Direct expansion ground-coupled heat pump systems：a review

Presents direct expansion ground-coupled heat pump (DX-GCHP) systems and secondary loop ground-coupled heat pump (SL-GCHP) systems, analyses the circulating characteristics and the problems be cared attended in design of DX-GCHP systems, summarizes present development conditions and related research literatures, and gives out the development prospects of DX-GCHP systems.