In one embodiment, a cooling system includes a thermosyphon cooler that cools a cooling fluid through dry cooling and a cooling tower that cools a cooling fluid through evaporative cooling. The thermosyphon cooler uses natural convection to circulate a refrigerant between a shell and tube evaporator and an air cooled condenser. The thermosyphon cooler is located in the cooling system upstream of, and in series with, the cooling tower, and is operated when the thermosyphon cooler is more economically and/or resource efficient to operate than the cooling tower. According to certain embodiments, factors, such as the ambient temperature, the cost of electricity, and the cost of water, among others, are used to determine whether to operate the thermosyphon cooler, the cooling tower, or both.