Research into the impact of innovative sustainable energy experiments and demonstrations is crucial to diversifying, scaling up, and accelerating the sustainable energy transition. Although there is vast research into sustainable energy experiments and demonstrations, research literature offers a fragmented collection of findings. A coherent overview of themes and insights regarding the transformative impact of innovative sustainable energy experiments and demonstrations on sustainable energy systems from the past, present, and near future is lacking and necessary to increase experiments and demonstrations' impact on the sustainable energy transition. The research in this study fills this knowledge gap by providing such an overview and yields novel insights into the organized function and impact of experiments and demonstrations. It spans a broad spectrum of sustainable energy technologies, the empirical domains where these are invented, developed and applied, and the stakeholders involved. The overview is the outcome of a Delphi study in which the insights of 47 international scientific research experts in sustainable energy experiments and demonstrations are bundled and explained. This study presents a thematic overview of the significant insights regarding past and current sustainable energy experiments and demonstrations and outlines a research agenda for the future. Policymakers, practitioners, and scientists can leverage this to inform their sustainable energy policies, business strategies, and research programs.@en

Rising temperatures are leading to an increase in cooling energy demand and thermal discomfort due to overheating. Despite dynamic switchable glazing being a promising solution for controlling solar radiation while preserving user access to outdoor views, their cost is currently a barrier to their widespread adoption. The recent development of low-cost inkjet-printed switchable glazing offers a cost-effective alternative; however, its performance remains uncertain concerning its contributions to energy efficiency and user satisfaction in terms of thermal comfort and visual experience. This study presents a multi-domain evaluation of the performance of a novel low-cost inkjet-printed glazing with users in terms of their satisfaction with the environment, personal control and interaction. In comparison to a conventional façade with static glazing and external roller blinds, the EC glazing performed better than the conventional façade if the shading is fully down. In this case, higher satisfaction was measured in terms of view clarity, daylight access and colour in the room with the EC glazing. When comparing the performance of the EC glazing at the clearest state with conventional glazing with blinds raised, users’ satisfaction was not significantly different, except for the satisfaction with view clarity. Despite the long transition time of the EC glazing, users were not significantly dissatisfied with the speed of transition. Overall, these preliminary results show that this novel EC glazing is well-accepted by users especially as an alternative to traditional dark roller blinds, but further research is required to investigate its performance during summer.@en

Energy renovation of residential buildings is a key strategy for a just energy transition, involving complex socio-technical challenges and increasingly requiring attention to social implications and equity. However, what constitutes just energy renovations remains undefined and often limited to more abstract conceptualizations, lacking a field-specific definition, with integrated, implementation-oriented guiding strategies. Limiting the scope to developed countries, this study systematically reviews 104 interdisciplinary studies on energy renovation that consider social and resident dimensions. The literature is analysed through a synthesised framework of energy and spatial justice theories, adapting the principles of recognition, procedural, and distributive justice to residential environments and energy renovation requirements. Firstly, the study provides a comprehensive overview of socially oriented renovation research, demanding greater attention to vulnerable contexts, stakeholders' dynamics, design and post-renovation phases, through iterative, co-creative field research. Secondly, the study identifies critical domains, subdomains and related (in)justice trajectories within the three justice principles, offering context-sensitive application pathways and highlighting the relevance of beyond-energy-efficiency aspects and trust-building strategies. This results in a flexible framework of decision-making criteria that align environmental and social needs, supporting researchers, policymakers, and practitioners. Achieving justice requires interconnected mechanisms across decision-making levels and renovation phases, that rely on collaborative mutual-learning dynamics among actors. To complement strategic policies, design and implementation criteria emerged as crucial for ensuring effective engagement and user-centred interventions. This study contributes to validating energy justice as a decision-making guide, demonstrating the added value from spatial justice integration for a just urban transition, and laying fertile ground for further empirical research.@en

