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The zero-energy challenge in districts. Introduction of a methodological decision-making approach in the case of the district of Cuesmes in Belgium

The zero-energy challenge in districts. Introduction of a methodological decision-making approach... INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 2021, VOL. 13, NO. 3, 585–613 https://doi.org/10.1080/19463138.2021.1985504 The zero-energy challenge in districts. Introduction of a methodological decision-making approach in the case of the district of Cuesmes in Belgium a a b a c Sesil Koutra , Noémie Denayer , Nikolaos-Fivos Galatoulas , Vincent Becue and Christos S. Ioakimidis a b Faculty of Architecture and Urban Planning, University of Mons, Mons, Belgium; Faculty of Thermodynamics, Physics and Mathematics, University of Mons, Belgium; Inteligg P.C, Athens, Greece ABSTRACT ARTICLE HISTORY Received 2 November 2020 Transforming cities with the aim of achieving cleaner energy targets is a major bet Accepted 12 September 2021 worldwide, dealing with the immense stress of the rapid urbanisation, the depletion of natural resources, the climate change and its impacts during the post- KEYWORDS industrialised period. Struggling with this problematic, in this work we develop Case-study analysis; energy a horizontal and cross-sectoral process as an integral part of the city planification transition; holistic approach; towards the energy transition. Along with demonstrating the applicability of the zero- zero-energy district energy idea in more universal approach, we validated its feasibility at the case-study Cuesmes (Belgium), a social district with high energy requirements along with the RE- SIZED research project. In response to this, in this work we articulate the feasibility of the concept (zero energy) in urban scale, in a comprehensive toolkit. Comparisons and similarities with previous empirical analysis are discussed as well to complete the work and its findings. 1 Introduction Administration 2013). In fact, these trends release the need for comprehensive planning actions towards high Cities are living organisms with dynamic changes and energy performance in modern communities. processes. The post-industrial European city is charac- Looking closer at the 2030, European Commission terised by dispersed urbanisation with increasing rolls out the regulatory framework to reach the inter- trends, resulting in increased travel, substantial use of mediate target of −55% of net-zero emissions. In land social disparities and rising demand for energy a more detailed review, Taylor provides an analytical (Riera Pérez and Rey 2013). By 2035, the shift of the study on related topics; the share of renewables in global population to urban centres will be accelerating energy consumption with a projection of a 30% sharing and that figure is expected to achieve the level of 60% by 2030 is the starting point of the process (Taylor by 2050 (United Nations Development 2014). The 2020). building sector remains a pivotal consumer worldwide, At the same time, the report discusses the headline representing more than 40% of the European con- to achieve an energy efficient target for 2030 of at sumption (UNEP 2009), confirming their importance in least 32,5%, which is prioritised on European global meeting the Europe’s 2030 climate and energy targets action plan accounting that we meet a continuous (Saheb et al. 2019). At the same time, the CO emissions failure to meet this reduction as its review of the have been increased by 43% with an average annual climate plans shows that there is a gap of 2.8 percen- increase of 2% and 1.8% respectively, while current tage points for primary energy consumption and 3.1% predictions prove that this trend will continue drama- points for final energy consumption. tically in the future (US Energy Information CONTACT Sesil Koutra sesil.koutra@umons.ac.be Faculty of Architecture and Urban Planning, University of Mons, Mons, Belgium © 2021 Informa UK Limited, trading as Taylor & Francis Group 586 S. KOUTRA ET AL. Strengthening the climate objectives and policies, summarise the main comparative findings with the EU boosts for a more innovative and cross-sectoral previous pilot analysis of Epinlieu; both cases are reflexion contributing to resilient ecosystems to ‘social housing projects’ situated at Mons and are achieve the 2020 failures. In 2008, Europe introduced part of the RESIZED project demonstration studies; its targets by leveraging the arising of directives and summarised findings are provided in subsequent policies towards the reduction of the energy consump- section. tion and the carbon neutrality by 2050 (European The manuscript is structured accordingly: Section 1 Commission 2011). In fact, to overcome these chal- introduces and describes the problem and the objec- lenges, Europe outlines a ‘Green Deal’ (European tives of the research, Section 2 highlights the impor- Commission 2019a) to boost the resource-efficient tance of the urban structure for the reduction of the and to ensure an inclusive transition to cleaner and energy demand and consumption by its users, green energy aiming at the protection, conservation Section 3 presents the main methodological steps of and enhancement of the European capital but also the the introduced approach as well as the challenges and protection of European citizens’ health and well-being limitations for its applicability. Section 4 provides the from the environmental impacts and the risks’ (United main findings and results of the proposed application Nations 2019). in Cuesmes, while Section 5 summarises the main Embracing the European roadmap by turning conclusions of the work. environmental and climate challenges into opportu- nities, the Deal highlights the importance to boost 2 Understanding the zero-energy concept. efficient energy use in communities. Nevertheless, Previous works achieving operations along with the energetically autonomous communities requires intensive plan- The first indications and traces around the zero- ning processes and endeavours of synergies among energy idea were introduced already in 2010 in build- the different stakeholders. The challenge is multifa- ing level: ‘a building that has a very high energy per- ceted and the preponderance of the (net) zero energy formance. The nearly zero or very low amount of energy concept affects the planning and the decision-making required should be covered to a very significant extent processes in city level. by energy from renewable sources, including energy In response to this problematic and to articulate the from renewable sources produced on-site or nearby’ feasibility of the concept (zero-energy) in urban scale, in (European Commission 2010). In the literature, the this work we introduce the outcomes of a holistic and ‘zero-energy’ objective is mostly considered in build- comprehensive toolkit developed in European FP7 ings or the potential of solar energy utilisation for research project RESIZED (Research Excellence for active and/or passive solar heating with different defi - Solutions and Implementation of Zero Energy Districts) nitions, which co-exist, and it is presented as ‘the (ERA Chair Team 2015). In line with the national direc- building, in which a balance is underlined between the tives of Belgium for 2030 (National Energy and Climate energy taken from and supplied back to the grid over Plan (European Union 2018) for a reduction of more than a specific period (nominally a year)’ (Marique and Reiter 30% of the GHG emissions (compared to 2005) and the 2014). adjustment to the Paris Agreement and the commit- The statement of the NZEB principles became ment of the Walloon region (2019–2024) towards car- mandatory since 2018 for new public buildings in bon neutrality by 2050 (Déclaration de Politique de an effort to intensify the actions for decarbonisa- Wallonie (Service Public de Wallonie 2019), this study tion and energy efficiency in an effective manner. aims to reinforce the guidelines along with the zero- Since then, the concept gains a rising scientific energy planning. The empirical studies in demonstration interest and studies are increasingly appeared to projects of the research outcomes validated the com- explore its dimensions. Carlisle et al. document plexity of the concept but also the need for dynamic diverse contexts of the term to establish processes, citizen empowerment and effective stake- a grading definition from the building as holders’ synergies. a starting point to progress to the urban scale In this manuscript, we investigate the feasibility of applying a more general view that a ‘net-zero our toolkit in the district of Cuesmes in Belgium as energy community’ is one that has greatly less a continuity of our downstream phase and we energy requirements and that the balance of energy INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 587 for vehicles, thermal, and electrical energy is met carried out by a series of simulations with the use of principally by renewable resources and the local pro- Design Builder software and the integrated Energy duction’ (Carlisle et al. 2009). Plus tool aiming to minimise the energy consumption It is commonly true that definitions of (net) Zero of each set of buildings. Different scenarios were Building vary from one country to another – depend- assessed in terms of installing renewable energy con- ing on the climatic, economic, political conditions – , version technologies while the developed simulation but they all share a common goal: to reduce or neu- model was calibrated by means of maximising the tralise the environmental impacts on the built coefficient of correlation between measured and environment. simulated data. Over the past decades, the trends of energy- Alternatively, energy system design for transition- oriented projects are increasing in building sector, ing to NEZD can be formulated as exploiting effi - while the latest ones aims at setting the zero energy ciently the useful work potential (exergy) of and carbon objectives even on city scale (Brown and available energy resources. This approach was pro- Vergragt 2008); examples of these initiatives are posed in (Kilkis 2015) and developed as a four-step already met in the existing reviews, for instance the analysis process in order to reach NZEXD (net zero case of Beddington Zero Emission Development exergy district) and NZCED (net zero compound CO (BedZED) (Dunster 2002), the pilot plan for the city emissions district) targets. A detailed demonstration of Copenhagen to set carbon neutrality by 2025 (City of the applicability of this modelling method is per- of Copenhagen Technical and Environmental formed in (Kilkis 2014). Setting financial objectives in Administration 2012). the epicentre of reaching NZED targets entails the From the lessons-learned, and as the benefits of inclusion of extra-economic benefits generated by improving energy efficiency at building level have the suggested intervention developed a five step been understood, interest has been rising in extend- integrated evaluation framework for a NZED ing those benefits to larger scales (Pless et al. 2018). (Becchio et al. 2018). Building stock properties for A review from 1992 to 2018 by European Commission, their studied district in Turin were derived from the an insight on existing