Impact of Bedroom Ventilation Strategy on Air Change Rates and Indoor Air Parameters in the Autumn–Winter Seasons—In Situ Study in Poland

Hybrid ventilation is indicated as one of the effective methods of maintaining thermal comfort and indoor air quality and reducing energy consumption in buildings. It assumes the capacity to switch between natural and mechanical ventilation, allowing the most efficient use of the outdoor air potential. This article aims to quantify the impact of changing ventilation system, from natural to hybrid, on indoor air parameters and air change rates in a bedroom of a single-family house. The distinct aspects of this study include longitudinal measurement over three years, natural ventilation substituted by hybrid ventilation halfway into the monitoring period, and unaltered building and user characteristics. The analysis is based on measurements of temperature, relative humidity, CO2 concentration, and window opening for three seven-month measurement periods from September 1 to March 31. The measurements are complemented by in-depth user feedback and an audit of the building structure and installed HVAC systems. A clear correlation was observed between the values of relative humidity and carbon dioxide concentration and the type of ventilation strategy. A significant influence of residents’ behavior on the achieved indoor air parameters was observed.