The awareness of the importance of air purification increased significantly during the pandemic caused by the SARS-CoV-2 coronavirus. This trend is reflected in the initiative by the National Centre for Research and Development (NCBR) called “Ventilation for Schools and Homes,” inspired by the European Green Deal strategy.

Sources of indoor air pollution can be divided into external (e.g., smog) and internal (bacteria, viruses, fungi) pollutants, the presence of which in the air results from the occupants themselves. The proper selection of the air filtration level depends primarily on the type of pollutants present in the room, prevention against potential pollutants, and the assumed effectiveness of their elimination. From the investor’s perspective, operational costs related to electricity consumption due to the operation of air purification devices (including fans in heat recovery units) and maintenance costs (e.g., the frequency of air filter replacement) are crucial considerations.

Why Are Air Purifiers Not Enough?

In rooms equipped with gravity or hybrid ventilation systems, outdoor air is usually supplied through humidity-controlled air inlets, mounted in the window frame or directly in the outer wall. Selected inlets allow for the installation of special filtration fabrics; however, during winter and transitional periods, users are often forced to replace these fabrics weekly, making this solution impractical and inefficient. When unfiltered contaminated air enters a room, the use of local air purifiers becomes necessary, which have their own sensors to activate the device and generate the appropriate airflow. However, it is important to emphasize that air purifiers can never replace mechanical ventilation, whose primary function is organized air exchange, including stabilizing carbon dioxide levels in the room.

Air purifiers can work in tandem with existing mechanical ventilation systems in the building. When is this cost-effective or advisable? Primarily when the ventilation unit cannot be upgraded with an additional air filtration section, and the installed fans do not provide adequate pressure.

Ventilation as a Research Challenge

To address these issues, the National Centre for Research and Development (NCBR) implemented the “Ventilation for Schools and Homes” project, funded by European funds under the Smart Growth Program. During its implementation, contractors developed ventilation systems designed for classrooms and residential spaces. One of the main challenges was to design a ventilation system that would not allow an increase in PM 2.5 and PM 10 particle concentrations in the room, despite high levels of these particles in the external environment, while also reducing microbiological contaminants, thereby minimizing the risk of illness.

Test Results

The ventilation systems developed by the project’s contractors were tested in a specially prepared climatic chamber located in the laboratory of the Department of Heating, Ventilation, and Dust Removal Technology at the Faculty of Environmental and Energy Engineering at the Silesian University of Technology (Figure 1).

Figure 1. View of the climatic chamber with control and measurement equipment and the installed mechanical ventilation system.

During the tests, concentrations of particulate pollutants PM 2.5 and PM 10 from the external environment, as well as microbiological contaminants generated in the test room, were monitored.

The ventilation systems‘ response was assessed in two independent tests—EAQ and IAQ. In the EAQ test, the operation of the ventilation system was simulated for two class hours, during which the system had to respond to particulate matter PM 2.5 concentrations of approximately 90 mg/m³ and 130 mg/m³ and generated carbon dioxide concentrations. The average 5-minute difference between CO₂ levels in indoor and outdoor air could not exceed 550 ppm. Energy consumption by the system was also recorded during the tests. The IAQ test, on the other hand, evaluated the system’s response to generated bacterial contaminants, including GRAM (+) and GRAM (-).

Figure 2. View of the climatic chamber during microbiological tests.

The tests confirmed that the developed solutions ensure the intended air quality while minimizing energy consumption.