case-studies revealed that the TABULA database and comprised the engaging point transition to zero-energy districts is underway and for subsequent envelope retrofitting strategies. All ambitious targets to reduce the energy demand with considered strategies assumed district heating as the parallel increase in share from local renewable the heat network solution for a set of buildings energy sources. Municipalities consider the energy linked via heating loop. Results are hierarchised transition as a mandatory step and a consensus to according to their calculated social return on invest- achieve the local energy targets but also to emerge ments followed by a cost-benefit analysis. Last, the new and set initiatives and policies towards this direc- data inputted in the cost benefit analysis are validate tion (Saheb et al. 2019). To achieve this ambitious through a sensitivity analysis in terms of percentage target, Becchio et al. introduce a scenario planning changes on initial costs and how they affect the analysis to support the decision-making in the choice social return on investment. between policies in which energy demand forecasting In this work, a broader approach from energy models are suitable quantitative tools for an energy- efficiency is adopted contemplating for urban func- oriented planning (Becchio et al. 2016). Kilkis provides tions closely related to the urban morphology of the an analysis of a pilot ‘zero-energy’ project of Östra Sala district of Cuesmes. The methodology focuses also backe in Uppsala Municipality in Sweden within the on the spatial impact of the proposed repurposing use of Rational Exergy Management Model to curb actions since detailed data on construction age and primary energy consumed and CO emissions by building envelopes were accessible. Net zero district means of considering the level of crossing the quality targets are tackled for infrastructure concerning of resources (exergy) and the energy citizens’ needs waste management, transportation, soft mobility, (yearly) (Kilkis 2011). service provision apart from solving the net zero A comparison of the thermal comfort, the energy energy balance problem and enhancing load match- consumption, and the carbon emission rate in two ing capabilities of the heating and power technolo- types of neighbourhoods located in Madagascar was gies. Given that the vast majority of the building presented in (Nematchoua 2020). The study was stock consists of extremely aged construction, 588 S. KOUTRA ET AL. space heating needs would exhibit significant fact when moving to urban scale, additional factors improvements by enacting essential envelope retro- in regards to the design influence the energy perfor- fitting procedures. mance (Amaral et al. 2018). Saheb et al. explain that zero-energy initiatives are driven either by urban ‘retrofitting’ and are usually the 2.1 The zero-energy district and the RESIZED impacts of the urban metabolism by the transforma- European project tion of industrial areas into districts or the develop- ment of new agglomerations with high outcomes for In an effort to ‘translate’ the EPBD principles in dis- all residents, etc. (Saheb et al. 2019). In fact, the sus- tricts (Concentrated action: Energy Performance of tainability criteria considered by local actors are dif- Buildings 2002), we assume that: ‘a NZED is ferently ‘interpreted’ by different communities to a delimited part of a city with high energy performance assess the ‘zero energy’ concept and its applicability. and a nearly zero or very low amount of energy con- This work intends, thus, to contribute to fill this gap, sumed to a significant extent by its local production’. by establishing a knowledge base to support further Broadly speaking, the NZED adjusts the (nearly) zero- developments in urban agglomeration along with energy principles to the urban context to assess its a holistic toolkit as proposed in RESIZED European potential impacts and feasibility assuming that the project (ERA Chair Team 2015). energy requirements on districts are assessed as part of its components (public lighting, landscape, etc.). 2.1.1 The RESIZED research project Sornes et al. at the research project ZenN (Nearly In 2015, the University of Mons and the Research Zero Energy Neighbourhoods), introduce the defini - Institute for Energy proposed a multi-disciplinary tion where the global energy demand of a cluster of approach (Figure 1) in the field of NZED through the residential buildings is met by renewable energy ambitious RESIZED project aiming at: sources which are produced on site, without further details by considering the neighbourhood as a sum of Enhancing the scientific excellence around the buildings (Sornes et al. 2014). In this sense, a NZED is topic with the development of holistic approaches not a sum of NZEBs but as a group of buildings with and synergies among the Departments and the different consumptions, whose overall balance must Public Bodies and private companies. almost reach zero; nevertheless, the buildings remain Developing a toolkit to enable the process the most important consumer of the total amount of (urban planning, building design, energy pro- the energy demand (Amaral et al. 2018). duction system design, green mobility etc.) of Undeniably, one of the main challenges of going zero-energy design in urban scales. beyond the building level, is the definition of bound- Developing a project portfolio and validate the aries as it is commonly understood that enlarging the results on demonstration cases to ensure the perimeter of intervention the constraints influencing research results and spread the best practices the energy performance become stronger and the (Koutra et al. 2019). level of complexity as well. Geometry has a significant role to mitigate the factors for minimising 3 Methodological approach the consumption, while in parallel to maximise the (local) production. To this A preliminary definition for NZED, proposed by the topic, several studies in the existing literature U-ZED approach, is: search for the assessment of geometric factors to ‘NZED is the district, where the potential of the evaluate the performance, such as the aspect or the energy supply (on-site) is equal (or nearly equal) to the depth ratio (Hachem et al. 2013), compactness or final energy demand of its users. Estimating this bal- ground and floor indexes (Rodriguez-Alvarez 2016) ance is not always a straightforward process; for or site coverage and shape (Mauree et al. 2017). instance, Marique and Reiter consider factors related However, even when the methodologies propose to the space heating/cooling, ventilation, appliances, strategies to district (or even city) scale, these studies cooking etc., while a particular emphasis for calculat- still remain on the buildings’ performance ignoring ing the mobility flows is defined with the introduction more dynamic phenomena (i.e. mobility flows); in of the Energy Performance Index as INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 589 Figure 1. The toolkit of NZEDs’ approach developed in RESIZED European project. energy production annually. U-ZED process is evolved Dmifm=Ti (1) along with three pillars to achieve this equilibrium in the district in an attempt to optimise the energy where i represents the territorial unit, m the means of requirements of the district’s users/citizens and build- transportation used, Dmi the total distance travelled, ings (Pillar 1). This step is primordial for the zero- fm the consumption attributed to the means of trans- energy objective; the ‘demand’ (usually expressed in portation and Ti the number of persons in the terri- kWh) refers to the requirements in energy to fulfil the torial unit i (Marique and Reiter 2014). metabolic functions but also to ensure the operations Equation 2 provides the mathematical representa- of the existing building stock. Complementary to this, tion of this concept: the Pillar 2 proposes the energetic ‘hybridization’ X X on-site implying the balanced combination between f Demand f Offer (2) the use of the on-site resources and the installation of the diverse technologies on-site, while Pillar 3 indicates where the f Demand is calculated as the sum of the another strong feature of the interdisciplinary planning energy requirements in the districts and the offer on- of physical flows of energy, water and waste, implying site (RES potential). NZED aims at optimising (mini- the share of renewable resources and the generation of mising) the energy demand (annually) with the paral- local energy and the need for energy storage systems lel maximisation of RES’ use for the local energy (Figure 2). Some examples of these implementations are production (on-site) (Equation 3). ensuring the liveability of the concept can be: NZE Dobjective : X X (3) ● Energy: renewable fuels, biogas products, reuse min f Demand with a parallel max f Offer of waste heat coupled with efficient energy con- sumption of built environment etc. For instance, U-ZED approach is developed along with three pillars energy storage systems should be used in order of action (Figure 2). U-ZED ‘defines’ the zero-energy to maximise and use effectively the solar thermal application in districts as the balance between the energy. Indeed, the stored solar thermal energy demand and the on-site offer to maximise the local 590 S. KOUTRA ET AL. Figure 2. Description of the three pillars of action in NZEDs by the U-ZED approach. can be used to cover the peaks of the thermal Phase 2: Diagnosis and analysis demand in winter and in the transitional The second phase of the approach is the diagnostic months, while in summer the solar system can on-site analysis and the initial screening of the studied even cover the whole thermal demand of the area, the identification of the problems, limitations and district, if the solar system is properly designed. opportunities. ● Water: sewage treatments and saving Kristensen studied the chains and connections of ● Waste: thoroughly sorted in practical systems, the DPSIR model starting with the ‘driving forces’ with material and energy recycling maximised through ‘pressures’ to ‘states’ and impacts on eco- wherever possible. At the same time, this evokes systems, human health, etc. leading to political the opportunity to dominate the role of storage responses. At his works, Kristensen explains the energy systems, such as battery recycling to components of the DPSIR model by using store energy, which is quite challenging due to (Kristensen 2004): the scale and the technological and financial barriers for their installation. Analysis of applying D for Driving Forces to express a ‘need’. Examples waste energy utilisation techniques in different of primary driving forces are the need for shelter, sectors of economy identifies more possibilities food, wateretc. in electricity and heat energy saving and pollu- P for Pressures. Driving forces lead by human tion prevention. activities. These human activities exert ‘pres- sures’ on the environment, as a result of pro- duction or consumption processes and 3.1 Detailed description of the methodological are mainly divided into three main types: (i) steps excessive use of environmental resources, (ii) Four phases describe the dynamic process of the changes in land use and (iii) emissions to air, U-ZED methodology water and soil. Phase 1: Strategic