On the Optimal Indoor Air Conditions for SARS-CoV-2 Inactivation. An Enthalpy-Based Approach

Abstract

In the CoViD-19 pandemic, the precautionary approach suggests that all possible measures should be established and implemented to avoid contagion, including through aerosols. For indoor spaces, the virulence of SARS-CoV-2 could be mitigated not only via air changes, but also by heating, ventilation, and air conditioning (HVAC) systems maintaining thermodynamic conditions possibly adverse to the virus. However, data available in literature on virus survival were never treated aiming to this. In fact, based on comparisons in terms of specific enthalpy, a domain of indoor comfort conditions between 50 and 60 kJ/kg is found to comply with this objective, and an easy-to-use relationship for setting viable pairs of humidity and temperature using a proper HVAC plant is proposed. If confirmed via further investigations on this research path, these findings could open interesting scenarios on the use of indoor spaces during the pandemic.

Predicting SARS-CoV-2 Weather-Induced Seasonal Virulence from Atmospheric Air Enthalpy

“…The asymmetry of the curve, even if weak, appears significant. While extinguishing slowly at the higher values of h, which seems to be complementary with our cited findings regarding significantly shorter coronavirus survival in the range of 50-60 kJ/kg of dry air [9], the suddenly sinking shape at the lower values of h clearly confirms that however high the RH value, the seasonal virulence of SARS-CoV-2 expires upon approaching 0 • C. Table 1.…”

“…In contrast, the IR appears to have been practically negligible in cities whose average h value fell in the range of 50-60 kJ/kg dry air, which we recently identified as the environmental h interval with the lowest virus survival [9].…”

“…Temperature and humidity play a key role in the survival of a number of viruses, including severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome-related coronavirus (MERS-CoV), and the influenza viruses [1][2][3][4][5][6][7], to which SARS-CoV-2 has recently been added [8]. In a previous work we noted that, although temperature or humidity cannot be independently correlated with virus viability, as demonstrated by the controversial outcomes from literature, a strong relationship between virus survival and the specific enthalpy of moist air, hereafter denoted as h, appears to exist [9]. In fact, according to the analyzed data, when the environmental conditions are such that the h value falls within the range of 50 and 60 kJ/kg of dry air, virus survival decreases dramatically.…”

Aerosol Transmission of SARS-CoV-2: Physical Principles and Implications

“…Many viruses are sensitive to temperature and humidity (86) but effects of humidity on SARS-CoV-2 in aerosols have been considered quite small (5,7), in contrast to its effect on viability in surface residues (84). A suggestion that SARS-CoV-2 is inactivated by specific combinations of temperature and humidity needs experimental confirmation (87). Strong sunlight reduces the halflife in aerosols to 2-3 min (7).…”

“…To minimize infection, heating and ventilation in public buildings and in transportation may need to be modified or operated in different ways from those intended at installation (87). This provides opportunities for rapid, simple interventions (17,(99)(100)(101)(102).…”