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Nowadays, cities and districts are becoming more and more interconnected in terms of energy supply systems, and the transition towards smart connected thermal and electrical grids is inevitable. While single building-level modelling has demonstrated numerous technical and economic benefits, it is vital to scale up the approach and consider the larger picture of cluster of buildings, districts, and cities. The island of Ærø in Denmark has an ambitious goal to become the first CO2 neutral and renewable energy self-sufficient Danish Island by 2025, as well as becoming a fossil-fuel free island by 2030. With the ambitious energy and environmental aims of Ærø island, this work aims to investigate the capability of establishing part of the island as the first Danish positive energy district (PED) and assess various design scenarios and possibilities of upgrading/modifying the current scheme and composition of energy supply and distribution. An open-source urban scale modelling tool is used, City Energy Analyst (CEA), where the district is modelled considering all specifications and characteristics of buildings and the corresponding energy supply systems. The base case scenario is simulated, and the performance is calibrated using actual data. Then, multiple energy improvement measures targeting the buildings envelope as well as the energy generation and supply systems are developed and simulated to assess the impact on the overall energy consumption for heating and electricity. The results show that a PED can be established employing an improvement package of envelope-targeting measures, energy systems upgrades and renewable energy systems expansion. [ABSTRACT FROM AUTHOR]

The circular economy has become an important topic in the building industry, and life cycle assessment (LCA) is often used to quantify its benefits. Through chemical analysis, this article demonstrates that the current LCA is not yet well-adapted to assess the circular economy of building materials and components. It is shown that current inventory data and models are insufficient because they do not consider the uptake and emission of chemicals during use, the migration of chemicals within the value chain across the multiple phases in the circular economy, and because current characterization models lack a large fraction of the potentially emitted chemicals from said uptake and emission identified in the tested building material samples. Thus, it is shown that impacts relevant for LCA in the circular economy of buildings remain unaddressed because they are currently either omitted in the LCA that covers a limited number of impact indicators, or are ostensibly covered in the LCA covering a full set of indicators but missed due to inadequate characterization models. To ameliorate this, a definition of embedded toxicity and its relationship to the toxicological footprint is presented and a method for measurement is proposed, illustrating how assessing embedded toxicity can yield information for facilitating safe building-material reuse. Finally, a suggestion for the improvement of life cycle impact assessment methods is proposed. [ABSTRACT FROM AUTHOR]