Evaluation of the effectiveness of humidity control strategies in preserving a heritage library.

Abstract

Ensuring an appropriate and stable indoor environment is of the utmost importance when the preservation of historic heritage buildings and collections is at stake. As hygrothermal conditions are one of the determinant parameters of the indoor environment for safeguarding these valuable assets, their long-term monitoring is imperative in attempting to achieve the requirements established by different guidelines through a process of analysis and consequent implementation of mitigation strategies. The present study addresses the continuous monitoring and assessment of the hygrothermal conditions to evaluate the effectiveness of a humidity control strategy, which was implemented in a case study to meet its environmental needs for the preservation of collections. The case study is the 18th-century Baroque Library of the University of Coimbra, where air dehumidifiers were installed to help reduce extreme peaks in relative humidity. The approach consists of surveying the data collected from two different types of loggers, thermo-hygrometers placed inside the Noble Floor of the heritage library and a paper hygrometer directly placed inside the collections. In this way, the comparative analysis of the hygrothermal data before and after the implementation of the new strategy indicated its level of effectiveness for this type of building. Moreover, the evaluation of the data according to the threshold ranges recommended by most guidelines was contested over the monitoring period. From the results, it was possible to assess the quality of the hygrothermal environment concerning the thresholds proposed by preservation guidelines and to evaluate the effectiveness of the implemented strategy on both the indoor environment and the collections.