Energy Retrofit Research Articles

Aesthetic appealing wall insulation: A novel approach for uptake of solid wall insulation in the UK

Solid wall dwellings in the UK are in urgent need for energy retrofit to support achieving the UK net-zero strategies in the building sector and reduce fuel poverty. Several barriers are a cause of uncertainty for householders about Solid Wall 1nsulation (SWI) and slow down the progress. This paper aims to examine people's perceptions of possible inclusion of aesthetics elements in Internal Wall Insulation (IWI), providing a suitable solution to promote wall insulation intake and attractiveness. To achieve this aim, first, the current literature is critically reviewed and analysed to highlight the gap between energy studies and design/aesthetic features of SWI retrofit. Then, an online survey is conducted, and the collected data are analysed. The results show that the aesthetic factor is very important for participants with more than 90% agreement. This level of agreement is as high as other well-known critical factors in renovation such as cost and energy saving. Also, aesthetic integration in IWI can surpasses negative concerns such as the retrofit cost or losing internal space. Furthermore, over 2/3rd of participants are in agreement with a suggested business model for delivering both aesthetic and energy improvement in combined retrofit plans by established approved organizations. It is concluded that aesthetic inclusion is the priority and an encouraging factor in the internal renovation to reduce the barriers and increase success. Finally, the findings from this research pointed to how the retrofit industry, policymakers, and designers should evolve to achieve the benefits of aesthetics in SWI.

Addressing housing shortage through energy and space-efficient retrofitting: The case study of a Swedish Single-Family house

Sweden's shortage of affordable housing has been evolving into a major in recent years. A 2021 report by the Swedish National Board of Housing, Building, and Planning (Boverket) stated a need for 60,000 new homes by 2030. In addition, the Swedish building stock is responsible for 39% of the country's total energy consumption and 21% of its greenhouse gas emissions. Therefore, solutions to address the housing crisis should go hand in hand with the need for increased building retrofits to meet Sweden's 2045 energy and climate targets. In this context, re-densification of the existing building stock is a possible option. This study examines possible space- and energy-efficient options for densifying the housing supply in Sweden's existing single-family home (SFH) segment. Using a case study in Kronoberg, Sweden, occupied by an elderly household, options for converting the unused space into new additional dwelling units (ADUs) and reducing per capita living space are explored. Most SFHs in Sweden are old, in poor condition, and in urgent need of structural and energy retrofits. In addition, about one- third of homeowners are over 60 years old and report living in homes that are too large compared to their needs - an excellent environment to study the proposed intervention. Revenues from renting the newly created ADUs suggest that the proposal is financially attractive because it capitalizes on the high initial investment costs of energy retrofits. In addition, spatial interventions combined with energy-efficient measures result in a 40 percent lower energy use and environmental impact per capita compared to energy retrofits alone due to a reduction in per capita living space. Finally, the study aims to initiate a discussion on sufficiency, innovative energy regulations, and housing policy tools needed to transition to the low-energy single-family housing stock.

Energy efficiency at what cost? Unjust burden-sharing of rent increases in extensive energy retrofitting projects in Sweden

Although renovation costs can lead to rent increases in energy retrofitting, it is often assumed that reductions in energy costs will counterbalance the rent increase. In Swedish multifamily housing, energy costs for heating are however generally included as a fixed component in the monthly rent, meaning that the rent increase after energy retrofitting corresponds to the net change in rent level as well as energy costs for heating. This makes Sweden a methodologically advantageous setting for studying tenants' cost burden of energy retrofitting. The aim of this study was thus to investigate how energy performance improvement has affected rent increases in Swedish renovation projects between 2013 and 2019. Utilising a national database of multifamily housing, it was found that energy retrofitting entailed a cost relief for tenants in renovation projects with smaller investments. However, in renovation projects with larger investments, energy retrofitting entailed a cost burden for tenants. Moreover, public housing companies had conducted a high share of the extensive energy retrofits, leading to low-income tenant groups being disproportionately subjected to cost burdens of energy retrofitting. On the contrary, light energy retrofits with a cost relief for energy efficiency had been rather evenly distributed across income groups. These results indicate ongoing conflicts with the ability-to-pay principle in the energy transition of Swedish multifamily housing, and suggest that if low-investment energy retrofits are not sufficient for upcoming objectives and requirements, subsidies could be needed to compensate low-income tenants for the cost burden of extensive energy retrofitting.

