COVID-19 and HVAC Programs | Cleansing & Upkeep Administration

Indoor air quality is extremely important to the productivity and health of residents in any industrial, commercial or residential building.

HVAC air conveying systems with associated air ducts and ductless mini-split systems ensure acceptable indoor air quality. However, they must be routinely inspected, maintained, and cleaned to operate efficiently and cost-effectively. This routine includes cleaning the interior of the duct and replacing filters.

Air handling systems filter out dust, particles, volatile organic compounds (VOCs), mold spores, bacteria and viruses. These systems also lower humidity while removing moisture in a building. Unfortunately, dust, particles, VOCs, mold spores, bacteria, and viruses can accumulate on the interior surfaces of air handling systems and interior ducts. This accumulated dirt can be aerosolized and carried over by air currents.

Channel with particle deposits.

Virus transmission studies

Regarding the transmission of SARS-CoV-2, a 2020 Florida Atlantic University study showed that a human sneeze or cough dispersed smaller droplets in air currents up to 12 feet away and in the air for more than a minute can linger. A study using high-speed cameras and lights done in an MIT laboratory confirmed that a fine mist of saliva and mucus can burst from a person’s mouth at a rate of nearly 160 miles per hour and travel up to 27 feet.

Research suggests that it is possible that coronavirus droplets can be nebulized, transported, and transmitted through HVAC duct systems.

A ducted HVAC system creates air currents that smaller virus particles are likely to be able to carry further. A published research letter The July 2020 journal Emerging Infectious Diseases of the U.S. Centers for Disease Control and Prevention (CDC) described an air conditioning-related COVID-19 outbreak in a restaurant in Guangzhou, China. Ten people from three families who ate in the restaurant became infected. The transfer of aerosolized droplets was triggered by air-conditioned ventilation. A video from the restaurant showed that many of these diners were seated more than two meters apart. The researchers concluded that a strong flow of air from the air conditioner could have carried droplets from one table to another and back.

A study published on nature.com in July 2020 detailed an ongoing pollution study that took surface and air samples in two Nebraska Biocontainment Units (NBUs) and nine residential isolation rooms with people who tested positive for SARS-CoV-2. The tested room surfaces included ventilation grilles, table tops and window sills. Virus samples with the highest Concentrations were obtained from an air treatment grate in the NBU.

Airflow in the NBU suites came from a register in the upper center of the room and came out of grilles near the head of the patient bed on either side of the room. Airflow modeling indicated that some of the airflow was directed under the patient’s bed, which may have caused the observed contamination under the bed, while the dominant airflow likely carried particles from the patient’s bed to the edges of the room and flew past the windows, which leads to some deposition there.

The New England Journal of Medicine published a letter to the editor in March 2020 from a research group investigating the stability of SARS-CoV-2 in aerosols and on various surfaces. Their research showed that infectious aerosol can persist on surfaces for several hours and up to two days. The longest viability virus was on stainless steel and plastic. The estimated mean half-life of SARS-CoV-2 was approximately 5.6 hours on stainless steel and 6.8 hours on plastic. In conjunction with a study published in August 2020 by the University of California, Davis and the Icahn School of Medicine at Mt. Sinai.

Particle formation on a register

A look at the airflow

Although the interior of ducts can be made of smooth metal, fine dust can build up on the surfaces of air ducts, vents, motors, and coils. Dead skin, hair and animal hair are caught in the dust, and after a short time this process creates a dense, mat-like environment in which viruses, bacteria, mold, dust mites and allergens can thrive. This is similar to the exterior of a vehicle during a spring pollen season as the pollen would coat the vehicle and windows.

For example, when dust is carried by air currents generated by air conditioners and similar devices, the dust acquires a positive or negative static electrical charge when it comes into contact with various objects. Dust with a positive electrical charge is attracted to objects with a negative electrical charge and vice versa. The more dust there is in the air, the greater the amount of dust that will stick to objects in the room.

