Energy Renovation Research Articles

How photovoltaics make energy refurbishment more affordable in apartment buildings

The costs of energy efficiency renovation of Germany’s postwar apartment buildings have sharply increased since pre-covid years, as have interest rates and hence the costs of servicing loans that finance these renovations. Despite increases in energy costs, it has become virtually impossible to recoup energy-efficiency renovation costs through energy cost savings, with many projects bringing substantial losses. The common method of third parties offering rotating finance to ease the initial costs, and being repaid after short payback periods, therefore no longer works. On the other hand, rooftop photovoltaics have decreased sharply in price, and continue to do so. This study explores the economics of installing photovoltaics, with or without heat pumps, along with energy-efficiency renovation, based on two typical case study apartment buildings in North Rhine-Westphalia. Using fine-grained energy flow modelling and net-present value cost-benefit analysis, it finds that energy-efficiency renovation brings losses of over 80% but that these can be substantially reduced by the gains from rooftop PV, especially when a heat pump is included. The larger the PV system, the larger the gains, but roof size limits this. The study recommends that shared rooftop PV systems be promoted as the norm with comprehensive energy-efficiency renovation in Germany.

Investigating Energy Renovation of Multi-Owner Buildings and Real Estate Market Issues in a Degraded Greek Urban Area

States establish ambitious policies and important measures to achieve targets for the energy upgrade of buildings but although some important barriers prevent their implementation in space, they are rather overlooked by research. In this paper, it is argued that extensive multi-ownership (MO) and weak performance of the real estate market in degraded urban areas impede the mass energy retrofitting of multi-owner buildings (MOBs), which are an important part of the urban building stock A deprived area of central Athens (Greece) that serves as a case study. With a pluridisciplinary approach based on extensive field surveys, cadastral data analysis and cases of energy renovation of buildings through a public–private partnership financing scheme as well as ways to overcome the MO issue were explored, according to the provisions of the Greek legal framework. The integrated urban regeneration approach is promoted as a means to encounter the MO issue and enhance the functioning of the real estate market by the generation of surplus values that will render the energy retrofitting of buildings more attractive to investors and thus achieve the deep renovation of MOBs towards the sustainability of the urban environment. This paper ultimately advocates the integration of energy planning with spatial planning.

Public Housing Stock between Recovery and Sustainability: The Case of Tor Bella Monaca in Rome

The buildings and construction sector is responsible for 37% of energy-related CO2 emissions and over 34% of energy demand globally. The redevelopment of the existing residential building stock has become a consolidated policy of the European Commission to implement the objectives of economic recovery and energy transition towards climate neutrality by 2050. This paper illustrates the design experimentation conducted by the Sapienza University team on the recovery of the public housing compartment R5 in Tor Bella Monaca, Rome. The research proposes an original methodology that is ideally replicable for regenerating large public housing districts built on the outskirts of major European cities, characterised by significant technological and social degradation and energy deficiency. This paper provides an overview of the interventions and an evaluation of the method and set of tools developed in drafting the Technical and Economic Feasibility Study at both the neighbourhood and building levels. This contribution is addressed to researchers and public and private organisations dealing with the complexity of the social housing recovery topic, emphasising overall sustainability aspects of interventions in terms of typological and energy refurbishment of buildings, re-activation of open spaces and enhancement of landscape components, and envisioning new services through participatory methods that promote social inclusion.

The effects of Energy Performance Certificates in energy poverty: A brief overview

<p class="MsoNormal" style="margin-top: 8pt; line-height: 14pt; text-align: justify;"><span lang="EN-US" style="font-family: verdana, geneva, sans-serif; color: black;">Energy Performance Certificates are a key tool for achieving energy efficiency in the building sector. The existence of this type of legislation provides incentives for the energy renovation of buildings, increases energy-efficiency investments, and improves social welfare. At the same time, informational asymmetries are mitigated and energy consumption is reduced. However, the decarbonization of the building sector might influence regional energy poverty, especially because the rural energy poor are more vulnerable to energy price increases than their urban counterparts. Empirical research on rural-urban differences and the effects of Energy Performance Certificates is urgently needed, given the rising fuel prices and vulnerabilities of the energy market.</span></p>

Improving the ventilation of a classroom to achieve heating energy savings and better indoor air quality

