Spain. The Spanish Technical Association of Air Conditioning and Refrigeration (Atecyr) published a guide of recommendations on operation and maintenance of air conditioning and ventilation systems for buildings for non-sanitary use for the prevention of contagion by COVID-19.
The Atecyr Technical Committee made this document with the participation of experts in HVAC facilities, and it was based on the information that the scientific community has published through guides of associations and organizations of which Atecyr is an active part (such as REHVA and ASHRAE), as well as the recommendations of the World Health Organization.
2 - Operation of air conditioning installations
Next, the different practical measures are developed, where there is an international consensus, which it is convenient to implement when operating and maintaining in the most common air conditioning systems in the administrative and commercial field.
It is important to note that many of the measures will have an impact on the operating costs of the building (higher energy consumption). It is a context of health priority where the safety of users in the face of contagion must be prioritized over thermal well-being and energy efficiency. The excess of ventilation will make a building safer, but that surely could not reach the conditions of comfort, in addition to increasing energy consumption.
2.1 Ventilation and outside air
It has been shown that the danger of contagion of the COVID-19 disease inside buildings is higher when there is little ventilation. Although the building stock is very diverse, and the reference standards for its design from different eras, it is necessary that the contribution of outside air is the maximum allowed by the system that serves the building.
Recommendations (hereinafter REC):
REC 1 Minimum Outdoor Air Flow
The most important parameter is the renewal of air per occupant. As a recommended value and given the uncertainty of a fixed value, a minimum of 12.5 L / second and occupant is recommended, even for commercial establishments, This is the value that the Regulation of Thermal Installations in Buildings attributes to IDA 2: good quality air. This type of measurement will only be possible if specific outdoor air treatment units are available. To ensure this minimum value, you can work in two directions: increase ventilation or reduce occupancy.
In this sense, it is possible that the maximum occupancy of the spaces should be recalculated based on ventilation per occupant. In an existing building or premises, the indoor CO2 level could be found to be less than 500 ppm that of the outside air. In an existing building or premises, it should be checked that the indoor CO2 concentration level is, above the concentration of the outside air, at most 500 ppm.
REC 2 Flow Verification
It must be verified that the equipment in charge of the air renewal works at least in its nominal design conditions and that possible pressure losses, especially internal to the system, are minimal (filters with clogging, etc.). If the operation of the engine is by means of a frequency inverter, observe that it is in expected conditions of service, and if possible, at the maximum speed of the engine following the limits set by the manufacturer. In this way, a maximum ventilation flow will be guaranteed.
REC 3 Modify Control to Increase Ventilation
If the system has specific air quality controls (CO2 probes, etc.) disconnect them giving priority to the continued use and maximum flow of the system (per schedule). It is recommended during working hours 2 hours before / after the opening / closing of the work center, work with the maximum flow allowed by the system. In the remaining hours of the week, including weekends, keep the system running at low flow. It is advisable not to fall below 25% of the established nominal.
REC 4 Reduce or Eliminate as Much As Possible the Recirculation of Air in the equipment
If treatment units with air recirculation are available, provided that the operating conditions allow it to close the recirculation gates working to the maximum with outside air. If you have a freecooling section, go directly to 100% outdoor air mode.
In the case of Rooftop units, reduce recirculation as much as possible. It should be noted that it is a priority to mortgage to some extent comfort and energy efficiency against health as long as it is a priority to avoid contagion.
REC 5 Stop of Heat Recuperators
If the unit has a rotary-type recovery system, stop it. Although in the new systems the leakage rate is limited, and can be compensated with an increase in outside air avoiding short circuit, it is complex to verify and the usual thing over time, if they have not been maintained properly, is that there is some decompensation in the extraction side that would generate it. If the unit has a plate recuperator, check for possible leaks in the section before putting it into operation. Until this fact is verified, it is preferable to bypass this section if there are gates for it in the air conditioner.
REC 6 Continuous Toilet Extraction
If there is a dedicated extraction system for the toilet area or other areas attached to the office (changing room, etc.) maintain them permanently (24 hours a day, 7 days a week), even if infiltrations and outside air entry are generated in hours of minimum contribution of ventilation air. This will limit fecal-oral contamination.
