Effects of Energy and Microclimate Variations on the Sound Propagation in Historical Buildings. San Salvatore Church in Bologna (Italy)

Air stratification and inefficient heating and cooling systems can negatively impact indoor microclimates and acoustics in tall, historical buildings like churches. Moreover, the design of HVAC systems solution in this type of buildings is highly constrained, due to their historical and cultural value. Organ pipes located in such structures are particularly vulnerable, as variations in temperature, relative humidity, and convective air flows can compromise tuning, dependent on the thermal behaviour of metal pipes. This study investigates microclimate conditions and their acoustic effects in the Church of Santissimo Salvatore in Bologna, Italy. Temperature and relative humidity measurements were taken throughout the church for over one year. The impacts of occupant load, thermal conditions, and microclimate variations on sound propagation were assessed. Results from the long-term monitoring campaign show fluctuations in temperature and relative humidity levels depending on outdoor conditions, internal heat gains, and number of occupants. Variations in indoor microclimate are hypothesized to alter various acoustic parameters by thermally expanding pipes and altering sound propagation. By quantifying real-time microclimate variations and their impacts on acoustics, this research sheds light on an understudied factor challenging the preservation of organs in historic religious buildings where strict conservation constraints limit modern HVAC retrofits. The findings also have implications for improving indoor environmental quality and occupant comfort in tall structures with inefficient climate control systems.