On this page you will find a number of questions raised in relation to COVID-19. When clicking on the question, the answers will appear.
Disclaimer: Answers to technical inquiries are provided as a service to the public. While every effort is made to provide accurate and reliable responses, they are advisory, are provided for informational purposes only. They are not intended and should not be relied upon as official statements of IEQ-GA nor of its members.
Are HVAC systems responsible for SARS-CoV-2 diffusion as they are for the spread of the Legionella bacteria?
NO. Legionella is a bacterium which can grow naturally in fresh water as well as in some of the HVAC equipment where water is used and collected (humidification AHU sections, cooling towers, etc.). It is usually spread by breathing in mist generated in cooling towers, though it may be found in other HVAC equipment where water has accumulated. The bacteria can eventually enter into the building through air-conditioned infected air.
On the other hand, SARS-CoV2 is a virus that can live only inside humans and infection occurs only via human-to-human transmission.
What are the officially recognised ways of human-to-human transmission and what relation is there with HVAC systems?
The WHO officially recognised transmission routes are: 1) By close and direct contact with an infected person; 2) by contact with surfaces contaminated by the virus with hands that later unconsciously touch mouth, nose or eyes; and 3) By inhalation of liquid droplets produced by the infected person. According to these officially declare transmission routes, HVAC systems do not any direct relation with the COVID-19 pandemic. However, HVAC systems in ICU in hospitals play a vital role as an engineering control for any airborne contaminants, including virus in droplets.
Yes. WHO recognises that in special situations such as in health care facilities, the COVID-19 virus can be transmitted by air currents. Therefore, following the ALARA (As Low As Reasonably Achievable) principle, it is important to minimise such a risk. In such cases, the HVAC system for the ICU’s and other areas of the hospital where COVID-19 patients are present can help to vent all air pollutants, including the virus. This can be accomplished through the ventilation of close common spaces with outdoor air and air filtration, i.e. through achieving and maintaining an elevated Indoor Air Quality (IAQ) by use of the HVAC system.
Can opening windows, as WHO suggests in some cases, give the same result of a mechanical ventilation system with respect to COVID-19 pandemic?
To dilute any kind of contaminant below a concentration level that may adversely affect human health, a specific amount of outdoor air must be provided at the positions of the building occupants. The amount of outdoor air needed depends on the source strength of the contaminant. With aeration by windows opening and closing (if it is possible), there may not be a method to control the amount of, or the distribution of, the outdoor air inside the space. Control of the amount and distribution of outdoor air is instead achievable with mechanical ventilation systems with different efficacy depending on their specific design. In addition, a mechanical ventilation system (usually a part of some HVAC systems) will facilitate the filtration of the outdoor air, which is usually performed to remove dust, particulate matters, and other airborne contaminants.
An example: An office building consisting of several floors is owned or rented by the same company, and, due to a smart working application, the number of employees actually present in the office is very small compared to the usual expected number of employees. Is it possible to place them on one floor only in order to be able to switch off the HVAC system in the other floors and save energy and money?
No. Social distancing is the main WHO recognised procedure to reduce pandemic spread. Therefore, the occupancy index reduction is the right direction to go, while concentrating all of the employees on one floor is contrary to what is needed. It is recommended that you maintain the overall occupancy on each floor. There will be a lower power requirement due to lower internal gains, and at the same time, you maintain or increase the ventilation air flow rate to improve the IAQ.
The ways of managing an HVAC system to reduce the risk as much as possible at the same time to reduce the airborne levels of COVID-19 as low as reasonably achievable can be quite different depending on the system’s file user and the typology of the duct layout. Thus, you have to refer to the specific system applications and typology. What is common to reduce the risk is the goal: to provide as much as possible outdoor air to dilute and remove through the exhaust air vents any possible SARS-CoV2-19 virus exhaled by an asymptomatic person present in the space or room serviced by the HVAC system. . This including sufficient and effective ventilation, possibly enhanced by particle filtration and air disinfection, and avoidance of air recirculation and avoiding overcrowding.
In the absence of people infected in the home, there can be no COVID-19 in the air. Therefore switching on the heating and air-conditioning systems does not affect the risk of contagion in any way. If there are infected people in the house, then their presence would determine the risk. However, the risk of COVID-19 in the air would not increase due to the operation of the HVAC system. In this case, the occupants in the living space must take all the necessary precautions regarding personal protection and behaviour (e.g., social distancing). Using the system or not is therefore only a question of the comfort level regarding the temperature to be kept in the living space. Ultimately it is the doctor who must decide what to do about the infected individual(s). In any situation involving infected individual(s), the premises must be as ventilated as much as possible. In the absence of a DOAS (dedicated outdoor air system) with adequate outdoor air flow rate, it is necessary to ventilate by keeping the windows open as much as possible. This including sufficient and effective ventilation, possibly enhanced by particle filtration and air disinfection, and avoidance of air recirculation and avoiding overcrowding.
