There have been many recommendations in recent months regarding the healthiness of the environment. Since the beginning of the health emergency, measures of prevention have been updated according to the increasing knowledge about viral particles transmission and surviving.

The first recommendations were for people, then came some specifications regarding objects and surfaces with which one comes into contact and finally the recommendations referring to closed spaces, houses and workspaces.

Several studies have shown a possible link between air quality and the virus spread; if we first focused on the level of pollution in our cities, the measures of social distancing, which have forced us to stay homes, have moved public attention to indoor air quality. Besides, the prospects of restarting and returning to the offices have raised the question of the healthiness of workspaces.

The effects of indoor air quality on psychophysical well-being are known for some time. Two years ago, the book INDOOR POLLUTION - Architectural, bio-legal and medical-scientific aspects of living, edited by Umberto Veronesi Foundation, with the scientific contribution of Goldmann & Partners, described not only the effects on the body of toxic substances in the environment but also traced in architecture the origin of some problems resulting from indoor pollution. Goldmann & Partners' research identified solutions to these problems through the application of bio-architecture principles, addressing issues ranging from the design of spaces to the choice of low emitting materials and furnishings, from plant management to green cleaning.

The current health emergency has brought to the attention of public opinion all these issues on which, in the current circumstance, not only health professionals but also technicians, engineers' organizations and plant engineers have expressed their opinions. They provided specific recommendations regarding the reduction of the risk from the spread of Coronavirus through air conditioning and ventilation systems in healthcare environments and workplaces.

At the end of March, the ISS (Health Institution) Environment and Indoor Air Quality Working Group published the ISS COVID-19 Report No. 5/2020 - Interim recommendations for the prevention and management of indoor environments about the transmission of SARS-CoV-2 virus infection. The document provides essential indications for the maintenance of a right level of air quality in indoor, work and home environments.

Among the recommendations for domestic environments, there is that of ensuring a good air exchange through natural ventilation to reduce the concentration of pollutants, such as VOC, PM10, CO2, etc., as well as aerosol. It recommends maintaining suitable thermo-hygrometric conditions and to clean the intakes carefully, ventilation grilles and filters of air conditioning systems. Compared to the latter, the report is in favour of the interruption of air recirculation.

Similar measures suggested for working environments, for which there is also the critical issue of controlled mechanical ventilation. According to the ISS guidelines, ventilation systems must keep the air inlet and exhaust air active 24 hours a day, 7 days a week. During the emergency period, the air recirculation function must be stopped to avoid the possible transport of pathogens (bacteria, viruses, etc.) into the air.

On the management of the mechanical systems during the emergency has also been expressed by AiCARR, Italian Association of Air Conditioning Heating Refrigeration through a series of protocols and documents, declined on the possible case history in the workplace, which confirms and integrate the indications contained in the ISS report. To minimize the effects of the presence of an infected person in the workplace, AiCARR recommends reducing the level of occupation of the rooms significantly. On the ventilation systems, the suggestion is to operate them at nominal or maximum allowed speed to remove airborne particles (aerosols) and contain the deposition on surfaces.

Also, AiCARR affirms the need to close the recirculation pathways to avoid that the introduced air is mixed with the air extracted or expelled from the rooms.

Similar recommendations come at international level from REHVA Federation of European Heating, Ventilation and Air Conditioning Associations, which has published on its website guidelines on the management of air conditioning systems, keeping them updated.

The opinion of the technical-scientific community on the management of building systems during an emergency is unanimous. The measures to be adopted require putting on stand-by all those functional operations for energy-saving. The operation of h24 systems, regardless of the level of occupancy of the buildings, as well as the interruption of air recirculation, with the consequent supply of fresh air as much as possible from outside, are measures that will require greater energy expenditure. The current spring season will only partially contain the scale of the phenomenon.

Among the many opportunities for reflection offered by the Coronavirus is that relating to the design of the next buildings, then the consideration of passive strategies is essential.

_{Photo credits: Bru-nO; Tama66; Juhasz Imre}