decision of the NZEDs’ ● S for States. As a result of pressures, the ‘state’ of installation the environment is affected; that is the quality of The first step of U-ZED’s application is the strategic the various environmental compartments in decision by planners and city stakeholders towards relation to the functions that these compart- the zero-energy district planning. This step is mainly ments fulfil. related to the political decisions and strategies to I for Impacts. The changes in the physical, eco- engage stakeholders, planners but also to empower nomic, societal or urban environment determine citizens towards the successful application of the the quality of ecosystems and the welfare of concept. human beings. INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 591 R for the expression of responses as solutions for fourth Phase of the U-ZED approach concerns the policymakers to minimise the impacts as empirical study, the validation and the monitoring of described previously. the proposed action plan. Figure 4 explains the flow of the four proposed U-ZED hereby, being inspired by the DPSIR assess- phases of the methodology. ment tool analyses in detail the potential of a district Developing the U-ZED process in four phases (2), to be designed in line within the zero-energy princi- as previously described, is a complex process requir- ples (Figure 3). ing well-defined coordination procedures, collecting Phase 3: Assessment of scenarios and analysing accurate data, managing the risks and At the previous step, we evaluated and devel- the budget, ‘adapting’ the users’ behaviour etc. oped our diagnosis to identify the studied area, its Further steps and perspectives are expected with actual problems, the on-site constraints and oppor- the involvement of local authorities and citizen par- tunities. In this Phase, planners and city stake- ticipation for the conception of the zero-energy holders assess the diagnostic study and develop planning at their district, surveys and on-site analysis a scenario analysis explaining the different possibi- are proposed, as well but also evaluation of costs and lities for the district’s re-arrangement or its concep- benefits for the suggested actions for each case- tion. Planners develop and examine diverse study. scenarios towards the achievement of the zero- energy strategy and its application in the studied district. In the case of data lack, the process returns 3.1.1 Limitations of the methodology to the previous step (loop). As previously explained, the application of the U-ZED Phase 4: Implementation approach revealed the complexity of the zero-energy Following the strategical decision for the zero- applicability in urban scale; for this study, we analyse energy planning actions and the selected scenario, basically the pillar (1) of the needs’ optimisation, which will ‘optimize’ the zero-energy strategy, the which is the first and important step of the concept. Figure 3. DPSIR approach is developed in U-ZED phase 2 analysis. 592 S. KOUTRA ET AL. Figure 4. Algorithmic description of the U-ZED process. The main limitations of our study are cited below: influencing the successful application of the zero- energy concept in districts is not exhaustive. Table 1 Ambiguous definitions regarding the zero- presents the KPIs included for the current study and as energy concept and limited real case studies a preliminary application of the U-ZED approach; the and lessons-learnt in urban scale to retrieve suc- selection is realised along with the objective of balan- cessful stories of the past; cing the annual demand and on-site offer related to the ● Limited access in open (and not confidential) data availability for each of them as a first overview of data regarding mainly the energy consumption the theoretical application of the key factors influencing per household; the energy performance in districts and the limitation of ● Social behaviour and adaptation to zero-energy this study to pillar 1. transition, need for continuous actions and mon- For this study, we focus our scope and objec- itoring actions by planners and city stakeholders; tives at: ● Limitations on costs of proposed technologies and systems to achieve the zero-energy balance; Site opportunities: the index is related to the Administrative obstacles and difficulties in poli- site’s geography, the concrete localisation, the tical engagement and related policies. specific climate conditions and the resources’ on-site potential. These components identify as well the connections of the studied area (acces- 3.2 Key performance indicators sibility/proximity) with its surroundings. KPIs are a concept originating from business adminis- Mobility: Complementary to the previous KPI, the tration with the aim to provide tools for measurement ‘mobility’ is a key index to assess with tangible and in business fields. In reality, they are quantifiable metrics more quantified methods the accessibility of the reflecting the performance of achieving wider goals and studied area; this index seeks for the assessment help in the implementation of different strategies of the integration of mild transport modes as well. (Bosch et al. 2017). For this study, we considered, as ● Functional/Social/Dwellings’ mixing: this index is key aspects of the energy performance of NZEDs, site basically significant for the first axis of our analysis opportunities and attributes. The list of the KPIs (optimisation of energy requirements by users). INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 593 Table 1. Key performance indicators (KPIs) in NZEDs. KPI Description U-ZED References Location/ RES potential City centre: 3–5 km (ARENE 2005); Τopography/ Proximity to city centre Between the ‘stops’: 200–500 m (Amaral et al. 2018) Climate conditions Mobility Offer in mild means of 1.500 m from IC/IR or less (Teller et al. 2014) transport 700 m around the perimeter (Reiter et al. 2014a), (Senel 2010), 300 m between the ‘stops’ (Marique and Reiter 2012) 30 passages/day (poles) 20passages/day (suburban) 5–10 min between the ‘passages’ Functional Mixing Mixed-use, highly dense 300 m of a commercial centre (Teller et al. 2014), (Reiter et al. 2014a) and compact 300 m of a primary school 500 m of an activity centre Social Mixing and Number of social 15% in social dwellings (Shnapp et al. 2020) Equity dwellings/surface (ha) 10% accessible to ‘middle’ revenues (Teller et al. 2014), (Laroche 2010), Affordability for the (Chouvet 2007) housing and diversity Mixing in Variety of dwellings’ 10% of studios and/or dwellings of ‘one-room’ (Teller and Marique 2014), Dwellings functions, number of 10% of dwellings of ‘two rooms’ (Schulz 2006), (ARCEA 2016), rooms/floors etc. 10% of ‘three rooms’ or more (Ministère du logement, de l’égalité, 10% of public dwellings des territoires et de la ruralité 2014) R + 1 to R + 5 (max) Low energy Buildings’ low energy Heating: ≤60 kWh/m /y (Yepez-Salmon 2011), consumption standards Electricity: ≤20 kWh/m /y (Service Public de Wallonie -DGO4, 2010) The three cases are related to a diversity on func- to maximise or minimise the objectives of the city tions, populations and a mixed built stock, which planning (Chuvieco 1993). For the current analysis, will enable and promote the autonomy. QGIS is used for the cartographical analysis of the Standards of low energy consumption: quantified representative attributes of the built and urban to define the consumption on low energy build- environment of the diagnostic study of the ing design. Cuesmes district. As a toolbox, GIS allow planners and architects to perform a spatial analysis with Figure 5 represents the KPIs’ selection along with the use of different actions and the integration of the three pillars of action in the U-ZED approach. diverse factors (Chuvieco 1993). Interest for the current manuscript provides the first pillar regarding the optimisation of the energy require- 3.3.2 HOMER ments of the users in the studied districts. In this figure, Bahramara et al. claim HOMER is a powerful tool for we analyse the key parameters to explain the three energy planning in cities with the aim of determining proposed pillars in figure 5. the optimal size of specific system elements through a techno-economic analysis considering the compo- nents in grid-connected or autonomous implementa- 3.3 Methods and tools tions (Bahramara et al. 2016). HOMER requires six As analysed above, at the second phase of the U-ZED types of data including the: meteorological data; the method, we developed a roadmap towards the zero- load profiles; the attributes of the selected compo- energy transition in districts within the use of different nents; the space; the economic and other technical software explained briefly below: data and can be adjusted to simulate or optimise an examined grid configuration. Energy system design 3.3.1 QGIS tool and optimisation with the use of HOMER software Chuvieco argues that the association of the spatial has been reported in (Rahman et al. 2016) assessing optimisation models with the use of GIS formulates the implementation of a hybrid energy system for the and develops the planning options in an attempt off-grid Sandy Lake community in Canada while 594 S. KOUTRA ET AL. Figure 5. Representation of KPIs’ selected in U-ZED approach. proposing the hybrid energy resource combination 3.3.3 The Method of Degree Days which could serve the electricity demand. Seven Day and Karayiannis explain that the method of Degree energy scenarios were developed from 0 to 100% Days is mainly used for estimating the heating energy renewable energy shares. A process for modelling demand in buildings for nearly 70 years (Day and electricity generation based on multiple configura - Karayiannins 1998). Moreover, attempts have been tions of hybrid renewable energy sources was pre- made to formalise the energy consumption monitoring sented and tested on an identified off-grid village targeting in buildings. The way in which the method of location in India. In addition, Shahzad et al. proposed Degree Days is applied involves assumptions and an economical and optimised design for electricity approximations introducing the uncertainties into the generation using hybrid energy source PV/Biomass problem. It is expected that the method of Degree Days for an agricultural farm and a residential community provides the smallest contribution to errors and it is centred in a small village of district Layyah in the important to quantify this contribution; for this study, Punjab province of Pakistan (Shahzad et al. 2017). the Method is used in its simplified application for the Last, He et al. employed HOMER in order to evaluate rough estimation of the current demand in district. the techno-economic performance of renewable energy-based microgrid scenarios in residential com- 4 Case-study analysis munities in Beijing (He et al. 2018). In this study, HOMER is utilised for the energy The validation of the toolkit developed is materialised analysis of the district’s power requirements under along with two main demonstration cases at the sur- two scenarios integrating rooftop PV on the build- roundings of the city of Mons. As explained in Koutra ings (a) without and (b) with a coupled battery et al. the district of Epinlieu constitutes of the first energy storage component (detailed results pre- experiment of empirical analysis for