{"id":4694,"date":"2026-09-20T18:14:06","date_gmt":"2026-09-21T01:14:06","guid":{"rendered":"https:\/\/www.26yc.com\/air-changes-per-hour-ach\/"},"modified":"2026-10-08T23:36:08","modified_gmt":"2026-10-09T06:36:08","slug":"air-changes-per-hour-ach","status":"publish","type":"post","link":"https:\/\/www.26yc.com\/zh_cn\/air-changes-per-hour-ach\/","title":{"rendered":"Air Changes per Hour (ACH): The Ventilation Rate Behind Recovery Load"},"content":{"rendered":"<h2>Definition<\/h2>\n<p>Air changes per hour is the volumetric airflow divided by the room volume, expressed per hour:<\/p>\n<p><code>ACH = (volumetric_flow_rate \/ room_volume) x 3600<\/code><\/p>\n<p>An ACH of 6 means the room air is theoretically replaced six times in an hour.<\/p>\n<h2>Typical values<\/h2>\n<ul>\n<li>Classrooms: about 4-6 ACH (see <a href=\"\/zh_cn\/heat-recovery-ventilation-schools\/\">school ventilation<\/a>)<\/li>\n<li>Laboratories and fume hoods: 6-12 ACH (<a href=\"\/zh_cn\/laboratory-heat-recovery\/\">lab recovery<\/a>)<\/li>\n<li>Operating theatres: 20+ ACH (<a href=\"\/zh_cn\/hospital-heat-recovery\/\">hospital recovery<\/a>)<\/li>\n<li>Offices: 2-4 ACH<\/li>\n<\/ul>\n<h2>Why ACH matters for recovery<\/h2>\n<p>Higher ACH means more outdoor air to condition and more exhaust energy to reclaim. Spaces with high ACH and high hours of operation are exactly where an <a href=\"\/zh_cn\/ahu-heat-recovery\/\">AHU\u96c6\u6210\u5f0f\u56de\u6536\u82af<\/a> pays back fastest, because the recovered energy scales with the airflow.<\/p>\n<h2>Frequently asked questions<\/h2>\n<p><strong>Does high ACH mean better air quality?<\/strong> Up to a point; beyond code minimums, filtration and distribution often matter more than raw rate.<\/p>\n<p><strong>Is ACH the same as outdoor-air rate?<\/strong> Not always &#8211; ACH can include recirculated air; the recovery benefit tracks the outdoor fraction specifically.<\/p>\n<p>Need help specifying the right air-to-air heat recovery for your project? <a href=\"\/zh_cn\/contact-us\/\">Contact the QIYU engineering team<\/a> &#8211; WhatsApp +86 157 5335 5505, or email kuns913@gmail.com.<\/p>\n<p class=\"yc-faq-title\"><strong>\u5e38\u89c1\u95ee\u9898<\/strong><\/p>\n<div class=\"yc-faq\">\n<h3>What is ACH in ventilation?<\/h3>\n<p>Air changes per hour is the volumetric outdoor-air supply divided by the room volume, i.e. how many times the room air is replaced each hour.<\/p>\n<\/div>\n<div class=\"yc-faq\">\n<h3>Why does higher ACH increase recovery value?<\/h3>\n<p>More outdoor air means more conditioning load to recover; at high ACH the energy carried by the exhaust is large, so even modest effectiveness saves substantial heating or cooling energy.<\/p>\n<\/div>\n<div class=\"yc-related\">\n<h3>\u76f8\u5173\u6587\u7ae0<\/h3>\n<ul>\n<li><a href=\"https:\/\/www.26yc.com\/zh_cn\/seasonal-energy-recovery-efficiency\/\" title=\"Seasonal Energy Recovery Efficiency: Why Nameplate Effectiveness Is Not the Year\">Seasonal Energy Recovery Efficiency: Why Nameplate Effectiveness Is Not the Year<\/a><\/li>\n<li><a href=\"https:\/\/www.26yc.com\/zh_cn\/membrane-air-conditioning-systems\/\" title=\"\u819c\u5f0f\u7a7a\u8c03\u7cfb\u7edf\">\u819c\u5f0f\u7a7a\u8c03\u7cfb\u7edf<\/a><\/li>\n<\/ul>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>Definition Air changes per hour is the volumetric airflow divided by the room volume, expressed per hour: ACH = (volumetric_flow_rate \/ room_volume) x 3600 An ACH of 6 means the room air is theoretically replaced six times in an hour. Typical values Classrooms: about 4-6 ACH (see school ventilation) Laboratories and fume hoods: 6-12 ACH [&hellip;]<\/p>\n","protected":false},"author":0,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[243,197],"tags":[288,287,182,199,289],"class_list":["post-4694","post","type-post","status-publish","format-standard","hentry","category-design-calc","category-encyclopedia","tag-ach","tag-air-changes-per-hour","tag-energy-recovery","tag-hvac","tag-ventilation-rate"],"_links":{"self":[{"href":"https:\/\/www.26yc.com\/zh_cn\/wp-json\/wp\/v2\/posts\/4694","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.26yc.com\/zh_cn\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.26yc.com\/zh_cn\/wp-json\/wp\/v2\/types\/post"}],"replies":[{"embeddable":true,"href":"https:\/\/www.26yc.com\/zh_cn\/wp-json\/wp\/v2\/comments?post=4694"}],"version-history":[{"count":1,"href":"https:\/\/www.26yc.com\/zh_cn\/wp-json\/wp\/v2\/posts\/4694\/revisions"}],"predecessor-version":[{"id":5109,"href":"https:\/\/www.26yc.com\/zh_cn\/wp-json\/wp\/v2\/posts\/4694\/revisions\/5109"}],"wp:attachment":[{"href":"https:\/\/www.26yc.com\/zh_cn\/wp-json\/wp\/v2\/media?parent=4694"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.26yc.com\/zh_cn\/wp-json\/wp\/v2\/categories?post=4694"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.26yc.com\/zh_cn\/wp-json\/wp\/v2\/tags?post=4694"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}