The optimization of architectural elements in response to local climatic conditions has long been a crucial factor in achieving thermal comfort and energy efficiency within buildings. In traditional Iranian architecture, passive strategies such as central courtyards and semi-open spaces like the Iwan have played an integral role in moderating microclimatic conditions, reducing dependence on mechanical systems, and ensuring thermal equilibrium throughout seasonal changes. This research investigates the thermal and energy performance of the Iwan as a passive architectural element in hot and dry climates, focusing on the Moghadam Museum House in Tehran as a representative example of historical architecture adapted to local environmental conditions. The study aims to analyze how the presence, orientation, and geometric configuration of the Iwan influence indoor thermal comfort, natural ventilation, and overall building energy consumption. For this purpose, a three-dimensional model of one of the rooms in the Moghadam Museum House was developed and simulated using DesignBuilder software, which is powered by the EnergyPlus dynamic thermal simulation engine. Two primary scenarios were tested: the baseline model without an Iwan and an alternative model with the existing northern Iwan as depicted in the historical plan of the building. Additional simulations were performed by rotating the Iwan to the southern, eastern, and western orientations to determine the optimal configuration for thermal and energy performance under Tehran’s climatic conditions. The simulations were conducted under natural ventilation without any mechanical HVAC systems to isolate the passive effects of the Iwan. All boundary walls except the façade containing the Iwan were treated as adiabatic surfaces, ensuring consistent heat transfer conditions for accurate comparison. The study focused on analyzing annual and monthly variations in air temperature, mean radiant temperature (MRT), operative temperature, relative humidity, Predicted Mean Vote (PMV), and Predicted Percentage of Dissatisfied (PPD), all evaluated according to ASHRAE Standard 55 for thermal comfort.
The results of the annual simulation revealed significant differences in indoor environmental conditions across various orientations of the Iwan. In the absence of an Iwan, the average indoor air temperature reached 23.50°C, with a mean radiant temperature of 24.18°C and an operative temperature of 23.84°C, whereas the inclusion of a northern Iwan reduced these values to 22.88°C, 23.49°C, and 23.19°C, respectively. The southern Iwan demonstrated slightly higher thermal gains, with an operative temperature of 25.91°C, but provided more effective solar shading during peak summer months. The eastern and western Iwans resulted in higher indoor temperatures (above 25.5°C), indicating increased exposure to low-angle solar radiation during the morning and afternoon. Relative humidity also varied across configurations, averaging 27.12% in the base case and 22.91% with a southern Iwan, reflecting the interaction between ventilation rates and indoor air dryness. The Fanger comfort indices indicated that the northern and southern Iwans provided the most balanced thermal comfort conditions. The annual average PPD values were 76.16% for the northern Iwan and 68.52% for the southern one, while the PMV indices were -0.58 and +0.17, respectively, indicating that the southern Iwan produced slightly warmer conditions but still acceptable comfort levels.
Further analysis revealed that the presence of an Iwan contributed to the mitigation of temperature fluctuations throughout the day, leading to improved thermal stability and lower cooling demand. The absence of an Iwan resulted in increased solar radiation penetration, especially during summer, causing overheating and higher PPD values exceeding 90% in July and August. The inclusion of a southern Iwan reduced the cooling load by approximately 10% compared to the base case, highlighting its shading effectiveness against high-angle solar radiation. The total annual cooling energy demand in the no-Iwan model was 36,850.09 kWh, while the Iwan model consumed 33,259.98 kWh, demonstrating a substantial reduction in energy consumption due to passive architectural adaptation. Heating demand, conversely, slightly increased in the Iwan case (211.96 kWh compared to 61.43 kWh) as a result of shading effects reducing solar heat gain during winter. Despite this, the net annual energy performance favored the Iwan-equipped configuration due to its improved summer efficiency. Moreover, airflow analysis indicated that natural ventilation rates (ACH) were highest for the open southern Iwan configuration, reaching 1.31 ACH, while the no-Iwan scenario had a lower rate of 0.87 ACH. Enhanced cross-ventilation contributed to efficient removal of internal heat and improved air quality, reducing reliance on mechanical fans and active cooling systems. Simulation outputs for PMV and PPD further confirmed these results: the southern Iwan maintained PMV within the ±0.5 comfort range during 63% of annual hours, while the northern Iwan achieved acceptable comfort during 59% of the time. These findings align closely with previous research emphasizing the critical role of semi-open architectural spaces in moderating heat exchange and enhancing occupant comfort in arid regions (Zhou et al., 2023; Heidari & Sharples, 2022).
In addition to thermal comfort, the study examined the effect of the Iwan on lighting and energy efficiency. The Iwan acted as a passive shading device, mitigating glare and distributing daylight more uniformly across interior spaces. This effect reduced direct solar penetration, preventing localized overheating near windows and reduced cooling loads. Although artificial lighting consumption was slightly higher in Iwan-equipped scenarios due to reduced direct sunlight, the overall energy savings from reduced cooling demands outweighed this increase. The total electricity use for mechanical systems, including fans and pumps, was 7,314.65 kWh in the Iwan scenario, compared to 7,790.69 kWh in the scenario without the Iwan, representing an approximately 6% reduction in auxiliary energy use.
From a seasonal perspective, the southern Iwan demonstrated superior performance in the warm months (May to September), mitigating overheating and stabilizing indoor temperatures around 26°C. The northern Iwan and the no-Iwan configurations performed similarly during cooler months (November to February), indicating that the northern shading had limited but positive effects during winter. The eastern and western Iwans, although contributing to shading, introduced higher thermal loads due to direct morning and evening sun exposure, suggesting that they are less effective in Tehran’s climatic context.
Overall, the findings confirm that the incorporation of a southern Iwan provides optimal thermal and energy performance in hot and dry climates. The results emphasize that passive architectural elements, when designed based on climatic data, can substantially enhance the environmental performance of buildings. The presence of the Iwan effectively balances solar gain, ventilation, and daylight distribution, thereby enhancing thermal comfort and minimizing reliance on mechanical systems. This corroborates traditional Persian architectural principles, in which spatial hierarchies and semi-open courtyards were historically employed to regulate microclimates naturally.
In conclusion, the simulation-based assessment demonstrates that integrating Iwans into modern residential architecture in hot and dry regions can play a significant role in achieving sustainable building performance. The study highlights the potential for combining traditional passive strategies with modern simulation tools–such as DesignBuilder–to optimize design decisions. Implementing such elements can lead to measurable reductions in cooling energy demand, enhanced thermal comfort, and improved indoor environmental quality, thereby fostering more resilient and energy-efficient buildings. The Moghadam Museum House case study exemplifies how architectural heritage can inform contemporary sustainable design practices, bridging the gap between traditional wisdom and modern technology. These results underscore the importance of climate-responsive architectural design, particularly the reintroduction of Iwans and courtyards as integral components of building envelopes in regions characterized by high solar radiation and low humidity. The study suggests that future research should expand upon these findings by incorporating occupant behavior modeling, multi-objective optimization of geometric parameters, and hybrid systems integrating photovoltaic shading devices to further enhance building performance and energy resilience in arid environments.