Municipal governance and energy retrofitting of owner-occupied homes in the Netherlands

The building sector is responsible for more than one-third of global greenhouse gas (GHG) emissions. The Netherlands has set an ambitious target to reduce GHG emissions by 95% by 2050 compared to the 1990 baseline. Several factors, such as low retrofitting rates, lead to uncertainties in achieving these targets. In the residential sector, the energy retrofit rate of the owner-occupied homes is low. Homeowners encounter different types of barriers when deciding to make energy retrofits. The purpose of this study is to explore the policy implications of the main identified influencing factors and consequently the potential mismatch between current policy and the homeowners’ actual needs. We used semi-structured interviews and focus group meetings with experts from the largest cities in the Netherlands as the data collection methods. We identified the discrepancy between current policy and the actual needs of homeowners as follows: (a) less attention to the right message and the right messenger: policymakers cannot motivate the households using the word sustainability. Policymakers can convince homeowners to make energy retrofits through the improvement in quality of life, the expected cost savings, and the integration of energy retrofits into the maintenance of the home (message effect). Moreover, the trustworthiness and familiarity of the energy ambassador with the households are the main characteristics of these ambassadors (messenger effect). (b) the lack of integrated financial, informational and technical support: the main identified transaction cost barriers (non-monetary costs) are difficulties to inspire homeowners to carry out energy retrofits, lack of knowledge on how to start the energy retrofits, many steps in carrying out energy retrofits of old houses. More importantly, there is a lack of an active and accessible party in the market to reduce the financial, technical and informational barriers.

Existing tools enabling the implementation of EN 16883:2017 Standard to integrate conservation-compatible retrofit solutions in historic buildings

• Review of computer-based decisional tools for conservation-compatible energy retrofit. • Collaborative information-search methodology. • Three levels of action (single building component, whole building, district level). • Analysis of tools’ structure, aim, limitations and link to EN16883 procedure. • Overview of potential future developments of the tools to enable the use of EN16883. The heterogeneity of historic buildings and environmental conditions, as well as the variety of possible technical solutions, introduce great challenges to the decision-making process for the definition and implementation of energy retrofit projects. The variety of stakeholders involved in the process, each bringing specific skills and goals, further add to this complexity. How can the decision be finalised when multiple and often conflicting objectives and different stakeholders are involved? In this context, the European Standard EN 16883:2017 provides guidelines to improve the energy performance of historic buildings while respecting their heritage significance. It presents a normative working procedure to select conservation-compatible retrofit solutions, which is based on a step-by-step investigation, analysis and documentation of the building. However, the recommendations provided in the Standard remain at a general level and it is the task for the stakeholders to tailor the intervention to the specific case. This paper investigates how the implementation of the EN 16883:2017 can be enabled by adopting a selection of existing computer-based tools to support the identification, assessment, and selection of retrofit solutions in historic buildings. To this end, a number of tools were analysed, highlighting their advantages, input data, outcomes and main limitations, in relation to their possible use in support of the implementation of the Standard procedure (or steps of it).

Digital Twin solutions to historical building stock maintenance cycles

The purpose of this work is to provide a framework for the vulnerability of traditional historical buildings. Buildings that are not constrained and do not have a design obligation for minor energy retrofit interventions. The digitization of the construction sector can help to design interventions with Digital Twin methodologies that can be integrated into a single document that collects them as the Digital Building Logbook. We propose a definition of an innovative workflow that defines integrations and technological innovations in the historical building stock. In this work are presented operational proposals to ensure and increase the protection and conservation of the Italian historical building stock, trying to strengthen the activities of designers and companies for the reduction of seismic vulnerability in case of maintenance or energy retrofit.