the RESIZED tool- sented in the Annexe). box (Koutra et al. 2019). The common attribute of the INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 595 two pilot analyses (Epinlieu and Cuesmes) is their ‘social mobility flows, the functional and social mixing, etc. project’ character and the fact that their location pre- An important component of the diagnostic study sents similarities. Nonetheless, the urban context of the completing the analysis of its profile is undoubtably (non)-built environment differentiates; some prominent the demographic data and the population profile. comparative results are presented in this section. Exploring the potentialities for the ‘zero-energy’ Cuesmes is a district close to the city of Mons (4 km spatial ‘re-structure’, we studied the opportunities from the city centre) (Fig. 6) with an old building stock and the constraints on-site and we defined the and high energy requirements (despite the renovation attributes of the demographic profile of the stu- strategies); however, with interesting site opportunities. died cases. The district selected is basically comprised of social hous- In 2018, the district counted 1202 citizens with ing with poor quality and unfavourable living conditions a significant number of non-active residents (City for its population. In this section we will present the Population – Cuesmes 2018). Indeed, the district of application of the four U-ZED steps in Cuesmes district. Cuesmes is considered as the district where a lowest rate of people has a high educational level Table 3; (only 15% of the local population 4.1 Phase 1. Strategic decision of the NZEDs’ has a university degree); the unemployment rate installation is high (~10%) and the average income is relatively low (app. 1300€/month). Compared to Cuesmes, The diagnosis of the district’s dysfunctions along with the district of Epinlieu has similarities in terms of the site opportunities are the motivations for the zero- its demographical analysis. energy transition towards the ‘zero-energy’ planning. 4.2.1 KPI. Site opportunities (Location/ 4.2 Phase 2. Diagnosis and analysis Topography) Formerly agricultural land, the district of Cuesmes The main criteria considered for the phase of diagno- was created during the years ‘50–‘60 to accommo- sis are summarised in Table 2; among them, the ana- date low-income populations due to its urban lysis of the built and non-built environment, the Figure 6. Geographical location of selected case-study (perimeter of analysis). 596 S. KOUTRA ET AL. Table 2. Calculations of energy requirements for apartment blocks non-renovated. Degree Losses UAmin One building Total (D ) UAmax One building Total (D ) tmin tmax 2 2 Month days (m ) U (W/m K) (W/K) (D ) (kWh) (kWh) (W/K) (D ) (kWh) (kWh) 1min 1max J 436 2,079 2,2 3.659,04 38.288,19 153.152,78 5.488,56 57.432,29 229.729,17 F 544 47.772,43 191.089,70 71.658,64 286.634,56 M 457 40.132,35 160.529,40 60.198,53 240.794,10 A 228 20.022,27 80.089,07 30.033,40 120.133,60 M 149 13.084,73 52.338,91 19.627,09 78.508,36 J 96 8.430,43 33.721,71 12.645,64 50.582,57 J 78 6.849,72 27.398,89 10.274,58 41.098,34 A 85 7.464,44 29.857,77 11.196,66 44.786,65 S 185 16.246,14 64.984,55 24.369,21 97.476,83 O 214 18.792,83 75.171,32 28.189,24 112.756,98 N 397 34.863,33 139.453,33 52.295,00 209.180,00 D 474 38.288,19 153.152,78 62.437,86 249.751,43 Total 290.235,1 1.160.940,21 440.357,7 1.761.432,59 growth. At the time being, RES conversion technol- 4.2.3 KPI. mixing ogies remain undeveloped in the district, however 4.2.3.1 Functional mixing. The district has a total a potential biomass energy production facility sup- surface of 46,17 ha and 1.245 buildings and Table 5, it plied by organic waste has been planned. Another is an ancient and highly energy consumer district option examined is connecting to the geothermal principally composed of residential land-use without inventory in the city of Mons. The meteorological mixed-use attributes. data provided by the IRM (2013) (IRM 2020) related to the solar radiation per year as well as the direc- 4.2.3.2 Social mixing. Regarding the criterion of tion and the average velocity of the wind attest ‘social mixing’, we observe a mixed district in terms Cuesmes’ potential towards an energetic retrofit - of age categories and a diversity of nationalities (50% ting suiting net-zero energy district objectives. As of the local population in the Community of Mons are for the previous analysis in the case of Epinlieu, the French and Italian and the rest comprises of diverse ‘geothermal’ opportunity remains still nationalities, Germans, Spanish, Greek) (Wallonie underexplored. Familles 2018). 4.2.3.3 Mixing of dwellings and built environ- 4.2.2 KPI. Mobility and public means of transport ment. Regarding the diversity in building morpholo- During the ‘on-site’ analysis in the district (16–31/ gies in Cuesmes, the current building stock consists of 3/2019), we observed that citizens are ‘car depen- completely terraced housing. However, the buildings dent’ for their daily movements inside and around consist of a R + 1 (64%), constructions on the ground the district. The district is not well-connected by floor, at 20%, constructions in R + 2 (10%) Table 6 and the public means of transport; nonetheless, it is constructions in R + 3 (6%). The built stock of the situated close to the city of Mons and surrounded district is dated basically before 1850 (more than 70% by other cities, as well (5 km far from Mons, of the existing dwellings) with the terraced form to be 56 min walk or 25 min by bike from Jemappes, predominant (Fig. 8). The district has low mixed-use 1h15walk or 16 min by bike from Frameries, etc.). attributes including basically residential activities, while The district is not well-served by public means of the land use is occupied partially by public and socio- transport Table 4: the only railway stations at cultural equipment as well as commercial centres. 5 km around the district are in Quaregnon, The built inventory for Epinlieu district has Frameries, and Mons between 4 and 5 km of the analogous characteristics of a ‘social housing’ Table district’s surroundings (Fig. 7). Similar to these 7 project of the Hainaut area with renovated dwell- findings, in Epinlieu the analysis proves a well- ings of moderate construction quality and important served district by bus and in a walkable distance deficiencies in terms of energy losses and heating from the city centre (2.5 km distance). (cooling) requirements, as visualised in Fig. 9 INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 597 Figure 7. Walkability analysis in the Cuesmes district and educational infrastructure to surroundings. Figure 8. Analysis of the built environment in regard to the criterion of ‘construction age’ (Cuesmes). 4.2.4 Estimation of energy requirements After the first estimations and the outcomes, we It is expected that the corresponding space heating encoded the U-values using the calculation tool of the needs of the majority of the district’s building stock buildings’ thermal requirements provided by the would present a high value as it is concluded by Belgian Building Research Institute (BBRI). More infor- examining the age of construction data (4). mation can be retrieved regarding the calculation tool 598 S. KOUTRA ET AL. Figure 9. Analysis of the built environment in regard to the criterion of ‘construction age’ (Epinlieu). Figure 10. Energy consumption per building typology in the selected case study. INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 599 provided by BBRI in (CSTC 2020). An illustration of the UA = 0,8 * U*S min energy requirements is provided in Fig. 10, while the UA = 1,2 * U*S max detailed calculations of the annual heating energy D = (UA X Degree Days * 24)/1000 1min min requirements are explained in tables below D = Number of units * D 1tmin 1min Explanations for the calculations D = (UA *Degree Days * 24)/1000 1max max Table 3. Calculations of energy requirements for apartment blocks non-renovated. Degree Losses UAmin One building Total (D ) One building Total (D ) tmin tmax 2 2 Month days (m ) U (W/m K) (W/K) (D ) (kWh) (kWh) UAmax (W/K) (D ) (kWh) (kWh) 1min 1max J 436 2,079 1,1 1.829,52 19.144,10 134.008,68 2.744,28 28.716,15 201.013,02 F 544 23.886,21 167.203,49 35.829,32 250.805,24 M 457 20.066,18 140.463,23 30.099,26 210.694,84 A 228 10.011,13 70.077,93 15.016,70 105.116,90 M 149 6.542,36 45.796,54 9.813,55 68.694,82 J 96 4.215,21 29.506,50 6.322,82 44.259,75 J 78 3.424,86 23.974,03 5.137,29 35.961,05 A 85 3.732,22 26.125,55 5.598,33 39.188,32 S 185 8.123,07 56.861,48 12.184,60 85.292,22 O 214 9.396,41 65.774,90 14.094,62 98.662,35 N 397 17.431,67 122.021,67 26.147,50 183.032,50 D 474 20.812,62 145.688,34 31.218,93 218.532,50 Total 146.786,05 1.027.502,34 220.179,07 1.541.253,51 Table 4. Calculations of energy requirements for single-family houses non-renovated. Degree Losses UAmin One building Total (D ) One building Total (D ) tmin tmax 2 2 Month days (m ) U (W/m K) (W/K) (D ) (kWh) (kWh) UAmax (W/K) (D ) (kWh) (kWh) 1min 1max J 436 269,86 1,4 302,24 3.162,67 2.030.435,97 453,36 4.744,01 3.045.653,95 F 544 3.946,09 2.533.387,99 5.919,13 3.800.081,99 M 457 3.315,00 2.128.232,19 4.972,51 3.192.348,29 A 228 1.653,87 1.061.787,62 2.480,81 1.592.681,42 M 149 1.080,82 693.887,52 1.621,23 1.040.831,28 J 96 696,37 447.068,47 1.044,55 670.602,70 J 78 565,80 363.243,13 848,70 544.864,70 A 85 616,58 395.841,87 924,86 593.762,81 S 185 1.341,96 861.538,20 2.012,94 1.292.307,30 O 214 1.552,32 996.590,13 2.328,48 1.494.885,20 N 397 2.879,77 1.848.814,40 4.319,66 2.773.221,60 D 474 3.438,32 2.207.400,57 5.157,48 3.311.100,85 Total 24.249,58 15.568.228,06 36.374,36 23.352.342,09 Table 5. Calculations of energy requirements for social houses non-renovated. Degree Losses UAmin One building Total (D ) One building Total (D ) tmin tmax 2 2 Month days (m ) U (W/m K) (W/K) (D ) (kWh) (kWh) UAmax (W/K) (D ) (kWh) (kWh) 1min 1max J 436 175,36 1,60 224,46 2.348,76 575.445,66 336,69 3.523,14 863.168,50 F 544 2.930,56 717.987,25 4.395,84 1.076.980,88 M 457 2.461,89 603.162,08 3.692,83 904.743,12 A 228 1.228,25 300.921,13 1.842,37 451.381,69 M 149 802,67 196.654,60 1.204,01 294.981,89 J 96 517,16 126.703,63 775,74 190.055,45 J 78 420,19 102.946,70 630,29 154.420,05 A 85 457,90 112.185,51 686,85 168.278,26 S 185 996,61 244.168,46 1.494,91 366.252,69 O 214 1.152,83 282.443,51 1.729,25 423.665,27 N 397 2.138,66 523.972,31 3.207,99 785.958,47 D 474 2.553,47 625.599,18 3.830,20 938.398,78 Total 18.008,94 4.412.190,03 27.013,41 6.618.285,05 600 S. KOUTRA ET AL. Table 6. Calculations of energy requirements for social houses renovated. Degree UAmin One building Total (D ) One building Total (D ) tmin tmax 2 2 Month days Losses (m ) U (W/m K) (W/K) (D ) (kWh) (kWh) UAmax (W/K) (D ) (kWh) (kWh) 1min 1max J 436 175,36 0,7 98,20 1.027,58 251.757,48 147,30 1.541,37 377.636,22 F 544 1.282,12 314.119,42 1.923,18 471.179,13 M 457 1.077,08 263.883,41 1.615,61 395.825,12 A 228 537,36 131.652,99 806,04 197.479,49 M 149 351,17 86.036,39 526,75 129.054,58 J 96 226,26 55.432,84 339,38 83.149,26 J 78 183,83 45.039,18 275,75 67.558,77 A 85 200,33 49.081,16 300,50 73.621,74 S 185 436,02 106.823,70 654,02 160.235,55 O 214 504.36 123.569,04 756,55 185.353,56 N 397 935.66 229.237,89 1.403,50 343.856,83 D 474 1.117,14 273.699,64 1.675,71 410.549,47 