Microclimatic monitoring in an historic church fitted with modern heating: Implications for the preventive conservation of its cultural heritage

Conservation of historic churches' interior artistic and architectural heritage may be severely compromised by heating systems that alter indoor microclimatic stability. The modern centralised heating systems installed over the last 20 years, are claimed to guarantee comfort without jeopardising heritage assets by warming only the lower, occupied areas. Each building is a case unto itself, however, and even in recently installed facilities where it may still be too soon to determine possible harm to the cultural heritage, a plan to monitor the microclimate and its heating-induced fluctuations must be designed to guarantee the conservation of artworks. In this case study, the impact of heating was observed to vary due to architectural differences within the building, the type of facility and daily usage patterns. Within 1 h, the church's latest generation heating system raises the air temperature in nearly the entire building, including the upper heights, to the programmed 18 +/- 1 degrees C, while lowering the environmental relative humidity by up to 1/3. Although (Category II and III) thermal comfort is reached in 1 h, daily heating of that duration is not recommended, for it would result in short-term relative humidity values below the target relative humidity range for preventive conservation of the church's indoor heritage. The mechanical damage (fissures and cracking) that may be inflicted on these assets is related to thermal contraction-expansion and hygroscopic contraction-swelling cycles.