{"id":39017,"date":"2026-11-02T10:17:03","date_gmt":"2026-11-02T13:17:03","guid":{"rendered":"https:\/\/fortalezaequipamentos.com.br\/?p=39017"},"modified":"2026-11-02T10:17:03","modified_gmt":"2026-11-02T13:17:03","slug":"bananzia-buffer-tank-retrofit-a-300-litre-case-study-for-a-1930s-semi","status":"publish","type":"post","link":"https:\/\/fortalezaequipamentos.com.br\/index.php\/2026\/11\/02\/bananzia-buffer-tank-retrofit-a-300-litre-case-study-for-a-1930s-semi\/","title":{"rendered":"Bananzia Buffer Tank Retrofit: A 300-Litre Case Study for a 1930s Semi"},"content":{"rendered":"

Context: one house, one undersized emitter circuit<\/h2>\n

The case property is a 96 m\u00b2 semi-detached house in Bananzia with uninsulated cavity walls, 100 mm loft insulation and original 1970s steel radiators. A heat-loss calculation gave 5.8 kW at an external design temperature of \u22123\u00b0C and a flow temperature of 45\u00b0C. The existing gas boiler had run at 70\u00b0C, so the radiator circuit was oversized for the boiler but undersized for a low-temperature air-source heat pump. The retrofit therefore paired a 7 kW monobloc heat pump with emitter upgrades in four rooms and a 300-litre buffer tank on the return line. The buffer was not included as a default accessory; it was sized to solve a measured control problem.<\/p>\n

Problem: part-load short cycling below 3 kW<\/h2>\n

The selected heat pump could modulate down to 3 kW, but the house\u2019s average winter load was 2.1 kW and mild-day demand fell below 1.5 kW. Without hydraulic separation, the compressor cycled roughly every 12 minutes at 8\u00b0C outdoor temperature, which reduced seasonal efficiency and increased wear on the compressor. The cause was not the heat pump alone: the low water volume of the upgraded radiators, about 38 litres, gave the system too little thermal inertia. A buffer tank adds volume and decouples the heat pump from the emitter circuit, allowing longer run times. The design target was a 300-litre buffer operating with a 7 K design delta T, providing hydraulic separation and a stable return temperature.<\/p>\n

Development: control logic and the bananzia guidance<\/h2>\n

The installation followed the bananzia<\/a> retrofit guidance, which treats buffer volume as part of the emitter and control design rather than a fixed add-on. The 300-litre tank was fitted on the return line with a close-coupled primary and secondary pump arrangement. A three-port valve diverted flow to the tank only when the heat pump was modulating below 4 kW or when the compressor was in defrost. Above that threshold, the tank was bypassed to reduce standing losses. The cylinder also received a 22 mm bypass with an automatic balancing valve and a 6 kW immersion heater for legionella protection. Controls were set to a 5 K heating curve and a 48\u00b0C maximum flow temperature, with weather compensation adjusted after commissioning.<\/p>\n

Result: longer cycles and a measurable efficiency gain<\/h2>\n

After two weeks of monitoring, the average compressor run time at 8\u00b0C outdoor temperature rose from 12 minutes to 41 minutes, and the cycling rate fell by about 70%. The measured seasonal performance factor over the first heating season was 3.4, compared with a predicted 3.1 for the same system without the buffer. Standing losses from the tank added roughly 0.4 kWh per day, but the longer cycles and reduced defrost interruptions more than offset that penalty. For installers, the lesson is specific: size the buffer from the minimum modulation of the chosen heat pump and the water volume of the actual emitter circuit, not from a generic rule. In Bananzia, that means recording the part-load behaviour during commissioning and adjusting the bypass threshold before handover.<\/p>\n","protected":false},"excerpt":{"rendered":"

Context: one house, one undersized emitter circuit The case property is a 96 m\u00b2 semi-detached house in Bananzia with uninsulated cavity walls, 100 mm loft insulation and original 1970s steel radiators. A heat-loss calculation gave 5.8 kW at an external design temperature of \u22123\u00b0C and a flow temperature of 45\u00b0C. The existing gas boiler had […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"spay_email":""},"categories":[1],"tags":[],"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/fortalezaequipamentos.com.br\/index.php\/wp-json\/wp\/v2\/posts\/39017"}],"collection":[{"href":"https:\/\/fortalezaequipamentos.com.br\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/fortalezaequipamentos.com.br\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/fortalezaequipamentos.com.br\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/fortalezaequipamentos.com.br\/index.php\/wp-json\/wp\/v2\/comments?post=39017"}],"version-history":[{"count":1,"href":"https:\/\/fortalezaequipamentos.com.br\/index.php\/wp-json\/wp\/v2\/posts\/39017\/revisions"}],"predecessor-version":[{"id":39018,"href":"https:\/\/fortalezaequipamentos.com.br\/index.php\/wp-json\/wp\/v2\/posts\/39017\/revisions\/39018"}],"wp:attachment":[{"href":"https:\/\/fortalezaequipamentos.com.br\/index.php\/wp-json\/wp\/v2\/media?parent=39017"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/fortalezaequipamentos.com.br\/index.php\/wp-json\/wp\/v2\/categories?post=39017"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/fortalezaequipamentos.com.br\/index.php\/wp-json\/wp\/v2\/tags?post=39017"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}