Children spend a large part of their growing years in schools, and as they are more sensitive to some pollutants than adults, it is essential to monitor and maximize the indoor air quality (IAQ) in classrooms. Many schools are located in historic and heritage buildings, and improving the IAQ, preserving the architectural features, poses a great challenge. The aim of the study is to evaluate the effectiveness of a low-invasiveness, low-cost, smart CO2-based visual alerting systems to manage natural ventilation and improve IAQ in historic school buildings. Indoor and outdoor parameters were monitored for three weeks in four schools with different levels of education (two classrooms per school; device installed in one only). Based on indoor CO2 concentration, air temperature and relative humidity, the device suggests when windows should be opened to ventilate. The comparison between the two classrooms show that the effectiveness of the device is highly dependent on the occupants: (i) reduction in the average CO2 concentrations of up to 42% in classrooms with frontal lesson and full occupancy, (ii) the device is not the most ideal solution for kindergarten due to the young age of the pupils, and (iii) it is more used during mild outdoor temperatures.

Nowadays, people spend an average of 87% of their time inside buildings, and about 69% at home. Hence, it is essential to ensure the highest possible level of indoor air quality (IAQ). Providing that the quality of the outdoor air is acceptable, the IAQ level is improved by increasing the ventilation rates. However, this means that a larger volume of air must be cooled down or warmed up to ensure the same level of thermal comfort. The aim of this study was to conduct a cost–benefit analysis of the IAQ in residential buildings. A case-study building was defined, and three sets of materials with different pollution emission levels were chosen: High, low, and very low. For each option, the ventilation rates required to have the same IAQ level were calculated, and the consequent energy consumption and costs were estimated by means of dynamic thermal simulation. The results show the range of the initial capital cost that could be compensated for by lower running costs, and the effect of each energy and economic input assumption on the appraisal of the affordable capital cost. In the discussion, insights into the IAQ co-benefits are also given.

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