Data　centers　must　be　cooled　appropriately　through　indoor　temperature　control　in　order　to　improve　information　technology　(IT)　equipment　reliability.　Free　cooling　is　a　promising　technology　for　energy　conservation　in　data　centers.　A　miniature　pump-driven　loop　heat　pipe　(PLHP)　unit　for　free　cooling　is　developed　for　a　small　data　center.　The　unit　consumes　low　power　and　has　a　high　energy　efficiency　ratio　(EER)　compared　with　air　conditioners.　The　operating　performance　of　the　PLHP　unit　installed　in　the　case　data　center　in　Beijing　was　tested　and　studied.　The　EERs　under　different　outdoor　temperatures　were　analyzed,　and　the　fitting　variation　rules　were　obtained.　Compared　with　air　conditioners,　the　annual　energy　savings　of　the　PLHP　unit　for　both　hours　and　days　were　tested　and　analyzed　based　on　the　fitting　formula.　Results　show　that　indoor　temperature　is　maintained　at　18-25　degrees　C,　and　that　the　test　energy　saving　ratio　is　over　20.18%.　Hence,　the　PLHP　unit　can　replace　air　conditioners　for　cooling　the　case　data　center.　(c)　2017　Elsevier　Ltd.　All　rights　reserved.