Buildings of historical significance, which were traditionally, constructed using locally sourced materials and adapted to regional climates, offer unique opportunities for improving energy efficiency while maintaining cultural heritage. This research focuses on analyzing the indoor environmental performance of Lawang Sewu, a historic structure completed in 1904 during the Dutch colonial period. The protected historical site Lawang Sewu stands as a Semarang symbol in its red-brick structure with its neo-Gothic architectural design. Temperature and humidity measurements at Lawang Sewu took place over one year across four different spaces that experienced varying occupancy and usage patterns. Temperature distribution patterns in rooms were heavily affected by the active number of building occupants and also by when they used and inhabited the spaces. Researchers examined different retrofit modifications as means to minimize energy usage. The combination of advanced glazing systems with roof-based photovoltaic panels generated impressive energy savings worth 90.46% compared to original scenarios annually. The study demonstrates that seasonal variation together with occupant actions and usage patterns substantially impacts the interior climate conditions. The research underlines that architects need to maintain equal emphasis on energy efficiency alongside thermal comfort coupled with architectural preservation throughout building retrofit processes

Energy retrofit, Thermal comfort, Photovoltaic, Energy Efficiency, Heritage building, Lawang Sewu

This study presents a comprehensive evaluation of innovative retrofit strategies aimed at improving energy efficiency and thermal comfort in heritage buildings, with Lawang Sewu in Semarang, Indonesia, serving as a representative case. By integrating passive, active, and renewable energy interventions, the research demonstrated that energy demand and occupant comfort can be optimized without compromising the architectural and cultural integrity of historical structures. The implementation of electrochromic glazing, energy recovery ventilation (ERV), and CIGS photovoltaic systems yielded a measurable improvement in both annual energy performance and thermal comfort indices. Among all configurations tested, the combined passive and renewable strategy (PA_RN) achieved the highest energy savings—reaching up to 90.46% annually—while maintaining indoor comfort within acceptable PMV thresholds. Moreover, the application of these strategies validated the potential of low-impact technologies to retrofit heritage buildings in tropical climates where temperature and humidity fluctuations are significant. The study also confirms that data-driven simulation tools are essential for predicting the thermal behavior of historical structures and guiding retrofit decisions that respect conservation ethics. Ultimately, this research contributes to the evolving discourse on sustainable heritage preservation by offering a replicable and adaptable framework that balances environmental performance with cultural value. The methodological integration of environmental data, simulation modeling, and heritage-sensitive technologies provides a pathway for future retrofitting efforts in similar contexts globally. It is hoped that these findings will inform policy, practice, and design strategies that prioritize both sustainability and heritage conservation in the built environment

Hassan Gbran, Siti Rukayah, Atik Suprapti and Edward E. Pandelaki (2025). Innovative Strategies for Optimizing Energy Efficiency and Thermal Comfort in Heritage Architecture: The Case of Lawang Sewu. International Journal on Emerging Technologies, 16(2): 90–101