A　defrosting　initiation　strategy　based　on　tube-encircled　photoelectric　sensors　(TEPS)　was　previously　proven　effective　for　enhancing　the　frosting-defrosting　performances　of　air　source　heat,　pumps　(ASHPs)　in　cold　and　dry　regions.　To　verify　its　applicability　to,　and　evaluate　the　energy-saving　potential　when　using　the　TEPS-based　strategy　in　mild　and　humid　regions,　field　tests　were　conducted　in　Guiyang　City,　China,　where　the　outdoor　averaged　air　temperature　and　relative　humidity　were　4.5　degrees　C　and　80%　in　winter,　respectively.　Two　ASHPs　of　the　same-make,　one　with　the　TEPS-based　strategy　and　the　other　with　the　commonly　used　temperature-time　(TT)　strategy,　were　tested.　Totally,　seven　test　cases　were　organised.　Cases　1-5　were　for　short-term　tests　to　verify　the　technical　feasibility　of　TEPS-based　strategy　by　comparing　the　defrosting　accuracy　of　the　two　strategies.　Cases　6-7　were　for　long-term　tests　to　validate　the　reliability　and　effectiveness　of　the　TEPS-based　strategy　by　comparing　two　ASHPs＇　operating　performances.　The　test　results　demonstrated　that　the　use　of　TEPS-based　strategy　in　mild　and　humid　regions　can　initiate　defrosting　more　accurately,　reliably　and　efficiently,　and　thus　improve　the　COP　and　heating　capacity　by　11.3%　and　12.1%,　respectively,　compared　to　the　use　of　the　TT　strategy.　Therefore,　it　was　proven　that　the　TEPS-based　strategy　was　more　effective　for　the　ASHPs　used　in　mild　and　humid　regions,　for　a　more　accurate　defrosting　initiation　and　higher　energy　efficiency.　(C)　2018　Elsevier　B.V.　All　rights　reserved.