Ground-buried tube heat pump system: For areas wich littlesurface water and groundwater sources, the ground-heating system is used for for outdoor heat transfer systems. The heat exchange coil is deeply buried in the underground soil, and the circulating water directly exchange heat with the soil through the water pipe wall. In summer, the circulating water release heat from refrigeration units to the soil; In winter, the heat pump system transfers heat from the soil to indoor rooms. Due to the complexity of the buried pipe technology, the lengths of required pipelines and its overall cost, the system is generally suitable for relatively small building areas.