The increasing frequency and intensity of heatwaves raises questions about the thermal vulnerability of buildings and, in particular, on how to assess their resilience to extreme heat. In this context, thermal fragility curves, which describe the probability of achieving or exceeding specific temperature thresholds for a building, serve as an effective measure to define the thermal vulnerability of existing buildings and identify tailored retrofit strategies. This study focuses on deriving thermal fragility curves for a case study: a 6-storey residential building constructed in the 1980s with a reinforced concrete structure and masonry infill walls. Dynamic thermal modeling and simulation were conducted over a one-year period using synthetic weather files generated to account for future heatwaves. The simulation results provide useful relationships in particular between: outdoor temperature and indoor Standard Effective Temperature (SET); and between outdoor daily maximum temperature and indoor SET. These relationships were finally analyzed to create and compare fragility curves using maximum likelihood fitting and the so-called Cloud methodology.@en

The renovation of existing buildings is widely recognized as a powerful strategy for reducing emissions and land use. However, when it comes to residential buildings, the socio-technical challenges are particularly complex. The necessity and urgency of increasing energy efficiency often lead to retrofit processes that overlook residents’ needs and fail to consider the impact of renovation techniques on their lives. This study conducts a systematic and interdisciplinary literature review to explore how and to what extent social aspects, particularly residents and their needs, are considered in building renovations. An analysis of 40 studies from the Web of Science and Scopus databases is presented. The holistic overview focuses on two interrelated aspects: the orientation of decision-making processes towards residents and social components of multi-stakeholder involvement, and the relationship and interaction between design choices and residents. By doing so, the review enables a collection of meaningful and heterogeneous criteria for process management and retrofit solutions selection. Recognizing the existing gaps in the literature and clarifying relevant criteria, this review can help identify areas that require further research and intervention.@en

In typical practice of building renovation design, distributed teams communicate through technical drawings, but the construction industry lags in digitalization. This study addresses this gap by proposing a methodological framework integrated into digital tools for early-stage renovation processes. The framework, implemented as a web-based tool, gathers user inputs related to building details and preferences to generate alternative renovation scenarios. It utilizes databases for building characteristics, technologies, and life cycle assessment (LCA)/life cycle cost (LCC) calculations. The information flow involves user inputs, database storage, and processing layers, enabling simulations and scenario evaluations. The framework facilitates quick, cost-effective, and customized decision-making in the early design phases, aiming for energy-efficient retrofits. Results highlight the importance of databases, such as building characteristics and LCA/LCC, while emphasizing a clear communication protocol among stakeholders. Overall, the study seeks to accelerate and streamline the renovation process, promoting efficient collaboration and reducing time and costs.@en

Roughly 97% of the European Union (EU) building stock is not considered energy efficient, and 75–85% of it will still be in use in 2050 (Artola et al., Boosting building renovation: What potential and value for Europe? 2016). Residential buildings account for around two thirds of final energy consumption in European buildings. The rate at which new buildings either replace the old stock or expand the total stock is about 1% per year. Similarly, the current renovation rate of existing buildings in the EU is about 1–2% of the building stock renovated each year. Renovation strategies on building levels need to be derived from a combination of energy efficiency upgrades to buildings and the use of renewable energy to decarbonize the energy supply, on a district or city scale. IEA EBC Annex 75 subtask D2 focuses on promoting cost-effective building renovation at district level combining energy efficiency and renewable energy systems, by focusing on the business models that can make implementation possible. This paper intends to provide an overview of the business model archetypes that can support the development of district demand and/or supply of energy-efficient building renovations and/or renewable energy solutions by targeting various types of stakeholders. It builds upon existing literature to gain insights into the current distributed energy business model landscape. Further, implementation strategies are identified that focus on a holistic evaluation of the expected energy and CO₂ performance of the site and optimized infrastructure investment pathways.

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The implementation of Positive Energy Districts (PEDs) is recognized as a promising approach to achieving energy efficiency and reducing the negative environmental impact of climate change through the surplus of local renewable energy generation. However, several barriers to the implementation of PEDs, coupled with the lack of a joint definition and clarity surrounding PEDs, need to be addressed. These barriers include governance, incentives, social, process, market, technology, and context challenges, requiring a profound understanding of the priorities, ambitions, strategies, contextual conditions, administrative conditions, policies, economic and technical resources, and existing solutions of cities.

