{"id":94,"date":"2026-10-16T08:44:02","date_gmt":"2026-10-16T08:44:02","guid":{"rendered":"https:\/\/fgvhp.com\/tools\/air-change-rate-recovery-time-calculator\/"},"modified":"2026-10-16T10:24:35","modified_gmt":"2026-10-16T10:24:35","slug":"air-change-rate-recovery-time-calculator","status":"publish","type":"page","link":"https:\/\/fgvhp.com\/pt\/tools\/air-change-rate-recovery-time-calculator\/","title":{"rendered":"Calculadora de renova\u00e7\u00e3o de ar, caudal de insufla\u00e7\u00e3o e tempo de recupera\u00e7\u00e3o de salas limpas"},"content":{"rendered":"\n\n<section class=\"phero\"><div class=\"wrap\">\n  <div class=\"crumb\"><a href=\"\/\">Home<\/a> \/ <a href=\"\/tools\/\">Tools<\/a> \/ <span>Air change rate and recovery time calculator<\/span><\/div>\n  <span class=\"mono eyebrow\">Cleanroom \u00b7 Calculator<\/span>\n  <h1>Cleanroom Air Change Rate, Supply Airflow and Recovery Time Calculator<\/h1>\n  <p class=\"lead\">Enter the room size and either the supply airflow or the air change rate you want. The calculator gives the other one, the number of HEPA terminals, and an estimate of the 100:1 recovery time measured under ISO 14644-3.<\/p>\n<\/div><\/section>\n<section class=\"fgv-sec\" style=\"padding-top:40px\"><div class=\"wrap\">\n  <div class=\"tool\" data-tool=\"ach\"><noscript><p>This calculator needs JavaScript. The method is described below.<\/p><\/noscript><\/div>\n  <p class=\"note\" style=\"margin-top:14px\">Engineering estimate only. Confirm by testing and validation for your equipment and load.<\/p>\n<\/div><\/section>\n<section class=\"fgv-sec alt\"><div class=\"wrap narrow\"><div class=\"art\"><h2>How the calculation works<\/h2>\n<h3>Air change rate and supply airflow<\/h3>\n<div class=\"keyp\" style=\"font-family:'IBM Plex Mono',monospace\"><b>Formula<\/b>N = Q \/ V<br><small style=\"font-family:'IBM Plex Sans',sans-serif\">N = air changes per hour (h<sup>\u22121<\/sup>), Q = filtered supply airflow (m\u00b3\/h), V = room volume (m\u00b3)<\/small><\/div>\n<p>The number of HEPA terminals is the supply airflow divided by the airflow of one terminal, rounded up. A 1220 \u00d7 610 mm terminal at a face velocity of 0.45 m\/s supplies about 1,200 m\u00b3\/h; check the filter and diffuser data for your design.<\/p>\n<h3>Recovery time<\/h3>\n<p>In a non-unidirectional (turbulent, mixed) cleanroom, particles released into the room are removed by dilution. With perfect mixing the concentration falls as C(t) = C<sub>0<\/sub> \u00d7 e<sup>\u2212N\u00b7t<\/sup>. Real rooms do not mix perfectly, so the calculator applies a mixing efficiency \u03b5:<\/p>\n<div class=\"keyp\" style=\"font-family:'IBM Plex Mono',monospace\"><b>Formula<\/b>t<sub>100:1<\/sub> = ln(100) \/ (\u03b5 \u00d7 N) \u2248 4.6 \/ (\u03b5 \u00d7 N)<br><small style=\"font-family:'IBM Plex Sans',sans-serif\">t in hours (\u00d7 60 for minutes). For a 10:1 reduction use ln(10) \u2248 2.3.<\/small><\/div>\n<p>ISO 14644-3 describes the recovery test: the room is loaded with test particles, the source is stopped and the time for the concentration to fall by a factor of 100 is measured at representative locations.<\/p>\n\n<h2>What the numbers mean<\/h2>\n<ul>\n<li><strong>Air change rate is a design figure, not a class.<\/strong> ISO 14644-1 classifies a room by its measured particle concentration. The air change rate needed depends on how many particles people and processes generate, the heat load, room shape and how well the air mixes.<\/li>\n<li><strong>Recovery time.<\/strong> EU GMP Annex 1 expects the time to return from &#8220;in operation&#8221; to &#8220;at rest&#8221; to be established during qualification. A clean-up period of 15\u201320 minutes has long been used as a guidance value.<\/li>\n<li><strong>FDA.<\/strong> The FDA guidance on sterile drug products produced by aseptic processing (2004) describes an air change rate of at least 20 per hour as typically acceptable for Class 100,000 (ISO 8) rooms.<\/li>\n<li><strong>Unidirectional airflow<\/strong> (Grade A, ISO 5 zones) is designed by air velocity over the protected area, not by air changes. This calculator is for mixed-airflow rooms.<\/li>\n<\/ul>\n\n<h2>Limits of this calculator<\/h2>\n<ul>\n<li>The dilution model assumes particles are spread through the room. Near a source, behind equipment or in dead corners, local recovery is slower.