Analytical approach for energy retrofit of waste gas-to-energy units

• Energy demand of waste gas-to-energy (WGtE) units can be significantly reduced by performing the Energy Retrofit (ER). • A new tailor-made analytical method for the ER of the WGtE units is proposed. • The suggested procedure does not require the use of any simulation and optimization tools. • Supporting graphical tool, called the Heat Recovery Shifting Diagram, promotes the useŕs interactivity. • The accuracy of the proposed method is verified by comparing its results to the non-linear simulation of two case studies. Thermal oxidation represents an efficient and reliable technology for processing industrial waste gases containing combustible pollutants, for example, Volatile Organic Compounds. Thermal oxidation units (or waste gas-to-energy units) enable the heat utilization of the waste gases, which thus become a promising energy source. This is, however, very energy-intensive process requiring a huge amount of primary fuel, which is dependent on the heat recovery efficiency. This paper presents a straightforward and fairly accurate graphic-numerical method for the Energy Retrofit of waste gas-to-energy units, which doesńt require any advanced computational approach. There are provided tailor-made formulas for estimation of maximum reachable fuel savings and tools for the design of specific technological modifications, which results in the increase of the heat recovery efficiency, energy demand reduction, operational costs savings and environmental pollution mitigation, while the unit́s operational safety is also considered. The method is further applied to the Energy Retrofit of a standard industrial unit and a modern compact unit for thermal processing of waste gases. Finally, the developed method́s accuracy was successfully verified by the comparison with non-linear simulation of both studied industrial units.

Does energy retrofitting pay off? An analysis of German multifamily building data

Several studies have investigated the relationship between the energy performance of buildings and housing prices. First, this paper identifies a price premium for energy efficiency within the German rental market. Then, the generated price differences and associated marginal benefits are compared to the marginal costs of energy retrofits. An extensive database of Germany’s largest online platform for housing over a time span from 2016 to 2020 is used in a hedonic regression approach. Additionally, to extract the marginal costs of energy consumption abatement, a dataset of 1.048 rental units regarding green-retrofit measures is utilized. While a significant green premium is identified in the rental market, the findings suggest that it is not high enough to compensate landlords for the money they have to spend to retrofit. The marginal costs exceed the marginal benefits by far. Furthermore, it is found that the German government’s recent plans to split the CO2 tax between landlords and tenants does not change this because the price per metric ton of carbon is insufficiently high. The findings can help both tenants and landlords in their decision-making, as well as policy makers in the implementation of decarbonization efforts.

Hygrothermal characterization of bio-based thermal insulation made of fibres from invasive alien lake plants bounded with mycelium

The European program ‘Renovation Wave’ aims to fasten the energy retrofit of the building stock by increasing by a factor 4 the current renovation rate. Mycelium-based materials gained momentum as insulation solutions in recent years due to their 100% biological composition. However, their durability issues, particularly the risk of fast decay due to high moisture content, need to be investigated to promote a safe use in construction. Two bio-composites were set up at a lab scale, a combination of hemp shives and mycelium and a novel mixture based on the combination of mycelium binder and fibres from a lake plant, Lagarosiphon major, an alien invasive species locally available in many EU internal waters. Samples with different dimensions were used to characterize through experimental tests the thermal conductivity, water absorption (capillarity) and vapor permeability. The results show that these mycelium-based composites present both hydric and thermal properties similar to other bio-based material used in construction. The capillarity tests highlighted that hemp composites absorb more water than lake plant ones. The thermal conductivity is similar for both biocomposites, i.e., around 0.05 W/m.K, while the moisture buffer position both analysed biocomposites in “WS 3” according to the German classification DIN 18947 for water regulators.

Trends in the cost-benefit analysis of energy efficiency measures as part of the renovation wave

The goal of sustainable development within planetary boundaries poses new challenges to the actors of the real estate industry. One task is to improve the energy performance of existing buildings by deep energy retrofit measures. The aim is not only to conserve resources and reduce emissions, but also to ensure that buildings can be rented out and marketed, and that a loss of value is avoided. In addition to technical issues and aspects of dealing with existing building fabric, questions of assessing their economic viability play a role in the selection of suitable measures. Against the background of a project in Germany to develop a methodological convention, this paper introduces basics for cost-benefit analyses of energy efficiency measures. Furthermore, the following questions will be discussed: (1) How can the introduction of carbon pricing conventions be aligned with external climate and environmental costs? (2) How can be dealt with non-monetary factors in investment appraisals? (3) How can typical perspectives of actors be classified and what are the consequences for the necessary adjustment of appraisal methods? (4) How can the general trend towards greater consideration of uncertainties be taken into account? Possible solutions are discussed and recommendations for action are presented.

