PROCEDURE FOR EQUIPMENT SELECTION IN MECHANICAL SYSTEMS BASED ON CAPITAL COST MINIMIZATION AND OPTIMAL LOADING.
Chilled water systems, FPSO, Mono-objective optimization, Multi-objective optimization, Optimal equipment selection, Optimal loading problem.
Providing maximum performance at minimum cost is a major challenge in the design of mechanical systems. One of the key problems is determining the optimal schedule of a set of units operating in parallel that minimizes the overall energy consumption. This is a widely studied problem in the literature known as \economic dispatch" (in power systems) or as \optimal loading problem" (in air-conditioning systems). However, the loading problem requires the units to be previously selected. This work proposes a procedure to solve the selection problem and the loading problem at the same time. The proposal is a novel procedure that allows determining, in a rigorous manner, the units that have to be purchased and the corresponding operation schedule. It was applied to two case studies: i) selection of chillers in cooling plants, and ii) selection of utility plants in oil and gas o_shore platforms. Both cases are analyzed using two alternative optimization approaches. First, a mono-objective optimization of a single cost-based function and, second, a multi-objective optimization of capital cost and energy consumption. The results in all cases showed that the total nominal capacity of the selected units is not necessarily closed to the peak load, which is a common rule-of-thumb guideline for equipment selection. For instance, the total nominal capacity of the solution with three 500 TR chillers in the cooling plant case is considerable greater the peak load (900 TR). Likewise, the solutions obtained in the selection of utility plants in FPSO platforms are better than the standard solution of three aeroderivative gas turbines model GE LM2500+RD (G4) (with a capital cost of 40.05 Millions of USD and a fuel consumption of 9:999 _ 104 TJ at the optimal setting during the lifetime of the system). These counter-intuitive results demonstrate the importance of using a systematic selection procedure.