Climate monitoring in World Heritage List buildings with low-cost data loggers: The case of the Jeronimos Monastery in Lisbon (Portugal)

The knowledge of the indoor climate in cultural heritage buildings plays a prominent role in their conservation and sustainability. Monitoring campaigns are becoming more frequent, however, the high cost associated with commercial data loggers along with the lack of flexibility in programming and handling is a considerable hindrance. In the scope of this paper, a set of prototypes based on the Arduino technology were developed to measure the temperature, relative humidity and ventilation and to test the possibility of reducing costs to monitor cultural heritage buildings without compromising the robustness of the campaigns. In parallel, questions related to the importance of calibrating the sensors, the registration frequency, the duration of the campaigns and the location of the sensors were addressed. To overcome the mistrust usually associated to low-cost and home-made devices, the accuracy of the sensors was checked in the laboratory and then used to monitor the indoor climate of a World Heritage List church - the Jeronimos Monastery in Lisbon (Portugal). The monitoring campaign was carried out during 15 months with records every 10 min. The obtained results demonstrate the feasibility of using low-cost devices as long as the quality of the sensors is adequate. The assessment of the indoor climate was performed based on statistical and graphical analysis to characterize the typical climate inside the building and the CO2 measurements were used to estimate the ventilation rate and to analyse the visitor's impact at the monastery. Finally, a methodology based on the historic climate and described in Standard EN 15757 was used to optimize the indoor climate in order to control the mechanical degradation of organic hygroscopic artefacts in a sustainable way.