Assessment of passive ventilation efficiency of a thermally modernized residential building

The article deals with the problem of reducing the efficiency of natural ventilation in thermally modernized residential buildings, which are typical for mass construction in the mid-twentieth century. The study is a continuation of the complex applied work within the framework of the municipal project to support condominiums and the Warm House program aimed at increasing energy efficiency and improving sanitary and hygienic living conditions in the multi-apartment housing stock. The paper analyzes the changes that occur after facade insulation, window and door sealing, and a reduction in outdoor air infiltration, which traditionally ensured the operation of exhaust ducts in buildings without mechanical ventilation. The study used a step-by-step methodology: an instrumental survey of 10 apartments on different floors, field measurements of microclimate parameters, and aerodynamic calculations of pressure drop and volume air flow in exhaust ducts. Particular attention was paid to the analysis of the ventilation system in kitchens and bathrooms, which, according to current standards, must have a constant exhaust air removal. The measurements showed that without an organized supply of outside air, the flow rate from the exhaust ducts does not exceed 3 to 5 m³/h, which is critically insufficient. There were also cases of airflow inversion on the upper floors and an excess of CO₂ concentration in the bedrooms at night up to the level of 1200 – 1500 ppm. To solve the identified problems, a combined technical solution was proposed based on the installation of supply wall valves and turbo deflectors at the exhaust channel heads. Tests have shown that after the introduction of these devices, the volume air flow rate increased by 5 to 10 times: up to 30 to 40 m³/h from the kitchen and up to 20 to 30 m³/h from the bathrooms. There was also a significant improvement in indoor air quality: the CO₂ concentration in the bedrooms dropped to 750 – 900 ppm. A decrease in humidity and volatile organic compounds was recorded, which was confirmed by both objective measurements and feedback from residents. The proposed solution does not require capital intervention in the supporting structures and additional energy costs, so it can be effectively applied in conditions of limited budget. The research materials can be used to develop recommendations for the modernization of ventilation systems in residential buildings of the secondary stock. In further work, it is planned to investigate the effectiveness of natural ventilation in the warm season and extend the analysis to buildings with other types of ventilation systems