A　thermal　storage　unit　(TSU)　with　flat　microheat　pipe　arrays　(FMHPAs)　as　heat　transfer　core　is　experimentally　investigated　in　this　study.　A　comprehensive　evaluation　parameter　of　the　TSU　defined　as　thermal　power　intensity　is　proposed.　The　effects　of　the　length　proportion　of　the　air　side　and　the　phase-change　material　(PCM)　side　on　the　heat　transfer　properties　of　TSU　are　also　examined.　Phase-change　behavior　of　the　PCM,　heat　transfer　characteristics,　and　thermal　resistance　distribution　are　analyzed　and　discussed.　Results　show　that　the　FMHPAs　greatly　enhanced　the　heat　transfer　rate　between　the　air　and　the　PCM.　The　thermal　resistance　of　the　air　side　is　nearly　three　times　greater　than　that　of　the　PCM　side.　Keeping　the　length　of　the　storage　section　480　mm　long　and　varying　the　length　of　the　heating　and　cooling　sections　from　130　to　160　mm　and　190　mm,　the　best　performance　was　obtained　for　the　length　of　160　mm.　(C)　2017　American　Society　of　Civil　Engineers.