Total 7.878,91 1.930.333,14 11.818,37 2.895.499,71 Table 7. Calculations of energy requirements for social houses for elderly people non-renovated. UAmin One building Total (D ) One building Total (D ) tmin tmax 2 2 Month Degree days Losses(m ) U (W/m K) (W/K) (D ) (kWh) (kWh) UAmax (W/K) (D ) (kWh) (kWh) 1min 1max J 436 175,36 0,70 98,20 1.027,58 251.757,48 147,30 1.541,37 377.636,22 F 544 1.282,12 314.119,42 1.923,18 471.179,13 M 457 1.077,08 263.883,41 1.615,61 395.825,12 A 228 537,36 131.652,99 806,04 197.479,49 M 149 351,17 86.036,39 526,75 129.054,58 J 96 226,26 55.432,84 339,38 83.149,26 J 78 183,83 45.039,18 275,75 67.558,77 A 85 200,33 49.081,16 300,50 73.621,74 S 185 436,02 106.823,70 654,02 160.235,55 O 214 504,36 123.569,04 756,55 185.353,56 N 397 935,66 229.237,89 1.403,50 343.856,83 D 474 1.117.14 273.699,64 1.675,71 410.549,47 Total 7.878,91 1.930.333,14 11.818,37 2.895.499,71 D = Number of units * D itineraries and mild transportation systems. The pro- 1tmax 1max Combining the above, it can be supported that the posed action plan introduces the idea of a more com- district presents numerous problems related to con- pact, mixed-use and dense district with more struction, the building typologies, structures and forms infrastructure responding to the daily citizens’ as well as a low grade of renewable energy resource requirements and less ‘car dependent’. Inspired by integration. Rogers’ planning theory (Urban Task Force 1999). In comparison with the case of Cuesmes, the urban Pillar 2: Maximisation of local energy production, context of Epinlieu district consists of terraced houses enhancement of RES. The analysis considers the solar with gabled, flat or mansard roofs or gabled roofs with potential and we proposed the PVs’ installation as parking. The energy (annual) profile is presented in a preliminary step; similar was the case for the case Fig. 11 (Koutra et al. 2019). of Epinlieu after the diagnostic phase. In the scope of sizing (the solar panel installation per typology), the study included indicators, such as the temperature 4.3 Phase 3. Assessment of the scenarios and solar irradiance. Three types of annual loads In particular, the proposed actions are: were calculated per typology based on the average Pillar 1: Emphasis on actions in the KPIs of: mobility consumption. Energy flow data were provided on an and mixing. The implemented scenario focuses its hourly basis for an average year. Specifically, terraced analysis on the expansion of the existing bus network houses with flat roofs and houses with double- and the passages per day with complementary pitched roofs were considered as a common typology INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 601 Figure 11. Average energy requirements in the diverse typo-morphologies of the district of Epinlieu. with respective 5566 kWh/yr consumptions. For types by a Cost-Benefit Analysis to investigate the possible 3 and 46,123 kWh/yr, and finally the large apartment profits of this installation (Ioakimidis and Ferrao 2010). blocks had 22,264 kWh/yr. (Koutra et al. 2019). What is important for the biomass scenario, which was Pillar 3: Energy storage PV electric storage: hardly to assess at our current analysis in Cuesmes, is Balancing from the one side the dysfunctions and the estimation of the demand for the installation of the problems described at the diagnostic phase of the technology and the carriers needed to serve the the analysis, as mentioned previously, we analysed requirements. Modelling tools are proposed at the the scenario of PVs’ installations. The HOMER micro- same work for this analysis, such as TIMES (a dynamic grid optimisation tool was used for the study of the model) as a further analysis. optimised integration of rooftop PV panel installa- tions on the district’s building stock related to the 4.4 Phase 4. Implementation maximisation of locally available RES exploitation as part of the second pillar of the U-ZED approach (ener- Following the analysis carried out in previous sections getic hybridisation). of the manuscript, we note that the district has var- The energetic and financial analysis in HOMER ious dysfunctions related to mobility, social equity, demonstrated that the region of Mons offers a good a high energy consumption, a strong dependency by solar irradiance potential with an annual average of car, etc. It, therefore, appears important in this work to 2.91 kWh/m /day. Consequently, as a more affordable propose solutions to match the citizens’ expectations and accessible renewable energy conversion technol- and to achieve the NZED’s objectives. In this section, ogy, in line with the intended zero-energy application we will establish a general situation in which we will in the district, we proposed the scenario of PVs’ instal- deal with the problems mentioned at the diagnostic lation as an initial energy retrofitting intervention. study Table 8. In a projected situation, we propose the Nonetheless, as explained already, the district appears analysis of the energy criterion with regard to the interesting agricultural activity, therefore, the scenario energy potential/inventory of the region to see how of the energetic hybridisation could be the subse- to make the district autonomous in renewable ener- quent step of the U-ZED application on-site. gies, the possible energy hybridisations and what Ioakimidis and Ferrao at their works explain the ben- would be the solutions allowing to reach and main- efits of the biomass on the influence of local electric tain this autonomy in the future. power production and fuel consumption; however, an In order to better meet the population needs, the analytical methodological and holistic approach is requirements towards the NZED transition and bring required to assure the application of the data and attractiveness to the district, we propose the use of the implementation of the strategy ‘on-site’ followed Rogers’ theory to allocate the functions in relation to 602 S. KOUTRA ET AL. the diverse distances. By living in closer proximity to In the proposed scenario, we studied the possi- each other, we can accommodate far more of the bility of energy production by PVs. As a reminder, world’s population, use less energy, concentrate the region of Mons has a good solar irradiance goods and services and move from one place to potential allowing an interesting rate of its exploita- another more efficiently. For instance, building at 50 tion. The availability of solar irradiation at the desig- homes to the hectare and above has created all the nated location is calculated from the global solar attractive spaces we like best. At below 50 homes per irradiation incident on the surface of the PV array. hectare, it is hard to keep shops, buses, doctors, nur- Fig. 13 presents the monthly averages of daily inci- series and schools within walking distance; the less dent solar radiation throughout a year for the stu- dense cities are, the further they sprawl, the worse the died location. In addition, the buildings on-site are traffic problems are. Phase 4 and U-ZED’s contribution suitable for PV application as, firstly, the size and at the re-arrangement of a highly dense and compact distance of the buildings do not cast shade on their district is inspired by the graphs provided below. respective rooftops, and, secondly, their east west Addressing the problem of infrastructure and ser- orientation allows to capture solar radiation vices’ proximity, we recommended actions such as: throughout the day. the establishment of new services to handle the In the case of placing the panels required to ‘mono-functional’ attributes appeared in the district match the district’s annual electric demand on (2,3 Fig. 12), educational activities (1 and 4, Fig. 12) a single location, this would yield a total area of and the re-arrangement of green and public spaces (5, 25 ha, equivalent to almost half of the total land 6 and 7, Fig. 12). In terms of accessibility, we recom- area of the studied district. A solution promoting mended the expansion of the existing bus network a large-scale centralised solar power plant, or with additional itineraries (streets of Ciply and a photovoltaic power plant is therefore not feasible Espinette) and the reinforcement of mild transporta- due to space limitations. Moreover, this solution is tion networks with cycling secure lanes connected to not to be preferred since it entails a significant the existing Ravel and the Vélib system for bike rental, alteration on the environment and infers constraints (8, Fig. 12). on land use. Hence, an applicable solution would be Figure 12. Proposal for the district’s re-arrangement towards the transition of the zero-energy concept in Cuesmes. INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 603 Figure 13. Annual profile of average daily incident solar radiation (kWh/m2/day) with monthly resolution for the area of Cuesmes. Table 8. Results of the rooftop PV installation optimisation run. Estimated annual electricity Net present Calculated PV Levelized cost of Annual energy Scenario consumption (kWh/yr) cost (€) output (kWh/yr) energy (€/kWh) savings (%) Including storage 3.300 € 19.942 5.434 € 0.273 77.3 Without storage 3.300 € 5.843 5.434 € 0.065 42.8 placing PV rooftop installations on the buildings, rooftop, which can be placed on a 3 × 5 array. The taking into account that the average available roof- electricity tariffs were imported from the Eurostat top surface area was estimated at 25 m per build- database and were defined at 0,275 €/kWh for grid ing according to the findings of the diagnosis phase purchase and 0.15€/kWh as an indicative feed-in-tariff on the built environment. Following the proposed resulting from the Qualiwatt established averages scenario, an optimal rooftop PV-electrical storage (Eurostat 2018). system for buildings located in the Cuesmes district It is important to mention that PV installations in has been sized and optimised with the use of the the Wallonia region are subsidised through green HOMER software tool on a 15-year project lifetime. certificate programmes and net metering, however Furthermore, the panels’ optimal rooftop orienta- they have been inactive since the end of June 2018, tion (slope and azimuth) was calculated with the when the Qualiwatt programme expired. Error! online tool PV-GIS (European Commission 2019a) Reference source not found. presents the key findings enabling increased efficiency on the conversion of of the optimisation study, distinguishing between an incident solar irradiance. Although HOMER optimises installation including an electrical storage unit and the installation subject to the minimisation of its one without any storage provisions. The purpose of respective Net Present Cost, the component capacity introducing subcases is two-fold: (a) to highlight the search space is configurable, offering an option for advantages of coupling the PV array mainly reflected setting an upper boundary on each component’s on the percentage of annual energy savings and (b) to parameter search space. Acknowledging the total contrast the trade-off between system costs and rooftop installed capacity limitations applying in potential energy savings. Regarding energy consump- Belgium (max. PV capacity <10 kW), an upper bound- tion, a synthetic annual electric load profile (3.300 ary value was