Deep Retrofit Research Articles

The co-design of building deep retrofitting in distressed urban areas: lessons from e-SAFE

ABSTRACT This article addresses the realm of co-design in building deep retrofitting in distressed urban areas. Drawing from a pilot experience conducted between 2020 and 2023 in Catania, Italy, as part of the Horizon 2020 project e-SAFE, the authors discuss the scholarly relevance of the lessons learned through a process of engagement of public housing residents in the co-design of their building’s retrofitting. Drawing from both socio-technical and urban planning literature, the paper conceptualises co-design as a process that should provide spaces for shared learning and creativity, on the one side, and negotiability between residents and experts, on the other. In the Catania experience, co-design has encountered several obstacles, especially due to strings attached to the funded grant as well as the unfortunate socio-political conjuncture. While these obstacles made it hard to keep spaces of shared creativity open, it was crucial to at least provide spaces for negotiation, especially over those technological choices having a direct impact on residents’ relational economics. In general, the paper argues the importance of distinguishing between these two dimensions ensuring flexibility, so that even if shared creativity is constrained by circumstances, negotiable spaces can still be provided.

A meta-analysis of the schematic design process of deep retrofit projects

Deep retrofits of the existing building stock will be necessary to meet global emissions reductions targets. One building archetype, low-rise MURBs have been neglected in terms of research and funding for deep retrofits. A meta-analysis was conducted that compares and contrasts the schematic design approach taken for six such buildings in British Columbia which are scheduled to undergo deep retrofits with the goal of reducing GHG emissions by 80%. The analysis showed that design teams had converged toward common solutions for each building while achieving the GHG reduction target. The recommended measures include electrification of space and domestic hot water heating, adding insulation through overcladding, air sealing, ventilators for each unit, and double pane windows. A life cycle cost analysis showed that the economic viability of deep retrofits were dependent on energy price forecasts, capital cost reductions through market forces and transformation, or incentives cover the non-monetizable co-benefits of deep retrofits such as improved resiliency to climate-change or reducing overheating and air quality risks. The meta-analysis can help to streamline the early-stage and schematic design process for such buildings, which is critical to increasing the retrofit rate. This process could be replicated for other building types and construction archetypes.

Reducing the cost of home energy upgrades in the US: An industry survey

Decarbonizing the US residential building stock requires a substantial acceleration in home energy upgrades. Numerous barriers exist to accelerating adoption of efficient and electric building technologies, but foremost among these is high upfront costs. This study uses an industry survey delivered to a sample of home energy professionals to examine promising cost reduction strategies across a range of project types, including HVAC, water heating, and envelope/insulation projects. The survey included quantitative and qualitative questions to collect evidence on the estimated cost reduction potential of these strategies and their likelihood of use in the construction industry. The 167 survey respondents included contractors, energy consultants, architects, manufacturers, and others with experience in delivering energy upgrades in single-family and multifamily buildings in the US. Results show that significant cost reductions are achievable by minimizing additional infrastructure costs (such as replacing electric panels), streamlining project planning/management, and deploying innovations that simplify installation. We find that for a typical deep retrofit project, including heat pumps for space and water heating in addition to envelope upgrades, the strategies could result in a total installed cost reduction of nearly 50 %, dramatically improving the customer economics of such a project. This research makes a novel contribution to the literature on strategies to reduce the costs of residential retrofits. We discuss how our study's insights on the highest-value cost reduction strategies for home energy upgrades can further accelerate their uptake in the US housing stock.