This study explores the creation and implementation of PEDs, seeking to uncover the potential and challenges of this innovative concept in the pursuit of climate neutrality and energy efficiency. Through a peer-to-peer analysis of PED case studies and qualitative interviews with key stakeholders in Brussels, Stockholm, Vienna, Évora, Lisbon, and Salzburg, challenges such as the lack of clarity in the definition of PEDs, diversity of ownership, administrative complexity, resistance to change, limited knowledge exchange, financing constraints, technological limitations, and inadequate involvement of relevant actors are identified. Moreover, success factors and enabling strategies from these case studies are highlighted, including clear roadmaps, stakeholder collaboration, integrated decision-making processes, political commitment, and coordination platforms.@en

The Dutch government aims to eliminate natural gas for residential heating in 1.5 million homes by 2030. One strategy is connecting existing dwellings to lower-temperature district heating (DH) systems, although these dwellings might require energy renovations. The heterogeneous dwelling stock causes varying renovation needs that complicate the energy transition. The present study addresses this issue by assessing the building-level parameters affecting the readiness of the Dutch terraced-intermediate and apartment types for lower-temperature heating (LTH) supplied by DH systems. A sampling-based approach was employed to capture variability within these dwelling types, addressing the limitations of archetype-based methods. The findings suggest a sample size of 1300 to represent the variations in these dwelling types. Parametric simulations and machine learning methods were used to identify significant building-level parameters for medium-temperature (MT: 70/50 °C) and low-temperature (LT: 55/35 °C) supply levels. These include heating setpoints (desired indoor temperature) and ventilation-related parameters (ventilation system type and air infiltration rate), followed by fabric-related parameters (roof, glazing, wall, ground, and door insulation) and geometric properties (orientation, compactness ratio, and window-to-wall ratio). Additionally, radiator oversizing also impacts LTH readiness. These results broadly apply to the studied dwelling types, although feature importance varies by supply temperature and dwelling type. The findings can guide stakeholders in assessing current conditions and prioritising renovation measures, aiding the development of targeted renovation solutions. Encompassing the representative variations within studied dwelling types enhances the robustness of the results. However, incorporating more refined data could improve the accuracy of the findings, better supporting the energy transition of these dwellings.@en

The construction industry, accounting for a significant portion of energy consumption and greenhouse gas emissions, is pivotal in achieving Europe's ambitious climate neutrality goal by 2050. Circular Economy (CE) principles and the renovation of existing buildings are identified as promising strategies to reduce raw material and energy consumption. However, the lack of knowledge and guidelines for effective CE design and construction in the built environment, along with heterogeneous metrics and standards, pose challenges. The research outlines an investigation study aimed at developing Key Performance Indicators (KPIs) for evaluating building products based on CE principles, focusing on façade renovation. The study emphasizes the need for a holistic approach, considering both material input and output flows, and introduces qualitative and quantitative KPIs addressing aspects such as recyclability, modularity, and local materials. The research proposes established frameworks like Life Cycle Assessment (LCA), Material Flow Analysis (MFA), and the Level(s) framework, but recognizes their limitations in assessing circularity comprehensively. The methodology involves a comprehensive analysis of material streams and circularity potential for nine components crucial to achieving a net-zero façade renovation. Results from the material flow analysis demonstrate the environmental impact of selected building products, such as insulation panels and photovoltaic panels. The research underscores the importance of informed design choices, leveraging adaptable KPIs, and visualizing resource flows to enhance decision-making for sustainable construction practices aligned with CE principles.@en

The European building stock demands urgent renovation due to the age of the buildings, their expected lifetime, and their excessive energy consumption, which accounts for more than a third of the EU’s total emissions. However, the complexities involved, such as time, costs, and structural modifications, often discourage clients, tenants, and occupants from undergoing a building renovation process. Textile membranes, despite their long history in various architectural applications, have only been employed in façades in the last decades. Their intrinsic properties, such as lightness and flexibility, together with rapid assembly and low maintenance make these materials particularly suitable for façade retrofitting. Therefore, they are worth exploring as a way to promote the development of lightweight and easy-to-assemble façade products that could help overcome the current limitations of building retrofitting efforts. This paper aims to establish relationships between textile membranes and potential building retrofit applications. To this end, this study builds on the categorization of traditional façade retrofit strategies and proposes a new classification for textile façade retrofit products. The methodology includes a comprehensive literature review of textile properties and characteristics, along with a thorough assessment through case studies, of membrane use in façade applications. A sequential investigation leads to the main outcome of identifying three clear pathways for the development of new textile-based façade products for building retrofit.