Indoor air quality and heating energy consumption are closely linked, especially in densely occupied spaces, as classrooms. In a classroom of Rennes University, a transient thermal simulation highlights the impact of ventilation on heating consumptions for different cases: (1) without controlled mechanical ventilation (CMV), (2) with a single flow CMV (SF CMV) of a regulatory flow of 18 m3.h−1. person−1 during periods of occupancy, and (3) a double flow CMV (DF CMV) whose flow is during periods of occupancy either equal to 18 m3.h−1. person−1 or (4) to 35 m3.h−1.person−1. The infiltration flowrate was evaluated experimentally using CO2 concentration measurements in the first case, which corresponds to the actual situation. In the normal use of the classroom with 30 persons inside, CO2 concentration exceeds 5000 ppm and the heating energy consumption is equal to 52 kWh.m−2.year−1. In case (2) and (3), CO2 concentration has a maximum level of 1350 ppm and the energy consumption is equal to 65 and 53 kWh.m−2.year−1, respectively. In case (4), the maximum CO2 concentration stays in the range 800-900 ppm without excessive heating consumption (58 kWh.m−2.year−1). Finally, by limiting the fresh air flowrate to 18 m3.h−1.person−1 in DF CMV and coupling it to a façade insulation (extra Case 5), the heating consumption is reduced to 32 kWh.m−2.year−1. These results are valuable within the context of the upcoming energy renovation strategy of the campus. Practical application In most schools, in France and elsewhere, insufficient ventilation flowrates are often observed compared to regulatory requirements. If compliance with ventilation standards and the subsequent revision of CMV installations are necessary to ensure the health of users, it is important to evaluate the energy cost of these renovations, and to identify the best choice to reduce heating consumptions. Our contribution is to compare different renovation choices in terms of two indicators: energy consumption and indoor air quality evaluated using CO2 concentration.

CO2 Emissions Reduction Potential with Novel Energy Renovation Technologies in English and Spanish Climate Conditions

CO2 Emissions Reduction Potential with Novel Energy Renovation Technologies in English and Spanish Climate Conditions

Understanding transaction costs of energy efficiency renovations in the Swedish residential sector

The residential sector has a large potential to reduce its energy use. Improving the energy performance of buildings is one way to realise this potential. For single-family buildings, improving the energy efficiency by energy renovations can produce a net financial gain. However, there are unaccounted barriers that act as impediments for house-owners to undertake energy efficiency measures. This study postulates that transaction costs are such a barrier. Transaction costs are defined as the cost of making an economic exchange on a market in addition to the market price. The purpose is to empirically estimate the magnitude of the transactions costs and its determinants for energy efficiency measures in the residential sector. Specifically, the transaction costs for heat insulation and energy-saving windows in Swedish single-family buildings are assessed. The analysis is based on a unique dataset, constructed from a web-based survey. The results indicate that transaction costs for energy efficiency measures are considerable. The average transaction cost to make additional heat insulation is SEK 18,046 (EUR 1,510) and SEK 21,106 (EUR 1,766) to install energy-saving windows. The determinants of the transaction costs are cognitive limitations, social connectedness, asset specificity and previous experiences. Therefore, to reduce the transaction costs, the complexity of energy efficiency measures must be addressed, potential opportunistic behaviour must be reduced, and financial options expanded.

Incidence of circular refurbishment measures on indoor air quality and comfort conditions in two real buildings: Experimental and numerical analysis

The application of Circular Economy to construction sector is a key to attain carbon neutrality, since it is responsible of 40 % of natural resource consumption. In this frame the importance of an efficient building refurbishment process throughout recycled material and renewable energy is fundamental. From an overview about building refurbishment emerges the need to investigate aspects related to Indoor Environmental Quality and the comparison between in-field measurements with output of dynamic simulation models. The present study aims to fill these two gaps by means an energy renovation of two real buildings in Greece. The work develops within the European project “Drive 0″, born to promote deep environmentally friendly retrofitting by means of circular renovation concepts. The methodological approach involves on-site monitoring of a series of parameters describing the energy, microclimate environmental and air quality, before and after the energy requalification. In addition, a numerical model developed in Building Energy Simulation program is calibrated and a Computational Fluid Dynamics is developed. From the in-field measurements emerges that, on one hand, the refurbishment of heating system shows a great improvement of indoor thermal conditions, with Total Volatile Organic Compounds concentration that sometimes exceed 3.0 mg/m3; on the other hand an integrated thermal insulation reduces infiltrations and changes the envelope behaviour, with a global energy saving of 30 % during winter and autumn periods.Another result of the study shows that a numerical model developed in Building Energy Simulation program and calibrated on energy consumption can greatly fit the local thermal comfort distribution of the occupant zone and predict the indoor air quality, if it outputs are used as input data in a Computational Fluid Dynamics study. These results can be beneficial to decision makers and designers for evaluating emitters positioning, opening design and mechanical ventilation strategies, aimed at reducing energy costs.

