Indoor air quality in classrooms is an important research topic today. Studies have shown that poor or inadequate indoor air quality has negative effects on students' performance and active participation in classes. The aim of this study is to examine the local air velocity and air age parameters to determine the ventilation needs of crowded, but limited-sized classrooms that are not connected to a central ventilation system, and to investigate the applicability of ventilation systems that can provide adequate indoor air quality. In the study, a primary school classroom with a capacity of 30 students was examined. Ventilation requirement is determined per person according to “ASHRAE 62.1-2022” Standard and “Building Bulletin 101” directive. For ventilation of the classrooms, counter-fluid heat recovery ventilation units mounted embedded in the wall. It is aimed to reduce the total volume allocated for the ventilation device in the classroom compared to the use of a single device. To slow down fresh air entering the room at high speed and mix it before reaching breathing zone, blowing directions of the neighboring devices are intersected. With these information, a classroom model was created to be analyzed with the Computational Fluid Dynamics method. In addition, another classroom model was created for investigating personal ventilation scenario. By a comparative analysis, average air velocities, age of air values around heads of students and students' perception of indoor air quality according to Fanger's "Predicted Average Vote" method were investigated.