A thermal management system includes a heat rejection device configured to fluidly couple to a refrigeration system, a fan configured to provide an entering airflow across the heat rejection device to cool a flow of water within the heat rejection device, and a controller configured to control a speed of the fan based on at least two of (i) a relative humidity of the entering airflow, (ii) a percentage of capacity one or more components of the refrigeration system are operating at, (iii) a ratio of water to energy costs, and (iv) a ratio of a design power of a compressor of the refrigeration system to a design power of the fan to minimize a total utility operation cost of the thermal management system including (i) energy costs to operate the fan and the refrigeration system and (ii) water costs of the flow of water.