Improving the Energy Performance of Public Buildings in the Mediterranean Climate via a Decision Support Tool

Addressing Europe’s decarbonisation challenge involves widespread deployment of nearly zero-energy buildings, deep energy renovations and renewable energy integration in the building sector. Enhancing energy efficiency in public buildings necessitates tailored solutions and strategic planning involving Local Public Administration. This work focuses on advancing insights into the application of the PrioritEE Decision Support Tool in Portuguese public buildings, highlighting the energy and financial savings and carbon dioxide emission reduction potential. Using detailed building characterisation data from energy performance certificates, we applied the tool across 22 public buildings of diverse typologies in three distinct regions of Portugal, representing various public entities. Results demonstrate the tool’s adaptability, enabling a comprehensive assessment of energy performance and facilitating the exploration of customised energy efficiency and renewable energy solutions. The research emphasises the critical role of user-friendly tools in aiding policymakers and local administration technicians in meeting national renovation targets and contributing to the broader energy transition objectives.

A Holonic Construction Management System for the Efficient Implementation of Building Energy Renovation Actions

In the architecture, engineering and construction (AEC) industry, many efforts have provided remarkable contributions to construction planning and control processes during work execution. Nevertheless, frequent coordination issues among stakeholders and difficulties in dealing with unexpected events can be explained by the complexity featuring the construction sector. Several approaches to deal with this issue were investigated in the manufacturing area, among which this paper looks at the holonic approach as one of the most promising strategies. This study first analyzes the more fragmented and dynamic nature of the construction industry as compared with the manufacturing one. Secondly, it suggests developing a process-based holonic construction management system based on building information modeling (BIM) and a conceptual architecture for manufacturing control called Product Resource Order Staff Architecture (PROSA). The process-based paradigm ensures exploiting the benefits of BIM towards the development of sustainable and efficient regeneration methods of the built environment. Subsequently, a first management system prototype was developed and tested for the purpose of renovation works management. For the first time, results from an actual implementation of PROSA were applied to a real construction site, and its feasibility was assessed using the data on the field. Key performance indicators (KPIs) evaluated during the onsite demonstration confirmed a good performance of PROSA and the presented holonic approach, which contributed to the overall success of the energy efficient refurbishment project.

An Indicator Framework for Evaluating Building Renovation Potential

Implementation of a new European Union directive on energy renovation in Denmark can be expected to have a strong impact on the country’s energy renovation requirements. Accordingly, an indicator framework has been developed with the aim of identifying and quantifying the energy renovation potential of a specific Danish municipality. We identified and selected four indicators—energy consumption, CO2 emissions, heating costs and current energy labels—specifically for detached dwellings. The physical renovation potential was then quantified based on the indicator results, and an average score for the four indicators was calculated for each of the 10,228 detached dwellings in the municipality. All four indicators were weighted equally in the calculations of the total renovation potential score. The methods used in this study can be applied more widely as they rank detached dwellings according to their renovation potential. However, we also found that more detailed data are necessary to determine the specific renovation potential of detached dwellings. A greater effort to collect more data on the part of the municipalities would improve the accuracy of analyses.

Evaluation of Energy Renovation Measures for Hospital Buildings using the PSI Method

This study investigated the potential for energy savings and reduction in CO2 emissions in hospital buildings in Bosnia and Herzegovina (B&H), through the implementation of energy renovation measures. The building sector in B&H is characterized by significant energy consumption, and hospitals account for a substantial portion of the total energy consumption in public buildings. This study analyzes certain energy renovation measures for selected hospital buildings, including the installation of thermal insulation on exterior walls and flat roofs, and the installation of a photovoltaic plant on the flat roof. The Preference Selection Index (PSI) multicriteria decision-making method was employed to evaluate and rank renovation scenarios based on energy, environmental, and financial criteria. The results indicate that the most preferred measure is the installation of a photovoltaic plant on a flat roof, resulting in significant primary energy and CO2 savings, with an acceptable discounted payback period. The findings emphasize the effectiveness of energy renovation measures in enhancing energy efficiency and reducing the environmental impact of hospital buildings in B&H.

