The importance of air quality

This fact raises some reflections on this matter that involve the adaptation to the technical regulations of the centers by professionals experts in air quality and in air conditioning and ventilation installations, since otherwise, a great risk in the case of finding opportunists who are abundant lately, and whose only aim is to take advantage of these situations without any guarantee

Many centers should follow a series of urgent and effective recommendations for better management of the current situation in order to minimize as much as possible the possible risk of airborne transmission of SARS-VOC-2. It must be said that currently there are no air conditioning and ventilation systems or equipment capable of guaranteeing, under official scientific and technical criteria, a "COVID FREE" seal for establishments and activities with the presence and rotation of people in indoor spaces. By studying the facilities, it is possible to adapt their operation so that they act as a further measure of prevention against contagion, forming part of the solution.

We must not forget the need to continue working on future solutions to the risks that the current situation does not allow us to achieve and which, at least known, we must face by applying the available resources and the guidance of the known as the least common of the senses.

Therefore, in terms of air quality we breathe and its relationship with the airborne infection of COVID-19, we should follow a series of recommendations:

• Research indicates that the risk of airborne transmission of COVID-19 in enclosed environments with poor ventilation is greater than in outdoor environments. This does not depend so much on the quality of the air of these environments as on the adequate renovation that gives the same realize by contributing external air.
• With the obvious exceptions of very recently built schools, or in those in which energy efficiency actions have been carried out that include measures to improve indoor air quality, we can say that most do not have mechanical systems. indoor air renewal or controlled mechanical ventilation (VMC) that guarantee air quality within the mandatory or recommended parameters and its renewal by outdoor air.

There are many effluents that affect the quality of indoor air, with the concentration of carbon dioxide (CO2) one of the key parameters to determine it in meeting places for people. The maximum value recommended by the WHO for healthy environments of 1000 ppm. This is therefore a widely used parameter when assessing whether the effective air renewal that occurs in an occupied enclosed enclosure is suitable for use in healthy conditions.

In the Regulation of Thermal Installations in Buildings (RITE), the main regulatory framework for indoor air quality, classifies it into 4 categories IDA 1, IDA 2, IDA 3 and IDA 4

IDA 2 (good quality air) category is required in "classrooms" and offices to which the RITE assigns a limit value of + 500 ppm on the CO2 concentration from the outside.

In "nurseries" and hospitals, the requirement for IDA 1 (optimal air quality) is increased, to which the RITE assigns a limit value of + 350 ppm on the CO2 concentration outside.

Good indoor air quality does NOT guarantee a reduction in the risk of airborne infection, but it does favor it, as the achievement of the minimum recommended and required levels of compliance with indoor air quality is achieved through renewal. of indoor air by outdoor air.

The RITE sets minimum outdoor air flows based on the IDA category to be guaranteed, which in the case of classrooms and nursery schools are:

• "Classrooms and offices (IDA 2)" sets a minimum flow of 12.5 dm3 / s per person.
• "Nurseries and hospitals (IDA 1)" sets a minimum flow of 20 dm3 / s per person. "

The current real situation is that most existing schools do not have VMC (Controlled Mechanical Ventilation) systems suitable for classrooms, being the only option to achieve the renewal of air in them natural ventilation through the window opening.

The effectiveness of this form of ventilation will always depend on particular parameters of each classroom, being remarkable those of its windows or ventilation gaps (typology, location, surface) and fundamental unpredictable as are the climatic conditions (atmospheric pressure, wind , etc).

Being aware of the reality described and the emergency situation for COVID-19, we consider it essential and recommend not to give up in the desire to raise awareness among the educational community and society as a whole of the importance of renewing the indoor air of classrooms, although the only possible solution is direct natural ventilation (windows) and this is associated with a higher energy expenditure and may not reach the optimal conditions of comfort.

This recommendation should be taken as a short-term stance, based on preserving health first and foremost, but never taken as a definitive solution. We consider it essential that the Administration continue to work without interruption in planning the implementation of adequate and sustainable VMC systems that guarantee the correct renewal of its indoor air and thus the improvement of health conditions in schools and other buildings in the which concentrate people, whether for reasons of leisure, work, management, sport, etc.

Having an optimal or good quality of the indoor air and an adequate renewal of the indoor air, can never lead to relaxation in compliance with other measures provided to prevent infection by other transmission routes (separation distances, gauging ratios, hygiene standards, mask, etc.)

As the ventilation systems are regulated by RITE, we cannot forget to mention the necessary return to the field of industrial safety of all the systems and equipment that it regulates, to guarantee their safety, correct maintenance and with it the their contribution to the energy efficiency of the buildings in which they are installed and to an appropriate ecological transition.

In classrooms, offices ... where only natural ventilation is possible, we consider it a great help and we recommend having a double-probe CO2 concentration meter (indoor-outdoor) which, in addition to its real function of controlling the indoor air quality, now serves as a "guide" device to determine when it is necessary to ventilate the classroom by opening windows, doors, etc., and when the renovation has been effective and can be re-used. close open items.

If there are no double-probe meters, the center must have general meters that indicate the concentration of external CO2, so that those responsible for the classrooms have a reference for comparison with the internal values of the same.

This is an economically affordable solution, easy to implement and will help to improve indoor air quality for the benefit of classroom occupants and reduce the risk of airborne infection of COVID-19 by facilitating the operations of ventilation and with it the renewal and contribution of outside air.

If a VMC system exists, attend to the mode of operation for which it was designed (continuous, timed, sensors, etc.) and if no control is detected to regulate its operation (ie on / off to user decision), based on the CO2 sensor measurements that should be implemented.

It is VERY IMPORTANT to determine if the existing VMC system is of the "extraction only" type without the supply of outside air being guaranteed, as it may in its operation lead to an incorrect renewal of the indoor air of the classroom with vitiated air from other unsafe downtown areas.

Other generic recommendations in this regard could be:

• Modify the Control to Increase Ventilation
• Reduce or eliminate Air Recirculation in equipment as much as possible
• Heat recuperators
• Continuous Toilet Removal
• Operation of the Terminal Units with Air Recirculation in facilities equipped with external ventilation
• Air filtration and purification systems.
• Centralized filtration and purification systems
• Portable filtration and purification systems.
• Preventive maintenance before reopening
• Duct cleaning is not mandatory
• Inspection and cleaning of air filters
• Inspection and cleaning of drive and return units

Antoni Escarré

Dean of the College of Industrial Technical Engineers of Tarragona

Tarragona, 14 September 2020