HVAC and COVID-19
The term “coronaviruses” refers to a family of viruses that can cause illness to both humans and animals. On December 31st 2019, a new coronavirus called COVID-19 was first reported in Wuhan City, China. In general, symptoms of the virus can include mild illness or even pneumonia. If you have COVID-19, you may experience fever, or flu-like symptoms such as shortness of breath, fatigue, sore throat, and coughing.
It is known that the transmission of the virus happens from person-to-person. In most cases, it is via close contact with an infected individual, or contact with fluid droplets from an infected person’s sneeze or cough. It is also believed that this virus can be transmitted by touching the surfaces that contain droplets from an infected individual and then touching your face or mouth. Most scientists believe that, in the right conditions, the virus might survive for up to 9 days on certain surfaces.
Once a person infected with illness sneezes or coughs, droplets of fluid consisting of pathogens could be discharged in the air. It is believed that different illnesses lead to different droplet sizes. As of now, it is not yet defined the exact size of droplets that are released by people infected with COVID-19.
It is believed that relatively large droplets (>60 ppm) are usually so large that they can’t remain suspended in the air and end up falling and landing on surfaces. Some of the fluid may evaporate in some cases, and the large droplets could turn into tinier particles called droplet nuclei, and these might remain suspended in the air. It is believed that droplet nuclei (2.5 to 10ppm) can remain suspended in the air for many hours and thus be entrained into HVAC systems.
What Are HVAC Systems?
There are many formats when it comes to Heating Ventilating and Air Conditioning (HVAC) systems. The diagram below shows a typical HVAC system popularly found in institutional and commercial buildings. It primarily works as a recirculating system with a percentage of outside air added continuously while a similar percentage is exhausted. Since there are different types of systems, the outside air rate can also be different. Before recirculation, the air is well-filtered and moved throughout the system by the use of fans. Typically, heating and cooling are offered by finned coils that use either heating or chilled water.
The path that a virally infected droplet will go through to get back in an occupied space would generally entail multiple changes in air velocity and direction, extended ducted airways, and various impacting surfaces such as grilles, dampers, fans, and air filters. There is a high chance that a particle could adhere, entrain, and dry on a surface.
When it comes to healthcare ventilation systems and scenarios, published research suggests that the transmission of droplets consisting of viral material is theoretically possible. However, it is known to be less likely in a properly designed and well-maintained standard HVAC system in a public setting.
In general, to minimize the likelihood of a virus spreading, several practical HVAC operational measures can be considered together with possible system changes.
These include the following:
– Cleaning and disinfection
– Essential safety measures and maintenance regimes
– Air filtration and cleaning options
– Commissioning and operation of the system, and outside air rates
Cleaning and Disinfection
Typically, standard HVAC systems are quite challenging to clean and disinfect effectively. This is due to the lack of access to most of the system parts and ductwork. Generally, some systems in acute care health laboratories or facilities are specifically designed to offer adequate access and other features to ensure effective and regular cleaning.
When it comes to commercial HVAC systems, you can readily change the air filters and clean and disinfect the cooling and heating coil surfaces using approved techniques and chemicals. Typically, most other surfaces and features in HVAC systems can’t be readily cleaned physically. If your HVAC systems include chilled beams, wall-mounted, or console type units, it is prudent to clean these units if need be.
Fumigating or fogging using approved chemicals and techniques for disinfection can be used in HVAC systems and facilities that are specially designed for this treatment. These are typically in laboratories and certain acute care areas. Fumigating or fogging isn’t recommended for normal facilities and typical HVAC systems that are not designed for this treatment. There are high chances it will be ineffective and might be dangerous in these situations.
Essential Safety Measures and Maintenance Regimes
The continued practice of proper housekeeping and preventative maintenance regimes are vital. Not only is it imperative to carry out HVAC maintenance as prescribed by the recognized standards, but maintenance procedures must also be followed.
It is essential to remember that in most modern buildings, the critical safety measures consist of operating HVAC systems and are thus needed for occupancy. Therefore, the scheduled statutory maintenance of these HVAC systems, together with fire protection and other vital systems is imperative.