Evaluating the performance of six 1970s off-gas deep retrofit bungalows

This paper presents the energy and environmental performance of whole house energy systems implemented in six 1970s bungalows in South Wales, owned by Swansea Council. The objective was to reduce energy demand and carbon emissions, maximise renewable supply whilst ensuring a comfortable and affordable home for the residents. The whole house energy system for each home involved the installation of a combination of passive and active low carbon solutions. Detailed monitoring was carried out for a year before and for more than 2 years after the work, annual figures have been validated and normalised for weather. Analysis of monitored data confirms that Standard Assessment Performance ratings improved from 12 to 95. The average annual energy consumption across the six bungalows was reduced from 16,117 to 4560 kWh. 2418 kWh was provided by the PV panels and battery, with 1963 kWh of excess electricity that could be sold back to the grid. Real-life average Ground Source Heat Pump CoP was monitored at 3.3. Embodied carbon for retrofitting each house is estimated at 22,980 KgCO2e +/−20%, approximately 5-years carbon payback. Indoor conditions have been improved with internal temperature and relative humidity achieving standards with residents reporting levels of improved comfort satisfaction. Practical Application A whole house energy system demonstrates the benefits of a holistic, fabric and systems retrofit approach. The work informs how gathering data using appropriate methods assists modelling predictions and decisions throughout the retrofit stages. The study demonstrates extensive monitoring as a vital tool to evaluate the performance of the individual components and the whole system within the home, as used by the residents. Performance evaluation is critical in identifying issues, allowing resolutions to be made both immediately on-site as well for longer term, follow on retrofit programmes. Real-life performance evaluation and visualisation methods are transferable across global building industry.

Evaluation of Exterior Insulated Panels for Residential Deep Energy Retrofits

This paper provides an analysis of challenges and available solutions for exterior insulated panels suitable for deep energy retrofits of existing building envelopes. The analysis covers a review of available technologies that provide flexible retrofit insulated panels suitable for multiple climates and building typologies. Moreover, the paper proposes a new design for insulated retrofit panels that account for the majority of identified technical risks including cost, architectural diversity, climate variations, structural concerns, moisture resilience, air sealing, and water sealing. Additionally, the proposed design can be easily installed with minimal disruption to the occupants. A series of parametric and optimization analyses is carried out to identify the optimal design specifications for insulated panels suitable for deep retrofits of existing US housing stocks. The analysis results show that the optimal design criteria for the insulated panels can reduce heating and cooling energy consumption by up to 80% and HVAC capacities by 70%. Moreover, the results indicate that these insulated panels are highly cost effective for retrofitting US housing units located in cold climates.

Lime thermal plasters and energy efficiency in traditional buildings : Ancient materials combined to optimise building performance

Traditional buildings have a central role to play in Europe’s plans to be the first climate-neutral continent by 2050, with the building sector being the single largest energy consumer in the EU with 40 per cent of total energy use. Seventy-five per cent of the existing housing stock is energy inefficient with minute numbers renovated each year. Existing buildings offer huge potential for energy use reduction. Research has shown that a historic retrofit can emit less carbon compared to demolishment and rebuilding. Reductions in carbon emissions of up to 62 per cent were observed across a body of case studies by Historic England, including a 95 per cent reduction in the mews case study described in this paper. Moreover, carefully managed thermal retrofits, taking a ‘whole house approach’, have many benefits, including improved indoor comfort and air quality as well as reduced operational costs. These are factors which are fundamental in ensuring the continued use of historic constructions while improving their standards of preservation and durability. Thermally upgrading traditional building is still a much-debated topic. Inappropriate thermal interventions with unsuitable materials and finishes can have unforeseen consequences, resulting in building damage and a reduction in internal comfort, health and well-being. This paper aims to contribute to this discussion by providing an overview of key considerations when thermally upgrading the walls of traditional buildings while preserving unique characteristics and functionality. Advantages of adopting thermal mortars such as cork lime are put forward, and their potential efficacy is discussed, concluding with a case study focusing on the deep retrofit of a London mews within a conservation area.

