A research team from the University of Burgos in Spain has found that cross-ventilation is the most effective form of natural ventilation for maintaining healthy indoor air. However, their findings also highlight a pressing issue: more than half of the public buildings they surveyed cannot realistically apply this method due to architectural limitations.

Why Ventilation Matters More Than Ever?

Since the COVID-19 pandemic, there has been heightened awareness around air circulation in shared spaces. From schools and gyms to offices and government buildings, ensuring clean air has become a public health priority. The Burgos researchers developed a model to evaluate real-world ventilation capacity, using carbon dioxide levels as the primary indicator of air quality.

CO₂ as an Indoor Air Quality Indicator

Carbon dioxide is considered a reliable marker because its concentration increases steadily with human activity. Good indoor air quality is defined by the European IDA2 standard, which requires the CO₂ difference between indoor and outdoor air to stay under 500 parts per million. The study measured how many air changes per hour, or ACH, are needed to meet this benchmark. About three ACH is typically recommended for effective infection control, though exceeding five ACH can cause discomfort and reduce the effectiveness of ventilation.

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The Cross-Ventilation Challenge

Cross-ventilation occurs when air enters and exits a room through openings on opposite sides, creating a steady flow. Among the 183 rooms analyzed in the study, more than half had no option for natural ventilation. Even rooms with windows often fell short of acceptable standards. One example was a city council hall designed for 77 people, which could safely accommodate only 20 while maintaining healthy air levels.

Only a small fraction of rooms just 11 percent were able to meet IDA2 standards for occupancy and ventilation. Depending on room size and use, between 28 and 57 percent of rooms met the lower benchmark of three to five ACH. The findings suggest that most existing buildings are not designed to provide sufficient ventilation through natural means alone.

Combining Natural and Mechanical Solutions

To overcome these shortcomings, the researchers recommend a hybrid approach. Natural ventilation through windows should be supported by mechanical systems to ensure consistent air exchange. Real-time CO₂ monitoring could be used to trigger interventions, such as automated window openings or restricted room access, based on air quality levels.

This kind of system can also support energy efficiency. In spaces that rely on air conditioning, automated ventilation triggered by sensors can limit the need for manual adjustments, balancing safety and comfort.

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Designing for the Future

The study stresses the need to rethink how public buildings are designed. Many existing structures were not built with ventilation in mind, which now presents challenges for both health and energy efficiency. Incorporating natural airflow into future building plans can reduce reliance on energy-intensive systems while improving occupant well-being.

Cross-ventilation is a low-cost, scalable method for improving air quality. When paired with technology such as CO₂ sensors, it becomes a practical tool for day-to-day health management in public spaces. The researchers argue that building design should start with the premise that air needs to move. This can help prevent the spread of airborne illnesses and improve overall respiratory health.

A Clear Path Forward

The research concludes that creating healthier public spaces requires a two-step strategy. First, older buildings should be upgraded with hybrid ventilation systems. Second, architects and urban planners should prioritize cross-ventilation in the design of new public structures.

The study reinforces the idea that natural ventilation is not only viable, but essential. With proper planning and technology, it can play a major role in making public spaces safer, more comfortable, and better prepared for future health challenges.

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