There are many different factors affecting indoor air quality: environmental ones such as temperature, humidity, human activities within the building, smoking, cooking, and cleaning, but also external pollutants such as particulate matter, biological contaminants, and viruses or allergens. This study investigated the indoor air quality (IAQ) of a primary-school classroom in Cracow, Poland, based only on CO₂ concentration levels exhaled by occupants. In the 1960s, over a thousand schools were built in Poland using similar technology. Most of them are still in use, and in many cases, modernization works are being carried out to improve their building envelope and the comfort of their use. The analyzed school is one of several hundred similar ones in southern Poland. Therefore, analyzing the possibilities of improving IAQ is an important topic, and the results can be used in the modernization process for many other buildings. Measurements indicated that the CO₂ levels significantly exceeded acceptable standards, signaling poor air quality during usage time. This problem was connected mainly with the low efficiency of the natural ventilation system being used in the classroom. It is worth emphasizing that this type of ventilation system is the most commonly used ventilation solution in Polish schools. To address this problem, the classroom environment was simulated using CONTAM software, and the model was validated by comparing the simulated measurement data against the collected measurement data. Next, simulations for the entire heating season in Cracow were conducted, revealing that the IAQ remained consistently poor throughout this period. These findings highlight the persistent problem of inadequate ventilation in the classroom, which can have adverse effects on the health and performance of students and teachers. This article shows the usefulness of CONTAM for modeling not only gravity ventilation but also the window-opening process. The validated CONTAM model will be subsequently utilized to simulate annual IAQ conditions under various ventilation strategies in order to identify the most effective methods for maintaining acceptable IAQ while minimizing energy consumption. In our future analysis, the validated model will be used to test the following systems: demand-controlled ventilation (DCV), exhaust ventilation, and DCV/balanced ventilation with heat recovery.

The aim of the research was to design and validate the prototype of a device developed to improve the quality of indoor air by supporting the natural ventilation in building. A CO₂ sensor and thermo-hygrometer were used to measure the physical parameters of the indoor air. The developed device is based on the Raspberry Pi single-board-computer (SBC) and optical sensors. The prototype casing was made using 3D printing technology. The software was written using the Python 2.7 programming language. The key algorithm of control uses fuzzy logic. The effectiveness of the developed device has been confirmed. The use of the device enabled improvement of the indoor air quality. The presented device may be a solution to improve the indoor air quality by supporting the ventilation system.

Poor indoor air quality (IAQ) in naturally ventilated school buildings remains a widespread problem, particularly during the heating season, when limited ventilation leads to elevated CO₂ concentrations. At the same time, increasing ventilation rates may significantly increase energy demand, creating a conflict between IAQ and energy efficiency. This study aims to evaluate whether CO₂-based demand-controlled mechanical ventilation, particularly with heat recovery (HRV), can improve IAQ while maintaining acceptable energy performance in existing school buildings. A previously validated CONTAM model of a Polish primary school classroom was used to simulate natural ventilation, mechanical exhaust ventilation, and balanced ventilation with heat recovery. In mechanical systems, CO₂-based demand-controlled ventilation (DCV) was applied. The resulting airflow rates were then used in EnergyPlus simulations to assess seasonal heating and primary energy demand under Kraków climatic conditions. Increasing the outdoor air supply rate significantly reduced indoor CO₂ concentration but led to higher heating demand in exhaust ventilation systems. In contrast, HRV reduced heating energy demand by more than 80% compared with exhaust ventilation while maintaining comparable indoor air quality. Although HRV required additional electricity for fan operation, the total primary energy consumption remained low. The results demonstrate that CO₂-based DCV systems with heat recovery provide an effective balance between indoor air quality and energy performance. These findings support the application of HRV as a practical retrofit solution for improving ventilation in existing school buildings.

Children spend on average 7–10 hours per weekday at school, that’s why the indoor air quality in the classrooms plays a key role in the assessment of the effects of their personal exposure to the air quality. Many scientific articles indicate the substantial influence of carbon dioxide (CO2º levels and overall air quality within educational environments on the well-being and cognitive performance of children. This article presents the case study of the classroom in the primary school in Cracow with very unfavourable indoor air quality caused by the usage pattern. In the classroom, there is a natural ventilation system, still the most common in the Polish existing buildings. The very high level of CO2 exceeding the standard requirements connected with low ventilation efficiency effects in harmful indoor conditions. Based on the measurements conducted in the classroom during the lessons with the users in and taking into account formal requirements authors assessed the quality of indoor air. The main reason for those unfavourable conditions is an inefficient natural ventilation system. This paper is also supposed to answer the question of whether temporary opening windows can assure proper concentration of CO2 in a standard classroom and, if not, what would be the optimal ventilation rate. In the next step, this optimal minimum required ventilation rate for the classroom was calculated. It could be used as a design assumption in the selection of a ventilation system.