Deep Retrofitting Study of Government Buildings in the UAE

This report summarizes the findings of a deep retrofitting modelling study of four government buildings across the UAE. Buildings envelope assessment, HVAC, and electrical systems design, installed conditions, maintenance practices and operation methods, and rigorous engineering analysis has been performed for the four buildings to produce calibrated energy models that confirm a good correlation between actual annual energy consumption and advanced simulated energy modeling results. IES-VE software, ASHRAE Guideline 14, and IPMVP were the basis of the energy model calibration based on actual data. Energy retrofitting options were applied to the calibrated energy models of the four government buildings where advanced computational modeling studies have been utilized to analyze different thermal envelope components and external fabric energy efficiency measures in conjunction with the actual HVAC systems. The results have shown that it may be financially challenging to implement a single envelope retrofitting measure on any of the four buildings due to high payback periods. Nevertheless, when conducting an optimization through a holistic building approach targeting the overall envelope enhancements, the financial modeling results provide significantly improved and provide reduced payback periods of the solutions, making them more attractive to investors. Based on the energy modeling results and the cost of the various proposed building envelope solutions provided by Saint-Gobain, the payback period in all cases varies between 15 to 20 years. However, huge savings in terms of carbon emissions are achieved by implementing the deep retrofitting measures, crucial to achieving carbon neutrality within the UAE built environment. Deep retrofitting is a promising segment of the execution roadmap as part of the UAE's decarbonization journey; even though it is capital-intensive upfront, it has a major impact on long-term operational savings. Moreover, it is often more cost-effective than building new and energy-efficient structures from scratch. The findings indicate that deep retrofitting can be a techno-financially viable solution if it is well-planned during major refurbishment or as part of building maintenance. It has significant potential to reduce carbon emissions while also providing a range of benefits such as operational cost savings, improved thermal comfort a feature which has a direct impact on perceived efficiency and productivity at work, indoor air quality, improved asset value, reputational enhancement, and better choice for environmentally-cautious tenants or buyers.

Comparative cost analysis of traditional and industrialised deep retrofit scenarios for a residential building

In this paper, the economic competitiveness for deep retrofit actions between the industrialised off-site and the traditional on-site approaches are discussed by using a comparative Life Cycle Costing (LCC) analysis. This assessment was based on a deep analysis of all renovation-related cost and timing processes, from design to operation and maintenance phases. The study was based on three retrofit scenarios for an existing building in Italy undergoing a deep renovation. The Life Cycle Inventory (LCI) was developed starting from real costs and a list of bills collected by the design team and the industrialised technologies developers. Afterwards, the LCC modelling was performed for all scenarios. The results show that the two deep retrofit approaches (traditional and industrialised) are comparable in terms of investment costs, even if a gap of around -7% and +16% still exists. This highlights a potential for technological optimisation. Moreover, the operation and maintenance phase has shown to be key to transforming the expected higher quality of the industrialised components into a prolonged life expectance, hence highly impacting the whole cumulated Net Present Value. Finally, the analysis of the End of Life (EoL) phase in case of possible reusing of some dismantled components in the industrialised scenario resulted in contributing in a relevant way to increase the final value of such an approach.

Reviewing the contribution of retrofitting for climate resilience in residential buildings

Purpose Over the years, the significance of retrofitting has gained much attention with the unveiling of its different applications, such as energy retrofit and deep retrofit, to enhance the climate-resilience of buildings. However, no single study comprehensively assesses the climate-resilience of retrofitting. The purpose of this study is to address this gap via a systematic literature review. Design/methodology/approach Quality journal studies were selected using the PRISMA method and analysed manually and using scientometrics. Three dimensions of climate-resilience, such as robustness, withstanding and recovery, were used to evaluate the contribution of retrofit measures for achieving climate-resilient houses across four climate zones: tropical, arid, temperate and cold. Findings Most passive measures can enhance the robustness of residential buildings but cannot verify for withstanding against immediate shocks and timely recovery. However, some passive measures, such as night-time ventilation, show excellent performance over all four climate zones. Active measures such as heating, ventilation and air conditioning and mechanical ventilation with heat recovery, can ensure climate-resilience in all three dimensions in the short-term but contribute to greenhouse gas emissions, further exacerbating the long-term climate. Integrating renewable energy sources can defeat this issue. Thus, all three retrofit strategies should appropriately be adopted together to achieve climate-resilient houses. Research limitations/implications Since the research is limited to secondary data, retrofit measures recommended in this research should be further investigated before application. Originality/value This review contributes to the knowledge domain of retrofitting by assessing the contribution of different retrofit measures to climate-resilience.