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The present research proposes a framework to design and evaluate façade products integrating solar cooling technologies (SCTs), applied in an office building in a Southern Europe region. The building comprises various types of façade elements, such as opaque walls, glazed curtain walls, overhangs, and balconies. Key regulatory measures were implemented considering national energy saving regulations. The results represent annual energy consumption (kWh/m2/year) and the average daily cooling demand in Summer Design Week (kWh/day) of the simulated base model. This energy consumption lies within range of a previously simulated generic office and the average annual energy consumption of office blocks. Potential scenarios for integrating SCTs were outlined and evaluated using the solar fraction (SF) as an indication to measure the potential performance of the system based on nominal efficiencies, providing an initial reference of its ability to meet cooling demands, an essential step in early design stages. Scenarios per configuration related to double-effect chillers with evacuated tubes collectors and water-cooled vapor compression chiller and photovoltaic (PV) panels were the only one having an SF value of 1 or more, meaning that they can be able to handle the required cooling demand. Future steps should consider a second level of technical evaluation of scenarios having SF values of 1 or more, which should involve aspects related to how to physically integrate the technology, considering compactness and space usability and also maintenance requirements, among other relevant criteria.@en

Energy renovation processes in vulnerable neighbourhoods are complex decision-making endeavours. The JustPrepare project aims to develop inclusive strategies attuned to local needs to enhance energy renovation and transition effectiveness, considering economic, environmental, and social benefits.@en

This study introduces a systematic framework to facilitate decision-making in selecting renovation options for preparing existing Dutch dwellings for utilising lower temperature heat (LTH) supplied by district heating (DH) systems. The framework was applied to an archetype terraced intermediate house built between 1945 and 1975 to identify the renovation options required for transitioning from existing High-Temperature (90/70℃) supply from gas-boilers to Medium Temperature (70/50℃) supply from DH systems. The framework's effectiveness was demonstrated by systematically assessing the readiness of the archetype dwelling for LTH use, reducing the number of viable renovation options, evaluating the financial feasibility using a life cycle costing approach and generating decision support insights through comparative analysis. The framework identified an optimised solution involving cavity wall insulation, exhaust ventilation and switching to low-temperature radiators. This solution incurs low initial investment and global costs while significantly reducing space heating and underheated hours. As a result, the framework provides tangible solutions for the specific use case and can serve as a valuable tool for dialogue among stakeholders during the decision-making process.@en

This report describes the methodology for identifying and assessing cost-effective strategies for renovating urban districts towards far-reaching objectives regarding reducing carbon emissions and energy use. The report proposes different scenarios considering boundary conditions and different interventions on building envelopes and thermal systems. The proposed methodology builds on the methodology previously developed for individual buildings in IEA EBC Annex 56 (developed by the same main authors of this report), extending it to the level of districts/groups of buildings. Furthermore, it also makes use of results from other related Annexes. The idea is that the methodology supports decision-makers in evaluating the efficiency, impacts, cost-effectiveness and acceptance of various strategies for renovating urban districts, and in identifying suitable renovation strategies. The methodology defines the boundary conditions set for the assessments carried out, the research questions/hypotheses mainly investigated with the assessments, and the type of outputs generated from the assessments. It is intended that, based on the methodology developed, existing tools can be identified, or existing tools can be adapted to support the application of the methodology in case-specific assessments. In addition, an online Calculation Tool (Annex 75 CT) was developed to support the application of this methodology, which is available at: https://annex75.bim.energy and at https://annex75.iea-ebc.org/publications.@en

The present report provides guidance on the main concepts regarding building renovation and aims to set a common language for communication between local authorities, professionals, researchers, inhabitants and, in general, all the stakeholders and international partners. Each term is defined in the context and scope of IEA EBC Annex 75, namely building renovations at the district level, and combines definitions from the European legal framework, common definitions of English dictionaries, related projects, research papers, and other professional@en

