A hybrid heat exchanger apparatus adapted for cooling a hot fluid flowing from a hot fluid source, the heat exchanger apparatus having: an indirect heat exchanger device; a direct heat exchanger device; an air inlet at a bottom portion and an air outlet at a top portion; both heat exchangers being horizontally adjacently in a central chamber portion of the apparatus; a cooling fluid distribution system including a fluid distribution manifold having a first fluid distribution manifold section and a second fluid distribution manifold section in fluid communication with each other; means for distributing the hot fluid to be cooled from the cooling fluid distribution system onto the direct heat exchanger device; and means for causing ambient air to flow across both the indirect heat exchanger device and the direct heat exchanger device to generate hot humid air from the ambient air flowing across the direct heat exchanger device and hot dry air from the ambient air flowing across the indirect heat exchanger device; characterised in that means are provided for conveying the hot fluid to be cooled from the hot fluid source through the indirect heat exchanger device to the cooling fluid distribution system; in that the air flow means is effective to cause air to flow upwardly from the inlet across both heat exchangers in parallel and thereafter through the outlet; and in that the two manifold sections (24a, b) are configured to be in selective fluid communication, and the apparatus is configured to operate in either a wet mode or a hybrid wet/dry mode, wherein in the wet mode the fluid to be cooled is distributed from the first and second distribution manifold sections (24a, 24b) onto the direct and indirect heat exchangers (106a, 106b) respectively, and in the hybrid mode the second distribution section is closed off from the fluid and the fluid is distributed only onto the direct heat exchanger. an indirect heat exchanger device; a direct heat exchanger device; an air inlet at a bottom portion and an air outlet at a top portion; both heat exchangers being horizontally adjacently in a central chamber portion of the apparatus; a cooling fluid distribution system including a fluid distribution manifold having a first fluid distribution manifold section and a second fluid distribution manifold section in fluid communication with each other; means for distributing the hot fluid to be cooled from the cooling fluid distribution system onto the direct heat exchanger device; and means for causing ambient air to flow across both the indirect heat exchanger device and the direct heat exchanger device to generate hot humid air from the ambient air flowing across the direct heat exchanger device and hot dry air from the ambient air flowing across the indirect heat exchanger device; characterised in that means are provided for conveying the hot fluid to be cooled from the hot fluid source through the indirect heat exchanger device to the cooling fluid distribution system; in that the air flow means is effective to cause air to flow upwardly from the inlet across both heat exchangers in parallel and thereafter through the outlet; and in that the two manifold sections (24a, b) are configured to be in selective fluid communication, and the apparatus is configured to operate in either a wet mode or a hybrid wet/dry mode, wherein in the wet mode the fluid to be cooled is distributed from the first and second distribution manifold sections (24a, 24b) onto the direct and indirect heat exchangers (106a, 106b) respectively, and in the hybrid mode the second distribution section is closed off from the fluid and the fluid is distributed only onto the direct heat exchanger.