The present invention relates to an air-cooled condenser (1) for condensing steam. The air-cooled condenser comprises one or more roof-shaped heat exchanger assemblies (51,52,53,54,55,56).
A plenum space (60) is located between a top boundary delineated by the one or more roof-shaped heat exchanger assemblies (13,14) and a bottom boundary delineated by a deck cover (17). A ducted fan (5) is provided for generating an air-flow. The air-cooled condenser according to the invention comprises an air-flow diffuser (8) having an air inlet side connected to an upper side of the cylindrical duct (7) of the ducted fan and an air outlet side coupled with the deck cover such that, when in operation, an air-flow generated by the fan is flowing through the air-flow diffuser before entering the plenum space via a deck opening (18) in the deck cover. The cross sectional area and the height of the air-flow diffuser are optimized to reduce the electrical power consumption of the fan.