When sources of dust (mainly people and clothing) are electrically charged, the dust generated by these sources is also electrically charged. This force of attraction created by static electricity is known as the “Coulomb force”. In addition, the return air streams from ducts contain moisture and moisture. As a result, this moisture can stick to the inside of the duct and trap dust particles.

HVAC air filters can help trap the virus particles and dust particles. A high efficiency particulate air filter (HEPA) effectively removes small particles, 99.7% of the particles as small as 0.3 microns. A MERV (Minimal Efficiency Reporting Value) filter removes larger particles from 0.3 micrometers to 10 micrometers. A MERV filter with a rating of 17 or higher is considered HEPA-like efficiency. However, most commercial buildings have MERV filters with a rating of 12 or lower. Unfortunately, a coronavirus particle is around 0.1 micrometers in size and cannot be viewed with the human eye. So there is no guarantee that a HEPA filter will stop virus particles and dust particles.

Current standard air handling units (AHUs) in HVAC systems circulate up to 80 to 90% of the air in regular systems during peak load conditions such as winter and summer when the outside air flow rate is set to the minimum percentage to conserve energy. Standard filter units in HVAC systems cannot effectively remove the virus in a stream of air. The HVAC system has become a focal point for the spread of the virus by recirculating contaminated air into space.

Based on the investigations cited, inspection, testing, surface and air sampling, cleaning and disinfection of HVAC air duct systems and associated pipes can help prevent the transmission of SARS-CoV-2.

Particles on the back of registers

Best practices for cleaning and disinfecting HVAC systems and ducts

1. Review HVAC air handling systems and associated drawings and diagrams of air ducts.
2. When putting on the correct Personal Protective Equipment (PPE), visually inspect the exterior and interior of the HVAC air handling system and associated ducts, registers / vents, motors, coils, and filters. If necessary, use a video endoscope camera and take digital pictures. Document and log all observations, even if the channel “looks clean”.
3. Test and inspect for air leaks, VOCs, particulates, and metal seam problems on ducts.
4. Perform swab samples before and after the surface of the HVAC air handling systems and associated ducts, registers / vents, motors, coils and filters. Sampling the smear in front of the surface can identify all hazardous substances and hazardous particles.
5. Carry out a pre- and post-air sampling of the project area. These samples help identify and isolate specific systems and affected areas along with hazardous substances and / or particles.
6. Use environmental controls and infection control risk assessment protocols to contain and isolate the cleaning and disinfection project. This includes setting up HEPA air washers, negative air machines, and containment barriers using a particle counter and air pressure monitor.
7. Implement ultra-low-volume (ULV) fogging with acid-free, chlorine-free, EPA (EPA) registered virucidal, biocidal, and fungicidal disinfectants outside and inside ducts, on registers / vents, motors, coils , and the entire project area to inactivate viral aerosols. To be effective, maintain a dwell time of at least 10 minutes on surfaces or follow the dwell time according to the virucidal label.
8. Clean the inner duct surfaces of major dust and particles using HEPA suction, rotobrushing, air whipping, and mechanical cleaning. Fiberglass-lined ducts inside require special attention and cleaning to prevent fiber damage and release. Perform a visual inspection to avoid recontamination.
9. Clean and disinfect internal metal ducts, registers / vents, motors and coils with an acid-free, chlorine-free, EPA-registered virucidal, biocidal and fungicidal disinfectant. To be effective, maintain a dwell time of at least 10 minutes on surfaces or follow the dwell time according to the virucidal label.
10. Replace and install new HEPA filters. Ductless mini-split systems can have a washable filter. It is best to vacuum the air handling unit (with HEPA filter) and frequently disinfect the washable filter with an EPA registered virucidal, biocidal, and fungicidal disinfectant. To be effective, maintain a dwell time of at least 10 minutes on surfaces or follow the dwell time according to the virucidal label.

Remember, it is important to routinely inspect, maintain, and clean HVAC systems. When you do this, your air handling system works most efficiently, contributes to a healthier indoor air environment, and saves operating costs over time.