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Can HVAC systems help prevent transmission of COVID-19

The world is fighting against the deadly and highly contagious pandemic, Covid-19, that has changed almost every aspect of our lives. Almost every day, there are new information and guidelines about how to deal with this life-threatening, mass spreading virus. As per the observation and studies by scientists, it has been established that the coronavirus spread through droplets. Now the concern is whether COVID-19 is an air-borne disease? World Health Organization has recently stated that chances of coronavirus getting transmitted via air cannot be ruled out. The 0.1 microns particles of coronavirus can release particles known as aerosols in the air that can remain active for almost three hours, thereby increasing the chances of contamination in closed rooms. Thus, the time has come for all to concentrate on improving the quality of air by modifying ventilation and air conditioning system for better air management. The purpose of this article is to identify the various ways in which sensible functioning of the HVAC system can actually help in tackling the problem of the spread of this highly contagious virus more effectively.
HVAC systems – Upgrading and better configuration
One such technical step that can lead to better air circulation and ventilation is by configuring and adjusting the HVAC ducted systems. The point is to increase the amount of fresh air flow from outside to cut on recirculation. Running the HVAC systems continuously, without any shutdown, can help in increasing the replacement of air and also help in minimizing airflow speed. Thus, with mere adjustments in the settings, it is possible to limit the spread of COVID-19. But for buildings that are using outdated and inflexible systems, upgrading the HVAC system will turn out to be beneficial for them in this fight against coronavirus.

This can be done by:-
1. Ideally replacing the fixed-speed fan motors with variable speed fan motors. This increases the capacity to control airflow and permits simple settings that produce airflow at a lower speed.
2. Adopting a sophisticated and sensitive airflow-control system to permit smooth airflow adjustments
3. Or by simply installing a high-performance air-purification system.

Methods of Air-Purification in the HVAC system
Coming to air-purification options for the HAVC system, the most common and effective method is Filtration. In this method, the air is made to pass through the fiber-based membrane and the performance depends on the type of filter used. Irradiation and Thermal Sanitization are the other known HVAC air-purification technologies that work by inactivating the biological particles in the air without removing them. Further, for proper cleaning of the air, the HVAC system can also incorporate ozone generators, ionic purifiers, and many other devices.
About Filters – their installations and ratings
What makes the HVAC system ideal for residential or commercial usage is that the filters are located either in the point of an air inlet or air outlet or within the central handling unit. To lessen the amount of contaminated external airflow into an HVAC system, technicians also sometimes install a much-needed pre-filter for the incoming air. Moreover, in HVAC mechanical filters, there are tangled fibers that are useful in trapping large particles and reducing the chanced of contamination. The mechanical filter performances are rated based on the capacity of trapping particles that exhibits the level of efficiency and effectiveness. Based on this criterion, the HVAC mechanical filters can be rated as High-Efficiency Particulate Air (HEPA) and Minimum Efficiency Reporting Value (MERV). HEPA, as per the US rating policies, is supposed to be the most effective in filtering and removing almost 99.97 % of particles that maybe even as small as 0.3 microns. Based on the size of particles, which may vary from 0.3 to 10.0 micron in size, the MERV system can further be assigned different rating levels. Like MERV 11-12 can capture 60 to 80 % of particles of 1 to 3 microns in size whereas MERV can capture up to 95% of particles of 0.3 to 1.0 microns in size. Based on the ability to capture particles, the place of installation varies. However, this rating system may vary country wise.
Here it is important to mention that the process of upgrading the HVAC system can be expensive and even with HEPA filters, not all concerns about air-transmission can be eliminated. It has been documented by NASA study that HEPA filters can stop the spread of coronavirus due to its ability to capture particles as small as microns but other studies specify the size to be 0.3 microns. Thus, more studies and research is needed in this direction to determine the finest filtration system to stop the spread of the contagious coronavirus in the air. But, under the present circumstances, HEPA filters can definitely be considered as the best possible mean of limiting the spread of this deadly virus.
Air-Flow Management – Indoor and Inter-Room
As more and more research and studies are carried on in finding the best way to stop the spread of coronavirus, more importance is given to better air-flow management. The important indoor airflow management related suggestions are:-
1. Going for a vertical laminar airflow, as in hospital rooms and clean rooms, in which air moves in a given path and in set speed
2. The airspeed within the room must be slow and steady
3. Keeping potentially contaminated air out of rooms

Similarly, it is important to address the concern of inter-room airflow to limit the contamination from one room to another. It is important for technicians to identify the air movement pattern.
ASHRAE has published two important statements on 20th April 2020, that further established the there can be a positive influence of HVAC systems in limiting the spread of this virus. In the statements, ASHRAE has clearly indicated that changes in building operations that also include the operation of heating, ventilation, and air-conditioning systems can help reduce the “airborne concentration of SARS-CoV-2 and thus the risk of transmission through the air”.

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