This article is written based on the optimal setup we have seen. Some situations may require a different strategy based on specific needs.
As the air returns to the air handler, it contains any particles it has picked up from the occupied area (dust, odors, virus and allergens) and anything that has been introduced through the fresh air intake (pollen, dust and outdoor molds). A bipolar needlepoint ionizer installed ahead of the filters will cause all of these pollutants to bind to each other, becoming larger in size enabling the filtration to be more effective. This has been done for many years and has proven a very effective way of reducing airborne particles of all types.
There is one drawback, however, to having the ionizer ahead of the filters. This is that many of the ions do not get past the filters.
Ions have a distinct advantage of travelling with the airstream for up to 60 seconds and bring benefits as they do this. For this to happen they need to be installed as far into the supply as possible. This may be at the fan or in the trunk line before the first split. These ions are then able to enter the occupied area dropping particles from the air space and doing their disinfecting work.
UV lights have been used in HVAC systems for many years to control bio-growth on the coil and to sterilize the air in medical facilities. Air sterilization, when accomplished at the coil, gives the added advantage of efficiency gains and reduced power consumption associated with keeping the coil free of mold. When a documented kill rate is desired, UV lights have a distinct advantage due to the many years of testing on all forms of mold, bacteria, pathogens, and viruses.
Based on what we have already covered, our recommendation is to use the best filtration your equipment is able for. In many cases this is a MERV 13 pleated filter, but where final filters are used, such as bags, mini pleats, or cell filters, then a MERV 15 or possibly higher can be used. This will allow the ionizer to be placed in the supply airstream.
In most cases the ideal setup is:
1. Best possible filtration
2. UV lights at the coil for a documentable kill rate and coil irradiation.
3. Ionizer in the supply to further clean the air in the occupied area.
Steps 2 and 3 can be used alternately based on need or budget, but they work together very well.