Improving the Quality of Natural Ventilation in Classrooms of Mazandaran Province Based on the Position of the Openings Using CFD Method

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.

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

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.

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.