REC 7 Increased Natural Ventilation
If the building at source does not have mechanical ventilation systems, it is advisable to open accessible windows. Although it can generate some discomfort due to air currents, or thermal sensation, the benefit of air renewal by cross ventilation is demonstrated to lower the rates of pollutants in the rooms. Even in buildings with mechanical ventilation it is advisable to perform regular ventilation with windows. In the case of practicable windows in the toilets, it is recommended not to open them because this could establish a reverse air flow and remove air from the toilets to the rest of the building and facilitate contamination by fecal-oral route.
2.2 Thermohygrometric Operating Conditions
Although there are different studies on the deactivation of COVID 19 based on the temperature and humidity of the surface where it is located, in some cases they are contradictory. The points common to all of them and therefore advisable are the following:
REC 8 Common setpoint temperatures
The operating conditions of the building imposed by rd 1826/2009 in force do not significantly affect the deactivation of the virus, and the conditions that would allow it, especially due to thermal conditions (above 30º) are not compatible with a conventional administrative activity. Therefore, it is recommended not to change the heating and cooling setpoints.
REC 9 Relative Humidity in the Usual Values
Although there is more controversy in the control of humidity, according to the different studies provided, the regulatory ranges in force (30 to 70% RH) are considered adequate so it is also recommended to maintain the setpoints previously established in the building.
2.3 Terminal Units
If the building has fancoils or indoor units linked to direct expansion systems, the following actions are recommended:
REC 10 Operation of Terminal Units with Air Recirculation
It is recommended that fans of indoor units such as fancoils and splits operate continuously and at their minimum speed, since, in case of shutdown, the virus can settle in the filter and spread again when it starts. During non-occupancy hours, its use can be programmed at minimum speed.
3 Air purifiers
There is a high scientific uncertainty about the contagion of the SARS CoV-2 coronavirus. There is certainty that air renewal is a first-rate safety aspect. However, some buildings do not have forced ventilation and natural ventilation through doors and windows may be scarce. For those premises where existing systems cannot guarantee an air renewal equivalent at least to IDA-2, or as an additional method for the reduction of airborne pathogens, there are specific systems for cleaning and sanitizing air from the air in premises
In the particular case of spaces with the impossibility of ventilating mechanically or naturally, these facilities should be complemented with technologies and equipment that improve indoor air quality. Minimizing the risks of spreading droplets during its operation and whose effectiveness provides us with measures equivalent to good ventilation with outside air.
REC 11 Air purification systems
Regardless of the mandatory compliance with the RITE, there are specific teams, either to incorporate existing ones or as autonomous teams, with different technologies and combinations of them.
In the case of autonomous units located in the same treated spaces, it is recommended that they have a significant hourly movement index and according to the applied technology, they must also have hePA type mechanical filtration, in order to guarantee a good air treatment.
Special care should be taken with the indoor use of toxic systems such as ozone (O3) that cannot be used when there is occupation.
The solutions available on the market that each technician will apply at his discretion are set out below. These are assistive technologies that if not sized or applied correctly may not meet the objectives for which they are prescribed.
The effectiveness of the treatments will be the result of the combination of all the technologies used.
1. HEPA filtration. This air filtration process is considered the standard for air purification. Highly efficient, it traps particles and does not release them into the air, it is safe for all respiratory problems. Difficult to incorporate into existing equipment, there are autonomous equipment with this type of filtration.
2. Electrostatic filtration. It is a filtration based on the charge of the particles and their electrostatic attraction on a medium. It is both in version to attach to existing equipment and in small autonomous teams. With this filtration, particles of all kinds are retained, some that may contain viruses. The equipment manufacturer must ensure that the equipment does not generate ozone.
3. Ultraviolet germicidal light (UV-C). Unlike previous ones, this technology emits an invisible light that attacks contaminants by destroying your DNA instead of passing them through a physical filter. This technology, of proven efficacy, is only good at killing viruses, bacteria and germs. It does not remove particles in the air.
Direct radiation to people and animals is very dangerous, so its use must be carried out by qualified personnel. It is relatively easy to incorporate into existing duct-type units or UTAS. It often comes as an added bonus in a HEPA or ionic air filter in stand-alone equipment.
The equipment manufacturer must ensure that the equipment does not generate ozone.