Hotel Adapted to the Requirements of an nZEB Building—Thermal Energy Performance and Assessment of Energy Retrofit Plan

Recently, emissions and the energy use of the building and construction sector globally increased. Therefore, energy retrofit processes and reducing the energy consumption of buildings are increasingly often discussed by the academic community, industry, and end-users. The application of high-performance technologies and highly insulating materials results in a low energy demand in newly constructed buildings. A crucial challenge is to reduce energy consumption in existing buildings. The article presents an energy analysis of the reconstruction of a historic building adapted to hotel functionality. Based on the available information on the design of the facility, and the annual demand for cooling and heating energy, simulations of the energy performance were carried out. The proposals to exchange the heat source and replace the existing systems were simulated and assessed. Three different retrofit options were analyzed, including the replacement of the air handling unit (variant 1—v1), bathroom fixtures (v2), and, in the last scenario analyzed (v3), the above-mentioned activities and the usage of tri-generation units. As the results show, such solutions allow for the reduction in final energy consumption of 20%, to 73% regarding the baseline variant.

Aerogel composite for cavity wall rehabilitation in the Netherlands: Material characterization and thermal comfort assessment

Energy retrofitting of existing building stocks is essential to reduce building-related energy consumption. Cavity wall insulations are commonly applied, however, their hygrothermal performance is not well established. This study focuses on the hygrothermal performance of rehabilitated cavity walls in the Netherlands. A state-of-the-art aerogel composite developed for cavity wall retrofitting using the blown-in method is presented. The aerogel composite has a dry thermal conductivity of 22.5 mW⋅m−1⋅K−1 and low sorption isotherms. A retrofitted masonry wall with a 6 cm cavity using the aerogel composite can achieve thermal transmittance (U-value) of 0.32 W⋅m−2⋅K−1, well below the 0.71 W⋅m−2⋅K−1 required in the Netherlands. It can reduce the annual heating and cooling demand by up to 72% in a simulated building, and also provides better thermal comfort to the occupants, lowering the percentage of thermally dissatisfied occupants from 51% to 18%. The tested aerogel composite outperforms conventional insulation materials in the market, without sacrificing the thermal comfort of its occupants.

An energy retrofit roadmap to net-zero energy and carbon footprint for single-family houses in Canada

Building decarbonization initiatives have gained momentum in recent years as many cities and governments are establishing net-zero emission targets. Although many municipalities have already introduced energy requirements and metrics to promote new high performing and net zero constructions, decarbonization of existing residential buildings suffers from a lack of a clear roadmap. This study establishes a comprehensive roadmap for decarbonization and electrification of typical existing single-family houses in Canada in two different climate zones. A typical single-family dwelling-with two floors and a basement was energetically modeled and the results were validated versus utility bills. Afterwards, a range of energy conservation scenarios and measures were applied to the case study building using an individual and cumulative approach, with an analysis of the energy use and carbon footprint reductions. The results indicated that when a phased approach for the retrofits is considered, an approximate investment of 40,000 CAD could result in 78% energy saving and 96% emissions reduction in an existing residential building in Ontario. For Vancouver, the energy and emission savings are reported as 85% and 100%. The results were further investigated using a sensitivity analysis considering future scenarios for grid emissions and carbon costs. Finally, an embodied carbon inventory analysis was conducted showing that, in particular, the positive impacts of adding exterior wall insulation dominantly sways the negative impact of its carbon footprint from material production. The study concludes by highlighting the key findings and presenting a number of avenues for future research.

Deep energy retrofits: How effective and robust are policy instruments?

Motivating landlords to deep energy retrofits is challenging, particularly if only tenants benefit from energy savings. We introduce the concept of net-benefit curves to quantify how the reduction in CO2 emissions on the macro level and the economic viability-based retrofit decision on the micro level are connected, and how climate policy instruments influence this connection. Applying this method to a typical multi-unit dwelling, we derive the parameter levels at which different policy instruments start to show an effect on the building owner’s decision to retrofit. The shape of the net-benefit curve suggests a tipping-point effect, where a slight change in policy parameters will lead from no retrofit at all to substantial retrofitting. Further policy tightening will not lead to a significant further effort, but make the retrofit decision more robust, that is, narrow the range of economically attractive retrofits. As policy instruments, we analyze prototypical systems that share energy savings, retrofit costs, or carbon taxes between landlord and tenants.

