Assessment of an underfloor heating system in a restored chapel: Balancing thermal comfort and historic heritage conservation

Abstract

Heating historic buildings always entails a greater or lesser impact on indoor air temperature and humidity, on which the conservation of historic interiors depends. As modern rehabilitation prioritises such interiors, local heating is the system of choice to prevent possible harm while delivering high levels of occupant comfort. Such heating systems (radiant flooring, for instance) are marketed and have proven to be ideal, although installation conditions and especially system operation and use may disrupt the fragile comfort-conservation balance. Santas Formas Chapel at Alcalá de Henares, in Greater Madrid, Spain, provides a good example. The underfloor radiant heating installed on the occasion of a recent restoration has proven to effectively ensure maximum occupant comfort (Categories I-II) up to a height of 2 m off the floor with no impact, for the time being, on the dome mural paintings, located at a much higher elevation. At heights over 56 cm, fluctuations in relative humidity (RH) and temperature (T) barely exceeded the target (–8.1 % to +9.1 %, ΔRH) and (−2.5 °C to +2.5 °C, ΔT) ranges that ensure preventive conservation of building interior. Theoretically at least, then, conservation of assets lying above that height would be guaranteed. Future conservation will nonetheless call for changes in system operation. The abrupt disturbance of the indoor microclimate induced by initial system start-up in the winter should be avoided. Unprogrammed interruptions and restarts lasting hours or days are equally unadvisable, for the resulting fluctuations in T and RH may affect heritage conservation without modifying thermal comfort.