{"id":10954,"date":"2026-06-19T14:31:26","date_gmt":"2026-06-19T11:31:26","guid":{"rendered":"https:\/\/altal.md\/?p=10954"},"modified":"2026-06-28T19:20:49","modified_gmt":"2026-06-28T16:20:49","slug":"revenirea-uleiului-in-pompele-de-caldura","status":"publish","type":"post","link":"https:\/\/altal.md\/en\/revenirea-uleiului-in-pompele-de-caldura\/","title":{"rendered":"Oil return in heat pumps | 2026"},"content":{"rendered":"<h2><span style=\"color: #003300;\"><strong>Oil return in heat pumps <span style=\"text-decoration: underline;\"><a href=\"https:\/\/altal.md\/en\/air-to-water-split-dc-evi\/\" target=\"_blank\" rel=\"noopener\">SPLIT<\/a><\/span> and <span style=\"text-decoration: underline;\"><a href=\"https:\/\/altal.md\/en\/air-water-premium-dc-evi\/\" target=\"_blank\" rel=\"noopener\">FULL SPLIT<\/a><\/span>: causes, risks and technical solutions<\/strong><\/span><\/h2>\n<h3><span style=\"color: #000000;\">Introduction<\/span><\/h3>\n<p><span style=\"color: #000000;\"><strong>Return of oil to <a href=\"https:\/\/altal.md\/en\/heat-pump-altal\/\" target=\"_blank\" rel=\"noopener\"><span style=\"text-decoration: underline;\">heat pumps<\/span><\/a><\/strong> is an essential aspect for the safe operation of refrigeration systems <strong>SPLIT<\/strong> and <strong>FULL SPLIT<\/strong>In practice, oil circulation depends on the correct design of the installation,\u00a0<\/span><a style=\"color: #000000; outline: 0px;\" href=\"https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/porsh.webp\" target=\"_blank\" rel=\"noopener\"><img decoding=\"async\" class=\"wp-image-11833 alignright\" style=\"margin: 0.5em 40px 0.5em 0px;\" src=\"https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/porsh.webp\" alt=\"Oil return in SPLIT and FULL SPLIT heat pumps 1\" width=\"276\" height=\"175\" title=\"\" srcset=\"https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/porsh.webp 500w, https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/porsh-450x285.webp 450w, https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/porsh-300x190.webp 300w, https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/porsh-18x12.webp 18w\" sizes=\"(max-width: 276px) 100vw, 276px\" \/> <\/a><span style=\"color: #000000;\">by the speed of the refrigerant and the configuration of the routes.<\/span><\/p>\n<p><span style=\"color: #000000;\">If oil return is not ensured, efficiency losses, noise, protective shutdowns and compressor failure may occur. For this reason, controlling the oil circulation in the refrigeration circuit is critical from the design stage.<\/span><\/p>\n<p>&nbsp;<\/p>\n<h3><span style=\"color: #000000;\">The importance of oil circulation in the system<\/span><\/h3>\n<p><span style=\"color: #000000;\">The oil acts as a lubricant for the compressor and circulates partially with the refrigerant. In normal operation, it must constantly return to the crankcase.<\/span><\/p>\n<p><span style=\"color: #000000;\">Problems arise when <strong>oil return in heat pumps<\/strong> is disrupted, which leads to:<a href=\"https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/scroll-merged.webp\" target=\"_blank\" rel=\"noopener\"><img fetchpriority=\"high\" decoding=\"async\" class=\"wp-image-11834 size-full alignright\" src=\"https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/scroll-merged.webp\" alt=\"Oil return in SPLIT and FULL SPLIT 2 heat pumps\" width=\"500\" height=\"195\" title=\"\" srcset=\"https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/scroll-merged.webp 500w, https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/scroll-merged-450x176.webp 450w, https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/scroll-merged-300x117.webp 300w, https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/scroll-merged-18x7.webp 18w\" sizes=\"(max-width: 