placed on the PV module capacity kWh/yr) was compiled and inserted as the occupant optimisation search space. The equivalent peak usage pattern on which the energy dispatch algo- power capacity to a 25 m total array area is approxi- rithm would size the PV-system, based on energy mately 4.95 kW, in this case 15 PV modules per provider data for multiple categories of residential 604 S. KOUTRA ET AL. Figure 14. Annual daily hourly means of the power flows corresponding to each rooftop PV system configuration. electricity consumers (Lepage 2019). Annual energy 4.1 GWh, the 3.2 GWh can be supplied from rooftop savings are calculated as the percentage of the reduc- integrated PV-storage systems or 1.8 GWh directly tion on the purchased energy from the grid over the generated from rooftop mounted PV arrays. These assumed annual energy consumption. The LCOE is values are comparable to the maximum achievable defined as the average cost per kWh of useful elec- annual PV contribution towards diminishing the trical energy produced by the system, hence this fig - energy consumption on district scale, which is fixed ure also accounts the total injected energy to the on 3.6 GWh for the first configuration and 2.0 GWh for power grid. The values of annual cashflows use dis- the second configuration due to the imposed capacity count and inflation rates evaluated at 2% and 1%, limitations mentioned above. The geometric footprint respectively, accounting for a 0,99% real discount of each rooftop system is equivalent to 24.9 m . The rate, influencing the calculated net present cost. total cost of implementing subcase (a) is € 18.951.390 Fig. 14 depicts the annual daily hourly means of and (b) € 5.534.025 corresponding to a 1.11 k to CO the power flows corresponding to each rooftop PV and 2.0 k to CO emissions reduction attributed solely system configuration with and without the inclusion to reduced grid energy purchases. In the Appendix B, of a battery energy storage component against the we provide the key results from the HOMER analysis synthesised household demand. The benefits of cou- performed for a generic building located at the district pling PV generation with battery electric storage are of Cuesmes. reflected upon the reduction of grid purchases during day intervals with scarcity of solar resources, which under battery discharging demonstrate finer 5 Conclusions load matching capabilities than the PV only config - uration. In addition, the evening peak demand can be Rapidly growing world energy use and urban growth served with the charged energy driven to the battery in modern ‘mega-cities’ have already created con- from excess PV generation during daylight, leading to cerns regarding the RES’ exhaustion and the impacts an overall reduction in grid sales compared to the of the climate change. Undoubtably, increasing system without a storage unit. energy efficiency is commonly assumed as If the results for the rooftop installation of one a ‘difficult’ process in complex systems and living building are extrapolated to the district level as laboratories, as the cities are. In this current context a proxy for the calculation of the costs and benefits of rising uncertainties, prioritising the efforts towards of this intervention, it can be supported that from the reduction of the energy consumption among the a hypothetical cumulative annual consumption of European and national policies. INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 605 All these issues due to the uncontrolled urban Through three pillars of action: (1) the optimisation sprawl are well documented, while the energy con- of the energy requirements, (2) the energetic hybridisa- sumption derived from the built environment and the tion and (3) the organisation of energy storage, we transportation represents a significant problem to introduce a check-list of key performance indexes, consider. Although, some research is being developed which have a significant impact to the decision of the for more autonomous and optimised urban patterns, zero-energy district planning. Inspired by the DPSIR specific evaluation tools and methods to evaluate the model, we developed an algorithmic process of the urban strategic planning towards this direction are U-ZED application in districts with the introduction of still missing, while the existing ones basically focus four (4) phases of planning: (1) the strategic planning on individual buildings neglecting the complex phe- decision (derived mainly by the city stakeholders and nomena occurred in urban scale, for instance the the decision to the zero-energy transition), (2) the diag- mobility flows etc. nosis and the analysis of the current situation in the In this manuscript, and to reply to this gap, district (including the typo-morphological analysis of its assuming a strong correlation between the factors built and non-built environment as well as the calcula- of the energy consumption and the typo- tion of the actual energy requirements of its users and morphological structure of an agglomeration, we the offer by RES on-site), (3) the development of introduce a simplified methodological decision a scenario analysis towards the ‘optimal’ combination approach, the U-ZED, aiming at conceptualising and (4) the implementation. the zero-energy balance in larger territorial scales The first attempts to validate and experiment the as part of a holistic and interdisciplinary approach proposed methodology have been realised and of a toolkit introduced in the RESIZED European experimented in the various districts in Belgium, for project by the Faculties of the University of Mons. instance in Cuesmes, but also in previous attempts – The literature revealed the weaknesses of develop- district of Epinlieu; both pilot projects are of social ing methodologies for district scales to estimate housing character, close to the city of Mons with the overall consumption but mainly to assess prop- previous tentative of being renovated, but still are erly the factors influencing the zero-energy considered as low-quality housing areas. The main objectives. comparative attributes of both analyses are explained For this study, we consider the ‘district’ as an at the manuscript; nonetheless, among the perspec- urban block and a micrograph of a city. The analysis tives has been the continuity of the RESIZED project prioritised the review of several aspects for the and the involvement to the validation of the theore- understanding and the evolution of the concept tical findings of more case applications with different and the identification of the aspects that influence urban attributes and context (i.e. weather conditions, the energy performance from a design and opera- typologies etc.). At the same time, functional and tion insight. To do so, several indicators, namely social mixing are low; however, the district has inter- climatic or morphological, are discussed to develop esting possibilities towards its future transition to the a NZED strategy. Nonetheless, the variety of existing application of the zero-energy concept on-site. In the variables and indexes reveals that there is no spe- relevant section we provide the diverse scenarios fol- cific and standardised or broadly accepted checklist lowing our analysis as well as the cartographical simu- of indicators for energy efficiency and performance lations of the current and the projected situation with to NZED design. the implementation of the U-ZED approach. 606 S. KOUTRA ET AL. INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 607 Although the zero-energy idea can be conceptua- EPRES Energy Primary from Renewable Energy Sources PV Photovoltaic(s) lised in a district with an approach like individual build- NREL National Renewable Energy Laboratory ings by articulating the main energy uses, the concept LCA Life Cycle Assessment remains complicated and challenging for contempor- CBA Cost-Benefit Analysis ary cities because of various constraints and limitations GIS Geographical Information Systems in different levels of action. This implies innovative DPSIR Drivers-Pressures-States-Impacts-Responses KPIs Key performance indicators approaches to interdisciplinary planning that highlight HOMER Hybrid Optimization Model for Electric the importance of the zero-energy concept and aid city Renewables stakeholders and planners to define these structures. PEB Performance Energetique des Batiments Indeed, the interrelation between urban structure and BBRI Belgian Building Research Institute energy is a key aspect of this path. Related to this, IRM Royal Meteorological Institute of Belgium (Institut Royal Météorologique) a ‘well-structured’ area is a key point that increases LCOE Levelized Cost of Energy sustainable transport and the share of renewable resources. This study contributes to the scientific discussion on Acknowledgements the linkage between energy and urban structure to This research was funded by the European Commission increase the energy efficiency in districts. One of the under the RESIZED (Research Excellence for Solutions and main challenges around this topic resides on the com- Implementation of Net Zero Energy City Districts) project, plexity of the urban scale. Studies focussing on this as part of Grant Agreement no 621408, as well as by the problematic are still few and further analysis should be European Regional Development Fund and Wallonia Region, conducted to understand and identify in-depth the con- project reference FEDER C3E2D–Wal-e-cities. cept in an attempt to enable its feasibility in practice. The human factor but also the user (occupant) behaviour Disclosure statement and public awareness are significant for successful poli- cies and for the zero-energy concept in districts. Further No potential conflict of interest was reported by the author(s). research and works can contribute on extending the presented approach and applying it on diverse case Funding studies with diverse contexts, climate conditions, living standards and constraints with respect to the longevity This work was supported by the RESIZED european FP7 project of modern cities and the achievement of their sustain- (grant agreement: ID: 621408); European Regional Development Fund and Wallonia Region [C3E2D (UE+RW / FEDER)]. able objectives. The study reveals the need for more comprehensive and complementary approaches to embrace correctly all the dimensions of the zero- Notes on contributors energy concept and prioritise it in the forthcoming urban strategies of modern city planning. Sesil Koutra Sesil KOUTRA is an Engineer of Urban Planning and Design (2009) graduated from the Faculty of Engineering of Aristotle University of Thessaloniki (Greece). She holds a Master in Project and Construction Management from the Nomenclature Faculty of Civil Engineering of Aristotle University of EU European Union Thessaloniki (Greece) (2011). She began her professional career U-ZED Urban zero-energy district in 2009 as a Junior Urban Consultant for studies and urban GHGs (emissions) projects and the management and realisation of European pro- Greenhouse gases (emissions) jects. Since April 2015, she has been carrying out a doctoral MS Member state thesis at the Faculty of Architecture and Town Planning, under NZED Net-zero-energy district the supervision of Professor Vincent BECUE and defended her EPBD Energy Performance of