Ventilation - Filtration - Air Purification
Both official government recommendations and private standards now recognize a truth that a minority of experts has known for quite some time: effective management of indoor air quality (IAQ) necessitates the integration of ventilation, filtration, and air cleaning. Below, we provide an overview of why these three factors must collaborate to meet the indoor air quality goals of your organization.
Air ventilation
According to ASHRAE, ventilation is "the process of supplying outdoor air to or removing indoor air from a dwelling by natural or mechanical means." Natural ventilation occurs through doors and windows, driven by wind, pressure, and density differences. Mechanical ventilation is achieved through equipment such as fans and blowers.
However, the terms "filtration" and "air cleaning" seem to lack official industry definitions or consistent usage. Before the COVID-19 pandemic, filtration was often (inaccurately) portrayed as the sole viable air-cleaning technology. Since the pandemic, filtration and air cleaning have often been discussed as distinct concepts, both of which are technically incorrect.
The term filtration pertains to the mechanical capture of contaminants through a fibrous or occasionally electrostatic/adsorbent medium (i.e., filters.) Conversely, air cleaning encompasses any technology designed to capture, remove, inactivate, or neutralize airborne contaminants. Therefore, filtration represents just one among many air-cleaning technologies.
| Ventilation | Filter-Based Air Cleaning | Non-Filter Based Air Cleaning |
|---|---|---|
| HVAC intakes & exhaust | Window units & attic fans | Screen doors & windows |
| HEPA filters | Electret filters | Activated carbon |
| GI | Bipolar ionization | Advanced photocatalytic |
Air filtration
While ventilation is an essential and effective solution for carbon dioxide buildup, it requires assistance for many other contaminants due to the following reasons:
Ventilation can't entirely flush contaminants. Air changes per hour (ACH) is a common measure of ventilation, indicating how many times a room's worth of new air is brought in per hour. However, this doesn't mean all the old air is forced out; instead, new and old air mix, diluting contamination rather than removing it. Therefore, air filters/cleaners can assist ventilation by removing or neutralizing contaminants according to industry standards.
Inhaling contaminated air is possible before it exits a space, as highlighted in a study by the National Institute of Health. The crucial factor influencing contaminant transmission in enclosed, mechanically ventilated environments is the path between the source and exhaust, not just the air changes per hour.
A study from a U.S. Department of Energy lab revealed that increasing the air change rate expels SARS-CoV-2 from the source room faster but also elevates exposure rates in connected rooms. This underscores the necessity for active air cleaning during the ventilation process.
Ventilation strategies may necessitate renovations. According to the EPA, many residential heating and air-conditioning systems rely on infiltration and natural ventilation, lacking a mechanical mechanism to bring in outdoor air. When natural ventilation proves insufficient, alternatives include investing in a costly HVAC system overhaul or opting for portable air cleaning solutions.
Despite the need for outdoor air to replace indoor air, outdoor air itself is not devoid of contaminants. Demand control ventilation (DCV), which redistributes air between rooms, eventually draws in new outdoor air. While outdoor air typically lacks active viruses, it contains high levels of pollution and pollen, with 90% of nations globally breathing air that fails to meet WHO guidelines. Consequently, outdoor air requires filtration before entering buildings.
Air purification system
Filtration addresses various drawbacks associated with ventilation, particularly concerning indoor and outdoor particle pollution. Nevertheless, filtration itself has its own limitations:
The most efficient filters are incompatible with HVAC systems. Fibrous filters are assigned MERV ratings based on their effectiveness in filtering particles of different sizes. However, as the MERV rating increases, so does the power required to push air through the filter. When high-grade filters are integrated into an HVAC system, the heightened power demand and air pressure can potentially harm the system.
This is particularly evident in the case of HEPA filters. According to ASHRAE's filtration and disinfection guidelines, retrofitting existing HVAC systems with HEPA filters is generally impractical due to the associated high pressure drops and the need for new filter racks to ensure adequate sealing and prevent filter bypass.
Fortunately, numerous alternative options exist, ranging from induct air cleaners that impose minimal strain on the system to portable devices that combine both filtration and active air purification.
Filters inherently operate passively. Regardless of a filter's quality, it cannot filter air that hasn't come into contact with it. If occupants breathe in contaminated air before it reaches the filter, the filter essentially provides no value. Therefore, passive filtration is most effective when complemented by active air cleaning technology.
How can we keep the air clean
Being an air purification company, one might anticipate that ActivePure would assert the flawlessness of non-filter-based air cleaning. However, the reality is that air cleaning is intended to collaborate with other tools and technologies for the following reasons:
Carbon Dioxide Consideration:
Many air cleaners do not effectively address carbon dioxide. Although devices known as "carbon dioxide scrubbers" are utilized in spaceships and submarines to eliminate carbon dioxide, implementing them in offices or homes is not yet practical. In everyday scenarios, ventilation remains the most effective method for diluting CO2.
Specialized Nature of Air Cleaners:
Air purification technologies typically focus on specific types of contaminants. In the case of ActivePure, our technology is designed to target airborne viruses, bacteria, mold spores, and VOC gases. When a broader spectrum of cleaning is required, we complement our technology with HEPA filters to capture non-living particles and activated carbon filters to assist in dealing with odors.
The evolution of standards for clean air
No individual air quality approach is crafted to operate in isolation. Optimal air quality strategies encompass a blend of ventilation, passive filtration, active air cleaning, and source control. Each tool complements the others, striving to replicate the nearest possible equivalent to unpolluted outdoor air.
Presently, both governmental and private entities are actively working towards formulating Indoor Air Quality (IAQ) standards that comprehensively tackle the issue of infectious aerosols. Here, you can explore ActivePure's guidance on IAQ, specifically addressing the mitigation of infection risks in a post-pandemic world.