Decalogue of good practices in air conditioning and ventilation installations in front of the COVID-19

The document “ Ventilation and air conditioning systems in establishments and premises of human concurrence ” published by the Department of Health of the Generalitat de Catalunya, indicates the following:

“The main route of transmission of the SARS-CoV-2 virus is the airway, through small droplets that occur when an infected person coughs, sneezes or speaks, at short distances (drops larger than 5 microns). These drops are relatively heavy, do not travel far, and are quickly deposited on the ground or nearby surfaces. That is why one of the main measures to prevent infection is to keep the distance between people of 2 meters.

However, the virus can be viable in the air for a few hours in smaller aerosols (less than 5 microns) that can travel farther, transported by airflows or by air ducts in air conditioning systems. Although this route of transmission by small aerosols is less likely, it is necessary to take it into account and take some preventive measures in this regard.

It is important to consider ventilation as an effective measure of disease prevention and control. The renewal of the air has an effect mainly to reduce these smaller drops, which can remain suspended for hours in closed environments.

On the other hand, the recirculation of air produced by air treatment units can help keep aerosols in the environment, prevent them from precipitating by gravity and recirculate them, although these equipments, however, do not amplify. the concentration of viruses ”.

Based on the information published by the health authorities, as well as other voices of recognized prestige in the field of ventilation and air conditioning, the Council of Colleges of Graduate Engineers and Industrial Technical Engineers of Catalonia, as a representative of the professionals who design and put into service these types of facilities, has considered it appropriate to prepare this decalogue of good practices to help with the new situation arising from the pandemic.

It should be remembered that air conditioning and ventilation installations are regulated in Royal Decree 1027/2007, which approves the Regulation of Thermal Installations in Buildings (RITE), as well as their subsequent modifications. In this sense, article 26 of the same must be kept in mind where it is established that any installation from 5 kW of total rated thermal power installed, must be maintained by a duly authorized company. and that, for installations with a total rated thermal input installed greater than 70 kW, this maintenance must be carried out on the basis of the corresponding maintenance contract and also by an authorized company.

The RITE, in its IT-3 Technical Instruction Maintenance and use, develops a series of programs for preventive maintenance, energy management, use and operation, as well as others (listed in ITs 3.3 to 3.7), where 'establish the minimum operations that will have to carry out in the thermal installations.

However, given the exceptional situation already mentioned, it will be necessary to take a series of additional measures of an operational and preventive nature, apply improvements to existing systems or incorporate new technologies, to reduce the risk of transmission. In situations as complex as those caused by the emergence of COVID-19, each measure applied in this area will become effective, not individually, but in addition to a series of actions.

The following decalogue deals with the most important concepts, elements and actions in the face of the present problem, but any decision in this regard must be checked according to its particularities by a technician with proven ability and experience.

A - Actions on mechanical ventilation systems

1. Increase the flow of the system to 100% of its capacity, working with 100% outside air without recirculation, although we lose the energy efficiency of air recuperators.
2. Measure the amount of outside air that reaches the plants, terminal equipment or diffusers. It is necessary to reconsider the maximum employment of people by zones, in order to obtain a rate of renewal flow increased to 20 l / s person (IDA1), with a minimum of 12.5 l / s person (IDA2).
3. Establish ventilation system schedules other than people's work schedules. It is recommended to activate the ventilation systems 2 hours before the start of the activity and keep it 2 hours after it ends, in order to extract the pollutants generated by the occupants. If we have CO ₂ measurement systems, we will see the effectiveness of the action, even if it does not correspond to the indicator we want to control. Maintain the extraction systems of the bathing areas in continuous operation 24 x 7, to control possible infections via oral-fecal (another route of infection under study).
4. Check and correct, if possible, that the air extraction points of the building are away from the new air supply points, avoiding the return of polluted air.