The influence and adjust method of hyperparameters’ prior distributions in Bayesian calibration for building stock energy prediction

Energy consumption in the building sector accounts for more than 30% of total energy consumption, therefore the calculation and prediction of energy consumption of building stock is crucial for urban energy planning. One of the representative models for building stock energy consumption predicting is Bayesian Calibration. It adjusts the distribution of building stock thermal parameters to match the energy consumption output of the model with the actual energy consumption. But previous research ignored the matchiness between the calibrated distribution of thermal parameters and the actual situation, which lead to large deviations when apply this model to the pre-evaluation of the energy retrofit. This study analyzed and proposed a method to adjust the hyperparameter prior distribution in the Bayesian calibration to improve the matching of uncertainty parameters’ distribution with the actual situation in the prediction model. The results show that the hyperparameter prior distribution has significant influence on the performance of Bayesian calibration, not only for prediction accuracy of the building stock energy consumption, but also for the identification accuracy of uncertain parameters’ distribution. the proposed method of adjusting the hyperparameter prior distribution can significantly improve the energy consumption prediction performance and obtain a posterior distribution of the parameters which is closer to the actual distribution than the original model, and it can provide more accurate prediction of energy consumption after reginal energy retrofit.

Coupling of the electricity and district heat generation sectors with building stock energy retrofits as a measure to reduce carbon emissions

This study examined how the carbon dioxide emissions can be reduced in an energy system with coupling of the electricity and district heat generations, while considering different paths for the building stock development. As the building sector and the energy sector are interdependent on one another, it is important to consider them as a whole, to understand to what extent emission mitigation measures should be conducted in each of them, to avoid unnecessary costs. The problem was applied to a Finnish context and formed as a mixed-integer linear programming problem, which was used to minimize the emissions from highly renewable electricity and district heat generations, by using the flexible properties in both. A scenario-based analysis was performed, where simulations were conducted for the year 2050 and the effects to the emissions and energy system costs were examined over 30 years up to 2050. The set target of 90 % emission reductions in annual emissions, from the 2020 level, was attained with several combinations of wind power, deep heat well heat pumps, and thermal storage as part of the energy generation, for each of the energy retrofit scenarios of the building stock. However, both the building stock and energy system measures were required to reach the target. The amount of wind power had a major impact on the results, and in general the more wind power was utilized the less the other measures were required. Moreover, when the building stock was retrofitted to a lower environmental impact level, the costs to reach the target emissions were less than half compared to retrofitting them to a higher impact level. However, there was no major difference whether the building stock developed more towards household heat pumps or district heating. The least costly set of options to reach the target emissions for 2050, 1.83 Mt of carbon dioxide annually, attained them with a cost increase of 10.18 billion euros from the reference over 30 years. The emissions for the same period decreased by 56 %, from 488 to 217 Mt of carbon dioxide, resulting in a unit cost of 37.6 € per ton of carbon dioxide for the emission reductions.

Integrated retrofit solutions for improving the energy performance of historic buildings through energy technology suitability analyses: Retrofit plan of wooden truss and masonry composite structure in Korea in the 1920s

