This　study　presented　experimental　investigations　on　the　thermal　performance　of　a　thermal　energy　storage　(TES)　unit　with　coil　tubes.　A　designed　test　rig　was　built　and　the　melting　heat　transfer　characteristics　(melting　front　and　temperature　distribution)　inside　the　TES　unit　were　examined.　The　effects　of　charging　flow　rate　on　the　overall　phase　change　process　were　examined.　The　results　showed　that　natural　convection　accelerated　the　thermal　energy　transport　in　the　melt　phase　in　the　top　region,　but　weakened　the　heat　transfer　in　the　bottom　region;　this　resulted　in　the　unmelt　PCM　at　the　bottom.　The　melting　heat　transfer　was　overall　enhanced　by　the　increase　in　inlet　flow　rate,　indicating　that　the　full　charging　time　can　be　shortened　by　a　larger　flow　rate.　©　2017　The　Author(s).