Technical and economic assessment of a hybrid heat pump system as an energy retrofit measure in a residential building

Air to water electric heat pumps are one technological solution to achieve energy defossilisation goals for heating of residential building stock. Nevertheless, they may not necessarily be the only solution for all residential building stock. A case in point is where extensive fabric refurbishment is impracticable or where electric heat pumps are installed where low ambient temperatures prevail and/or high water delivery temperatures must be utilised. For such instances, hybrid (gas and electric) heat pumps offer an alternative option by facilitating fuel source switching between electricity and gas, when ambient temperatures are low or high water supply temperatures are required. In the current study, the effectiveness of an air-to-water electric heat pump and hybrid heat pump are examined for different building retrofit scenarios for a residential dwelling located in Ireland. This is achieved by means of a sensitivity study of a validated building simulation model, incorporating both heat pump systems, subject to different building retrofit scenarios. Relative to a conventional oil-fired boiler, for a deep building retrofit scenario, the hybrid and electric heat pumps achieve primary energy savings of 73% and 70%, respectively. For a minimal building retrofit scenario, the respective primary energy savings are 57% and 52%. For the deep retrofit scenario, compared to the baseline building with no retrofit measures, the carbon footprint reductions were found to be (8.5 gCO2e/m2/year or 44%) for the hybrid heat pump, (10.31 gCO2e/m2/year or 45%) for the electric heat pump, and (17-21 gCO2e/m2/year or 43-53%) for oil or gas boiler systems. Finally, the deployment of either an electric heat pump or hybrid heat pump for deep building fabric retrofit achieves approximately half heating system capital cost return within 20 years.

The effectiveness of building retrofits under a subsidy scheme: Empirical evidence from Switzerland

While retrofitting buildings is one of the key elements of reaching climate and energy goals, it is burdened by insufficient speed and depth. Governments have attempted to accelerate deep retrofits via subsidies, but scant evidence exists on these policies’ effectiveness. In this study, we investigate the effectiveness of retrofitting subsidies by using a range of econometric techniques and a unique dataset of over 400 Swiss buildings with 19,000 observations over 11 years. Specifically, we analyze whether retrofits reduce energy consumption, whether subsidized retrofits lead to deeper retrofits than non-subsidized retrofits, and we differentiate the impact by subsidy amount. We find that retrofits reduce average energy use by 10–20%, that the achieved savings through subsidized and non-subsidized retrofits do not differ significantly, and that the subsidy amount is correlated to a reduction in energy use by 0.42 CHF per kWh over a period of 20 years. Our study highlights the importance of policies that enhance retrofit depth, the need to further investigate the causes of the wide variation in retrofitting results, and to consider effectiveness studies within the policy design.

Exploitation of Mediterranean Cooperation Projects’ Tools for the Development of Public Buildings’ Energy Efficiency Plans at Local Level: A Case Study in Greece

Ever since European Directive 2012/27/EU, particular attention has been focused on the improvement of the energy efficiency of the public building stock. According to the directive, local public authorities, regions and municipalities, are expected to develop and implement energy efficiency retrofitting plans for their public building stocks. While conducting such plans, important challenges are raised mainly related to data collection and the manipulation of key performance indicators (KPIs) for many buildings. The present paper deals with the aforementioned challenges through (a) the evaluation of freely available tools developed in the framework of Mediterranean territorial cooperation projects, with respect to the main pillars of energy efficiency planning, and (b) the introduction of a stepwise methodology using selected tools toward a reliable energy efficiency plan extending from the classification of the building stock to the prioritization of projects in terms of a gradual renovation plan based on energy and cost criteria. The methodology is applied for a case study in Greece, which refers to 10 public buildings of the Municipality of Aigialeia in Greece. A reliable renovation plan is developed, taking into account the municipal authority’s directions in a specialized decision-making scheme. It is concluded that the suggested methodology is very practical for planning purposes, while for the case studied, a 6-year gradual renovation plan is emerged until a deep retrofit of all buildings, associated with an estimated primary energy saving and CO2 emissions avoidance of more than 1850 MWh and 400 tns, respectively, with a total investment of about EUR 3 million.

