Claves para garantizar una calidad de aire interior óptima

Indoor air quality (IAQ) is a direct determinant of public health, given that people spend on average between 85% and 90% of their time indoors according to the U.S. Environmental Protection Agency (EPA, 2022). Indoor pollutant concentrations reach levels 2 to 5 times higher than outdoor levels, and in some cases up to 100 times, according to the same agency. Volatile organic compounds (VOCs) — emitted by paints, varnishes, adhesives, furniture, and cleaning products — exhibit average indoor concentrations of 200-500 μg/m³ in European dwellings, according to the INDEX study by the European Commission (2005, updated 2019), versus limits recommended by the WHO of 100 μg/m³ for TVOC (total VOCs) and 30 μg/m³ for formaldehyde.

Indoor PM2.5 particulate matter originates from cooking (gas stoves generate peak concentrations of 200-400 μg/m³ during cooking), candle burning, and infiltration from outdoors. A study by the Lawrence Berkeley National Laboratory (2020) covering 350 Californian dwellings documented that gas stoves raise average PM2.5 concentrations to 35 μg/m³ during use, exceeding the WHO daily limit of 15 μg/m³. CO₂, a marker of ventilation quality, reaches levels of 1,500-3,000 ppm in school classrooms with deficient natural ventilation, versus the 1,000 ppm maximum recommended by the EN 16798-1:2019 standard for Category II air quality. Each increase of 400 ppm above 600 ppm is associated with a 21% reduction in cognitive performance, according to the COGfx study by Harvard University (2015).

Mechanical ventilation with heat recovery (MVHR) is the most effective strategy for ensuring optimal IAQ without energy penalties. Cross-flow heat exchangers achieve efficiencies of 80-85%, while rotary enthalpy-type units recover 85-92% of the thermal energy from extracted air, according to Eurovent Certita Certification (2023) data. A balanced MVHR system for a 100 m² dwelling with an airflow rate of 150 m³/h (equivalent to 0.5 air changes per hour) and a heat exchanger with 90% efficiency consumes 350-500 kWh per year of electricity and saves between 2,000 and 4,000 kWh per year of thermal energy, resulting in net savings of 1,500-3,500 kWh per year. Installation costs range from 3,500 to 7,000 euros for a single-family home, with payback periods of 5 to 8 years.

The EN 16798-1:2019 standard defines four indoor air quality categories: Category I (high expectation, airflow of 10 liters/second per person), II (normal, 7 l/s per person), III (acceptable, 4 l/s per person), and IV (below acceptable, <4 l/s per person). Passivhaus certification requires a minimum airflow of 30 m³/h per person with heat recovery of at least 75% and fan electrical consumption below 0.45 Wh/m³. In Spain, CTE DB HS3 (updated in 2019) sets minimum ventilation rates for dwellings of 8 l/s per bedroom and 12 l/s per kitchen, although it permits both mechanical and hybrid ventilation. According to the RITE + CTE report by IDAE (2021), only 12% of Spanish dwellings have mechanical ventilation with heat recovery, compared with 85% in Germany and 92% in Sweden.

Filtration systems determine the ability of a ventilation system to remove particles and aerosols from the supply air. The ISO 16890:2016 classification replaces the former EN 779 standard and classifies filters according to their efficiency across three particle size ranges: ePM1 (0.3-1 μm), ePM2.5 (0.3-2.5 μm), and ePM10 (0.3-10 μm). A filter rated ePM1 ≥ 60% removes at least 60% of submicron particles, including aerosolized bacteria and viruses, and is the minimum recommended by REHVA (Federation of European Heating, Ventilation and Air Conditioning Associations) for office buildings since the COVID-19 pandemic. HEPA H13 filters (efficiency ≥ 99.95% for 0.3 μm particles per EN 1822-1:2019) are reserved for hospitals, laboratories, and cleanrooms, with pressure drops of 250-450 Pa that increase fan energy consumption by 30-50%.

Active purification technologies complement mechanical filtration in spaces with high contaminant loads. TiO₂ photocatalysis degrades VOCs through UV-light-activated oxidation reactions, achieving removal rates of 40-80% for formaldehyde and 30-60% for toluene, according to a meta-analysis published in Building and Environment (2021) drawing on 45 experimental studies. Bipolar ionization systems generate positive and negative ions that attach to particles and pathogens, facilitating their capture by conventional filters; the company Global Plasma Solutions (GPS) documents reductions of 99.4% of SARS-CoV-2 in laboratory tests per ISO 18184. The combination of MVHR with heat recovery, ePM1 ≥ 80% filtration, and active purification reduces indoor PM2.5 exposure by 85-95% and total VOCs by 60-80%, according to measurements by the Belgian Building Research Institute (BBRI, 2022).

The regulatory framework for indoor air quality in the EU is structured around the EN 16798-1:2019 standard for non-residential buildings, CTE DB HS3 in Spain for dwellings, and Directive 2024/1275 (recast EPBD), which will require from 2028 the monitoring of CO₂ and humidity in new public buildings exceeding 250 m². The WELL v2 certification by the International WELL Building Institute (IWBI) devotes its Air category to IAQ, with 14 preconditions covering minimum ventilation, filtration, source control, moisture management, and continuous monitoring. In 2023, more than 4,500 projects in 75 countries were registered under WELL, spanning 55 million m².

Continuous IAQ monitoring using low-cost IoT sensors (50-300 euros per unit) enables real-time verification of compliance with quality thresholds. Sensors such as the Sensirion SCD4x series measure CO₂ (range 400-5,000 ppm, accuracy ±40 ppm), temperature, and humidity in a 10 × 10 × 7 mm form factor with a current draw of 19 mA. The ALDREN (Alliance for Deep Renovation in Buildings) project, funded by Horizon 2020 with 1.9 million euros, developed the TAIL (Thermal, Acoustic, Indoor Air Quality, Luminous) protocol that assigns a rating from A to G to the indoor comfort of buildings, integrating IAQ alongside thermal, acoustic, and luminous comfort. The protocol was validated in 48 buildings across 8 European countries and demonstrated that buildings rated TAIL A or B had 18% lower employee absenteeism rates and 24% higher occupant satisfaction levels than buildings rated D or below.