Penelope Canonico
06/21/2021 12:00
Clarín.com
Society
Updated 06/21/2021 1:16 PM
There is already enough scientific evidence that
air quality
in environments affects the spread of Covid-19.
The paradigm of windows and doors open for ventilation can be a bit overwhelming when
low temperatures
make us shiver with cold.
The risk of transmitting the coronavirus by aerosols (respiratory droplets that are generated when talking, coughing or sneezing) is latent in indoor spaces
without ventilation
, where particles accumulate increasing the chances of
inhaling the virus
.
So, how to solve daily, work and social life when the building infrastructure hinders the development of activities?
Technology offers support tools to advance the
return to normality
and meet the challenge of reproducing a safe and caring environment for a classroom, office, shop or airplane.
Carbon dioxide meters
They have long been used for air conditioning and air quality control.
They allow to measure the
concentration of carbon dioxide
(CO2) within an environment and are an
indicator of the degree of ventilation
of a space at a given time and under certain circumstances.
In a closed room, when people enter who begin to breathe and speak inside, the CO2 levels begin to increase.
If one of them is infected, it emits aerosols that contain viruses and that, over time,
accumulate
and can
infect
those who are several
meters away
.
Hurlingham University will provide CO2 meters to Hurlingham and Morón schools.
CO2 monitoring allows you to
regulate
the level of opening of the doors and windows necessary for adequate ventilation so as not to take too much cold.
In this way, it mitigates the risk of contagion while providing the best
possible
thermal comfort
in the context of low temperatures.
CO2 is a compound present in the environment with a concentration of approximately 400 ppm (parts per million) outside.
The air exhaled by a human being can have 40,000 ppm of CO2.
“
Measuring carbon dioxide is like taking the temperature
to be sure that the ventilation in the atmosphere is adequate and, if it is not, guide the necessary actions. The human being is a machine to produce CO2 because it transforms part of the oxygen that it inhales into carbon dioxide ”, explains Jorge Aliaga, physicist, former dean of Exactas at the University of Buenos Aires (UBA) and current Secretary of Planning at the University of Hurlingham.
“CO2 molecules move in the air with a similar dynamics to the aerosols that we exhale.
If, when measured, it is higher than that in the atmosphere, it is because that air is stale, it has already been
breathed by others
.
On the other hand, if the level of carbon dioxide is similar to that of the outside air, it is because it has been renewed and there is a low risk of contagion by aerosols ”, he continues.
Carbon dioxide meter, manufactured by Jorge Aliaga.
How to read results?
The device has a
display
for reading data, a light and sound indicator, a power button and a calibration button.
It takes
two minutes to start up
and, once in operation, measures from a non-dispersive infrared (NDIR) optical sensor.
The equipment does not warn about the presence of viruses in aerosols, but indirectly indicates
the accumulation of exhaled air
, which could contain viruses if an infected person were in that space.
They are calibrated according to the
international consensus
that indicates: 400 to 600 ppm (parts per million) indicates a low risk, 600 to 800 ppm, medium risk and
more than 800 ppm, high risk
.
"If this threshold is exceeded, a greater air flow must be generated, opening doors and windows, forcing circulation or, if this is not possible, evacuating the environment," says Aliaga.
And he adds: “Air filtering is
an additional measure
.
The filter
retains aerosols but does not replace the need to measure or
natural ventilation.
I recommend ventilating, if not improving it with a fan (pushing the air out) and, if not enough, filtering ”.
Depending on the characteristics of each team, they can be purchased
from $ 20,000.
Meters in Buenos Aires schools
Since Aliaga is part of the scientific advisory committee of the Province of Buenos Aires on issues related to the pandemic, he had the opportunity to present this idea to the highest authorities of the district.
Thus, the Province ordered the reinforcement of care measures, among which the “Buenos Aires in schools” initiative stands out, which plans to distribute
33 thousand
carbon dioxide (CO2) measuring
devices
to the more than 11 thousand schools in state management.
The investment in this program amounts to
$ 622 million.
The amount assigned to each establishment was made from statistical information.
