In recent days we are all thinking more about our health and the health of the people around us. Many of us are staying home more, heeding the advice on social distancing.
If it’s possible to safely take a walk or bike ride outside and get some fresh air, we probably should. Even if you are not a heating, cooling and ventilation professional, you’ve probably heard that people in many climates spend up to 95% of their time indoors, with or without social distancing. We also take into our lungs about 40 lbs. of air each day. These two facts alone should make indoor air quality (IAQ) an important health consideration.
General Indoor Air Quality
In any conditions, managing indoor air properly can help minimize hazardous volatile organic compounds and substances such as methane, propane, butane, acetone, formaldehyde, allergens, and of course, viruses.
According to the Canadian Centre for Occupational Health and Safety,1 indoor air contaminants can also include dust, dust mites, fibreglass, asbestos, gases from building materials, vapours from cleansers, solvents, pesticides, disinfectants, glues, off-gas emissions from furniture, carpets, and paints, microbial contaminants, fungi, moulds, bacteria, ozone from electric motors, electrostatic air cleaners and photocopiers, carbon dioxide, perfume, body odors, and tobacco smoke.
To remove some of these contaminants, ventilation professionals set up mechanical equipment so that fresh air can displace 100% of stale indoor air up to about three times per hour (on average), depending on the building and system involved. In some systems energy recovery ventilators help to retain cooling or heating energy during the expelling of stale air.
In other cases, fresh air from outside must be heated or cooled according to the comfort needs of occupants. To avoid unnecessary added energy use and expense, modern smart controls can be used to bring fresh air into the space at times of the day or night when the outdoor temperature more closely matches the indoor temperature.
Because there are a number of variables at play and because the temperature can fluctuate significantly, for example during the spring months, highly intelligent controls and sensors have been developed and are increasingly employed by HVAC professionals.
Good indoor air quality is implied in most building codes. Codes in Canada and the United States often refer to the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) Standard 62.1-2010 - Ventilation for Acceptable Indoor Air Quality,2 or other versions. The metrics in this standard were established to ensure the comfort of workers, so in extraordinary situations such as the current pandemic, they should
really be seen as minimum operating guidelines.
According to ASHRAE Standards, ventilation in school classrooms is based on the amount of outdoor air per occupant plus the amount of outdoor air per unit of floor area. Since indoor carbon dioxide comes from occupants and outdoor air, the adequacy of ventilation per occupant is indicated by the indoor concentration minus the outdoor concentration.
“The value of 615 ppm above the outdoor concentration indicates approximately 15 cubic feet per minute of outdoor air per adult occupant doing sedentary office work where outdoor air contains 385 ppm, the current global average atmospheric CO2 concentration. In classrooms, the requirements in the ASHRAE standard 62.1, Ventilation for Acceptable Indoor Air Quality, would typically result in about 3 air changes per hour, depending on the occupant density. Of course the occupants are not the only source of pollutants, so outdoor air ventilation may need to be higher when unusual or strong sources of pollution exist indoors. When outdoor air is polluted, then bringing in more outdoor air can actually worsen the overall quality of the indoor air and exacerbate some occupant symptoms related to outdoor air pollution. Generally, outdoor country air is better than indoor city air. Exhaust gas leakages can occur from furnace metal exhaust pipes that lead to the chimney when there are leaks in the pipe and the pipe gas flow area diameter has been reduced.”
General advice for HVAC professionals to improve indoor air includes the ventilation practices mentioned, plus regular duct cleanings, inspections, air filter replacement, opening and unblocking of air vents.
Along with ASHRAE guidelines, The International Building Code and International Mechanical Code have specific criteria on ventilation rates for building or use type, according to a 2019 article in Buildings Magazine by Joe Derhake.3
They dictate the position of HVAC louvers, and the sizing and positioning of ventilation fans. And they too provide suggestions for optimizing indoor ventilation using CO2 detectors to detect variable user loads. The data collected can then be used to adjust outside air flow in real time for a more efficient (and less expensive) operation. “CO2 detectors can also be used to detect occupancy levels on off hours, weekends, etc. to automatically optimize ventilation use,” writes Derhake
ASHRAE presidential member William Bahnfleth was interviewed about viral threats and HVAC systems in early March, 2020 by the ACHR News.4 He cautioned HVAC professionals to be exact in their understanding of how viruses move, what systems are effective in mitigating the spread, and the importance of not making inaccurate promises about prevention measures.
He noted that viruses can move via droplet transfer, however but can also be transmitted via intermediate surfaces and to some extent, airborne transmission. “It's not impossible that infectious particles in the air could stay aloft long enough to be collected, say at the return grille of an HVAC system, go through a duct, and infect someone in a different space,”
He listed ventilation, filters, and UV disinfection as all having some mitigation impact. “Using a dedicated outdoor air system also cuts down on contaminated air.”
Aaron Engel from Fresh-Aire UV stated that high-efficiency particulate arrestance (HEPA) filters are currently popular, and among the best we have as they have been shown to be effective at trapping particles down to 0.3 microns in size, but that viruses can be even smaller.
“Contractors are now learning that filters are designed to capture larger particulates in the air … [while] surface ultraviolet disinfection and airstream UV disinfection are effective at inactivating pathogens,” he said. “UV germicidal systems have also been shown to reduce microbial load and pathogens that are found within the HVAC system and drain pan that would otherwise be introduced and distributed throughout the envelope of the building.”
“Airborne droplets containing infectious agents can remain in room air for six minutes and longer,” said Daniel Jones, from UV Resources. “Scientists have found that viruses can remain infectious on surfaces at room temperature for up to nine days. Upper-air UV-C fixtures can destroy microbes when they are exposed to the UV-C energy in a matter of seconds.” Kill ratios up to 99.9 percent on a first-pass basis have been modeled, and concentrations are further reduced each time the air circulates.”
He also said “Surface-cleaning UV-C systems provide 24/7 irradiation of HVACR components to destroy bacteria, viruses, and mold that settle and proliferate on coils, air filters, ducts, and drain pans, preventing the growth of pathogens that can eventually become airborne and get circulated by HVAC systems.”
For homeowners, Bahnfleth suggests home UV products, room air cleaners, better filters, and humidity control. “The recommendation for a long time has been to try to keep minimum relative humidity between 40 and 60 percent, because viruses are least viable in that range. Many commercial buildings have humidity control…but in a home in the winter — especially if it's leaky and in a cold climate —humidity drops into the 20s or lower.”
Whether you’re an HVAC professional helping large facility managers and single-family homeowners, or any other citizen trying to breathe better at home and work during social distancing, it’s a good time to give thought to the indoor and outdoor air that you are breathing. Use the time to learn about your situation and take steps to make sure you and your family members are healthy and safe.