DX (Direct expansion) coil is one of the evaporator coils uses refrigerant as a cooling medium in a close loop system for cooling. DX coil directly cool the supply air to an occupied space.
Expansion refers to the treatment of the refrigerant (expansion valve is used to reduces its pressure and temperature) before entering the evaporator. There are 2 general type of DX systems:
1) Package system - equipped with all the components in a unit, and
2) Split system – the whole system split into indoor unit and outdoor unit.