TU.2.E || Tools, Metrics and Labels for a Circular Economy

Hummen, Torsten; Desing, Harald

A longer product use requires fewer resources and causes less environmental impact. While this assumption may seem intuitive, longevity is not per se environmentally beneficial. Imagine a product that causes significant impacts during its service life and loses performance through wear and degradation. Its prolonged use may cause higher impacts overall than early replacing it with an evolved alternative. We introduce a tool to efficiently estimate the best replacement time at which impacts become minimal, i.e. the optimal environmental lifetime. Non-linear dynamics of technological efficiency improvements and efficiency degradation during usage are taken into account, as well as different replacement scenarios, including lifetime extension strategies such as re-manufacturing. Optimization results are clearly communicated with a lifespan indicator to evaluate the environmental performance of an achieved lifetime in regard to the optimal circular economy strategy. In this way, the lifespan indicator accounts for unsustainable throughput of materials and waste of resources when deviating from the optimum. To illustrate the application of the tool, the optimal circular economy strategy of residential heating systems is determined. It reveals that gas boilers shall be replaced in short intervals with evolved gas boilers or – more effectively – with a heat pump.