Buildings’ Directive thesis in May 2020. (2002/91/EC) Sesil KOUTRA performed her thesis under the European FP7 NZEB(s) Net-zero-energy building research project RE-SIZED (Research Excellence for Solutions IEA International Energy Agency and Implementation of net Zero Energy City Districts). This RES Renewable Energy Sources work concerns the typo-morphological analysis of the autono- DHW Domestic Hot Water mous district in energy and the development of an assessment RE Renewable Energy tool on a parametric basis towards the territorial adaptation to EPGP Energy Primary Green Purchased the zero-energy concept and define the typo-morphology of the 608 S. KOUTRA ET AL. net-zero energy district. Since November 2019, she participates making it possible to optimise resilient projects according to in the research project ‘CoMod’, which he proposes to study this territorial vulnerabilities. notion of ‘compact city’ using graph theory in collaboration with Vincent Becue has a PhD in building art and urban planning, the Research Institute for Complex Systems of UMons and since applied research around the city and technical and environmen- February 2020, she is charged with the course on sustainable tal issues related to urban planning and, in particular for improv- urban planning in the Erasmus Mundus SMACCs (Smart Cities ing the spatial quality. Spatial organisation is an additional and Communities) program. dimension to the economic, environmental and social pillars and makes it possible to define the quality of sustainable Noémie Denayer Noémie is an Architect graduated in 2019 from urban planning and mainly the composition of urban places the Faculty of Architecture and Urban Planning of the University according to interrelations functional. This therefore requires of Mons performing her professional internship at the time a set of urban information in order to understand the distribu- being. tion of the different elements that make up the building, the Nikolaos-Fivos Galatoulas Nikolaos-Fivos Galatoulas is city, the territory and the landscape: forecasts for the whole city, a Research Assistant at the Department of Thermodynamics its future form, the distribution of activities and their many and Mathematical Physics of the Research Institute of Energy/ relationships. This is why he has chosen to favour research in UMONS, Mons, Belgium born in Patras, Greece. He served 3 the field of decision-aid systems based on space and allowing years as a Research Assistant at the ERA-Chair Net-Zero Energy the optimisation of projects and in particular the mix of urban Efficiency Unit (RESIZED project), hosted at the University of functions. He is interested in the development and use of such Mons, Belgium. He holds a Dip. Eng. in Applied Mathematics methods to provide project stakeholders with solutions to and Physical Sciences and a MSc in Microsystems and improve urban quality. This research has several key objectives Nanodevices both obtained from the National Technical which, put end to end, must allow the development of concepts, University of Athens (2013 and 2015). His MSc thesis was carried models and tools for the evaluation of sustainable urbanisation out in collaboration with the Institute of Nanoscience and (district level), integrating the content of the city (populations, Nanotechnology of the National Centre for Scientific Research activities and urban places). (NCSR) Demokritos. In addition, his experience includes 2 years Christos S. Ioakimidis University Professor with teaching on as a research student on e-tongue sensors (NCSR, Greece) and numerous under/post graduate courses related to energy, trans- 2-year employment in the renewable energy industry (Greece). port and Nanotechnology materials applied on energy issues. His current interests are related to microgrids, distributed Entrepreneur on cutting-edge technologies/services in the energy resources, combined energy studies (thermal/power), energy/transport sectors. data analysis and sustainable mobility. Experienced Researcher with extensive research portfolio on Nikolaos-Fivos Galatoulas’ work as a research assistant has cutting-edge research-driven projects on energy system analysis focused on developing data-driven methods for net-zero energy and modelling and Nanotechnology materials applied to energy district (NZED) planning. The main applications investigated issues. were on performance energy metrics of various hybrid renew- Engineer and Manager with large experience on Keys-in- able district energy system designs (power supply and heating), hands projects related with energy/renewable sectors (wind, sustainable mobility technology integration and air pollution solar PV/CSP, biomass, CHP, energy storage via batteries/ monitoring. Since the temporal profile of renewable power pumped, electro-mobility). generation is intermittent, the successful integration of renew- Specialities: (In general the new field of Integrated Large/ able resources into the NZED grid is dependent on the quality of Small Scale Complex Smart Energy and Transport Dynamic input (e.g. climate data, 24-hour forecasts, system component Systems towards a Sustainable District/City) on topics such as: characteristics etc.) for the unit commitment analysis, the opti- Energy management (HEMS,BEMS), modelling and energy/ mal operation of grid connected RES plants and the control of transport policy, demand side management, energy efficiency coupled energy storage systems. To this end, promoting the use on buildings (Smart Buildings), energy and electricity markets, of innovative quantitative methods and analysing urban data smart grids, energy/transport systems integration (RES, mRES, can contribute to informed decision-making within the scope of CCS, EVs, storage), Intelligent Transportation Systems (V2I, V2V, sustainable development. M2M, autonomous driving, etc), sustainable mobility (e-mobi- Vincent Becue Head of service for the Projects, City and lity), innovation/green economy and Nanomaterials on energy/ Territories, Vincent Becue is an architect and research professor transport problems. at the School of Engineers of the City of Paris (EIVP). He is also spokesperson for the doctoral school in architecture, urban planning and urban engineering in FNRS in Belgium. 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HOMER Analysis and Simulations Total Net Present Cost: €19.941,90 Levelized Cost of Energy (€/kWh): €0,273 System Simulation Report Location: Rue Louis Caty 196, 7033 Mons, Belgium (50°26.5ʹN, 3° 54.5ʹE) System Architecture Component Name Size Unit PV CanadianSolar All-Black CS6U-330P 4,95 kW Storage Sonnen Batterie 4 kW-6 kW eco 6 1 Strings System converter Studer Xtender XTM 4000–48 3,34 kW Grid Grid 999.999 kW Dispatch strategy HOMER Load Following Net Present Costs Name Capital Operating Replacement Salvage Total CanadianSolar €2.400 €1.933 €0 €717 €3.616 MaxPower CS6U-330P Studer Xtender €1.337 €0 €1.101 -€499 €1.938 XTM 4000–48 sonnenBatterie €10.785 €0 €8.853 -€4.017 €15.621 4 kW-6kWh eco Grid €0,00 -€1.933,00 €0,00 €0,00 -€1.933,00 Other €700,00 €0,00 €0,00 €0,00 €700,00 System €15.056,00 -€1.659,00 €5.393,00 -€6.700,00 €19.942,00 Annualised Costs Name Capital Operating Replacement Salvage Total CanadianSolar €186,23 €150,00 €0,00 -€55,67 €280,56 MaxPower CS6U-330P Studer Xtender €103,72 €50,00 €85,42 -€38,76 €150,38 XTM 4000–48 sonnenBatterie €836,89 €0,00 €686,95 -€311,69 €1.212,00 4 kW-6kWh eco Grid €0,00 -€149,97 €0,00 €0,00 -€149,97 Other €54,32 €0,00 €0,00 €0,00 €54,32 System €1.181,00 €0,03 €772,36 -€406,12 €1.547,00 612 S. KOUTRA ET AL. Electrical Summary Quantity Value Units Excess Electricity 118 kWh/yr Unmet Electric Load 0 kWh/yr Capacity Shortage 0 kWh/yr Production Summary Component Production (kWh/yr) Percent (%) CanadianSolar MaxPowerCS6U-330P 5.434 87,9 Grid Purchases 750 12,1 Total 6.184 100 Consumption Summary Component Production (kWh/yr) Percent (%) AC Primary Load 3.300 58,2 Grid Sales 2.374 41,8 Total 5.674 100 PV: CanadianSolar MaxPower CS6U-330P CanadianSolar MaxPower CS6U-330P Electrical Summary Quantity Value Units Minimum Output 0,00 kW Maximum Output 4,87 kW PV Penetration 165 % Hours of Operation 4.385 hrs/yr Levelized Cost 0,0516 €/kWh CanadianSolar MaxPower CS6U-330P Statistics Quantity Value Units Rated Capacity 4,95 kW Mean Output 0,20 kW Mean Output 14,90 kWh/d Capacity Factor 12,50 % Total Production 5.434,00 kWh/yr Storage: sonnenBatterie 4 kW-6kWh eco 6 sonnenBatterie 4 kW-6kWh eco 6 Properties Quantity Value Units Batteries 1 qty. String Size 1 batteries Strings in Parallel 1 strings Bus Voltage 240 V INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 613 sonnenBatterie 4 kW-6kWh eco 6 Result Data Quantity Value Units Energy In 1.373 kWh/yr Energy Out 1.186 kWh/yr Storage Depletion 6 kWh/yr Losses 193 kWh/yr Annual Throughput 1.279 kWh/yr Converter: Studer Xtender XTM 4000–48 Studer Xtender XTM 4000–48 Electrical Summary Quantity Value Units Hours of Operation 7.238 hrs/yr Energy Out 4.924 kWh/yr Energy In 5.129 kWh/yr Losses 205 kWh/yr Studer Xtender XTM 4000–48 Statistics Quantity Value Units Capacity 3,34 kW Mean Output 0,56 kW Minimum Output 0,00 kW Maximum Output 3,34 kW Capacity Factor 16,80 % Grid Grid Transactions: Month Energy purchased (kWh) Energy sold (kWh) Net energy purchased (kWh) Energy charge January 157,00 74,50 82,80 €32.,09 February 94,40 105,00 −10,60 €10,20 March 63,30 176,00 −113,00 -€8,98 April 14,90 251,00 −236,00 -€33,56 May 7,51 338,00 −331,00 -€48,69 June 5,15 332,00 −327,00 -€48,34 July 0,00 350,00 −350,00 -€52,54 August 6,01 322,00 −316,00 -€46,62 September 32,80 221,00 −188,00 -€24,12 October 50,30 103,00 −52,20 -€1,54 November 132,00 76,80 55,30 €24,79 December 186,00 25,60 160,00 €47,33 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png International Journal of Urban Sustainable Development Taylor & Francis

The zero-energy challenge in districts. Introduction of a methodological decision-making approach in the case of the district of Cuesmes in Belgium

