A district-cooling system (DCS) has been applied in a number of countries where chilled water from a central plant is delivered through a distribution network to groups of buildings in an urban district. Because of the expected considerable investment and lengthy payback period, well-planned and optimized system design and operation are crucial areas leading to the success of the implementation. Much saving can be achieved when the plant serves a group of buildings with diversifying daily cooling-load patterns. Among various design factors and solution schemes, one important planning decision is therefore to determine the desirable mix of building types, within the district of interest, to be served by the DCS. An approach to determine this optimal mix through the use of genetic algorithm (GA) was described in this paper. The thermal-load modeling technique and the objective function for optimization were derived. The case studies showed that the method was effective to give optimal or near-optimal solutions. (C) 2003 Published by Elsevier Ltd.