Source:

The Role of Air Conditioning in the Diffusion of Sars-CoV-2 in Indoor Environments: a First Computational Fluid Dynamic Model, based on Investigations performed at the Vatican State Children’s Hospital © 2020 Elsevier Inc. All rights reserved.

More than 60 million people worldwide are affected by the Sars-Cov-2 infection, which already caused 1.500.000 deaths. This virus is mainly transmitted through exhalations from the airways of infected persons, so that Heating, Ventilation and Air Conditioning (HVAC) systems might play a role in increasing or reducing the spreading of the infection in indoor environments.
It has been modelled the role of HVAC systems in the diffusion of the contagion through Computational Fluid Dynamics (CFD) simulations of cough at the “Bambino Gesù” Vatican State Children’s Hospital.
Both waiting and hospital rooms were modeled as indoor scenarios. A specific Infection-Index (η) parameter was used to estimate the amount of contaminated air inhaled by each person present in the simulated indoor scenarios.

Study Conclusions
The study shows that HVAC system in a closed waiting room generates a marked space diffusion of droplets from a cough event. Although the doubling of HVAC’s air flow allows for a marked reduction in the airborn contaminant concentration this also leads to a substantial increase of turbulent air motions resulting in an increased and faster long-range spreading of droplets and air contaminants in the room. In indoor environment, the doubling of the air conditioned flow allows a relevant (up to 77%) reduction in droplets mass concentration within the room compared to nominal air flow. In the first 5 seconds from the cough event, no particular differences in droplets concentration are detectable in the room, while the relevant differences occur within 25 seconds due to the air conditioned systems that induce droplets air dispersion. In absence of air conditioning, larger particles more easily settle on the ground, while for nominal or doulbe-flow HVAC air-flow even the largest particles are subjected to turbulent phenomena and follow the air conditioned flow remaining suspended for longer time (see Scenarios A, B and C here below). Despite that, the calculation of Infection Index for all the subjects in the room proved that a higher air exchange allows to reduce in the long term the overall amount of inhaled contaminated air.

Video Covid air diffusion.

Air flow scenarios - HVAC system

The right fan to allow large airflows?

As best practice denotes, fans will still need to be selected for optimum efficiency at normal working conditions, but also have the capability for a duty increase to supply additional air during high risk periods, or when high occupancy of an area is expected.

The performance charts below highlights the difference in performance envelope between a Large airflow plug fan (in this case our NPA range) vs the normal maximum you could expect to see on an EC equivalent plug fan.

Higher pressure and volume needs Comefri plug fans
Comefri plug fans performance

Infection risks & mitigation

CIBSE advise for safe working area’s

To minimise the risks of airborne transmission of SARS-CoV2 / COVD-19 the general CIBSE (The Chartered Institution of Building Services Engineers London - https://www.cibse.org/coronavirus) advice is to increase air supply and exhaust ventilation, supplying as much outside air as is reasonably possible. The underlying principle is to dilute and remove airborne pathogens.

Airborne transmission

Mounting Evidence for Airborne Transmission

While evidence for airborne transmission of COVID-19 is currently incomplete, several studies are underway; With the majority of the released or early findings from these studies testing positive samples for SARS-CoV-2 genome (RNA) within in the air.

This is also in keeping with the findings for other respiratory viruses, including SARS-CoV, MERS-CoV, RSV and influenza, with both short-range and longer-range airborne transmission being possible. Previous studies of general viral transmission have also provided strong evidence for indoor airborne transmission of viruses, particularly in crowded, poorly ventilated environments.

Market demand for HEPA Filters

In poorly ventilated spaces with a high occupancy and where it is difficult to increase ventilation rates it may be appropriate to consider using air cleaning and disinfection devices.

The most appropriate devices are likely to be local HEPA filtration units or other disinfection devices .Although ongoing studies are reviewing the effectiveness of HEPA filters to remove Covid-19 from the air, HEPA filtration / increased filter efficiencies are being specified.

Supplying a safe amount of air?

REHVA advise for improved air flows

With the recommendation to run ventilation at higher volume / flow rates to directly supply fresh air; changing CO2 set points, coupled with other recommendations from increased air flow through natural ventilation (windows), reduced occupancy & increased social distancing practices; There are multiple considerations to make in order to ensure a safe environment for ventilated areas.

Reviewing the requirements for safe practices for the amount of air to supply, the REHVA (Federation of European Heating, Ventilation and Air Conditioning Associations) guidance FAQ also offers some insight for the best ventilation working practices:

REHVA FAQ – Recommended rate of air exchange for workplace
Existing standards in non-residential buildings lead to about 10 L/s per person; Researchers are studying if this value should be increased to 20-25 L/s per person – with research ongoing on Covid-19.

