Indoor radon and energy efficiency: A “short blanket” problem that demands for balanced ventilation

Abstract

A historic school building was recently retrofitted. Due to its high architectural quality, the building is listed as National Architectural Patrimony, and therefore the rehabilitation process has met very challenging requirements regarding its conservation to maintain the original layout. In view of its age, the building is done with thick stone walls which help energy conservation and enhance thermal inertia. Its primitive architecture enables natural lighting, increases solar radiation gains, and favors natural ventilation, assuring, consequently, an improved energy efficiency. The implemented rehabilitation actions tried to preserve the original architecture and the building restorations were designed to conserve as much as possible the ancient distinctive architectural style. Given the imposed constraints, matters like Indoor Air Quality (IAQ) and thermal comfort in rooms and offices for administration and staff were not met. The current situation has resulted in justifiable complaints from the building users, reporting poor rooms IAQ due to a lack of air renovation. Because of the impossibility to install mechanical ventilation ducts, the building rooms are operated through natural ventilation, which makes the adoption of constant air flow regimes difficult to implement. To evaluate the problem and promote measures to deal with it, an experimental campaign to assess IAQ and building thermal comfort was implemented during the Winter of 2022. In the framework of the campaign, two identical rooms with similar occupancy, size, volume, building typology, heating regime, and with the same equipment installed, were measured in situ for 3 months, by monitoring continuously the following variables: indoor radon concentration, air temperature and relative humidity, under distinct regimes of ventilation. By using statistical analysis of the experimental data, the results show, as expected, that the room with a permanent air renovation has an improved IAQ than the other monitored room, operated with a restricted ventilation schedule, without jeopardizing the energy efficiency. Based on the results, natural ventilation in a steady state mode is the key to balancing IAQ and energy efficiency.