Capacity control of induced draft cooling tower using two stage optimization

We consider the problem of designing a capacity control method for induced draft cooling towers that can be operated in different modes (bypass, showering, ventilation) to meet the heat rejection requirement. Recent efforts provide an adequate solution using mixed integer model predictive controller, however the combinatorial formulation of the problem might result in prohibitively large computation time limiting its applicability in real time scenarios. To this end, we propose a computationally efficient capacity control method based on a two stage optimization approach for handling the mode selection and optimal fan speed of the cooling tower. The solution to the first stage optimization program provides optimal fan speed which is then utilized by the second stage optimization program to determine the best operational mode of the cooling tower. An algorithm is proposed which relies on the integration of autonomous dynamics of bypass and showering mode and the relationship between showering and ventilation mode to efficiently solve the two stage optimization problem. Numerical simulations are provided to validate the performance of the proposed capacity control method.