REHVA FAQ – Level of occupancy considerations
The amount of litres per person fresh air needed is directly related to occupancy. The amount of fresh air / ventilation rate per person matters, this can be increased by lowering the occupant density, or increasing air flow for higher occupancy density areas.

Fan selection considerations?

What does this guidance mean to your fan selection?

  • To help ventilate areas with increased air changes; An increased air flow within normal unit & duct sizes is required, creating higher velocity systems. This will have a knock-on effect of increasing system pressures & power requirements for the fans to work against.
  • Introduction of HEPA filters into the system will increase the unit pressures, increasing the fan working parameters.
  • Taking current Building specifications into account and the revised recommendations to have safety built into system for higher air flow and pressures, Plug fans, using AC Motors, should be considered to achieve adequate Ventilation.
Higher pressure and volume needs Comefri plug fans

How this will change your system & fan selections

The right fan to keep you safe?

As best practice denotes, fans will still need to be selected for optimum efficiency at normal working conditions, but also have the capability for a duty increase to supply additional airflow during high risk periods, or when high occupancy of an area is expected.

The performance charts below highlights the difference in performance envelope between a High pressure plug fan (in this case our NPA range) vs the normal maximum you could expect to see on an EC equivalent plug fan.

Higher pressure and volume needs Comefri plug fans
Comefri plug fans performance

The Coronavirus has spread fast and seriously affected our lives and businesses worldwide but in spite of the fact that Italy is one of the countries where this virus has hit hardest, Comefri SpA has kept going, kept producing and kept supplying our fans where they are needed.

We are proud to say that the Comefri Group is making a significant contribution to the war against this pandemic.

In fact, our fans have recently been installed in a large number of hospitals, which have been built or converted in record time to help cure Covid-19 patients around the world.

Here is a list of some of those hospitals:





  • Ospedale Maggiore Bologna
  • Presidio Ospedaliero Santo Spirito – Pescara
  • Ospedale Sacco Milano
  • Ospedale Niguarda Milano
  • Ospedale Covid Civitanova Marche
  • Varna St. Marina - Bulgaria
  • Guy’s Hospital, London
  • Great Ormond Street, London
  • Torbay Hospital, Devon
  • Freeman Hospital, Newcastle-Upon-Tyne
  • Kingston Hospital, London
  • Royal Berkshire Hospital, Reading
  • John Innes Centre, Norwich
  • Queen Elizabeth Hospital, Birmingham
  • Filton Blood centre, Bristol
  • Whittington Hospital, London
  • İstanbul Sancaktepe Sahra Hospital
  • Ankara Etlik Integrated Health Campus
  • Gaziantep City Hospital
  • İstanbul İkitelli – Başakşehir
  • İzmir Bayraklı City Hospital
  • Kocaeli City Hospital
  • Isparta Eğirdir Goverment Hospital
  • Bitlis Ahlat Goverment Hospital New Building
  • Afyonkarahisar Sinanpaşa Goverment Hospital
  • Samsun Training and Research Hospital Additional Polyclinic Building
  • Mersin City Hospital
MCE logo

MCE 2020 was posponed to September 2020.

Comefri SpA is participating to the 2020 MCE Mostra Convegno Expocomfort in Milan, 17-20 March 2020.

Visit us at Hall 9 - Booth R23

MCE 2020: THE ESSENCE OF COMFORT

MCE symbolizes the fullest synthesis of housing comfort in the future. Essence lies at its core and represents the soul of living pleasure.
MCE website.

Comefri is pleased to announce the completion of n.4 Atex Axial Fans Φ900mm in A316L and blades in Aluminum with Heresite coating. The final use is in the Oil&Gas industrial sector.

Once again, Comefri consolidates its presence in the Oil&Gas sector by widening the supplies with its own Axial Fans.

Axial Fan Comefri Axial Fan Comefri

We warn all our partners that the use of trademark and/or brand “Comefri” shall be considered authorized and lawful only if it concerns the products manufactured by one of our factories, which are exclusively the following:

Comefri Italy - Comefri Gmbh - Comefri UK Ltd - Comefri France - Comefri USA - Comefri China - Comefri Fan Systemleri (Turkey)

Please verify all the products labelled “Comefri” at your disposal and contact us whenever you find products which are not manufactured by one of the aforesaid factories.

Further, consider that the use of the trademark and/or the brand “Comefri” by third parties is unauthorized and unlawful without our prior formal authorization.

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