How can I best manage an all-air system (heating and air-conditioning) serving a single working space to reduce the risk of the spread of COVID-19?
It is the case for supermarkets (always open, even in an emergency period), or for some public places frequented by many people at the same time (such as shops, shopping centres, restaurants, bars, cinemas, theatres and gyms (closed during the emergency period), that crowding determines the greatest risk of the virus spread. This is true for both those who stay in the environment in their working hours, and for those who enter and stay only the time necessary to fulfil their needs. When the activities that are currently closed are reopened, it is likely that, for a certain period of time, people flow into the public places will be strictly controlled, as is the case in supermarkets today. In all cases, it will be essential to increase the outdoor air flow rate to reduce the risk. This can be done by carrying out what is proposed in the AiCARR document . In particular, internal recirculation should always be closed to increase the outdoor air flow rate. Where this is not possible due to the configuration of the system, as reported in  in the case of roof top HVAC units, the presence of recirculated air does not increase the risk of contagion in the public place.
How can I best manage an all-air systems (heating and air-conditioning) serving a large office building to reduce the risk of the spread of COVID-19?
This category includes VAV systems and other HVAC systems with terminal reheat or double duct, and with and without variable flow. These systems are generally designed for medium and large buildings where the system, whatever the type, connects areas of the building between which people have no reason to move. The greatest risk of viral infection remains the direct contact between people who are infected and those who are not infected. If the ownership of the spaces are different, or if the ownership is single but the movement of people is limited, at least between the various floors, the movement of people must be even more confined and the use of common areas must be managed very well, keeping in mind that toilets and elevators are extremely critical points. From the system engineering point of view, it is absolutely necessary to close each air recirculation damper following the indications given in , to avoid propagating the contagion through the HVAC system to places where it would not be carried by the movement of people from one zone to another.
How can I best manage all-air systems (heating and air-conditioning) serving a few spaces under the same ownership to reduce the risk of the spread of COVID-19?
This is the case of small HVAC systems with one or more ducted zone recirculation terminals (serving several rooms). This can be the most difficult case to discuss, because the aerosol containing the virus can propagate in all of the spaces served by the system. The aerosol with virus does not remain in the rooms where the possible asymptomatic infected person stays. This is certainly true, but it is equally true that it is of no use to close these HVAC systems that are serving small areas in a single property. The greatest danger regarding the risk of contagion is instead facilitated by the movement of individuals in the various rooms and in the common use of the toilets, where the spread of the infection is very likely. In these cases, the concentration of elemental viral loads per unit of volume decreases, because it is distributed over the entire volume served by the HVAC system. The risk is lower for a single person who stays in the same room of any infected person, but the risk is now extended to all the people present in the entire area served by the systems. This means that there is less risk for more people. Anyone who cannot work from home, and therefore is inside the area where the infected person is or has been present, is in any case at more risk from the other two other infection pathways (person-to-person, and touching contaminated surfaces). This does not mean that these HVAC systems perform better than those with primary air, because they still do distribute aerosols (including the virus) everywhere in the building. It also means that their closure does not lead to substantial risk reductions, precisely because of the inevitable movement of people from room to room. Once again, containment must be done by controlling frequentation, promoting smart working and accurately checking the health of those who enter the premises.
This category includes systems with room terminals equipped with a fan (fan coils, fan-powered terminal boxes, VRF – VRV systems), systems with chilled beams, radiant systems or any other system with recirculation in the single room. This recirculation depends on air movement induced by the fan, and on the flow of outdoor air in active chilled beams. In radiant systems, it is a function of their share of convective exchange, which can reach 50% in radiant floors in heating, and with radiant ceilings in cooling. Not all terminals are able to filter the air effectively. In any case the ‘normal’ air filters used in this system are unsuitable to filter the aerosol, which is characterized by an order of magnitude of tens of nanometres. Furthermore, for both ‘normal’ filters and other particulate filters, there is currently no evidence regarding the filtration efficiency of these filters with regards to SARS-CoV2-19. Thus, at present there can be no distinction between different terminals. Whatever the type of system, it is not necessary, or productive, to stop the operation of the terminals because the risk of contagion remains unchanged.