The Not Perfect Housewife

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ASHRAE Guidelines to Prevent Coronavirus Transmission Through HVAC

At Thomsons Cleaning, we know that medical professionals agree that most coronavirus infections occur from person to person, and at short distances.

When an infected individual coughs or sneezes, droplets with the virus are released into the air, and others can inhale them.

These droplets can also fall on surfaces, and others may be infected by contact – especially when touching their eyes, nose or mouth.

However, coronavirus infections are also believed to occur with smaller droplets, which stay in the air for longer. These droplets are called aerosols, and they can be spread indoors when HVAC systems circulate air.

Recognising this risk, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) published extensive guidance on how to prevent COVID-19.

The main ASHRAE recommendations can be summarised in three points: increasing ventilation with outdoor air as much as possible, improving the air filters in buildings, and installing ultraviolet disinfection lights. These measures help prevent COVID-19 infection through HVAC.

How a Higher Outdoor Air Ventilation Helps Prevent COVID-19

As mentioned above, small viral droplets can stay suspended in the air more time, increasing the risk of inhalation. However, this risk can be reduced by increasing the outdoor air supply, and reducing the recirculation of indoor air.

  • Since more outdoor air is being brought into the building, additional heating or cooling may be required to keep a suitable temperature.
  • While this may increase the building energy consumption, the reward is a lower risk of COVID-19 transmission through the air.

Many buildings use demand controlled ventilation or DCV: the ventilation control monitors occupancy, and it increases or decreases the outdoor air supply in response. Under normal conditions, ASHRAE recommends DCV to save energy.

However, DCV should be disabled during the coronavirus emergency, allowing as much outdoor air as possible into the building.

There are limits to how much outdoor air can be supplied. For example, if the weather is very hot, too much outdoor air can overwhelm the air conditioning system. The same applies during winter, when a large supply of cold air can exceed the space heating capacity.

Improving Air Filters to Trap Coronavirus and Other Germs

The efficiency of air filters can be described with a metric called Minimum Efficiency Reporting Value (MERV). The scale goes from 1 to 16, where a higher number indicates more filtering efficiency. ASHRAE recommends at least MERV 13 to trap viruses and bacteria effectively.

  • Filters in the range of MERV 13 to 16 are considered of medical grade.
  • They can capture 95-99% of particles with a size range of 0.3 to 10 microns, where one micron is 1/1000 of a millimeter.

High Efficiency Particulate Air filters (HEPA) are even more efficient. A filter with this rating can capture 99.97% of particles with a size of 0.3 microns. However, since these filters are so effective for trapping particles, they can restrict the airflow from an HVAC system.

Not all ventilation systems are designed for HEPA filters, and some may even struggle with the higher MERV ratings. However, HEPA filters are also available as portable air purifiers and vacuum cleaners, in case your HVAC system cannot handle them.

To determine the optimal filter rating for your ventilation system, the best recommendation is asking for a qualified HVAC engineering firm.

Eliminating Virus and Bacteria with UV Disinfection Lights

Ultraviolet germicidal irradiation or UVGI is also recommended by ASHRAE, especially for spots that may gather germs and moisture. UV light not only kills viruses, but also pathogens like bacteria and mold spores.

Some UVGI systems are designed for direct installation in your air-handling units or ducts, eradicating germs before they can spread through the air.

Choosing an adequate UVGI system is important for effective disinfection. Ultraviolet light can be classified into three frequency bands: UV-A, UV-B and UV-C. ASHRAE recommends UV-C for disinfection, since it has the highest germicidal effect.

You must also ensure that the UV disinfection system does not produce ozone. In the upper atmosphere, ozone protects the Earth from harmful space radiation. However, ozone is considered a dangerous air pollutant at ground level.

The gas produces respiratory irritation and lung pain, and persons with respiratory conditions like asthma are the most vulnerable. Before purchasing a UVGI system, make sure it meets the UL 2998 Standard for zero ozone emissions from air cleaners.

Bethany Thomson
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Author: Bethany Thomson

I'm a wife, a mother and a housewife. I've learned a lot of tricks that help me deal with the household in the fastest way. And I'm going to share them with you.

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