Building energy consumption and carbon emissions must be reduced to decrease the rate of global warming. To improve the energy efficiency of historic buildings, energy retrofitting can serve as an effective strategy. Retrofitting historic buildings is difficult due to the conflict between the historical value and usefulness of the building, but a modern scientific approach can help ensure that valuable historical records and artifacts remain protected and available. In addition, the retrofit of historic buildings can contribute, although a small part, to reducing carbon emissions nationally, and can have a symbolic meaning as a combination of history and modernity.This paper proposes a package of appropriate measures to improve energy efficiency, reduce the energy consumption of buildings, and preserve regularly used historic buildings for 100-year-old wooden truss and masonry composite structured historic buildings in Korea. The proposed measures are applied to most historic buildings in Korea built in the 1920s and have the potential to improve building performance. A new approach to applying energy technology to historic buildings is proposed. The energy application suitability analysis process was established by integrating three analysis techniques: the energy-saving effect analysis technique, historical value impact evaluation technique, and economic analysis technique. To achieve an appropriate retrofit plan, the condition of a building was evaluated through on-site diagnosis. Thermal transmittance rate assessments, temperature, and humidity monitoring, and infrared thermal imaging analyses were performed to evaluate the building's condition. Consequently, thermal transmittance rates for the wall and roof of the historic building were 1.18 W/m2K and 1.67 W/m2K, respectively, which indicated a risk of excessive energy consumption and condensation. Then, the suitability of each energy technology was evaluated by analyzing its economic feasibility and impact on the historical value and by simulating the reduction in energy consumption of the building. Thereafter, based on the analyses, the energy technologies deemed suitable were integrated to form an energy-efficient retrofit package, and an appropriate solution was elucidated. In conclusion, the package with the lowest impact on the historical value and the highest energy reduction decreased the total energy consumption by 15.9%. According to the results of this study, the process and package solutions proposed in this study are appropriate measures for historic buildings built in the 1920s in Korea, and can be a strategy with the potential to reduce carbon emissions and energy.

Thermo-economic evaluation for energy retrofitting building ventilation system based on run-around heat recovery system

With the increasingly stringent energy consumption and carbon emission policies enforced in China, the run-around heat recovery system has demonstrated significant potential for the energy retrofitting of existing ventilation systems. To explore the applicable regions of such projects and their optimal design schemes, a novel thermo-economic coupled evaluation model for the run-around heat recovery system is proposed in this study. Additionally, a site investigation for an energy retrofitting project based on the run-around heat recovery system is performed for model validation. The simulation results indicate that the lifecycle profitability of the run-around heat recovery system mainly depends on its heat recovery and initial investment, rather than the operating cost. Moreover, the optimal design scheme and corresponding regional adaptability for the system in China are evaluated in this study. It is observed that an run-around heat recovery system can be profitable in majority of the regions in China, except in certain southern regions; northern China is considered to have the largest application potential for this system. Based on the simulation results, another model based on polynomial fitting is proposed to simplify the evaluation process. Furthermore, the impact of the predicted future carbon cost on regional adaptability is discussed in this study.

Surrogate optimization of energy retrofits in domestic building stocks using household carbon valuations

Modelling energy retrofit adoption in domestic urban building stocks is vital for policymakers aiming to reduce emissions. The use of surrogate models to evaluate building performance combined with optimization procedures can optimize small building stocks but are insufficient at the urban scale. Recent methods train neural networks using samples of near-optimal solutions further decreasing the computational cost of optimization. However, these models do not make definitive predictions of decision makers with given environmental preferences. To rectify this, we extend the method by assigning a carbon valuation to households to derive their optimal retrofit solutions. By including the carbon valuation when training the predictive model, we can analyze the impact of households' changing attitudes to emissions. To demonstrate this method we construct an agent-based model of Nottingham, finding that simulated government campaigns to boost environmentalism improve both the number of retrofits performed and the mean emissions reduction of each installation.

Home Energy Upgrades as a Pathway to Home Decarbonization in the US: A Literature Review

This work aims to characterize how home energy upgrade projects and programs in the US have evolved over the past decade. It also identifies what changes are needed to drive expansion of the US energy retrofit market in such a way that addresses carbon emissions from buildings, improves resilience and upgrades the housing stock. This review focuses on whole-home energy upgrades, targeting deep energy retrofit savings of >30%. The topics we cover include trends in home electrification, US and European home energy upgrade programs, energy upgrade measure costs, business economics, and health effects. Key changes in project design noted in this review include: (1) the electrification of dwellings with rapidly improving heat pump systems and low-cost solar photovoltaic technology; and (2) a shift away from high-cost building envelope strategies and towards more traditional home performance/weatherization envelope upgrades. Promising program design strategies covered include: (1) end-use electrification programs; (2) novel financing approaches; (3) the use of carbon-based program and project metrics; and (4) “one-stop shop” programs. Based on the existing market barriers, we suggest that the industry should adopt new project performance metrics. Additionally, market drivers are needed to spur widespread energy upgrades in the US housing stock. Costs must be reduced, and projects designed to appeal to homeowners and contractors.