The surface water source heat pump system is composed of three sub cycle systems, namely the surface water circulation, the intermediate circulation and the terminal circulation. The main equipment of the system includes surface water pump, dredging type heat exchanger, terminal water circulation pump, heat pump unit and terminal circulating pump.

       The working process of the system is as follows:

       (1）Surface water cycle, sewage enters the heat exchanger at 2.5℃, transfer about 3℃ to the intermediate water, and back to the downstream water source at -0.5℃.

       (2)Intermediary cycle, intermediate water enters heat pump unit at 0.5℃，release the heat, then return to heat exchanger at about -3.5℃ to absorb heat again.

       (3)Terminal cycle, terminal water enters the heat pump units at 40 ℃ , absorb heat rise up to 47 ℃ ,then enter the end radiator, release heat to the building space.