Buildings are constructed and operated to satisfy human needs and improve quality of life. Good indoor air quality (IAQ) and thermal comfort are prerequisites for human health and well-being. For their provision, buildings often rely on heating, ventilation, and air conditioning (HVAC) systems, which may lead to higher energy consumption. This directly impacts energy efficiency goals and the linked climate change considerations. The balance between energy use, optimum IAQ and thermal comfort calls for scientifically solid and well-established limit values for exposures experienced by building occupants in indoor spaces, including homes, schools, and offices. The present paper aims to appraise limit values for selected indoor pollutants reported in the scientific literature, and to present how they are handled in international and national guidelines and standards. The pollutants include carbon dioxide (CO₂), formaldehyde (CH₂O), particulate matter (PM), nitrogen dioxide (NO₂), carbon monoxide (CO), and radon (Rn). Furthermore, acknowledging the particularly strong impact on energy use from HVAC, ventilation, indoor temperature (T), and relative humidity (RH) are also included, as they relate to both thermal comfort and the possibilities to avoid moisture related problems, such as mould growth and proliferation of house dust mites. Examples of national regulations for these parameters are presented, both in relation to human requirements in buildings and considering aspects related to energy saving. The work is based on the Indoor Environmental Quality (IEQ) guidelines database, which spans across countries and institutions, and aids in taking steps in the direction towards a more uniform guidance for values of indoor parameters. The database is coordinated by the Scientific and Technical Committee (STC) 34, as part of ISIAQ, the International Society of Indoor Air Quality and Climate.

Classrooms have more students per square meter than other buildings such as offices, making them more crowded. In addition, children respire more than adults and are in contact with one another more often. For appropriate student comfort, wellbeing, and health, including reducing the risk of transferring communicable diseases (for example, COVID-19) in the school setting, adequate ventilation and thermal comfort is recommended, along with regular cleaning, especially of high-contact surfaces. However, this may lead to increased energy usage, especially in mechanically ventilated schools. While natural ventilation conserves energy, its usage may be limited in temperate regions, especially during the cold seasons, as more energy will be required for heating in order to achieve thermal comfort. In the tropics, natural ventilation alone may be insufficient for students’ thermal comfort due to the possibility of unconditioned warm or cold outdoor air entering the classroom environment. Additionally, natural ventilation is difficult to control, as there may be overventilation or underventilation due to the ventilation rate being dependent on the outdoor environmental condition such as windspeed. This current traditional literature review appraises previous indoor environmental quality (IEQ) literature on ventilation, thermal comfort, moisture and mold, and cleanliness in schools. Furthermore, a further review was performed on the effect of IEQ (indoor air quality and thermal comfort) on student health and academic outcomes in order to summarize existing knowledge that can help other researchers avoid research duplication and identify research gaps for future school IEQ studies.

Microorganisms, especially fungi, from damp indoor environments are known to be one of the main causes of degradation of indoor air quality and can pose serious health hazard to occupants because of the production of airborne particles. Particles produced during microbial growth include both living and non-living particles, which can be submicrometer in size. Individuals are exposed to fungi from various sources and in various conditions. The exposure may occur when the fungi grow in hidden areas and on materials that are in common areas and released under various conditions. The proliferation of fungi detected in a particular area depends on the species of fungi, the growth material and the conditions under which they are grown and released. Fungi aerosolized from any growth material include intact spores, which grow when deposited on favorable material surfaces and other fragments of the growth ranging from a few millimeters to micrometers in size. The types and amounts of intact spores and fragments aerosolized depend on factors such as air velocity blowing over the growth surface, the type of substrate, type of fungi, and relative humidity of the growth and the age of the fungal growth.