Traditional　air　source　heat　pumps　(ASHPs)　only　can　work　above　about　-20　degrees　C　to　-25　degrees　C,　and　have　limitations　in　terms　of　performance.　This　paper　proposes　a　novel　three-cylinder　two-stage　variable　volume　ratio　(TSVVR)　rotary　compressor　to　improve　the　performance　of　the　ASHP.　Utilizing　the　variation　characteristics　of　the　compressor　optimal　volume　ratio　under　the　different　temperatures,　the　compressor　volume　can　be　switched　for　better　performance.　Experiments　are　conducted　on　the　improved　ASHP　with　the　TSVVR　rotary　compressor　and　the　two　traditional　ASHPs　with　the　single-stage　and　two-stage　compressor　using　the　simulation　of　the　residential　building　in　the　environmental　laboratory.　The　results　show　that　the　TSVVR　system　operates　in　a　stable　manner　with　the　COP　of　1.52　W/W　at　-30　degrees　C,　and　achieves　a　higher　COP　than　the　traditional　ASHPs.　The　optimal　volume　ratio　decreases　with　the　decrease　of　the　evaporation　temperature.　The　TSVVR　system　works　in　the　three-cylinder　mode　at　low　temperature　and　directly　expands　the　heating　capacity　and　compression　efficiency　because　of　the　increase　of　the　low-pressure　volume　and　suction　volume.　When　the　water　temperature　varies　between　40　degrees　C　and　the　maximum　possible　temperature,　the　COP　of　the　TSVVR　system　is　18.4-22.3%　higher　and　6.6-7.3%　higher　than　the　single-stage　and　two-stage　systems,　respectively;　when　the　indoor　temperature　varies　between　12.5　degrees　C　and　18　degrees　C,　the　COP　of　the　TSVVR　system　is　around　18.4-23.4%　and　5.2-8.8%　higher　than　the　single-stage　and　two-stage　systems,　respectively.　The　two-cylinder　mode　of　the　TSVVR　system　has　a　larger　volume　ratio　than　the　single-stage　and　two-stage　ASHPs　and　is　closer　to　the　optimal　volume　ratio,　which　is　more　suitable　for　the　high　temperature　and　low　load　conditions.　In　the　three-cylinder　mode,　the　TSVVR　system　has　a　smaller　volume　ratio,　and　the　compression　efficiency　and　system　refrigerant　flow　rate　increase,　when　the　evaporation　temperature　is　low.　Two　modes　ensure　that　the　TSVVR　system　always　work　in　the　efficient　states,　especially　in　the　low　temperature　environments.　(C)　2018　Elsevier　Ltd　and　IIR.　All　rights　reserved.