This report, therefore, focuses on the following objectives:
- Give an overview of various policy options that could target the district level, considering existing and emerging policy instruments with the potential to be successfully applied within that context, and how policy challenges specifically occurring in an urban context can be overcome;
- Develop, test and use a methodology which can be applied to identify best-practice policy instruments for specific districts by evaluating stakeholder’s acceptance of proposed policy instruments and the effects and impacts stakeholders expect for reducing carbon emissions and energy use in buildings in cities at the district level, combining both energy efficiency measures and renewable energy measures;
- Illustrate the development and assessment of innovative local policy instruments that could target the district level for achieving energy renovations and renewable energy systems;
- Provide the necessary background for recommendations to policymakers and their key partners on how they can influence the uptake of cost-effective combinations of energy efficiency measures and renewable energy measures in building renovation at the district level.@en

Lower temperature heating (LTH) involves using the lowest possible supply temperatures to meet residential heating demands, thus supporting the integration of sustainable heating sources and decarbonising the existing residential stock. However, choosing appropriate energy renovation options to prepare existing dwellings for LTH presents decision-making challenges due to the heterogenous dwelling stock with varying building characteristics, numerous renovation options, and various performance indicators for evaluating trade-offs. This study aims to review the scientific literature on integrating LTH into existing dwellings to identify the building characteristics for evaluating the potential of using LTH and the necessity for renovations, presents a systematic method for organising renovation options and summarises key performance indicators. The study employed the SALSA (search, appraisal, synthesis and analysis) framework for systematic review and identified 24 scientific publications. Findings show that dwelling characteristics such as compactness ratio, thermal insulation, thermal bridges, airtightness, ventilation systems, space heating system capacity and supply temperature level are essential for investigating LTH potential and the need for renovations. Most research lacks qualitative renovation criteria and product-level information for selecting renovation options. Key performance indicators related to energy efficiency, thermal comfort and quality-of-services can help indicate the possible solutions, while those related to environmental and economic performance indicate the feasibility of possible solutions. Nevertheless, there is a lack of standard set of criteria for indicating the dwelling's readiness for using LTH. These findings can help address the decision-making challenges of selecting appropriate renovation strategies to enable the use of LTH and contribute to decarbonising the built environment.@en

The guidebook illustrates that the district, as an action level for building renovation, allows for synergies through combinations of energy efficiency measures and measures that promote the use of renewable energy and opportunities for stakeholders to cooperate, compared to an individual building approach. But building renovation at the district level also presents challenges. These include high upfront costs, a long payback time, and risks of not being implemented due to a potential withdrawal of some building owners at different stages. However, the studies also show that often the opportunities are greater than the challenges in district approaches, even if the cost-effectiveness of certain measures may not necessarily be one of these opportunities.
One main conclusion from IEA EBC Annex 75 is that assessments must be carried out for each district renovation project since no "ready-made" or "one size fits all" solutions exist. Still, several techno-economic potentials for district solutions are apparent. Furthermore, the research indicates that the best renovation solutions for a district-level renovation depend on the district's starting situation. The building insulation level, the installed heating/cooling systems, the availability of renewable energy sources and the possibility of integrating renewable energy are determining factors.@en

This study presents an approach to determine the extent of renovation interventions required for existing Dutch dwellings aiming to transition to lower-temperature district heating (DH) systems. The proposed method is applied to a typical intermediate terraced house built before 1945 in the Netherlands, and it consists of two steps: first, assessing the potential of a dwelling to be heated with a lower temperature supply from DH systems and subsequently developing and evaluating alternative renovation solutions if necessary. This study defines a set of criteria for evaluating the readiness of a dwelling for lower-temperature heating (LTH), considering energy efficiency and thermal comfort as non-compensatory criteria. The application of the approach reveals that the case study dwelling is presently unsuitable for a medium-temperature (70/50 °C) and low-temperature (55/35 °C) supply compared to a high-temperature supply (90/70 °C), thus requiring energy renovations. Furthermore, this study indicates that moderate intervention levels are required for the dwelling to be lower-temperature-ready in both supply temperature goals. These interventions include strategies and measures that upgrade the building envelope to the minimum insulation levels stipulated by the Dutch Building Decree, improve airtightness, and replace existing radiators with low-temperature radiators. By systematically narrowing down renovation options, this approach aids in simplifying the decision-making process for selecting renovations for heating dwellings with LTH through DH systems, which could reduce stakeholders’ decision paralysis.@en