B - About air conditioning systems with air recirculation (all types)

  5. These equipments are not susceptible to stop as they maintain thermal comfort, recirculate air continuously and can become contaminated by sedimentation on the walls or battery when they have stop cycles. Periodic cleaning and disinfection of the interior of equipment should be increased and avoided. The virus, as well as the carrier particles, have a much smaller size than the retention capacity of the G3-G4 filters of this type of equipment.

6. It is important to maintain relative humidity between 40% and 60% inside the building. It has positive effects to protect people (low humidity less than 30% causes airway dryness which makes them more vulnerable to infections). In addition, this SARS Cov-2 virus is very stable with very high or very low humidity (above 80% and below 30%). We think that there are many buildings without minimum humidity control (eg nursing homes).

C - Improvements to existing systems

7. Install Medium - High Efficiency Filters. In systems with recirculation of air can improve the efficiency and capacity of retention of particles of 1micra (carriers of virus of size 0.1 micron), changing filters inside the UTAS or intercalating boxes carries filters in the network of return, being able to do serve class F9 filters (> 85% PM1) that help minimize the airborne infection capacity of the system. These filters are usually used as pre-filters, to protect the high-efficiency class H13 or H14, in the so-called clean rooms of laboratories, pharmaceutical industry, food, hospitals, so they are able to filter germs such as bacteria and viruses. It should be borne in mind that this type of filtration can cause an increase in the loss of load of the system, which forces to increase the power of the fan motor, to return to reach the point in the work flow curve air / pressure required.

8. Consider applying antimicrobial coatings to the interior surfaces of air treatment units (AUs) as well as sealing interior straight corners with fungicide silicone for better cleaning. It is also necessary to carry out a strict hygiene of UTA (racks, condensed trays, batteries, fans). As a general prevention measure, it is recommended that the units be clean and disinfected at the start of the season, commissioning or re-occupation of the building (post-confinement). 9. Replace air filters, as an additional measure, of whatever type, more often than usual. Check that the ducts comply with the requirements of the UNE100012 standard, as specified by RITE, even if it is not a measure specifically related to COVID-19.

D - Additional centralized or autonomous systems that can be incorporated

10 Install near people crowding points (lobbies, waiting rooms), air filtration and purification units, whether fixed or portable with point support. These units should preferably have HEPA (High Efficiency Particulate Air) class filters. Some of them also incorporate complementary purification technologies (ultra violet radiation, active polarization, etc.). These support purification units must be selected so that they have a significant amount of movements / hour of indoor air.

Although these measures, we repeat, are not specific in order to prevent the spread of the virus, applying them to the highest possible degree and suitable for the installation in question ensures good filtration and purification of the air.

As a complement and in that case where possible, the following additional measures that exist in the market can be considered, and that each technician will apply under his criterion:

• Install electrostatic filters where we usually have coarse dust filters (G3-G4), such as fancoil units, VRV duct evaporators, etc. .
• Install V8 active polarization filters replacing the last stage of filter type F7-F8 output of the air conditioning equipment.
• Install UV-C ultraviolet germicidal light systems next to the equipment batteries. This action causes the inactivation of viruses and other microorganisms as they pass through the units and prevents the formation of biolayers between the fins of the batteries.
• Install photocatalysis systems with TiO2 (combination of UV-C with a catalyst, which generates highly disinfectant reagents, to remove common pollutants in the atmosphere.
• Bipolar ionization that has good effectiveness for particle removal
• Systems based on O3 ozone generators as a disinfectant. Special care must be taken with the application because they are toxic in a certain concentration and cannot be used in premises in the presence of people.

All these technologies cannot be ruled out as long as their effectiveness and safety conditions are demonstrated, by the responsible technician and depending on the particularities of each installation.

The disadvantage that must be taken into account in the total or partial application of these measures is the inevitable increase in the cost of conventional facilities, current or new, which in some cases can significantly increase the investments initially planned. Perhaps we should think of a mandatory rule in certain places of public use, in which the presence of people at short distances may be important or very important.