One meter every three sections
that work simultaneously in the initial, primary and secondary levels of the common, artistic and professional technical education and
a meter every six sections
in the other levels and modalities.
“We bought one developed by the University of Hurlingham (UNAHUR), to know the concentrations in each classroom and to be sure that we are working well.
It is as if it were a cartridge belt that you transfer to the spaces at different times to
find out if the calculation we are doing
in terms of, for example, the number of students is correct ”,
Estela Dominguez Halpern
, rector of the Luis Industrial Institute
, tells
Clarín
A. Huergo.
Hepa filters
An alternative for environments where it is not possible to renew the air are Hepa filters (
High Efficiency Particle Arresting - High Efficiency Particle Collector
) that
reduce the concentration of the virus,
without lowering the temperature.
The appliance is installed in the same environment that it is intended to keep clean.
The purifier
filters aerosols, but not CO2.
How do they work?
As if they were a sieve, they allow to mechanically separate particles (
fungi, viruses and bacteria
) and to know in what percentage of efficiency the microorganisms can be filtered.
Purifiers are already in use in City schools.
They reduce the concentration of the virus and have the ability to retain aerosols in percentages
greater than 99.95%
, according to the European standard UNE1822.
They are approved and tested for the most technological air equipment and have filtration capacity for critical particles (0.3 microns).
Those used in
airplanes or operating rooms
, currently called ISO-35H, are capable of filtering 99.95% of critical particles. The filters are composed of a material similar to a paper, pleated to achieve a greater surface and cover more air flow. In most cases, they must be accompanied by high-pressure fans.
“The
size of the filters
is very important
. If they are small, they filter little air flow and cover a smaller cleaning area. This is important because if the speed of passage through the filters is increased, they stop being efficient and
stop being Hepa
”, underlines
Fernando Cani
, General Director of TROX Argentina and member of the American Society of Heating, Refrigeration and Air Engineers Conditioning (ASHRAE).
It also highlights that they allow the
generation of amounts of "virus-free air"
that can increase safety and lower the probability of infections to levels less than 1%, but warns that everything depends on the flow of filtered air and correcting the speed of fan rotation as filters get dirty.
The system makes it possible to generate "virus-free air".
Why is it a technology similar to that used in airplanes?
Cani explains that they are used both in airplanes, operating rooms, the pharmaceutical industry or laboratories, because they want to have a certain classification of air cleanliness regarding impurities.
Not only the filter is important, but also the correct distribution of the air.
This "virus-free" air flow must have a certain speed and range to sweep the entire space, but it must be outside the "breathing zone", that is, above 1.8 meters in height or below 1 , 2 meters which is equivalent to a seated person.
For example, in airplanes a vertical air flow is sought to minimize the breathing of air coming from another passenger.
In the case of other buildings, a good "throw" range of the "virus-free air" must be achieved to sweep the contaminants and they are captured by the return to be filtered.
Why is it so relevant? "
Because no matter how clean it is, it could bring exhaled air from one person to the noses of the others, collaborating with the contagion instead of minimizing it", develops Cani, who is also a member of the committee for the 80400/1/2 and 80450 standards. of IRAM that regulate the quality and quantity of outside air, in hospitals and buildings.
Residential purification equipment can cost between $ 50,000 and $ 80,000, while commercial applications start at $ 120,000.
In the first case, they lose the flow characteristic and need the replacement of filters which increases the cost of maintenance.
In the second case, they can last depending on the use, between 12 and 18 months.
For schools, restaurants, gyms, shops, cinemas, theaters, universities, Cani develops three different solutions:
-In the event that there is a central air conditioning installation and that, in addition, the fans can be adapted to overcome the pressure of the HEPA, they can be placed interspersed in the supply ducts.
-If there is a central air conditioning installation without the ability to "blow" through the HEPA, you can put a duct air purifier that already comes equipped with its own fan with the ability to overcome the resistance of the HEPA filters and to self-regulate the rotation speed to maintain the flow in a constant way.
-When there are no previous ducts, it can be solved with an environment purifier that should ensure both the flow and the correct distribution of air.
MG
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