Ventilation System

Ventilation systems encompass all mechanical or natural systems designed to maintain indoor air quality and optimize living conditions by expelling contaminated air and introducing clean air. These systems control physical and chemical parameters in ambient air, primarily temperature, humidity, CO₂, particulate matter (PM10, PM2.5), volatile organic compounds (VOCs), and harmful gases (CO, NOx, SO₂, etc.). Ventilation includes not only air exchange but also filtration, circulation, temperature control, and pressure balancing.

Modern ventilation structures integrated with climate control systems today are enhanced through building automation systems (BMS), SCADA, and IoT, making them more precise and efficient.

The primary purpose of ventilation systems is to sustain vital factors such as health, comfort, and safety in indoor environments. The main objectives related to these goals are summarized below:

• Health: Accumulated carbon dioxide, microorganisms, VOCs, and allergens in enclosed spaces pose threats to human health. Individuals with weakened immune systems, children, and the elderly are particularly affected.
• Comfort: Air at appropriate temperature, humidity, and cleanliness directly influences individuals’ physical and mental performance.
• Safety: In environments such as industrial facilities, laboratories, and rail system tunnels, gas accumulation, fire smoke, and toxic emissions create serious risks. Ventilation systems are critical for controlling these hazards.

During the COVID-19 pandemic, the effectiveness of ventilation in preventing diseases transmitted via aerosols became clearly evident. Authorities such as the World Health Organization (WHO) and ASHRAE emphasize the need for mechanical systems with high air exchange rates.

Underground rail systems (metro, light rail) require specialized ventilation systems due to high passenger circulation, dense electrical equipment, and limited natural airflow. Their main functions are:

• Thermal Comfort: Although the piston effect generated by moving trains creates air movement in passenger areas, this natural circulation becomes insufficient as passenger density increases. Therefore, mechanical ventilation systems are used to maintain stable ambient temperatures.
• Smoke Control: Smoke extraction systems, designed for emergency situations such as fires or explosions, are equipped with high-capacity fans and dampers. Critical areas include fire-resistant duct systems and automatic control panels.
• Equipment Rooms: In technical spaces such as electrical panel rooms, SCADA centers, and UPS rooms, continuous operation of equipment generates heat that can lead to hardware failures. Therefore, split air conditioning units, chiller plants, and controlled ventilation fans are used to maintain constant temperatures. These systems can be monitored both manual and automatically (e.g., via SCADA).

Hospitals are environments where hygiene is critical and infection risks are high. Therefore, ventilation systems are designed with greater precision:

• Hygienic Areas: Operating rooms, maternity wards, intensive care units, and sterile storage areas use positive pressure to prevent outdoor air from entering. HEPA (High Efficiency Particulate Air) filters capture 99.97% of particles sized 0.3 microns.
• Negative Pressure Rooms: In areas treating infectious diseases, air is prevented from escaping to the outside, thereby stopping contaminated air from spreading to other zones.
• Laminar Flow: In this system, used especially in open surgeries, air flows in a single direction from ceiling to floor at low velocity (0.2–0.35 m/s) after filtration. This prevents the transport of microorganisms.
• Filtration: Hospitals employ three-stage filtration: G4 (pre-filter), F7 (intermediate), and H13–H14 (HEPA). Additionally, UV-C lamps may be used to reduce microbial load.

Schools are spaces where children spend extended periods, making indoor air quality particularly important:

• Post-Pandemic Awareness: Studies conducted after the COVID-19 pandemic have demonstrated that inadequate ventilation in classrooms increases the spread of infectious diseases. Natural ventilation through open windows and doors is insufficient to reduce CO₂ levels to acceptable thresholds.
• CO₂ and IAQ Monitoring: Sensor-based measurement systems are installed to monitor indoor air quality (IAQ), particularly CO₂ levels. The air volume per student is increased.
• Need for Mechanical Systems: In modern educational facilities, heat recovery ventilation (HRV) systems supply outdoor air while achieving energy savings. In these systems, heat exchangers recover heat from exhaust air and transfer it to incoming air.

The success of ventilation systems depends on accurate engineering calculations and quality implementation during the design phase. The following criteria must be considered during the design process:

• Air Changes per Hour (ACH): Determined according to space usage. ACH of 20–25 is recommended for operating rooms; a minimum of 3 ACH is advised for classrooms.
• Airflow Rate: Calculated in m³/h. In metro stations with high passenger traffic, an outdoor air supply of 20–30 m³/h per person is required.
• Filtration Level: Filtration standards compliant with EN 779 and ISO 16890 must be applied.
• Temperature and Humidity Control: In hospitals, temperature should be maintained at 22–24 °C and relative humidity between 40–60%.
• Airflow Direction: Airflow must move from clean to dirty areas to prevent contaminated air from entering clean zones.
• Energy Efficiency: Energy consumption is reduced through EC fan motors, variable airflow systems, and automated control devices.
• Sound and Vibration Control: Sound attenuators and vibration isolators are installed in air ducts to minimize noise levels.

Ventilation systems are not merely comfort features; they are critical systems that directly impact human health and safety. With advancing technology, these systems are evolving into intelligent systems capable of more precise control, higher energy efficiency, and greater environmental awareness. Properly designed ventilation systems, built with appropriate design criteria and technological infrastructure across all sectors—from underground rail stations to hospitals, schools, and industrial facilities—enhance quality of life and contribute to sustainable building design.