How Can HVAC design minimize the risk of COVID-19 infection within indoor environments?

Currently, there are increasing cases of the recurrent waves of the COVID-19 pandemic across the world. These waves are mainly caused by the transmission of aerosolized droplets from infected persons to healthy people in indoor environments. . Something that has led to the urgency of designing and implementing new ventilation systems for indoor spaces. As a result, HVAC systems should be redesigned with anti-pandemic components to prevent cross-contamination caused by airborne bacteria, viruses, and other contaminants in indoor spaces. 

There are 3 vital anti-pandemic components for HVAC systems that can help reduce the risk of COVID-19 infection within indoor spaces. They include; advanced air filtration units, volatile organic decomposition units, and biological contaminant inactivation units. In this article, we’ll look at how HVAC designers can develop anti-pandemic components to reduce the transmission of airborne pollutants within indoor environments. 

The Role of HVAC systems in preventing and reducing the spread of COVID-19 

Appropriate ventilation rate, differential pressure, and airflow direction can effectively reduce the transmission risk of aerosolized SARS-COV-2 viruses in indoor spaces. However, an incorrect HVAC design may considerably intensify it. For that reason, it’s important to ensure that HVAC systems in indoor spaces are well-designed if they’re to reduce/ prevent the spread of COVID-19. 

That aside, fresh intake of outdoor air at a high Air Changes per Hour (ACH) will significantly dilute the concentration of aerosolized COVID-19 viruses produced by an infected person through sneezing and coughing, thus reducing the risk of airborne transmission. Besides, the rate of ventilation in indoor environments is mathematically correlated to the probability of infection. As a result, the rate of infection will be high in a crowded room with poor ventilation. 

In that regard, professional HVAC organizations in various countries, including the American Society of Heating, Refrigeration & Air Conditioning Engineers (ASHRAE) should consider issuing directions for the proper use of HVAC systems in facilities to reduce infection. Also, HVAC engineers should rethink the design of HVAC systems to increase their cleaning capacity and ventilation rates since most units in existing buildings are selected and sized according to standards under normal conditions. Alternatively, they can consider implementing operation strategies that improve the ventilation rates without significantly affecting the normal operations of HVAC systems in existing buildings. 

Moving on, indoor air quality in buildings can be improved by source elimination or diluting the concentration of airborne contaminants within indoor environments. However, implementing these measures may have other effects on the operation of the HVAC systems. For instance, using 100% outdoor air will significantly increase the heating energy consumption, while the use of a MERV 13 filter to remove airborne contaminants increases the total energy consumption by about 3%.

According to guidelines published by the WHO in relation to COVID-19, healthcare facilities should have minimum ventilation rates of 60 L/s per patient, while residential and non-residential buildings should have a minimum ventilation rate of 10 L/2 per person. Other strategies that are crucial in reducing indoor airborne transmissions are; installing C02 sensors to monitor the level of exhaled air, using aerosol sensors to assess the efficiency of HVAC filters, and avoiding air recirculation. 

Essential anti-Pandemic components for HVAC systems to reduce the spread of Covid-19 

Several anti-pandemic components may be needed when redesigning HVAC systems for existing buildings to completely protect the occupants from the hazards imposed by different indoor air pollutants. But as we mentioned earlier, the most vital components are; an advanced Particulate Matter filtration unit, a VOC decomposition unit, and a biological contaminant inactivation unit. Thanks to their ability to provide the building occupants with clean air that is free of contaminants like bacteria, viruses, gaseous contaminants, and other particulates. 

• Advanced Particulate Matter (PM) Filtration unit 

Suspended air particulate matters with various size distributions, especially ultrafine particulates (UFPs), PM10, and PM2.5 particles can have severe adverse health impacts on indoor occupants. For that reason, it’s important to remove these particles from the indoor environment through appropriate filtering for post-Covid-19 HVAC systems. 

Air filtrations systems can either capture particulate matter particles proactively or passively. Many promising materials, such as polymeric nanofibers, silks, metals, oxides, metal-organic frameworks, and carbon-based materials like carbon nanotubes can be used to design air filters for PM removal. 

These materials can be classified as fibrous media or porous membranes. Porous membranes are only effective for filtering large particles due to their pore size, while fibrous media are ideal for filtering smaller particles such as UFPs, PM2.5, and PM10 particles. Consequently, fibrous media are widely used in commercial; HEPA (High-Efficiency Particulate Air) Filtration Units. 

• VOC Decomposition Unit 

Volatile Organic Compounds present in the air like formaldehyde, acetaldehyde, toluene, acetone, and benzene pose a risk of severe health effects to the building occupants. For that reason, these compounds must be treated appropriately to reduce their concentration in the indoor environment. Luckily, almost all organic compounds in indoor air undergo photocatalytic oxidation in the presence of highly reactive species such as the hydroxyl radical. These highly reactive compounds can be used in HVAC systems to decompose Volatile Organic Compounds, thus providing clean air for the building occupants. However, this approach will depend on the types and quantity of VOCs present in the indoor air of a certain area. 

• Biological Contaminant Inactivation Unit 

Inactivation of biological contamination in indoor air through HVAC systems isn’t a new approach. For instance, this approach may involve the use of UVGI (UltraViolet Germicidal Irradiation) and plasma cluster ions, microwave heating, dispersion of atomized nanoparticles, ozone sterilization, photocatalytic oxidation, and disinfection using chlorine dioxide gas. 

According to recent studies, the use of UV-C is the most effective method of inactivating the SARS-CoV-2 virus in indoor environments. As a result, HVAC specialists are designing in-duct disinfection systems using UVGI to minimize the spread of the COVID-19 pandemic in indoor spaces. 

Conclusion 

In addition to offering thermal comfort, HVAC system design should be developed in the upcoming years to ensure safe breathing and good IAQ for indoor occupants. More importantly, conventional HVAC systems should be re-designed with anti-pandemic components to help them reduce and prevent the transmission of the COVID-19 pandemic in indoor spaces.