Numerical study of the heat and moisture transfer in subterranean historic structures and regulation of the conditions for protection and sustainable management

Cultural heritage can be considered as a non-renewable resource of values for humanity. Aiming to protect and safeguard this resource for future generations, the concept of “sustainability” should be applied in the management of monuments and historical sites, considering that the preservation of cultural heritage is a topic of the UNESCO Sustainable Development Goals (SDGs). This dissertation is a reference to the case study of Macedonian tombs in north Greece which are monuments of great historic importance and precious educational value. They are dated from the late 4th to the 2nd century B.C. and they are valuable examples of architecture and painting of this era, since they are the only buildings of this period that have survived intact and many of them are decorated with frescoes. About a hundred Macedonian tombs have been excavated in a relatively small geographical area and the majority of them are not widely known. Macedonian tombs present particularities in their hygrothermal status. Systematic monitoring and evaluation of the indoor climatic conditions has shown that the deterioration processes are mainly caused by cyclical changes of temperature and relative humidity when the monuments are exposed to the environment and the presence of visitors. Protection against future deterioration can only be assured through proper interventions to stabilize the indoor microclimate. Underground burial monuments have been the subject of research for at least 60 years, studies and proposals have been made to protect them, many of which have been implemented and are case study examples today, to draw valuable conclusions. What is important and remarkable is that all researchers on this subject worldwide agree that the protection of these monuments lies in the proper regulation of their indoor microclimatic conditions. This doctoral dissertation is a step towards raising awareness for the protection of Macedonian tombs and focuses on the issue of deterioration processes in their structural elements. The first part of this research deals with the understanding of the problem of damage to underground monuments and in particular the Macedonian tombs. Investigating the state of the enclosure created within the Macedonian tombs and understanding the effect of these particular microclimatic conditions on the processes of damaging the exposed walls of the tombs. Understanding the problem of deterioration of Macedonian tombs is attempted by the help of building physics. Then, a literature review is done about the “ideal” conditions for temperature and relative humidity set-points which are proposed by the international guidelines and standards for museum environments. This dissertation provides an evaluation methodology that is based on computer simulation, with which the decision making will be done having full understanding of the monument's behavior and the contribution of each individual factor to the deterioration processes. That way, decision making for strategic management and control of the microclimate in the tombs’ shelter will be based on the result of the evaluation, which can assess strategies using a simulation program. More precisely, through data collection, analysis, simulation and interpretation of the results, this research provides an assessment methodology of microclimate control strategies aiming to protect Macedonian tombs and proposes a framework for evaluation of the hygrothermal behavior of underground monuments that can simulate, evaluate and assist in management decisions, providing a view of the actual contribution of each microclimate selection. A methodology proposed that can be applied in all the Macedonian tombs: -First step is the investigation of the microclimatic conditions of the Macedonian tombs, with recordings in selected monuments, their evaluation and conclusions. To achieve this goal, three Macedonian tombs were selected which are very close geographically, at Pella and Agios Athanasios area. A specific recording methodology was followed, which lasted for at least three years. Thermo-hygrograph digital recorders with sensors were used. -Simulation in the computer and visualization of the deterioration processes using the simulation program WUFI©, based on the recordings. The simulation program provides data which, after analysis and interpretation, support the assessment the existing hygrothermal performance of the tombs’ structural elements. -Then, the same simulation program runs again to assess new control strategies, supposing a built shelter over the tomb, using as a museum. As input there are used the museum microclimate set-points for control classes proposed by the international guidelines and standards. These set-points are considered as the microclimate inside a hypothetical built shelter over the tomb. -Finally, the interpretation of the results lead to conclusions about the effect of the applied microclimate on the hygrothermal performance of the tomb and consequently, on the resulting deterioration processes. General principles are proposed that can be applied to similar monuments. This dissertation will contribute to the following aspects: -Raising awareness on the issue of the protection of the value of Macedonian tombs and promote the scientific research on their preservation issues. -Point out the sustainable approach to management and decision making for underground heritage structures. -Contribute to the standards, adding new parameters. -Contribute to the adaptation to climate change, according to the IPCC, that identifies four main categories of adaptation measures: technological, behavioral, managerial and policy. This study refers mainly to the managerial category, which includes monitoring and maintenance. -Finally, this dissertation deals with adaptation measures suggested by the UNESCO and by the ICOMOS that recommend increasing research, knowledge, education, engagement, the upgrading of management plans, including risk assessments and monitoring procedures to increase the resilience of the heritage sites.