usephase

Use phase is a term used in life cycle assessment (LCA) and sustainable design to denote the period during which a product or system is in operation by the user. It covers the operational energy and material inputs, such as energy consumption, water use, and emissions generated while the product is being used, as well as maintenance, replacements of consumables, and, in some cases, minor renovations carried out during its service life. The use phase begins when the product is first put into service and ends when it is decommissioned or disposed of.

Scope varies by product. For buildings, the use phase typically dominates environmental impact due to heating, cooling, lighting, and ventilation, and is heavily influenced by occupancy and behavior. For vehicles, motor fuel or electricity consumption during driving defines the use phase. For consumer electronics, standby power, active use, and software updates may contribute. In all cases, end-of-life and manufacturing are separate life cycle stages.

Assessment relies on functional unit and usage patterns. Data sources include energy bills, smart meters, standard consumption values, or product-specific testing. Key metrics include energy or fuel use per unit time, water use, emissions, maintenance intervals, and repair or replacement rates. Uncertainty arises from behavioral variability and weather, especially in buildings. Modeling can be bottom-up process-based LCA or hybrid methods.

Mitigation and design implications: improve efficiency during use, adopt durable components, design for modularity or service models, encourage behavior changes, monitor performance with built-in sensors, and provide feedback to users. Use-phase considerations affect policy and product development, often guiding eco-design requirements and metrics.