4. Photocatalysis. This technology similar to the previous one does not filter the air, it only sanitizes it through a combination of UV-C and a catalyst that generates highly disinfectant reagents. Its effectiveness against pathogens is very high. It does not remove particles in the air. It is relatively easy to incorporate into existing duct-type units or UTAS, although it is also found in autonomous equipment
5. Bipolar Ionization. There are a variety of technologies on the market based on the generation of ions, free radicals with positive and negative magnetic charges and redox reactions that contribute to neutralize pathogens and other volatile organic compounds.
It does not remove particles in the air, in most cases it encourages its precipitation on the ground and nearby surfaces.
The equipment manufacturer must ensure that the equipment does not generate ozone.
4 Maintenance of the facilities
As relevant as the operation of the system are the maintenance work, both preventive and corrective to be carried out in the described systems.
The maintenance of thermal installations is regulated by technical instruction IT.3 "MAINTENANCE AND USE" of the Thermal Installations Regulation in force. Those actions or tasks to be carried out as set out in tables 3.2 and 3.3 of that section and that may be more controversial are reviewed.
REC 12 Preventive Maintenance Before Reopening
In buildings and establishments that have closed or ceased their activity, it is advisable to carry out a general review of the installation of air conditioning and ventilation before reopening. In this case, it is convenient to clean grids, diffusers, ducts, filters and batteries.
In maintenance operations, after the reopening of the buildings, it must be extended to the rest of the thermal installations of the buildings and especially in relation to the cleaning and disinfection measures of the DHW facilities for the prevention of legionellosis.
REC 13 The cleaning of the ducts is not mandatory in relation to COVID-19
If the previous recommendations on the increase in the supply of outside air, absence of recirculation and stop of rotary recuperators have been followed, it is not expected that there will be transport or existence of viruses in the network of supply ducts that may contaminate the rooms they serve; therefore, in relation to COVID-19 it is not necessary to clean the duct network.
It should be borne in mind that once a season it is mandatory to review the duct network according to the criteria of the UNE standard 100012
REC 14 Review and cleaning of air filters
A filter that is filled or has an excessive pressure loss can reduce the flow of circulating air in the unit, conflicting with the initial recommendations made above. Therefore, it is recommended to replace the air filters in accordance with the maintenance program already established in each building.
On the other hand, changing the regulatory filters in the air handling units for more efficient ones would cause the same effect if the fan of the equipment is not prepared for that loss of load. Therefore, it is recommended that the change of filters be for others of equal performance or, as an exceptional measure, study the incorporation of other technologies (active polarization, ultraviolet lamps, etc.) provided that the replacement improves efficiency without loss of available pressure or affection to the unit where they are installed.
REC 15 Review and cleaning of drive and return units
Although it is necessary by regulation to carry out a review and cleaning of the air impulsion and return units once a season, it is considered convenient to reinforce the maintenance of the air conditioners especially in the following points:
- Verification of the tightness of the units and sections that compose it, as well as in joints, doors or registers.
- Verification of nominal pressures and flow rates of the unit (working point).
- Cleaning of equipment and components (batteries, interior surface, etc.)
REC 16 Increase Maintenance Protection Measures
All the tasks described must be carried out according to the security measures established in the protocols that each company and according to guidelines of the Ministry of Health.
One of the most complex tasks, from the point of view of personal safety, is the change of filters that may contain traces of contamination, always assumes that this is the case and extreme precautions. The protective measures will be the usual ones including mandatory respiratory protection and gloves for all of them.
Special care must be taken with the handling of dirty filters remembering that, apart from what is already indicated, it must always be done with the equipment off and maintaining the adequate custody of the replaced material, recommending its deposit in a sealed bag after entering the waste circuit established in each case.
5 Cleaning the facility in the event of a suspected case of COVID-19
Recommendations for cleaning the equipment are established in case of a suspected or confirmed case of COVID-19
REC 17 Actions before a Possible Positive contagion
Ventilation of the space where the person has stayed for at least 4 hours. Ventilation to the maximum, both forced and natural if possible. Ventilation should begin at least 2 hours before disinfection work begins.
Within the protocol of cleaning and disinfection of the space, include the grids of impulsion and return of air. Extraction and cleaning and disinfection of the filter of the indoor unit if any (fancoil, split). Cleaning and disinfection of the indoor unit (if any) by spraying a disinfectant solution (water with hypochlorite or similar).
Source: Atecyr.
