To　increase　the　heating　capacity　of　air-source　heat-pump　in　cold　regions,　an　improved　heat　pump　cycle　with　scroll　compressor　economizer　was　developed.　The　measured　results　of　the　prototype　demonstrate　that　it　can　provide　a　high　temperature　and　high-capacity　water　supply　even　under　a　low　ambient　temperature　of　-10　similar　to　-15　degreesC.　The　performances　of　the　improved　heat-pump　cycle　are　comprehensively　analyzed　with　aid　of　the　proposed　thermodynamic　model　in　this　paper.　The　design　parameters　and　the　components　of　the　cycle　are　optimized　and　the　predicted　results.　The　predicted　results　discussed　indicate　that　the　improved　heat　pump　has　high　efficiency　under　all　weather　conditions　and　that　this　improvement　is　conducive　to　enlarging　the　running　region　of　the　heat　pump　and　providing　an　alternative　heating　service　for　cold　regions.　(C)　2003　Elsevier　Ltd.　All　rights　reserved.