<\/li>\n<li>The mixing efficiency is an assumption. Measure the recovery time in the real room; use smoke studies to see where air does not mix.<\/li>\n<li>It does not size the air handling unit, return air or pressure cascade.<\/li>\n<\/ul>\n<p>Related: <a href=\"\/tools\/iso-14644-1-calculator\/\">ISO 14644-1 classification calculator<\/a>, <a href=\"https:\/\/fenggu-bio.com\/iso-14644-cleanroom-classification\/\" target=\"_blank\" rel=\"noopener\">ISO 14644-1 cleanroom classification<\/a> and <a href=\"https:\/\/fenggu-bio.com\/cleanroom-airlock-types-cascade-bubble-sink\/\" target=\"_blank\" rel=\"noopener\">cleanroom airlock types<\/a>.<\/p><\/div><\/div><\/section>\n\n<section class=\"fgv-sec\"><div class=\"wrap narrow\">\n  <span class=\"mono eyebrow\">FAQ<\/span><h2>Common questions<\/h2>\n  <div class=\"faq\"><details><summary>How do I calculate air changes per hour in a cleanroom?<\/summary><p>Divide the filtered supply airflow in m\u00b3\/h by the room volume in m\u00b3. For example 2,700 m\u00b3\/h into a 90 m\u00b3 room is 30 air changes per hour.<\/p><\/details><details><summary>How is cleanroom recovery time estimated?<\/summary><p>With mixed airflow the particle concentration falls exponentially. The time for a 100:1 reduction is about 4.6 divided by the air change rate (in hours), longer if the room does not mix well. ISO 14644-3 describes how to measure it.<\/p><\/details><details><summary>What is a good cleanroom recovery time?<\/summary><p>A clean-up period of 15\u201320 minutes from in operation to at rest has long been used as a guidance value under EU GMP Annex 1. The actual time is established during qualification.<\/p><\/details><details><summary>How many air changes does an ISO 8 cleanroom need?<\/summary><p>There is no fixed number in ISO 14644. The FDA aseptic processing guidance describes at least 20 air changes per hour as typically acceptable for Class 100,000 (ISO 8) rooms; the design depends on particle generation and heat load.<\/p><\/details><\/div>\n<\/div><\/section>\n<script type=\"application\/ld+json\">{\"@context\":\"https:\/\/schema.org\",\"@type\":\"FAQPage\",\"mainEntity\":[{\"@type\":\"Question\",\"name\":\"How do I calculate air changes per hour in a cleanroom?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Divide the filtered supply airflow in m\u00b3\/h by the room volume in m\u00b3. For example 2,700 m\u00b3\/h into a 90 m\u00b3 room is 30 air changes per hour.\"}},{\"@type\":\"Question\",\"name\":\"How is cleanroom recovery time estimated?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"With mixed airflow the particle concentration falls exponentially. The time for a 100:1 reduction is about 4.6 divided by the air change rate (in hours), longer if the room does not mix well. ISO 14644-3 describes how to measure it.\"}},{\"@type\":\"Question\",\"name\":\"What is a good cleanroom recovery time?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"A clean-up period of 15\u201320 minutes from in operation to at rest has long been used as a guidance value under EU GMP Annex 1. The actual time is established during qualification.\"}},{\"@type\":\"Question\",\"name\":\"How many air changes does an ISO 8 cleanroom need?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"There is no fixed number in ISO 14644. The FDA aseptic processing guidance describes at least 20 air changes per hour as typically acceptable for Class 100,000 (ISO 8) rooms; the design depends on particle generation and heat load.\"}}]}<\/script>\n<section class=\"fgv-sec\" style=\"padding-top:0\"><div class=\"wrap\"><p>More tools: <a class=\"go\" href=\"\/tools\/isolator-leak-rate-calculator\/\">Isolator leak rate calculator<\/a> \u00b7 <a class=\"go\" href=\"\/tools\/vhp-aeration-time-calculator\/\">VHP aeration time calculator<\/a> \u00b7 <a class=\"go\" href=\"\/tools\/vhp-equipment-selector\/\">VHP equipment selector<\/a> \u00b7 <a class=\"go\" href=\"\/tools\/iso-14644-1-calculator\/\">ISO 14644-1 cleanroom classification calculator<\/a><\/p><\/div><\/section>\n\n<section class=\"fgv-sec\" style=\"padding-top:0\"><div class=\"wrap\"><div class=\"cta\">\n  <div><span class=\"mono eyebrow\">Free application review<\/span><h2>Send your numbers to an engineer<\/h2><p>Use the button under the result to fill this form, or describe your space and equipment. 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