This paper analyses the possibility to apply energy refurbishment measures in restored historic buildings in order to ensure reuse. The objective of the paper is to provide an appropriate methodology for the structural restoration of historic buildings, their re-use and sustainable energy refurbishment in accordance with current needs and conservation principles. The study provides the analysis and evaluation of the realized goals regarding energy refurbishment and energy efficiency. The presented historic buildings belong to Hilandar Monastery, Mount Athos, Greece. Mount Athos has been listed in UNESCO World Heritage Site for decades. The paper deals with the expert analysis of abandoned and devastated structures included in the Haybarn Complex. This paper provides a positive outcome of the performed restoration in terms of energy refurbishment and repurpose, since these buildings were turned into unique accommodation facilities for visitors. This accomplishment can be seen as a useful recommendation for improving energy efficiency of historic buildings during their restoration. All the undertaken methods are in accordance with the environmental protection requirements. This study is a practical observation and analysis of energy refurbishment in the field of restoration of listed buildings. This certainly is the most important contribution of this paper. All energy efficiency measures and renewable energy sources were carried out in compliance with conservation requirements and visual authenticity of historic structures. Assessment and analysis of energy efficient refurbishment via Building Performance Simulation (BPS) method and energy efficiency optimization was applied to several different models of restoration that was carried out in the Haybarn Complex.