Our next installment in this series on reducing airborne contaminants is focused on increasing the effectiveness of new and existing filtration systems. Some of the concepts in this article are long-proven items, and some are on the forefront of innovation. This article is to provide information for available products, not to recommend a specific approach, as each system is unique.
As a filter’s MERV rating increases, its effectiveness at filtering out particulates of smaller size increases. Unfortunately, there is no free lunch, and all that filtering goodness comes at a cost, pressure loss across the filter. For an 8,000 cfm, 20-ton air-handling unit, assuming there is a MERV 8 prefilter in place, adding a MERV 11 filter may add up to $670 (1) per year in electrical charges if the fan can maintain the same airflow. For that same 8,000 cfm, 20-ton air-handling unit, assuming there is a MERV 8 prefilter in place, adding a MERV 14 filter may add up to $890 (2) per year in electrical charges. And it gets worse as you approach HEPA filters, which could cost upwards of $1,500 annually in power consumption.
What if there was a way to take your existing MERV 8 filter and make it perform more like a MERV 9, or take a MERV 11 filter and have it perform more like a MERV 13? Bipolar ionization doesn’t exactly do that, but it does cause particles already in your air-stream, that are otherwise too small to be filtered out by these filters, to cling to each other, increasing size, and allowing them to fall to a surface for cleaning, or be captured by the air filter on the subsequent trip through the system.
This type of product, just like many others, falls under the category of “buyer beware”, as all systems are not created equal, and while they may help filter particulates from the air-stream at a lower cost than added mechanical filtration, the wrong product may produce ozone, which has been shown to have “deleterious health effects” (3), on the respiratory tracts of humans.
Other technologies that can not only provide filtration, but reduce ventilation airflow requirements include air scrubbers. An air scrubber uses gas-phase sorbent technologies that trap gases, volatile organic chemicals (VOCs), and particulate matter, in some cases down to 2.5 microns (4). These devices allow less ventilation air to be used to achieve the same indoor air quality as the ventilation at the code-required rates.
While air scrubbers can be another strategy in providing a safe and comfortable indoor environment, most do not appear to provide filtration of viruses, necessitating the use of secondary or final filtration if the goal of the facility is to reduce or eliminate airborne viruses from the HVAC system.
For buildings that don’t have a central HVAC system, like a school with unit ventilators or an office building with fan-coil units, there are filtration and air scrubbing systems that are portable, or unitary that can be installed in a ceiling or mounted in an exposed application.
These systems, when appropriately applied, can significantly improve air quality within a space, and reduce the amount of airborne contaminants. Consult your professional engineer to determine which application works best for you. If you have any questions, please do not hesitate to contact Stephen E. Oskin, PE, LEED AP at (814) 880-6070 or firstname.lastname@example.org.
(1) Assuming an average pressure loss of 0.30” s.p., $0.10/kwh electricity, 60% fan efficiency, and a premium efficiency motor.
(2) Assuming an average pressure loss of 0.60” s.p., $0.10/kwh electricity, 60% fan efficiency, and a premium efficiency motor.
(3) ASHRAE Position Document on Filtration and Air Cleaning, January 2018.
(4) Enverid air scrubber performance.