Intervention
Air conditioning
Part of: HVAC systems
Also: air conditioner, air conditioning system, split unit, climate control, cooling
Cooling and dehumidifying indoor air mechanically. Most systems recirculate the air of the room rather than replacing it, so air conditioning changes temperature and humidity — and, through them, several exposures — without in itself providing ventilation.
What it is
The common misunderstanding is worth stating first: a room air conditioner takes the air of the room, cools it and gives it back. It does not bring in outdoor air, and running it in a closed room does nothing for carbon dioxide or for anything else that ventilation would remove.
What it does change is decisive in its own right. Cooling condenses water, so the relative humidity falls — which suppresses dust mites and mould growth — and the windows stay shut, which lowers the infiltration of outdoor particles in a polluted city. In hot climates these are among the largest effects any indoor measure has.
The cost is where the condensed water goes. Drain pans, coils and ducts that stay wet grow what wet surfaces grow, and a neglected unit becomes the source it was suppressing. Filters in these systems protect the coil, not the occupant, unless they were chosen otherwise.
What the studies report
| Linked to | Effect | Population | Study design | Source | Checked |
|---|---|---|---|---|---|
| Carbon dioxide (CO₂) | mean 2470 | surgical staff and patients · operating room | measurement of particle number concentration (0.3-10 μm) and CO2 in one surgical room with a window/wall air-conditioning system and the adjacent corridor in Brazil during a single surgery and two subsequent surgeries, with outdoor air ventilation calculated from CO2 and compared with the requirement | F-0483 Particle and Carbon Dioxide Concentration Levels in a Surgic… (2020) | machine |
| Particulate matter (PM₂.₅ and PM₁₀) | mean 22.3 | surgical staff and patients · operating room | measurement of particle number concentration (0.3-10 μm) and CO2 in one surgical room with a window/wall air-conditioning system and the adjacent corridor in Brazil during a single surgery and two subsequent surgeries, with outdoor air ventilation calculated from CO2 and compared with the requirement | F-0484 Particle and Carbon Dioxide Concentration Levels in a Surgic… (2020) | machine |
| Air exchange rate (air changes per hour) | other 51 | surgical staff and patients · operating room | measurement of particle number concentration (0.3-10 μm) and CO2 in one surgical room with a window/wall air-conditioning system and the adjacent corridor in Brazil during a single surgery and two subsequent surgeries, with outdoor air ventilation calculated from CO2 and compared with the requirement | F-0485 Particle and Carbon Dioxide Concentration Levels in a Surgic… (2020) | machine |
| Carbon dioxide (CO₂) | mean 1433.62 | university students · classroom | comparison of thirty university classrooms in Brazil, 15 air-conditioned and 15 naturally ventilated: indoor CO2, temperature, relative humidity, wind speed, viable mould and airborne dust measured; values as mean ± standard error | F-0521 Jurado et al. Indoor air quality in Brazilian universities (2014) | machine |
| Mould | mean 367.00 | university students · classroom | comparison of thirty university classrooms in Brazil, 15 air-conditioned and 15 naturally ventilated: indoor CO2, temperature, relative humidity, wind speed, viable mould and airborne dust measured; values as mean ± standard error | F-0524 Jurado et al. Indoor air quality in Brazilian universities (2014) | machine |
| Atopic dermatitis (eczema) | OR 1.57 (1.07–2.30) | preschool children · dwelling | descriptive cross-sectional online questionnaire study among parents of 964 preschool children in Hail City, Saudi Arabia (July-September 2022), self-administered pre-tested questionnaire distributed on social media, multivariate logistic regression of risk factors for parent-reported diagnosed eczema | F-0591 Prevalence and Influencing Risk Factors of Eczema Among Pres… (2022) | machine |
| Radon | higher recirculation lowered radon because the recirculated air was already depleted; the dose values are computed, not measured | university auditorium occupants · auditorium | measurement of radon and its short-lived progeny (attached and unattached fractions) with indoor air parameters in a university auditorium in Lublin, Poland, under different air-conditioning operating modes and recirculation rates | F-0641 The influence of air conditioning changes on the effective d… (2016) | machine |
| Radon progeny | the dose values are computed, not measured | university auditorium occupants · auditorium | measurement of radon and its short-lived progeny (attached and unattached fractions) with indoor air parameters in a university auditorium in Lublin, Poland, under different air-conditioning operating modes and recirculation rates | F-0642 The influence of air conditioning changes on the effective d… (2016) | machine |
Each row is one Finding — a sentence as printed in one study, recorded with its page in the Coridum Knowledge Base. Follow the Finding number for the exact wording and the citation. Checked says who verified the row: machine means every automatic check passed and the surrounding text was read; person means someone read the sentence in the document. Rows are re-checked by a person over time. The studies are curated in the Coridum Knowledge Base; the reading of them together is a Claim, shown separately.
Identifiers
- MeSH
- D000389
Cite this page
Coridum Research. Air conditioning. Coridum Knowledge G-0131, 16 September 2026. https://coridum.com/k/G-0131/