Finnish energy renovation subsidies in multifamily apartment buildings: Lessons learnt and best practices

This study analysed renovation measures implemented with ARA renovation subsidy in Finland in multifamily apartment buildings. Measured energy data was used to calibrate the energy simulation model of the most typical renovated building from the 1970 s. For the reference building, a comprehensive set of renovation packages were applied to assess the performance of ARA grants. It was noticed that official energy performance certificates (EPC) overestimated before the renovation energy use as well as energy saving by a factor of almost 2. It was notable that in calculated EPCs, after renovation, EP-value was higher than before renovation, EP-value based on measured energy use. The main reasons for faulty energy calculations were strong overestimations in the building leakage rate and ventilation airflow rate. Renovation packages reduced EP-value by 8 % to 27 %, including lighting and appliances. Those using district heat resulted in a small increase in electricity with a flat duration curve, but the combined ground source and exhaust air heat pump showed the highest peak electricity power increase by factor 6. Exhaust air heat pump, window replacement and photovoltaic were the most cost-effective options, while packages with additional insulation faced considerably higher costs than the sum of ARA support and monthly savings could cover bank loans; thus, ARA support was clearly too small to support deep renovation. The need to improve the accuracy of EPCs in assessing energy performance to facilitate more effective financial support was a finding that can be important for any support scheme to secure the necessary funding for renovation.

Application of the Typology Approach for Energy Renovation Planning of Public Buildings’ Stocks at the Local Level: A Case Study in Greece

According to the latest energy efficiency European directive (EED 2023/1791/EU), the expected energy renovation rate of at least 3% of the buildings’ floor area each year towards nearly zero-energy buildings (nZEBs) is extended to include public buildings not only of the central government (as per the first EED 2012/27/EU) but also of regional and local authorities. This poses a great challenge, especially for Municipalities that often manage large building stocks with high energy demands. In response to this challenge, this paper presents the application of the so-called “typology approach” for conducting public buildings’ energy renovation plans at the local level. A computational survey is initially introduced to decide the optimal set of building-stock clustering criteria among all possible combinations, involving the minimization of the RMSE index regarding the primary energy consumption of each building. For a representative building from each identified typology, the key performance indicators (KPIs) are computed for alternative energy-upgrading scenarios. Exploiting the IMPULSE Interreg-MED project tools, the KPIs from each representative building are at first extrapolated to all buildings of the examined stock and, finally, a gradual energy renovation plan is automatically produced based on user-defined decision parameters including the required annual renovation rate. The methodology is applied for the case of the Municipality of Hersonissos in Greece. For the specific 44-buildings’ stock it was found that the optimal clustering set included four criteria, building use, construction year, heating, and a cooling system, leading to 15 building typologies. Finally, assuming a 7% renovation rate per year, a 12-year gradual renovation (nZEB transformation) plan is obtained foreseeing an 85% CO2 emissions’ reduction.

The Open Data Potential for the Geospatial Characterisation of Building Stock on an Urban Scale: Methodology and Implementation in a Case Study

Energy renovation in buildings is one of the major challenges for the decarbonisation of the building stock. To effectively prioritise decision making regarding the adoption of the most efficient solutions and strategies, it is imperative to develop agile methods to determine the energy performance of buildings on an urban scale, in order to evaluate the impact of these improvements. In this regard, the data collection for feeding building energy models plays a key role in the accuracy and reliability of this issue, and the significant increase in recent years of available data from open data sources offers great potential in this respect. Thus, this study focuses on proposing a systematised and automated method for obtaining information from open data sources so as to obtain the most relevant geometric and thermal characteristics of residential buildings on an urban scale. The criteria for selecting the parameters to be obtained are based on their potential use as input data in different energy demand models aimed at assessing the energy performance of the building stock in a given area and, eventually, to evaluate the potential for improvement and the mitigation of different strategies. Geometric characterisation relies on obtaining and processing open data from cadastres to extract envelope surfaces categorised by orientation through QGIS (Free and Open Source Geographic Information System). For thermal characterisation, an automated process assigns different parameter-based information obtained from cadastral data, such as the year of construction. Finally, the applicability of the method is demonstrated through its implementation in the case study of Bilbao (Spain). The obtained results show that, although additional data should be collected when a detailed analysis of a building or building cluster has to be carried out, the existing open data can provide a first approximation, providing a first global view of the building stock in a region. It demonstrates the usability of the proposed method as an effective way to obtain and process these relevant data.

Scenarios for the energy renovation of a residential building

In this paper, the results of the energy renovation of a residential building, aimed at introducing it into a Renewable Energy Community (CER), are presented. A case study located in Florence (Italy) is discussed. Static and dynamic energy models have been used to evaluate the energy performance of the building, to compare different scenarios based on heat pumps (independent or centralised generator) and to evaluate them under the perspective of EPBD parameters. A comparison has been made concerning energy consumption and CO2 emissions. In its current state, the building presents an energy performance index of 129.8 kWh/(m2year) (class D). The energy refurbishment with heat pump (A4, 24.7 kWh/(m2year)) and VMC system (A4, 39.3 kWh/(m2year)) ensures a strong reduction in CO2 emissions, respectively 5.5 kg/(m2year) and 8.7 kg/(m2year) against 24.4 kg/(m2year) with the current gas fired boiler. The centralized heat pump configuration allows to further reduce the energy consumption. With the same thermal energy requirement, the results show a reduction of 14% of the power needs (without total recovery), thanks to the better sizing of the generator. Furthermore, the centralized heat pump opens a perspective of direct self-consumption of the energy product by the photovoltaic system into a CER configuration. The paper shows that the energy renovation with a heat pump is an effective way to reach the EPBD objectives and decarbonize the residential heating and cooling sector.

