Journal of Iranian Architecture & Urbanism(JIAU)

Abstract Extended Abstract
Background and Objectives: The central courtyard is one of the important architectural elements of traditional houses in hot and dry regions of Iran, which plays a major role in organizing space, improving climatic conditions, and providing comfort to residents. The physical dimensions of this courtyard, especially its depth and height, are effective in temperature balance and natural ventilation, and have a great impact on the surrounding air flow, especially in hot summers. Traditional Iranian architecture has provided suitable solutions to deal with heat by using this element appropriately. However, scientific investigation of the appropriate dimensional ratios of the central courtyard is still one of the research needs of Iranian architecture, especially in the contemporary period when attention to indigenous patterns and new technologies has increased. The aim of this research is to analyze the effect of the dimensions of the central courtyard, especially its depth and height, on natural ventilation in traditional houses in hot and dry regions of Iran, and by simulating the houses of Lariha and Golshan in Yazd, it seeks to determine the optimal dimensions to improve the quality of ventilation and thermal comfort, and to apply these findings in modern architecture.

Methods: This research is of a quantitative and qualitative type, and experimental, test, and case study strategies have been used to conduct it. The data collection method includes library studies, observations, field observations, measurements, and simulations. Since the aim of the research is to investigate the improvement and performance of natural ventilation of the central courtyard in traditional Iranian houses, the dimensions of the central courtyard were considered as the independent variable and the air circulation pattern inside the courtyard as the dependent variable. The statistical population of this research includes houses with a central courtyard in Yazd and two houses in Lariha and Golshan, Yazd, as study samples, which were also selected in a non-randomly targeted manner. Initially, field measurements of the dependent variable (airflow speed and direction) were taken as primary data and simulation validation was carried out over a 30-day period, 3 times a day (9 am - 12 noon and 3 pm) in August, using a 200kimo/v device. Then, the measured data and the 3D model of the case samples were simulated using Design Builder software with the aim of analyzing the air circulation pattern in the central courtyard. Finally, the variable size of the height of the central courtyard was measured through intervention in the simulations.

Findings: The initial findings of this study indicate that the ventilation performance and air flow velocity in the central courtyard are very complex and are affected by many factors, but in order to simplify the study, only the effect of the courtyard height was investigated. In this regard, the air flow velocity at different heights of the central courtyard, including an increase and decrease in height by 2 meters, was simulated and compared. The results indicate that in both the Golshan and Lariha houses, increasing the height of the courtyard by 2 meters compared to the initial state causes a relative increase in the air flow velocity. For example, in the Golshan house, an increase in height of 2 meters increases the wind speed by about 9 to 20 percent, and in the Lariha house by about 11 percent. Similarly, a decrease in height by the same amount causes a significant decrease in the wind speed inside the courtyard. However, in the continuation of the study and with a further increase in height (up to 4 and 6 meters), the trend of changes was reversed; that is, an excessive increase in height caused a sharp decrease in the air flow velocity in the central courtyard, and in some cases, the speed reached close to zero. In contrast, a significant decrease in height (4 to 6 meters) also caused a significant increase in the average wind speed, approaching the speed of the outdoor air. Overall, these studies indicate a direct relationship between a moderate increase in courtyard height and air flow speed, but an excessive increase in height causes a significant decrease in ventilation and efficiency of the central courtyard. This finding indicates that the ratio of the height of the central courtyard should be selected carefully and based on ventilation optimization in order to maintain optimal conditions of thermal comfort and natural ventilation efficiency in traditional spaces.

Conclusion: In traditional houses in the desert regions of Iran, the central courtyard plays a key role in improving ventilation and air conditioning. This study, using computer simulation using Design Builder software, investigated the effect of changing the height of the central courtyard on the speed and pattern of airflow in Golshan and Lari houses. The results of the study show that increasing the height of the courtyard to 2 meters increases the speed of airflow in the courtyard space, and decreasing the height by the same amount reduces the wind speed. However, with a further increase in height, i.e. to 4 or 6 meters, the speed of airflow decreases and the previous relationship is reversed; in other words, too high a height causes a loss of ventilation. The results also indicate that an excessive decrease in the height of the courtyard also causes the height of the surrounding spaces to reach an impractical or unsuitable level for habitation, and side effects such as reduced shade and increased temperature in the courtyard are created. Based on these findings, the appropriate height for the central courtyard in order to achieve optimal ventilation in the Golshan house is 9 meters and in the Lari house is 11 meters.