500px) 100vw, 500px\" \/><\/a><\/span><\/p>\n<ul>\n<li><span style=\"color: #000000;\">accelerated compressor wear<\/span><\/li>\n<li><span style=\"color: #000000;\">decrease in energy efficiency<\/span><\/li>\n<li><span style=\"color: #000000;\">abnormal mechanical noises<\/span><\/li>\n<li><span style=\"color: #000000;\">safety stops<\/span><\/li>\n<\/ul>\n<hr \/>\n<h3><span style=\"color: #000000;\">Oil transport mechanism<\/span><\/h3>\n<p><span style=\"color: #000000;\">In modern refrigerant systems <a href=\"https:\/\/en.wikipedia.org\/wiki\/Hydrofluoroolefin\" target=\"_blank\" rel=\"noopener\">HFC\/HFO<\/a>, the oil is partially miscible and is entrained in the form of a fine mist in the circuit.<\/span><\/p>\n<p><span style=\"color: #000000;\">The phenomenon is influenced by:<\/span><\/p>\n<ul>\n<li><span style=\"color: #000000;\">dissolving oil in refrigerant<\/span><\/li>\n<li><span style=\"color: #000000;\">aerosol entrainment<\/span><\/li>\n<li><span style=\"color: #000000;\">separation in low pressure areas<\/span><\/li>\n<\/ul>\n<p><span style=\"color: #000000;\">At startup, transient phenomena occur:<\/span><\/p>\n<ul>\n<li><span style=\"color: #000000;\">sudden drop in crankcase pressure<\/span><\/li>\n<li><span style=\"color: #000000;\">boiling of dissolved refrigerant<\/span><\/li>\n<li><span style=\"color: #000000;\">gas-oil emulsion formation<\/span><\/li>\n<li><span style=\"color: #000000;\">the occurrence of the \"oil foaming\" phenomenon<\/span><\/li>\n<\/ul>\n<p><span style=\"color: #000000;\">These effects directly influence <strong>oil return in heat pumps<\/strong>.<\/span><\/p>\n<hr \/>\n<h3><span style=\"color: #000000;\">SPLIT and FULL SPLIT systems<\/span><\/h3>\n<p><span style=\"color: #000000;\">The configuration of the installation has a major impact on oil circulation.<\/span><\/p>\n<h4><span style=\"color: #000000;\">SPLIT<\/span><\/h4>\n<ul>\n<li><span style=\"color: #000000;\">compressor located outside<\/span><\/li>\n<li><span style=\"color: #000000;\">internal condenser<\/span><\/li>\n<li><span style=\"color: #000000;\">oil return depends on the discharge line<\/span><\/li>\n<\/ul>\n<h4><span style=\"color: #000000;\">FULL SPLIT<\/span><\/h4>\n<ul>\n<li><span style=\"color: #000000;\">internal compressor<\/span><\/li>\n<li><span style=\"color: #000000;\">evaporator exterior<\/span><\/li>\n<li><span style=\"color: #000000;\">increased risk of accumulation in the suction line<\/span><\/li>\n<\/ul>\n<p><span style=\"color: #000000;\">In both cases, the correct circulation of the oil depends on the hydrodynamic balance of the system.<\/span><\/p>\n<hr \/>\n<h3><span style=\"color: #000000;\">Refrigerant speed<\/span><\/h3>\n<p><span style=\"color: #000000;\">A critical factor for oil transportation is the velocity of the gas in the pipelines.<\/span><\/p>\n<p><span style=\"color: #000000;\">Indicative values:<\/span><\/p>\n<ul>\n<li><span style=\"color: #000000;\">&lt; 2.5 m\/s \u2192 oil separation, high risk<\/span><\/li>\n<li><span style=\"color: #000000;\">~5 m\/s \u2192 minimum threshold for stable transport<\/span><\/li>\n<li><span style=\"color: #000000;\">8\u20139 m\/s \u2192 critical regime in vertical columns<\/span><\/li>\n<li>\n<blockquote><p><span style=\"color: #000000;\">20 m\/s \u2192 pressure losses and noise<\/span><\/p><\/blockquote>\n<\/li>\n<\/ul>\n<p><span style=\"color: #000000;\">When the speed drops below the minimum threshold, <strong>oil return in heat pumps<\/strong> becomes unstable.<\/span><\/p>\n<hr \/>\n<h3><span style=\"color: #000000;\">Influence of level differences<\/span><\/h3>\n<p><span style=\"color: #000000;\">Vertical paths directly influence the behavior of the oil in the system.