A review of the energy retrofitting goal and methods of the building stock across the EU

This study aims to compare and evaluate various energy retrofitting strategies and methods employed in the building sector, with a focus on analysing their effectiveness and feasibility in enhancing energy efficiency. Current renovations in the EU are mostly response to policies in force; however, there is an increasing demand for renovation projects to align with the goals set for 2050. Subsidies or barriers may differ across a whole spectrum, depending on various factors, but leaving the building with the same expected outcomes. It is also important to apply measures in design phases which end in feasible and flexible execution. The paper elaborates an assessment background for the selection of studies. It identifies four main key objectives: improving energy efficiency, phasing-out of fossil fuels, increase the share of renewable energy and applying circularity. These objectives were gathered from various studies and reports, in response to which quantifiable and non-quantifiable values of three energy renovations were compared. The results highlight not only energy, financial and carbon-saving aspects but also address current retrofitting trends and climate change. Performing a comparison along these points helps to understand what drives a renovation and what can be achieved with certain inputs in the beginning. This review explores the extent to which renovation case studies vary in terms of their goal, approach, and the way results are published. It aims to help deciding whether an intervention is adequate or not, through a set of criteria presented.

Technical-economic and financial feasibility of new technologies in the energy refurbishment of residential buildings

The revision of the Energy Performance of Building Directive (EPBD) provides for the construction of zero-emission buildings. The present work investigates possible solutions aimed at phasing out fossil fuel systems in buildings, in accordance with the EPBD requirements. An insulated residential building located in Rome is presented. The proposed refurbishment approach is based on the heating system replacement (heat pump, hydrogen fuel cell, hydrogen-ready boiler), and the use of renewable energy produced by a photovoltaic system. The results show that, although the energy optimal solution consists of the replacement of the heat plant with a heat pump coupled to both a PV and a fuel cell system, from the economicfinancial point of view the proven solution of heat pump coupled with PV is still the only feasible one.

The energy renovation pathway to ZEB in Italy: Analysis of typical buildings and methodological aspects

The evolution towards high-energy efficient buildings is one of the most important challenges today and is in line with the objectives set by the new European Directive on the Energy Performance of Buildings (EPBD) which provides for the decarbonization of entire building stock by 2050. The study starts from the analysis of the current regulatory framework in Europe and Italy, highlighting the lack of homogeneity in the methods of transposition of European directives by the Member States already at the “nearly zero energy buildings” level (nZEB). Starting from these considerations, the critical analysis of the European and Italian context highlights the need to overcome the standards currently in force and investigate new perspectives for the design of high-efficient buildings in the direction of “zero energy and zero emissions”. For this reason, two residential and office buildings typologies are examined to confirm whether the net Zero Energy Building (ZEB) objective can be achieved through the legislation in force in Italy, starting from nZEB level. The study analyses the energy balance through dynamic simulations and evaluates energy needs of buildings and renewable energy production in order to verify the compliance to ZEB target, on yearly and monthly basis.

Facing the Constraints to the Deep Energy Renovation Process of Residential Built Stock in European Markets

In many countries, depending on climatic conditions and the energy performance of buildings, the built stock is highly energy-consuming and constitutes a main source of greenhouse gas emissions. This is particularly true for Europe, where most of the existing buildings were built before 2001. For this reason, EU policies have focused on the Deep Energy Renovation Process of the residential building stock as the mainstream way for its decarbonization strategy by 2050. Based on a broad investigation of seven EU local retrofitting markets carried out within the H2020 re-MODULEES project, this paper defines a holistic methodology for understanding and facing the complexity of the renovation market and its inner constraints. Thanks to systematic surveys and the activation of stakeholders’ core groups (re-LABs), the main market barriers (cultural, social, technical, processual, and financial) were explored. Through a bottom-up clustering approach and vote analysis, a relevance classification of constraints of each pilot market and a detailed scenario of the most relevant market constraints at the European level were provided. This scalable methodology offers the baseline necessary for shaping more effective, cooperative, and tailored-made policies aimed at overcoming the current limitations to the full deployment of the Deep Energy Renovation Process (DERP) across the European markets.