A seasonal assessment of indoor air quality and thermal performance in naturally ventilated airtight energy-efficient dwellings

Background: Increased building energy performance requires improved thermal performance, elevating the risk of overheating and necessitating cooling strategies. Natural ventilation possesses the advantage of reducing cooling energy consumption in warmer seasons. Nevertheless, a consequence is decreased airflow in energy-efficient structures employing enhanced airtightness. Aim: This research evaluated the effectiveness of natural ventilation in maintaining acceptable indoor air quality in energy-efficient airtight households with no centralised active ventilation systems. Methodology: Bedrooms, living rooms, and kitchens were monitored for a week during summer and winter. Indoor air pollutants included PM_2.5, CO₂, TVOCs, NO₂, CO, beside temperature and relative humidity. Bedroom air exchange rates were extrapolated based on the metabolic CO₂ method. Results: Higher (p < 0.01) concentrations of gaseous pollutants were measured in bedrooms than in living rooms, and in winter than in summer. PM_2.5 concentrations exceeded the 24-hour WHO guidelines in kitchens (92% in winter, 51% in summer). CO₂ concentrations were above 1000 ppm for 94% of the sleeping time in bedrooms in winter, and 39% in summer. Weekly TVOC concentrations across the bedrooms were 463 ppb in winter and 293 ppb in summer. Temperature and humidity were broadly within acceptable limits. Air exchange rate ranged across the bedrooms from 0.08 to 0.35 h^-1 in summer and from 0.09 to 0.26 h^-1 in winter. Conclusions: Ventilation performance gap was identified between the design and operational performance based on the current operational strategy. The findings highlight significant seasonal variations in indoor pollutant concentrations and underscore the need to improve ventilation strategies.