<\/span><\/p>\n<ul>\n<li><span style=\"color: #000000;\">\u0394H &gt; 3 m \u2192 risk of progressive accumulation<\/span><\/li>\n<li><span style=\"color: #000000;\">\u0394H &gt; 7.5 m \u2192 oil film interruption<a href=\"https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/U-tip-returnare-ulei-2.webp\" target=\"_blank\" rel=\"noopener\"><img decoding=\"async\" class=\"alignright wp-image-11836\" src=\"https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/U-tip-returnare-ulei-2.webp\" alt=\"Oil return in SPLIT and FULL SPLIT 4 heat pumps\" width=\"355\" height=\"522\" title=\"\" srcset=\"https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/U-tip-returnare-ulei-2.webp 194w, https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/U-tip-returnare-ulei-2-8x12.webp 8w\" sizes=\"(max-width: 355px) 100vw, 355px\" \/><\/a><\/span><\/li>\n<li><span style=\"color: #000000;\">required: oil siphons at regular intervals<\/span><\/li>\n<\/ul>\n<p><span style=\"color: #000000;\">Without these measures, correct oil circulation cannot be guaranteed.<\/span><\/p>\n<h3><span style=\"color: #000000;\">Siphons and controls<\/span><\/h3>\n<p><span style=\"color: #000000;\">Siphons are used to stabilize the flow in vertical columns.<\/span><\/p>\n<p><span style=\"color: #000000;\">Main roles:<\/span><\/p>\n<ul>\n<li><span style=\"color: #000000;\">preventing oil accumulation<\/span><\/li>\n<li><span style=\"color: #000000;\">maintaining controlled transport<\/span><\/li>\n<li><span style=\"color: #000000;\">reducing the risk of hydraulic blockage<\/span><\/li>\n<\/ul>\n<p><span style=\"color: #000000;\">These elements are essential for maintaining stability in <strong>oil return in heat pumps<\/strong>.<\/span><\/p>\n<h3><span style=\"color: #000000;\">Variable load operation<\/span><\/h3>\n<p><span style=\"color: #000000;\">In partial load mode, the refrigerant flow rate decreases, which reduces the velocity in the pipes.<\/span><\/p>\n<p><span style=\"color: #000000;\">Example:<\/span><\/p>\n<ul>\n<li><span style=\"color: #000000;\">100% load \u2192 ~6 m\/s \u2714<\/span><\/li>\n<li><span style=\"color: #000000;\">50% load \u2192 ~3 m\/s \u2716<\/span><\/li>\n<\/ul>\n<p><span style=\"color: #000000;\">Under these conditions, oil transport becomes insufficient, and part of the oil remains in the evaporator or in the pipes.<\/span><\/p>\n<hr \/>\n<h3><span style=\"color: #000000;\">Transient problems<a href=\"https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/U-tip-returnare-ulei-3.webp\" target=\"_blank\" rel=\"noopener\"><img loading=\"lazy\" decoding=\"async\" class=\"alignright wp-image-11837\" src=\"https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/U-tip-returnare-ulei-3.webp\" alt=\"Oil return in SPLIT and FULL SPLIT heat pumps 5\" width=\"254\" height=\"234\" title=\"\" srcset=\"https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/U-tip-returnare-ulei-3.webp 150w, https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/U-tip-returnare-ulei-3-13x12.webp 13w\" sizes=\"(max-width: 254px) 100vw, 254px\" \/><\/a><\/span><\/h3>\n<p><span style=\"color: #000000;\">Instabilities frequently occur when starting and stopping:<\/span><\/p>\n<ul>\n<li><span style=\"color: #000000;\">foaming in the crankcase<\/span><\/li>\n<li><span style=\"color: #000000;\">insufficient evaporator supply<\/span><\/li>\n<li><span style=\"color: #000000;\">low pressure shutdowns<\/span><\/li>\n<li><span style=\"color: #000000;\">risk of mechanical shock to the compressor<\/span><\/li>\n<\/ul>\n<p><span style=\"color: #000000;\">These phenomena are directly related to the circulation of oil in the circuit.