Claiming-based allocation for waste-to-energy in district heating for life cycle assessments of buildings

Purpose The revised European Performance of Buildings Directive requires that all new construction projects must quantify life cycle emissions, but modelling choices for waste-to-energy in district heat remains arbitrary. Waste-to-energy creates a problem in life cycle assessment (LCA) as emissions must be allocated between the product system that produces and handles the waste and the one that makes use of the recovered energy. Claiming-based allocation methods are tailored to support environmental policy and ensure correct incentives, but no suitable methods exist for waste-to-energy in district heat. Methods We propose and demonstrate a claiming-based allocation method for waste-to-energy in district heat for LCA of buildings. The proposed method is described through mathematical notations and balances three key environmental claims of stakeholders for their products. For waste fractions where waste-to-energy is environmentally beneficial, allocation is set based on the relative environmental benefits from waste-to-energy as a joint production and from energy efficiency measures in buildings, whilst ensuring environmental competitiveness of district heat. For non-beneficial waste incineration, allocation is set based on benefits of shifting waste flows to other treatment. We apply the proposed method to two Norwegian case cities considering varying background conditions, waste composition, and technological availability (including alternative waste treatment, carbon capture and storage, separate energy production, and building energy efficiency gaps). Results and discussion Results show the effect of modelling choices on the emission intensity of district heat and how the multifunctionality problem can be solved to promote environmental policy. The environmental performance of waste-to-energy compared to decentralized heat pumps is extremely sensitive to allocation, technological performance, and waste composition. For environmentally beneficial waste-to-energy, we show a trade-off between ensuring its environmental competitiveness and enhancing incentives to energy efficiency in buildings. The relative importance of improved waste management and energy efficiency in buildings for climate change mitigation varies based on building types and available waste treatment options. Results demonstrate how the proposed claiming-based allocation method can help ensure that correct incentives are given to decision makers when analyzing waste-to-energy in district heat through building LCAs. Conclusions We call for a paradigm shift for modelling of waste-to-energy in district heat to facilitate a successful European-wide LCA implementation in construction projects that are potentially connected to a waste-to-energy district heat grid. Robust methods that capture variations in environmental performance from changing local and technological conditions are key for environmental decision-making. Claiming-based allocation methods for waste-to-energy can help support the implementation of environmental policy.