Developing an Integrated Method for Optimal Design of Chilled Water Plants in HVAC Systems

Buildings account for a large portion of energy use in the US. Many those buildings have equipped with central plants to produce chilled water supplied to central air handling units. The chilled water plant design can have a significant impact on building energy uses and costs. In this paper, an integrated method for optimal design of chilled water plants is developed in order to minimize life cycle cost. The method integrates an optimization procedure with models that perform detailed cooling load analysis, pump head and energy calculations and life cycle cost analysis. The pump heads are determined by friction and fitting equations with specified flow parameters. The energy calculations are achieved by using chiller, pump and fan models. Genetic algorithm GA is used to solve the constrained optimization problem. The optimal design variables are the condenser and chilled water piping sizes, the condenser and chilled water temperature differences and the chilled water supply temperature. The method is evaluated using an existing building on different climate zone locations. The evaluation results show this integrated method can achieve better results than traditional process. The saving in life cycle cost could be up to 8% depending on locations and project specifications.