Energy consumption in buildings has become one of the most pressing global challenges of the twenty-first century. The demand for heating, cooling, and ventilation systems continues to rise, particularly in regions characterized by extreme climatic conditions. In Iran, as in many other developing countries, the rapid growth of urbanization and the increasing reliance on mechanical systems for thermal comfort have placed significant pressure on both the economy and the environment. The high cost of energy, combined with the environmental consequences of fossil fuel consumption, has made the search for sustainable solutions in the built environment an urgent priority. Within this context, vernacular architecture offers valuable lessons, as traditional builders developed strategies that minimized energy demand long before the advent of modern mechanical systems.

The present study focuses on the Bam Citadel (Arg-e Bam), the largest adobe structure in the world and a prominent example of vernacular architecture in Iran’s hot and arid climate. The citadel, with its extensive use of mudbrick (khesht) and palm wood, represents centuries of accumulated knowledge in adapting architecture to harsh environmental conditions. While numerous studies have previously examined the role of traditional materials and design strategies in reducing energy consumption, this research distinguishes itself by conducting a comprehensive simulation of the thermal performance of the citadel’s interior spaces using advanced software tools. The aim is not only to validate the effectiveness of vernacular strategies but also to highlight their relevance for contemporary sustainable design.

The methodology adopted in this study is structured in two main stages. First, a detailed geometric model of the Bam Citadel was developed, including the zoning of interior spaces, the specification of construction materials, and the incorporation of natural ventilation pathways. Second, the model was subjected to energy performance simulations using DesignBuilder, which operates on the EnergyPlus engine. To ensure accuracy, the climatic data were sourced from the official EPW file for Bam, obtained from the EnergyPlus Weather Data repository. These data were cross-checked with Meteonorm outputs to validate consistency, although the EPW file served as the primary dataset. The simulation covered a full annual cycle (January to December 2002), with daily time steps to capture seasonal variations in thermal behavior.

Key concepts in energy analysis were explicitly defined and integrated into the research framework. Thermal comfort was assessed using established models such as PMV/PPD and adaptive comfort indices. Thermal mass was analyzed in terms of the capacity of adobe walls to store and release heat, thereby moderating indoor temperature fluctuations. Energy performance indicators included heating and cooling loads, operative temperature profiles, and ventilation rates. By clarifying these concepts, the study ensured that the results could be interpreted within a rigorous scientific framework.

The results of the simulation reveal several important findings. During the summer months, indoor temperatures stabilized around 30°C, while in winter they averaged approximately 18°C. These values indicate that the building materials and design strategies alone do not fully achieve international standards of thermal comfort. However, they significantly reduce the reliance on mechanical systems compared to a baseline scenario without vernacular strategies. The thermal mass of adobe walls dampens extreme temperature swings, while the spatial organization of rooms and the use of natural ventilation channels contribute to improved thermal conditions. In effect, the citadel demonstrates a partial but meaningful capacity to provide thermal comfort through passive means.

Beyond validating traditional practices, the study emphasizes the broader implications of these findings. The Bam Citadel illustrates how vernacular architecture can serve as a living laboratory for sustainable design. By integrating traditional materials with modern simulation tools, researchers can identify strategies that remain relevant today. For instance, the use of high thermal mass materials in contemporary buildings could reduce peak cooling loads in hot climates, thereby lowering energy consumption and greenhouse gas emissions. Similarly, spatial configurations that promote cross-ventilation could complement modern HVAC systems, reducing their operational intensity.

The novelty of this research lies in its comprehensive scale and methodological rigor. Unlike previous studies that focused on limited case studies or short-term analyses, this work simulates the entire citadel over a full year, using validated climatic data and advanced visualization tools. The results were further refined through post-processing in Tecplot, which enhanced the clarity and readability of output graphs. This level of detail provides a more holistic understanding of the energy performance of vernacular architecture and strengthens the argument for its relevance in contemporary practice.

In conclusion, while the Bam Citadel’s traditional materials and design strategies do not fully eliminate the need for mechanical heating and cooling, they substantially reduce energy demand and improve thermal stability. The study underscores the importance of reinterpreting vernacular principles in modern sustainable architecture. By bridging historical wisdom with contemporary simulation techniques, architects and engineers can develop innovative solutions that respond to the dual challenges of energy efficiency and environmental sustainability. The findings highlight that vernacular architecture is not merely of historical interest but represents a valuable resource for addressing global energy challenges. This research contributes to the growing body of knowledge that advocates for the integration of traditional design strategies into modern building practices, particularly in regions facing extreme climatic conditions.