This　study　investigated　the　optimal　design　of　a　capillary　heat　exchanger　device　for　the　heat　pump　system　and　its　innovative　engineering　application　in　a　building.　The　overall　aim　was　to　use　a　capillary　heat　exchanger　to　obtain　energy　in　coastal　areas　for　promoting　renewable　energy　in　low-carbon　building　design.　Initially,　the　main　factors　affecting　the　efficiency　of　the　capillary　heat　exchanger　were　identified,　a　mathematical　model　was　then　established　to　analyse　the　heat　transfer　process.　The　analysis　showed　the　flow　rate　and　the　capillary　length　are　the　key　factors　affecting　the　efficiency　of　the　capillary　heat　exchanger.　Secondly,　to　optimize　the　structural　design　of　the　capillary　heat　exchanger,　the　heat　energy　transfer　is　calculated　with　different　lengths　of　the　capillary　under　various　flow　rates　in　summer　and　winter　conditions,　respectively.　Thirdly,　a　typical　building　is　selected　to　analyse　the　application　of　the　capillary　heat　exchanger　for　extracting　energy　in　the　coastal　area.　The　results　show　the　performance　of　the　selected　capillary　heat　exchanger　heat　pump　system,　in　winter,　the　heat　energy　transfer　rate　is　60　W/m(2)　when　the　seawater　temperature　is　3.7　degrees　C;　in　summer,　the　heat　energy　transfer　rate　is　150　W/m(2)　when　the　seawater　temperature　is　24.6　degrees　C.　Finally,　the　above　field　test　results　were　examined　using　a　numerical　simulation　model,　the　test　and　simulation　results　agree　with　each　other　quite　well.　This　paper　is　conducive　in　promoting　the　development　of　the　capillary　heat　exchanger　heat　pump　as　an　innovative　sustainable　technology　for　net-zero　energy　and　low　carbon　buildings　using　renewable　energy　in　coastal　areas.