A critical question regarding the life-cycle design and management of any product system is, “What is its optimal service life?” The Center for Sustainable Systems at the University of Michigan has developed life cycle optimization (LCO) methods and models to evaluate optimal service life and asset management decisions from energy, emissions, cost, and policy perspectives. This LCO model is based on a dynamic programming method with inputs derived from life cycle assessment (LCA) and life-cycle cost analysis. From an environmental perspective, this is a particularly complex question to resolve for product systems with nonlinear use phase burdens and uncertain technology improvement trajectories.
This chapter presents the basic LCO methodology and demonstrates its application to automobiles and household refrigerators. In both cases, there exist multiple tradeoffs between utilizing an existing product model and replacing it with one that is more efficient. The operational efficiency gain from model replacement should exceed the additional resource investments required to produce the new model. LCO simulations indicate that optimal replacement schedules are strongly influenced by technology improvement rates, product deterioration rates, production vs. use phase impact ratios, and consumer use patterns.
Results from replacement case studies of automobiles, refrigerators, air conditioners, and highway infrastructure will be highlighted and general principles for enhancing sustainability will be presented. Life-cycle optimization is expected to become another important technique to add to the life-cycle modeling toolkit for informing design and policy decisions.