HVAC solves pandemics in cities.

COVID-19 is a respiratory disease caused by the virus SARS-CoV-2 that has affected millions of people worldwide. Although lacking in research clearly proving how the virus is transmitted and what parameters affect that, the most probable transmission modes currently identified are droplet and fomite transmission. Social distancing, personal protective equipment, quarantine and lockdown measures, have been identified as effective strategies to contain the transmission of the virus. However, growing evidence for airborne transmission has been observed, resulting in higher relevance for HVAC strategies in spaces with high occupancy and showing the importance of including the occupant's safety into the paradigm of future low-energy buildings and public transports.

Main established HVAC strategies to limit the spread of the COVID-19 in buildings and enclosed spaces include the increase of outdoor air and air change rates, the use of higher capacity filters, the use of UV light, etc. Although able to reduce airborne viral transmission, these strategies are responsible for an increase in energy consumption and a decrease in thermal comfort, making them not appealing as long-term strategies. In the view of identifying HVAC technologies able to provide a healthy environment for the occupants without affecting energy consumption, this paper demonstrated the potential of the liquid desiccant technology for use in crowded buildings (schools, gyms, libraries, etc.), enclosed spaces (elevators, locker rooms, etc.) and public transport, particularly for large scale buildings where large air change rates are supplied and humidity control and/or moisture removal is required. The technology could provide benefits in terms of (i) efficient use of energy such as low-grade heat sources, (ii) capacity to independently control temperature and humidity of the supply air, (iii) supply 100% outdoor air, (iv) control of humidity within the range of values less favourable to the growth, proliferation and infectivity of microorganisms (RH between 40% and 60%) and (v) virus inactivation characteristics of the desiccant solutions. The study showed how some conventional desiccant solutions, such as TEG and LiCl, have been largely studied due to their sanitising characteristics. The potential factors involved in the virus inactivation process performed by desiccant solutions (high temperature, increased salinity, effect of Li and Cl ions, exposure time, etc.) were suggested together with possible modifications of the solutions to enhance their sanitising characteristics. As a matter of fact, metal ions, such as titanium and copper oxide, could be added to conventional desiccant solutions with beneficial effects in terms of both increased heat and mass transfer and antimicrobial activity. The paper is the first step towards the development of a novel airborne pathogen scrubber system able to draw in the contaminated air, neutralise the airborne particles in the air (viruses, bacteria, fungi, particulates, etc.) thanks to the deactivation action of the liquid desiccant solution and push the sanitised air to the environment or recirculate it back to space.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.