In recent decades, many building owners have become more interested in saving energy, conserving water and reducing their overall environmental footprint. However, designing buildings that are healthy for occupants is also important, and this has been highlighted by the coronavirus outbreak. We spend 90% of our time indoors, according to the U.S. Environmental Protection Agency, and indoor air is typically 2 to 5 times more polluted than outdoor air.
Viruses are just one of many airborne threats that affect humans. Other biological hazards include bacteria, mold spores, dust mites and pollen. Negative health effects of substances such as volatile organic compounds (VOCs), particulate matter (PM) and nitrogen oxides (NOx) have also been identified. Carbon monoxide is especially dangerous because a concentration of just 1% in the air causes loss of consciousness within minutes and possibly death.
Improve indoor air quality and make your building healthier and more productive.
Every building design is unique, but there are three main strategies for improving air quality:
- Eliminate sources of indoor air pollution, or minimize them if complete removal is not possible.
- Using natural and mechanical ventilation, constantly replace stale air with fresh outside air. This reduces air pollution levels through dilution and extraction.
- Purify indoor air directly with methods that capture or destroy pollutants. This includes filtration, chemical purification and ultraviolet purification.
The most cost-effective approach is to first minimize sources of air pollution and then optimize ventilation and air purification. Removing sources of air pollution has a passive benefit, while the other two methods have an ongoing energy cost.
Eliminating Sources of Air Pollution in Buildings
Current efforts to improve air quality are focused on coronavirus prevention. However, many other airborne dangers are often ignored. For example, volatile organic compounds are released by many building materials and furniture, especially when new.
Indoor air quality starts with selecting the right building materials during the design phase. Many common building materials are now available in low-VOC versions. If you're planning to get LEED certified for your next construction project, these low-emission materials can help you earn points.
All equipment and appliances that use combustion must have adequate ventilation, as combustion releases many harmful substances. Carbon monoxide is especially dangerous, being highly poisonous to humans.
Air humidity is not a pollutant, but air quality is negatively affected when humidity is not controlled. Harmful organisms like mold, dust mites, and bacteria thrive in high humidity levels. On the other hand, viruses and other harmful particles remain in the air longer with low humidity. For these reasons, the US EPA and ASHRAE recommend a relative humidity of 30% to 60%.
- The scientific community is still analyzing and debating the effect of humidity on the new coronavirus.
- However, many viruses become less infectious at relative humidity values close to 50%. This behavior has not yet been studied in SARS-CoV-2, but there is evidence that other coronaviruses become less infectious with moderate humidity.
Regardless of how air humidity affects the new coronavirus, the air quality benefits of maintaining a moderate RH have been widely studied.
Improving air quality with smarter ventilation
Building ventilation systems are typically designed with prescriptive airflow values from ASHRAE standards. These values were determined experimentally by ASHRAE, based on the type of building, floor area and number of occupants. However, this is an indirect design approach, as ventilation systems do not respond directly to air pollution levels.
The following design features can make ventilation systems smarter and better able to control indoor air quality:
- Using air pollution sensors to constantly monitor air quality.
- Analysis of air pollution measurements with an intelligent control system.
- Increase the ventilation rate when an increase in pollution levels is detected.
- ASHRAE approves this method and design guidelines are provided in Standard 62.1.
Many building codes have established ASHRAE prescriptive airflow values as minimum requirements. When using smart ventilation controls, they must be configured to never reduce airflow below code-required values.
To deal with airborne pathogens, the combination of filtration and ultraviolet radiation is an effective complement to ventilation systems:
- High-efficiency particulate air (HEPA) filters capture 99.97% of particles with a diameter of 0.3 microns.
- Filtration can be combined with Ultraviolet Germicidal Irradiation (UVGI), which destroys the DNA and RNA of viruses and bacteria.
Improvements in indoor air quality can help control respiratory diseases inside buildings. However, keep in mind that IAQ measures do not replace guidance from health authorities, such as social distancing and frequent hand washing.
