HVAC SYSTEMS, COVID-19 INFECTION RISK MITIGATION AND ENERGY-COST ANALYSIS

It is well known that in March 2020 a state of emergency was declared, due to the worldwide spread of the new SARS-CoV2 virus. Since that time, all nations have put containment measures in place to avoid a health and social collapse. The main ways of spreading the Covid-19 infection are close contact with an infected person, inhalation of respiratory droplets produced by an infected person and contact with infected surfaces. Part of the droplets produced by an infected person are so small that they are not affected by the force of gravity, so they remain in suspension forming the bio-aerosol. The method of transmission via bio-aerosol is a mechanism recognized by the World Health Organization (WHO), which in that case highlights the important role of mechanical ventilation of building rooms to reduce the risk of contagion. Starting from this assumption, the aim of the paper is to analyse various HVAC systems, evaluating which of these is more efficient to reduce the contagion from Covid-19, and to carry out an energy-cost analysis of the different proposals. To date, there are no legal obligations for the correct design of an air conditioning system capable of countering the spread of the infection from Covid-19. In this paper, the Walles-Riley model was used to derive the number of external air changes per hour needed to reduce contagion. This model can be used for diseases that spread by air. The analyses were conducted on an existing building of the public administration for office use in Southern Italy. The model was dynamically simulated and validated through energy bills. The HVAC systems analysed were fan-coils with primary air and radiant panels with primary air. The energy analysis was first conducted under standard conditions and then in conditions that counter the spread of the virus. An analysis of energy costs was also carried out to assess the increase in expenditure compared to standard conditions. The results show that the number of external air changes per hour necessary to drastically reduce the probability of Covid-19 infection is equal to 5 vol/h. Acting on the air conditioning system is useful to counter the spread from Covid-19 but requires very high energy consumption. A solution to this problem could be to couple the intervention on the air conditioning system with one or more interventions on the building envelope.