Abstract Extended Abstract
Introduction: Providing clean and fresh air for students in the classroom is of paramount importance, especially in hot seasons. Based on research findings and evidences, mechanical air conditioning systems are not only expensive, but also consume a lot of energy and produce noise. In sultry conditions of Mazandaran province, this issue is more accentuated since the schools are cooled by evaporative air coolers, while it is possible to use the natural ventilation in a better share of the year, and the schools are closed in warm seasons. Hence, the purpose of this paper is to offer a practical solution that can be architecturally applied to the classrooms to improve the indoor airflow by inducing outdoor ventilation (natural ventilation), and provide a desirable and controllable indoor airflow according to the ASHRAE standard. In most Iranian schools, evaporative air coolers are used in hot seasons to reduce the high costs of air conditioning systems. Observations suggest that evaporative air coolers are also used in hot and humid climate near the Caspian Sea, resulting discomfort, particularly with high levels of humidity. In such cases, the evaporative air coolers are turned off and the windows are opened. Mostly, the induced indoor airflow is not effective, or a high flow of air enters the classroom in these situations.
Problem statement: Achieving comfort at schools in sultry conditions in hot and humid weather of northern Iran is challenging, and thus it is necessary to establish an effective air conditioning system in the classrooms. Moreover, natural ventilation is the best solution in these conditions according to the climatic and economic reasons. Natural ventilation should consistently induce airflow in all parts of the classroom at a reasonable velocity. Hence, this research investigates the criteria for designing classrooms in the climate of Amol, considering the position and the general configuration of the openings in the classrooms, and the direction of the prevailing wind to induce a controlled level of natural ventilation in all parts of the classroom. The main purpose of this article is to address these issues.
Research methodology: According to the literature, the present study is interdisciplinary in nature, and uses a combination of methods. The position of the openings and the composition of classrooms were examined as the independent variables, while the status of the indoor airflow was considered as the dependent variable in this research. The airflow velocity and direction were measured by precise digital devices during the test periods. The statistical population selected in this study includes all schools of Amol while a random case study was selected for further experimental tests.
In the next step, a simulation method was used to analyze the data for evaluating the architectural interventions. Simulations were performed by computational fluid dynamics method: The Gambit pre-processor was used for geometric modeling and grid generation, and Fluent Software was used to analyze the grid. In this study, the  standard model was used to simulate airflow. Thus, this research uses a combination of methodologies including experimentation, simulations and case study.
Results: After examining different tests, an optimal situation was selected according to the following criteria:

Increased velocity of the indoor airflow in classrooms which (1) is not disturbing and, (2) provides a consistent airflow for all of the students at all spots of the classroom.
Eliminated vortices in indoor airflow
Modified airflow direction
Properly directed outdoor airflow into the indoor space and an induced desirable airflow

According to the interventions made in this study, it was determined that both windows must act as air inlets to establish effective airflow in the classroom. The inlet air pressure to both windows must be approximately the same, and the outlet air flow from both windows must be approximately equal as well. This happens when the building facade and the exterior windows have a stepped configuration, and consequently the outdoor airflow can enter both windows equally. If there is no proper outlet considered for the air entering the classroom, the indoor air flow will be very turbulent. Therefore, devising an appropriate outlet based on the inlet airflow rate can balance the indoor air flow. According to the simulations, an outlet for the indoor air flow should be made within the wall facing the wind. In other words, if the wind is blowing from the west to the east, the indoor air outlet must be projected on the west wall of the classroom. In this case, the exit door should also be devised in the southwest corner of the classroom.
Some air outlets can be created (in the western wall) that act as a fan, a suction pipe, or an air outlet opening in the wall facing the wind, so that the air exits through the pipes in the wall. The suction rate of the western wall can regulate the internal air flow. Moreover, if the wind velocity is too high in the outdoor, the suction devices are turned off or slowed-down, and if the wind velocity is low, the suction devices can discharge more air. In this case, the shape of the indoor air flow is optimized and adjusted.

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