Optimization of a chilled water plant using sequential quadratic programming

Air in most non-residential buildings needs to be cooled to maintain occupant comfort. Typically, the air is cooled by using cold water provided by a chiller plant consisting of liquid chillers, cooling towers and pumps. This paper presents a mathematical programming approach for determining which available chiller plant equipment to use to meet a cooling load as well as the best operating temperatures for the water flows throughout the system. First, a mixed-integer, nonlinear formulation of the problem is developed. A heuristic approach for handling the integer variables is then presented which allows very good solutions to be obtained by solving a series of continuous problems using sequential quadratic programming (SQP). Finally, regression analysis of a large number of optimizations are presented which show a linear trend that can be used to help guide the chilled water control system to make long term control decisions.