some gas phase breakdown of VOC’s.
NBPI ions are produced simultaneously. This leads to ions neutralizing each other and little ion persistence, especially in large spaces and larger volumes of air.
NBPI operates at an ev of 12.07. This is done to prevent ozone generation but at this low power cannot produce ROS superoxide anion needed to form hydroxyl radicals and deactivate micro-organisms.
Since the brushes are a corona discharge and are exposed to open air, they can be fouled by air contaminants.
NBPI ions are produced in a focused stream straight from the emitters, very little scatter and diffusion into a large space.
NeedlePoint is an Active (not Passive) air purification system. However, it is limited since the equipment only works effectively when installed very close to the indoor space to be cleaned, preferably at the Fan Coli Unit
Ultra-Violet Germicidal Irradiation (UVGI)
Ultraviolet Irradiation, a.k.a. germicidal UV (UVGI), UV(C) wavelength deactivates pathogens.
Can be installed in the AHU or duct as an HVAC air purifier. Typically used to keep coils clean.
Not effective in occupied spaces
Needs exposure time (3-6 min) to be effective.
Intended only for the removal of pathogens.
This is a passive air cleaning method.
Dry Hydrogen Peroxide (DHP)
Hydrogen peroxide in liquid form has been proven as a disinfectant.
DHP technology is highly reliant on ambient humidity in the air. In drier air a lower conversion to peroxide would occur.
Very little performance documentation or case studies exist FOR DHP and peer-reviewed studies are minimal.
Hydrogen peroxide is known to be effective at a 3% solution. DHP systems claim to operate at 25 ppb, which is far lower than 3%.
DHP technology uses UVA bulbs, which contain mercury. UVA has also been linked to skin cancer.
Intended us - for microbial inactivation only.
An Active air cleaning method.
Photo Catalytic Oxidation (PCO)
The PCO method generates Hydroxyl radicals, very effective to deactivate micro-organisms and disinfect.
Hydroxyl radicals cannot be measured so difficult to quantify performance from PCO devices.
Hydroxyl radicals have a 1-2 second half life: at a typical air velocity of 800 FPM so hydroxyls can only travel 26 feet from the PCO device.
Targeted for microbial inactivation only.
Has been marketed under different descriptions. Photo-hydroionization (PHI) uses the same scientific principle.
PCO is an Active air cleaning method but limited.
