phc september 2017 www.phcnews.com
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THE FUTURE IS NOW
Focus on Indoor Air Quality
Not surprisingly, the more time they spend at home, the more consumers call HVAC professionals to discuss indoor air quality. At the beginning of the pandemic, international bodies had very little conclusive research related to COVID-19 and, thus, recommended not touching each other, not sharing germs on surfaces and not coughing on each other. As time went on and various parties studied the spread of the disease, it became clear that the virus was transmitted at least as often through the air as by droplets, shared surfaces and touching. In April 2020, the American Society of Heating, Refrigerating and Air-Conditioning Engineers stated airborne transmission of SARS-CoV-2 (the virus that causes COVID-19) was "sufficiently likely" that airborne precautions should be taken. At the time, both the World Health Organization and the Centers for Disease Control & Prevention were asserting that transmission of SARS-CoV-2 was by droplet and fomite modes, not airborne. An ASHRAE expert task force began issuing guidance documents related to ventilation, filtration, fresh air, disinfection, opening or closing buildings and other issues. In July 2020, 239 scientists wrote to the WHO, citing research showing the virus spreads not just in larger droplets but in aerosols, too. This was followed by an open letter from 680 built environment professionals in 51 countries, along with major industry organizations, urging public health leaders to adopt indoor air quality best practices to help protect occupants from the spread of the disease.
ASHRAE Gets More Unequivocal
Since then, the WHO and CDC acknowledged the risk of airborne transmission indoors. In April, the ASHRAE Epidemic Task Force released an updated, unequivocal statement: "Airborne transmission of SARS-CoV-2 is significant and should be controlled. Changes to building operations, including the operation of heating, ventilating and air-conditioning systems, can reduce airborne exposures." Earlier in the year, it had released some details as follows: "ASHRAE's Core Recommendations are based on an equivalent clean air supply approach that allows the effects of filters, air cleaners, and other removal mechanisms to be added together to achieve an exposure reduction target." Some additional specifics: Ventilation, Filtration, Air Cleaning Use outdoor airflow rates guidance for ventilation as specified by applicable codes and standards. Use HEPA filters and air cleaners with MERV 13 or better levels of performance. Only use air cleaners for which evidence of effectiveness and safety is clear. Use control options providing desired exposure reduction while minimizing associated energy penalties. Air Distribution Promote the mixing of space air. HVAC System Operation Maintain temperature and humidity design set points. Maintain equivalent clean air supply required for design occupancy. Operate systems for the time required to achieve three air changes of equivalent clean air supply. Limit re-entry of contaminated air. System Commissioning Verify that HVAC systems are functioning as designed. In reviewing comments from numerous industry leaders (ASHRAE and beyond), it seems that 40 percent to 60 percent relative humidity has become a rule of thumb for contributing to indoor air safety.
Devastation after a 2017 wildfire in Paradise, California. Lake water system for off-grid living with UV light to kill viruses.
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