Preserving art in historical churches: evaluating microclimate fluctuations due to visitor activity

In churches, especially those without mechanical climate control systems, indoor temperature and relative humidity can fluctuate significantly throughout the day and year, posing potential risks to the preservation of artworks such as frescoes and wooden objects. The intermittent presence of people in these environments can exacerbate the problem, as their sensible and latent heat contributions amplify microclimate fluctuations. However, the actual impact of people on the indoor microclimate and artwork degradation is challenging to estimate due to the difficulty of collecting data during periods of continuous absence. In this paper, we monitored indoor environmental parameters inside the Santos Juanes Church, a temple of historical value in Valencia, Spain, from 2019 to 2020. This allowed us to assess the actual impact of visitors on the indoor microclimate through a comparative analysis of data from a "typical" period of use and data from the COVID-19 lockdown, when the church was closed. The results indicate that the effects of indoor activities on the microclimate are limited, not causing specific damage related to daily fluctuations. However, the estimation of damage risk indicators shows that indoor conditions during the summer, influenced by high outdoor temperatures and solar radiation, are not adequate for proper preservation. This issue, potentially common to many other churches in hot climates, can be addressed with increased night ventilation. This simple solution avoids the use of complex mechanical systems, which increase carbon emissions and are not recommended in the context of historical buildings.