A French Residential Retrofit toward Achieving Net-Zero Energy Target in a Mediterranean Climate

Cities are paying more attention to building energy use and carbon footprint for attaining sustainability. Within this building sector, there is a growing attention toward development and adoption of energy efficient retrofit strategies. Plagued by the lack of efforts in achieving comprehensive energy efficient retrofit solution sets (passive, active, and renewable energy systems), the authors acknowledge the concept of NZEB toward achieving energy efficiency by 2050. Toward this end, a numerical energy simulation modeling is carried out to retrofit an existing French “Puccini house” using ‘passive, energy efficient building systems and renewable energy’ strategies toward an NZEB target in the Mediterranean climate of Nice. Using Design builder 7.0, the simulated baseline energy model (Case A) is retrofitted through variations in the proposed energy efficient retrofit measures using two case scenarios (Case B: passive retrofit; Case C: energy-efficient building) to achieve NZEB (Case D). Assessing the performance of energy efficient retrofits using % energy reduction, the implementation of a high-performance building envelope is achieved using a thermally insulated external wall (46.82%), upgraded airtightness (20.39%), thermally insulated pitched roof component (33.03%), and high-performance window type—a glazing system (3.35%) with maximized window-to-wall ratio (5.53%). The maximum energy-saving retrofit solutions provide an ambitious reduction in energy consumption by approximately 90% from the baseline. A deep retrofitting of the French house meets the NZEB targets, as it reduces the baseline energy consumption from 194.37 kWh/m2/year to 23.98 kWh/m2/year using both passive and active strategies. The remaining energy demand is met by the integration of on-site PV panels (EUI= −27.71 kWh/m2/year), which achieve an increase in energy production by 15.5%, while returning energy back to the grid (−3.73 kWh/m2/year). Findings of this study serve as a guideline for retrofitting traditional French single-family residences, while contributing toward the NZEB goal.

Decarbonization of district heating and deep retrofits of buildings as competing or synergetic strategies for the implementation of the efficiency first principle

This paper discusses the compatibility of district heating (DH) networks with deep retrofits of buildings under various European climate conditions and city typologies. The study analyses five cities with different DH market shares, climate zones, population densities, and transferability potentials. First, we have forecasted population, heated floor area, and share of floor area per construction period until 2050, and then calculated three different heat demand scenarios for varying building refurbishment rates of 1%, 2%, and 3% of the total floor area. Second, future suitable DH regions with min 25 GWh/km2 networks were identified. By applying a bottom-up GIS model, based on the type of city area, number of buildings, street length, and heat density, the DH distribution capital and operation costs were calculated. Lastly, to compare the total cost of heat supply for each scenario, the cost of individual heat per building type was calculated.The results show that even in the scenarios with high refurbishment rates of 3%, high percentage of the built-up areas, between 23% and 68% depending on the city typology, are suitable for DH supply in 2050. The share of DH from the total heat supply varies between 49% and 83%. An increase of the DH price between 14% and 35%, depending on the scenario and case study can be expected due to the reduced heat densities compared to the current ones. Nevertheless, maximizing the DH connection rates in the identified regions leads to lower total cost of heat in almost all the analysed case studies.

Αn integrated life cycle assessment and life cycle costing approach towards sustainable building renovation via a dynamic online tool

Building stock retrofitting is essential to achieve the ambitious sustainability goals of the building sector due to its high energy consumption rates. The evaluation of the various building interventions shall be holistically assessed in terms of environmental and costing impact. The aim of this paper is twofold: First, it presents the innovative characteristics of a developed online tool (Virtual intEgrated platfoRm on LIfe cycle AnalYsis - VERIFY) able to perform dynamic life cycle analysis and global warming impact assessments by capitalizing on the well-known LCA and LCC methodologies, applicable in the case of building renovation. VERIFY is able to analyse dynamic life cycle inventories that consider the temporal profiles of energy consumption, and the time-dependent temperature changes, while being also interoperable in terms of exchanging data with other available energy simulation engines, or even using real-time monitoring data from sensors, processing any data time granulation. Second, the paper evaluates, from a life cycle perspective, the impact of specific energy retrofitting measures, meeting the Passive House Standard, for the case of a multi-family residential building in Athens, Greece. The proposed energy-retrofitting scenario examines actions related to the deep retrofitting of the building envelope and the upgrade of the thermal components as well as to the incorporation of clean electricity generation based on renewable energy systems; all aiming to drastically reduce the environmental impact of the building, rendering it almost near zero energy. Through the planned infrastructure installations, the primary energy needs and CO2eq emissions were reduced by 91 % and by 95 % respectively, while for a building operational lifespan of 25 years, savings up to 515 k€ compared to the baseline scenario, can be achieved.