<\/span><\/p>\n<h3><span style=\"color: #000000;\"><a href=\"https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/U-tip-returnare-ulei.webp\" target=\"_blank\" rel=\"noopener\"><img loading=\"lazy\" decoding=\"async\" class=\"alignright wp-image-11835\" src=\"https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/U-tip-returnare-ulei.webp\" alt=\"Oil return in SPLIT and FULL SPLIT 3 heat pumps\" width=\"279\" height=\"286\" title=\"\" srcset=\"https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/U-tip-returnare-ulei.webp 314w, https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/U-tip-returnare-ulei-293x300.webp 293w, https:\/\/altal.md\/wp-content\/uploads\/2026\/06\/U-tip-returnare-ulei-12x12.webp 12w\" sizes=\"(max-width: 279px) 100vw, 279px\" \/><\/a><\/span><\/h3>\n<h3><span style=\"color: #000000;\">Design recommendations (OTHER GROUP)<\/span><\/h3>\n<p><span style=\"color: #000000;\">To ensure stable operation and correct <strong>oil returns in heat pumps<\/strong>, it is recommended:<\/span><\/p>\n<ul>\n<li><span style=\"color: #000000;\">maintaining speed \u2265 5 m\/s<\/span><\/li>\n<li><span style=\"color: #000000;\">pipe slope \u2265 12 mm\/m<\/span><\/li>\n<li><span style=\"color: #000000;\">avoiding stagnation areas<\/span><\/li>\n<li><span style=\"color: #000000;\">installation of siphons at 3\u20137.5 m<\/span><\/li>\n<li><span style=\"color: #000000;\">limiting level differences<\/span><\/li>\n<li><span style=\"color: #000000;\">optimization of frequent starts<\/span><\/li>\n<\/ul>\n<hr \/>\n<h3><span style=\"color: #000000;\">Conclusion<\/span><\/h3>\n<p><span style=\"color: #000000;\">Correct oil circulation in refrigeration systems is essential for system reliability. <strong>Oil return in heat pumps<\/strong> depends on the design of the pipes, the speed of the refrigerant and compliance with the installation rules.<\/span><\/p>\n<p><span style=\"color: #000000;\">Proper design reduces the risk of compressor failure and ensures long-term stable operation.<\/span><\/p>\n<hr \/>\n<p>&nbsp;<\/p>","protected":false},"excerpt":{"rendered":"<p>Oil return in SPLIT and FULL SPLIT heat pumps: causes, risks and technical solutions Introduction Oil return in heat pumps is an essential aspect for the safe operation of SPLIT and FULL SPLIT refrigeration systems. In practice, the oil circulation depends on the correct design of the installation, the speed of the refrigerant and the configuration of the routes. If\u2026<\/p>","protected":false},"author":1,"featured_media":11832,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_kad_post_transparent":"default","_kad_post_title":"default","_kad_post_layout":"default","_kad_post_sidebar_id":"","_kad_post_content_style":"default","_kad_post_vertical_padding":"default","_kad_post_feature":"","_kad_post_feature_position":"","_kad_post_header":false,"_kad_post_footer":false,"footnotes":""},"categories":[403],"tags":[],"class_list":["post-10954","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-pompe-de-caldura-ghiduri-utile"],"_links":{"self":[{"href":"https:\/\/altal.md\/en\/wp-json\/wp\/v2\/posts\/10954","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/altal.md\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/altal.md\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/altal.md\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/altal.md\/en\/wp-json\/wp\/v2\/comments?post=10954"}],"version-history":[{"count":8,"href":"https:\/\/altal.md\/en\/wp-json\/wp\/v2\/posts\/10954\/revisions"}],"predecessor-version":[{"id":11843,"href":"https:\/\/altal.md\/en\/wp-json\/wp\/v2\/posts\/10954\/revisions\/11843"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/altal.md\/en\/wp-json\/wp\/v2\/media\/11832"}],"wp:attachment":[{"href":"https:\/\/altal.md\/en\/wp-json\/wp\/v2\/media?parent=10954"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/altal.md\/en\/wp-json\/wp\/v2\/categories?post=10954"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/altal.md\/en\/wp-json\/wp\/v2\/tags?post=10954"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}