Chiller control systems and methods for chiller control use iterative modeling of cooling towers, heat exchangers, and pumps to determine the feasibility of integrated free cooling and the ability to take advantage of free cooling. The control systems and control methods can further include selecting the parameters for operating in the free cooling or integrated free cooling mode to improve efficiency and/or reduce energy consumption when operating in these modes. The models can have inputs and outputs that feed into one another, and converge at a solution over multiple iterations. The feasibility of integrated free cooling can be based on providing cooling to a cooling load process fluid at a heat exchanger. The availability of free cooling can be based on the cooling provided at the heat exchanger achieving a target temperature for the cooling load process fluid.