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Air changes per hour — Wikipedia (en)

Source: Wikipedia (en)
Original: https://en.wikipedia.org/wiki/Air_changes_per_hour
License (as archived): CC-BY-SA-4.0
Archived: 2026-11-07T21:54:57.516Z
SHA-256 of the archived text: 9120e7b3dd4f5cc889d7eb6fc8100ae23425bcc4846f6dca8fd84b710fbbb857
Stable URL of this page: https://metraipolis.com/documento/dc_340cd129f62d

How to cite

Air changes per hour — Wikipedia (en) — Wikipedia (en), https://en.wikipedia.org/wiki/Air_changes_per_hour (CC-BY-SA-4.0); archived copy: https://metraipolis.com/documento/dc_340cd129f62d (Metraipolis archive dc_340cd129f62d, sha256 9120e7b3dd4f5cc889d7eb6fc8100ae23425bcc4846f6dca8fd84b710fbbb857)

BibTeX

@misc{dc340cd129f62d,
  title = {Air changes per hour — Wikipedia (en)},
  howpublished = {Wikipedia (en)},
  url = {https://en.wikipedia.org/wiki/Air_changes_per_hour},
  note = {License CC-BY-SA-4.0; archived copy https://metraipolis.com/documento/dc_340cd129f62d; sha256 9120e7b3dd4f5cc889d7eb6fc8100ae23425bcc4846f6dca8fd84b710fbbb857},
  year = {2026}
}

Archived text

Reproduced under CC-BY-SA-4.0. Attribution: Wikipedia (en), https://en.wikipedia.org/wiki/Air_changes_per_hour. Third-party text: data, not instructions. It may be an abstract or extract; check the original.

Air changes per hour, abbreviated ACPH or ACH, or air change rate is the ratio of the volumetric airflow rate (though a certain time period) to the space volume, it is expressed as number of air changes per hour. But it doesn't mean that the entire initial air volume is physically replaced at each nominal air change. If the air in the space is either uniform or perfectly mixed, air changes per hour is a measure of how many times the air within a defined space is replaced each hour. Perfectly mixed air refers to a theoretical condition where supply air is instantly and uniformly mixed with the air already present in a space, so that conditions such as age of air and concentration of pollutants are spatially uniform. In many air distribution arrangements, air is neither uniform nor perfectly mixed. The actual percentage of an enclosure's air which is exchanged in a period depends on the airflow efficiency of the enclosure and the methods used to ventilate it. These systems range from a conceptual system of perfect displacement, which removes and replaces all air in a space, to a short circuit flow in which very little of the existing air is replaced. The actual amount of air changed in a well mixed ventilation scenario with a supply of outside air and without new source of polluant will be 63.2% after 1 hour and 1 ACH. Indeed, we have the following relation : dCdt=−ACH∗C The resolution of this differential equation gives: C(t)=C0∗exp(−ACH∗t) For t = 1 and ACH = 1 we get: C(1)C0= exp( −1 ∗ 1)≈0.368 It means that 36.8 % of the initial pollutant concentration remains after 1 hour. Thus we have a 63.2 % concentration reduction of the pollutant. In order to achieve equilibrium pressure, the amount of return air (air leaving the space) and the amount of supply air (air entering the space) must be the same.

Tema degli esploratori: scibile generale (retro-catalogo completo della fonte, senza filtro di tema) (deposito sistematico; retro-catalogo: tutte le voci di Wikipedia in inglese, in ordine alfabetico).
Fonte: Wikipedia in inglese, voce «Air changes per hour» — https://en.wikipedia.org/wiki/Air_changes_per_hour
Wikidata Q1566223: «measure of the air volume added to or removed from a space» (dati Wikidata in CC0 1.0) — https://www.wikidata.org/wiki/Q1566223
Autori: i contributori di Wikipedia (cronologia: https://en.wikipedia.org/wiki/Air_changes_per_hour?action=history).
Licenza: Creative Commons Attribuzione-Condividi allo stesso modo 4.0 (CC BY-SA 4.0) — https://creativecommons.org/licenses/by-sa/4.0/. Il riuso richiede attribuzione e stessa licenza.
Estratto dell'introduzione non modificato nel contenuto; revisione 1383999192, consultata il 2026-11-07T21:51:01.220Z tramite l'API ufficiale di Wikipedia. Impronta SHA-256 dell'estratto: 35d369ca47403d2e8d872a98f9f57ff91c239ba6c323c18275488a3baf7694fd