A Policy Roadmap for the Energy Renovation of the Residential and Educational Building Stock in Italy

The building sector is crucial in all of the possible net zero scenarios suggested for the European Union. In this area, the Italian situation is exemplary. Italy suffers from an aging and low-performance building stock and needs to increase its annual rate of energy retrofits in order to achieve its 2030 and 2050 targets. Even though since at least 2007, several different incentives schemes intended to stimulate energy-efficiency interventions have been in place, Italy has not been sufficiently able to promote deep retrofits. In 2020, in order to help the economy recover after the lockdowns that were introduced to face the first phase of the COVID-19 pandemic, the existing incentives were increased to up to 110% of investments for interventions that improved the energy class by at least two grades. This so-called “Superbonus” was also extended to the public social housing sector thanks to a credit assignment scheme. Given the results of this provisional phase, a possible policy roadmap for the energy renovation of the residential and educational building stock in Italy is presented in this paper through an analysis of data related to the implementation of current instruments in terms of number of interventions, investment needed, energy savings and evaluation of potential benefits and costs that can derive from an increase in the current deep-renovation rate. Through definition of a long-term renovation strategy, this paper illustrates how market barriers and other issues in instrument design can be tackled and how policymakers can help to develop a sustainable long-term roadmap for energy-efficient buildings. Beyond the residential sector, public buildings, particularly educational buildings, are taken into consideration as well, as they are places of collective use that represent the social values of fairness and sustainability and can therefore have an exemplary role for private initiatives.

Transformation and acceleration of the construction supply chain through smart factories

The European building stock is in high need of refurbishment due to its contribution to excessive global energy consumption. In the North-Sea Region (NSR) alone there are 22 million houses built between 1950 and 1985 with an annual CO2 emission of 79 Mton. Current deep retrofits are carried out on a limited-scale production, which may result in climate targets not being met in time. To tackle the need for rapid renovations, prefabricated insulation elements with integrated intelligent technologies, manufactured in novel smart factories using mass customization, could offer a solution. This approach is also followed by the Interreg project INDU-ZERO. The project examines a far-reaching automated production and develops a blueprint for a smart construction factory in the NSR that can produce 15 000 renovation packages per year. This paper aims to quantify the acceleration potential of the supply chain by improving its production, logistics, and on-site mounting processes for Dutch single-family terraced houses. First, the design of the renovation packages and smart construction factories are introduced. Then, the procedure is elaborated on how the supply chain can be abbreviated. The results show that the renovation cycle time can be completed within two weeks through coordinated efforts between production, logistics, and mounting.

Socio-economic impacts of large-scale deep energy retrofits in Finnish apartment buildings