Facilities might scale down occupancy and operations as the COVID-19 situation evolves. However, generally speaking, these essential safety systems should continue to be maintained as per the regulations.
Furthermore, building operators must consult with service providers whether measures are being considered to restrict or preclude buildings’ access to maintenance technicians.
Air filters must be replaced as scheduled or more frequently as needed. When servicing dirty filters, PPE (Personal Protective Equipment) such as P2 mask or well-rated respirator, gloves, and coveralls must be worn by trained technicians.
Once the air handling unit is turned off, filters must be carefully removed to prevent the release of dust or other particles into the air. What’s more, the dirty filters must be bagged and tied and then disposed of in a proper waste disposal process. Cleaning of surfaces will help in removing any residual particles. When it comes to servicing of washable filters, it should be performed with similar approved methods and PPE use.
Air Filtration and Cleaning Options
In most cases, air filtration in typical HVAC systems won’t be effective in filtering viruses or droplet nuclei, if these reach the filters. Due to the increased efficiency of particle filtration, there can be a lower airborne load of infectious particles.
Typically, High-Efficiency Particulate Arresters filtration systems (HEPA) filter 99.999% of dust particles and other airborne contaminants like bacteria and viruses. Usually, these filters are applied in cleaning rooms, acute care areas, and hospital operating rooms. Because of their high-pressure drop, HEPA filters are less likely to be a viable option for many existing HVAC systems. Besides, HEPA filters need particular housing and can’t be retrofitted as a direct replacement for traditional filter media.
Although conventional air filters that have an improved MERV (Minimum Efficiency Reporting Value) between 13 and 15 (F7 to F9) can lower levels of droplet nuclei, they aren’t likely to be effective at preventing unattached virus particles. Generally, these filters can help lower the chances of droplet nuclei from spreading and might be within the fan capabilities of existing HVAC systems.
Generally speaking, efficient filters comprise high-pressure drops that can increase energy consumption. However, advancements in technology suggest this isn’t always true.
Commissioning and Operation of the System, and Outside Air Rates
It’s imperative to make sure that HVAC systems have been correctly commissioned and are operating correctly. Typically, commercial HVAC systems to create internal conditions with relative humidity ranging between 40-60%. According to published research, this humidity range might have a positive impact on human vulnerability to viruses, virus deactivation, and cross infection rates.
Summary of Recommendations
In a modern commercial building, the risk of a properly maintained HVAC system causing the transmission of the COVID-19 is believed to be low. However, there are several practical measures that building operators and owners can consider to lower the risk further.
– Not only is it imperative to carry out HVAC maintenance as prescribed by the recognized standards, but maintenance procedures must also be followed.
– Building operators must consult with service providers whether measures are being considered to restrict or preclude buildings’ access to maintenance technicians.
– It’s crucial to ensure HVAC systems are well-commissioned and operating correctly.
– Ideally, internal humidity must be maintained in the range of 40-60% relative humidity.
– Checking the existing air filtration condition and type and replacing or upgrading the filter media to F7-F9 grade subject. It can minimize any transmission of the virus via the system.
– An audit of the system filtration and overall cleanliness, along with an analysis of the preventative maintenance inspection records, can help confirm the duty of care responsibilities have been achieved.
In the case of disinfecting or cleaning of the system:
- Air filters must be changed, and heating and cooling surfaces can be disinfected and cleaned using approved chemicals and procedures.
- If the HVAC system comprises chilled beams or induction type units, the units can be disinfected and cleaned using approved chemicals and procedures.
- Typically, most other surfaces and features in HVAC systems can’t be readily cleaned physically.
- Fumigating or fogging isn’t recommended for normal facilities and typical HVAC systems that aren’t specifically made for this treatment.
Although HVAC systems can help reduce the spread of infections, there’s only so much that can be attained. How HVAC systems work by regulating the transmission of infection should be regarded as a part of an extensive multi-modal infection control strategy in buildings.