Energy use in buildings is a major source of carbon dioxide (CO2) emissions in Europe. Energy use is a major expense for building owners, but also a source of tax revenue for the government. Deep energy retrofitting of buildings can significantly reduce the energy consumption and CO2 emissions of buildings. However, the environmental benefits are linked to the CO2 emissions of the national energy grid. Deep retrofits have a significant cost and are not always cost-effective for building owners. On the other hand, they require a lot of investments and labor, which provides employment for citizens and tax revenue for governments. This study examines the environmental and economic impacts of large-scale deep energy retrofitting in the Finnish apartment building stock continuing until 2050. Low and high impact retrofit configurations were obtained from a previous study, which utilized simulation-based multi-objective optimization to find cost-effective solutions. Four archetypes of apartment buildings from time periods of different building codes were used to form the building stock. A building stock model based on Finnish statistics was used to estimate the future changes in the building stock. The study combines optimized energy retrofitting configurations and the building stock model to estimate the energy consumption development in the building stock undergoing large-scale retrofitting. Three retrofitting timelines were tested to show the effect of immediate and delayed retrofitting action. Then, a new socio-economic model was used to calculate the impact of energy retrofitting on the CO2 emissions, life cycle cost, tax revenue, employment and foreign fossil fuel imports. The effect of energy grid decarbonization and long-term scheduling of the retrofits were also examined. The results show that by 2050, the CO2 emissions of the building stock were reduced by 12–30% compared to the reference scenario with energy grid decarbonization, but no building energy retrofitting. A million euros invested into retrofitting created 15–17 jobs. Economic viability for the building owners was inversely correlated with the changes in tax revenues for the government. Cost-effective retrofitting reduced energy-based tax revenues more than it created new tax revenues through direct employment, thus providing a funding challenge for governments desiring to advance building retrofitting. However, more money would be left in the local economy due to reduced fossil fuel imports, but induced economic effects were not analyzed in this study.

Retrofitting Buildings into Thermal Batteries for Demand-Side Flexibility and Thermal Safety during Power Outages in Winter

Decarbonizing heating in buildings is a key part of climate change mitigation policies, but deep retrofit is progressing slowly, e.g., at a pace of 0.2%/y of the building stock in Europe. By means of tests in two flats of a multiapartment housing complex recently renovated to very low values of energy needs, this paper explores the role of deep retrofitted buildings in providing energy flexibility services for the occupants/owners/managers and for the energy system. Key to this flexibility increase and capacity savings is the large reduction of energy needs for heating via a high level of external insulation, which allows the thermal capacity of the building mass to act as an energy storage, without the large energy losses presently affecting a large part of the building stock. Due to the limited number of case studies reporting experimental applications in real buildings, this research aims to offer an analysis based on a series of tests and detailed monitoring which show a significant increase in the time interval during which the low-energy-needs building remains in the comfort range, compared to a high-energy-needs building, when active delivery of energy is deactivated during the heating season. Intermittent renewable energy might hence be stored when available, thus enhancing the ability of the energy system to manage inherent variability of some renewable energy sources and/or increasing the share of the self-consumption of locally generated RES energy. Besides, two unplanned heating power outages which have involved the entire building complex allowed us to verify that deep retrofitted buildings are able to maintain thermally safe indoor conditions under extreme events, such as a power outage, for at least 5 days.

Energy-saving potential of deeply retrofitting building enclosures of traditional courtyard houses – A case study in the Chinese Hot-Summer-Cold-Winter zone

It is increasingly believed that energy retrofits are a protection tool to preserve cultural heritage for future generations. However, few studies are available regarding the deep retrofits of traditional courtyard houses in the Chinese Hot-Summer-Cold-Winter zone, although the winter conditions in these buildings are very uncomfortable based on existing studies. Besides, few studies analyzed the actual energy performance of still-occupied traditional buildings in this region. Therefore, this study investigated the energy-saving potential of deeply retrofitting the building enclosures of a traditional courtyard house in Tongren in southern China. The investigation was based on calibrated hygrothermal simulation with WUFI®Plus applying the multi-zone airflow modeling. For the calibration, short-term monitoring (two weeks) was conducted in winter and measured the air temperature, relative humidity, and heating energy consumption. The calibration showed satisfactory results by assessing the Normalized-Mean-Bias-Error, the Coefficient of Variation of Root-Mean-Square Error, and the Coefficient of determination. In contrast, the application of Goodness of Fit shows poorer performance and requires further discussion for short monitoring periods. According to this study, improving the U-values of building envelopes to meet at least the current Chinese energy-efficiency standard can reduce more than 56% energy demand for heating and cooling, with an estimated payback time of 2.5 years for the material cost. With growing expectations of building occupants on indoor thermal comfort, the improvement of the energy performance of traditional buildings will become more critical for their long-term preservation and should be implemented in China's energy efficiency policies and initiatives in the future.