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INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 2021, VOL. 13, NO. 3, 585–613 https://doi.org/10.1080/19463138.2021.1985504 The zero-energy challenge in districts. Introduction of a methodological decision-making approach in the case of the district of Cuesmes in Belgium a a b a c Sesil Koutra , Noémie Denayer , Nikolaos-Fivos Galatoulas , Vincent Becue and Christos S. Ioakimidis a b Faculty of Architecture and Urban Planning, University of Mons, Mons, Belgium; Faculty of Thermodynamics, Physics and Mathematics, University of Mons, Belgium; Inteligg P.C, Athens, Greece ABSTRACT ARTICLE HISTORY Received 2 November 2020 Transforming cities with the aim of achieving cleaner energy targets is a major bet Accepted 12 September 2021 worldwide, dealing with the immense stress of the rapid urbanisation, the depletion of natural resources, the climate change and its impacts during the post- KEYWORDS industrialised period. Struggling with this problematic, in this work we develop Case-study analysis; energy a horizontal and cross-sectoral process as an integral part of the city planification transition; holistic approach; towards the energy transition. Along with demonstrating the applicability of the zero- zero-energy district energy idea in more universal approach, we validated its feasibility at the case-study Cuesmes (Belgium), a social district with high energy requirements along with the RE- SIZED research project. In response to this, in this work we articulate the feasibility of the concept (zero energy) in urban scale, in a comprehensive toolkit. Comparisons and similarities with previous empirical analysis are discussed as well to complete the work and its findings. 1 Introduction Administration 2013). In fact, these trends release the need for comprehensive planning actions towards high Cities are living organisms with dynamic changes and energy performance in modern communities. processes. The post-industrial European city is charac- Looking closer at the 2030, European Commission terised by dispersed urbanisation with increasing rolls out the regulatory framework to reach the inter- trends, resulting in increased travel, substantial use of mediate target of −55% of net-zero emissions. In land social disparities and rising demand for energy a more detailed review, Taylor provides an analytical (Riera Pérez and Rey 2013). By 2035, the shift of the study on related topics; the share of renewables in global population to urban centres will be accelerating energy consumption with a projection of a 30% sharing and that figure is expected to achieve the level of 60% by 2030 is the starting point of the process (Taylor by 2050 (United Nations Development 2014). The 2020). building sector remains a pivotal consumer worldwide, At the same time, the report discusses the headline representing more than 40% of the European con- to achieve an energy efficient target for 2030 of at sumption (UNEP 2009), confirming their importance in least 32,5%, which is prioritised on European global meeting the Europe’s 2030 climate and energy targets action plan accounting that we meet a continuous (Saheb et al. 2019). At the same time, the CO emissions failure to meet this reduction as its review of the have been increased by 43% with an average annual climate plans shows that there is a gap of 2.8 percen- increase of 2% and 1.8% respectively, while current tage points for primary energy consumption and 3.1% predictions prove that this trend will continue drama- points for final energy consumption. tically in the future (US Energy Information CONTACT Sesil Koutra sesil.koutra@umons.ac.be Faculty of Architecture and Urban Planning, University of Mons, Mons, Belgium © 2021 Informa UK Limited, trading as Taylor & Francis Group 586 S. KOUTRA ET AL. Strengthening the climate objectives and policies, summarise the main comparative findings with the EU boosts for a more innovative and cross-sectoral previous pilot analysis of Epinlieu; both cases are reflexion contributing to resilient ecosystems to ‘social housing projects’ situated at Mons and are achieve the 2020 failures. In 2008, Europe introduced part of the RESIZED project demonstration studies; its targets by leveraging the arising of directives and summarised findings are provided in subsequent policies towards the reduction of the energy consump- section. tion and the carbon neutrality by 2050 (European The manuscript is structured accordingly: Section 1 Commission 2011). In fact, to overcome these chal- introduces and describes the problem and the objec- lenges, Europe outlines a ‘Green Deal’ (European tives of the research, Section 2 highlights the impor- Commission 2019a) to boost the resource-efficient tance of the urban structure for the reduction of the and to ensure an inclusive transition to cleaner and energy demand and consumption by its users, green energy aiming at the protection, conservation Section 3 presents the main methodological steps of and enhancement of the European capital but also the the introduced approach as well as the challenges and protection of European citizens’ health and well-being limitations for its applicability. Section 4 provides the from the environmental impacts and the risks’ (United main findings and results of the proposed application Nations 2019). in Cuesmes, while Section 5 summarises the main Embracing the European roadmap by turning conclusions of the work. environmental and climate challenges into opportu- nities, the Deal highlights the importance to boost 2 Understanding the zero-energy concept. efficient energy use in communities. Nevertheless, Previous works achieving operations along with the energetically autonomous communities requires intensive plan- The first indications and traces around the zero- ning processes and endeavours of synergies among energy idea were introduced already in 2010 in build- the different stakeholders. The challenge is multifa- ing level: ‘a building that has a very high energy per- ceted and the preponderance of the (net) zero energy formance. The nearly zero or very low amount of energy concept affects the planning and the decision-making required should be covered to a very significant extent processes in city level. by energy from renewable sources, including energy In response to this problematic and to articulate the from renewable sources produced on-site or nearby’ feasibility of the concept (zero-energy) in urban scale, in (European Commission 2010). In the literature, the this work we introduce the outcomes of a holistic and ‘zero-energy’ objective is mostly considered in build- comprehensive toolkit developed in European FP7 ings or the potential of solar energy utilisation for research project RESIZED (Research Excellence for active and/or passive solar heating with different defi - Solutions and Implementation of Zero Energy Districts) nitions, which co-exist, and it is presented as ‘the (ERA Chair Team 2015). In line with the national direc- building, in which a balance is underlined between the tives of Belgium for 2030 (National Energy and Climate energy taken from and supplied back to the grid over Plan (European Union 2018) for a reduction of more than a specific period (nominally a year)’ (Marique and Reiter 30% of the GHG emissions (compared to 2005) and the 2014). adjustment to the Paris Agreement and the commit- The statement of the NZEB principles became ment of the Walloon region (2019–2024) towards car- mandatory since 2018 for new public buildings in bon neutrality by 2050 (Déclaration de Politique de an effort to intensify the actions for decarbonisa- Wallonie (Service Public de Wallonie 2019), this study tion and energy efficiency in an effective manner. aims to reinforce the guidelines along with the zero- Since then, the concept gains a rising scientific energy planning. The empirical studies in demonstration interest and studies are increasingly appeared to projects of the research outcomes validated the com- explore its dimensions. Carlisle et al. document plexity of the concept but also the need for dynamic diverse contexts of the term to establish processes, citizen empowerment and effective stake- a grading definition from the building as holders’ synergies. a starting point to progress to the urban scale In this manuscript, we investigate the feasibility of applying a more general view that a ‘net-zero our toolkit in the district of Cuesmes in Belgium as energy community’ is one that has greatly less a continuity of our downstream phase and we energy requirements and that the balance of energy INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 587 for vehicles, thermal, and electrical energy is met carried out by a series of simulations with the use of principally by renewable resources and the local pro- Design Builder software and the integrated Energy duction’ (Carlisle et al. 2009). Plus tool aiming to minimise the energy consumption It is commonly true that definitions of (net) Zero of each set of buildings. Different scenarios were Building vary from one country to another – depend- assessed in terms of installing renewable energy con- ing on the climatic, economic, political conditions – , version technologies while the developed simulation but they all share a common goal: to reduce or neu- model was calibrated by means of maximising the tralise the environmental impacts on the built coefficient of correlation between measured and environment. simulated data. Over the past decades, the trends of energy- Alternatively, energy system design for transition- oriented projects are increasing in building sector, ing to NEZD can be formulated as exploiting effi - while the latest ones aims at setting the zero energy ciently the useful work potential (exergy) of and carbon objectives even on city scale (Brown and available energy resources. This approach was pro- Vergragt 2008); examples of these initiatives are posed in (Kilkis 2015) and developed as a four-step already met in the existing reviews, for instance the analysis process in order to reach NZEXD (net zero case of Beddington Zero Emission Development exergy district) and NZCED (net zero compound CO (BedZED) (Dunster 2002), the pilot plan for the city emissions district) targets. A detailed demonstration of Copenhagen to set carbon neutrality by 2025 (City of the applicability of this modelling method is per- of Copenhagen Technical and Environmental formed in (Kilkis 2014). Setting financial objectives in Administration 2012). the epicentre of reaching NZED targets entails the From the lessons-learned, and as the benefits of inclusion of extra-economic benefits generated by improving energy efficiency at building level have the suggested intervention developed a five step been understood, interest has been rising in extend- integrated evaluation framework for a NZED ing those benefits to larger scales (Pless et al. 2018). (Becchio et al. 2018). Building stock properties for A review from 1992 to 2018 by European Commission, their studied district in Turin were derived from the an insight on existing case-studies revealed that the TABULA database and comprised the engaging point transition to zero-energy districts is underway and for subsequent envelope retrofitting strategies. All ambitious targets to reduce the energy demand with considered strategies assumed district heating as the parallel increase in share from local renewable the heat network solution for a set of buildings energy sources. Municipalities consider the energy linked via heating loop. Results are hierarchised transition as a mandatory step and a consensus to according to their calculated social return on invest- achieve the local energy targets but also to emerge ments followed by a cost-benefit analysis. Last, the new and set initiatives and policies towards this direc- data inputted in the cost benefit analysis are validate tion (Saheb et al. 2019). To achieve this ambitious through a sensitivity analysis in terms of percentage target, Becchio et al. introduce a scenario planning changes on initial costs and how they affect the analysis to support the decision-making in the choice social return on investment. between policies in which energy demand forecasting In this work, a broader approach from energy models are suitable quantitative tools for an energy- efficiency is adopted contemplating for urban func- oriented planning (Becchio et al. 2016). Kilkis provides tions closely related to the urban morphology of the an analysis of a pilot ‘zero-energy’ project of Östra Sala district of Cuesmes. The methodology focuses also backe in Uppsala Municipality in Sweden within the on the spatial impact of the proposed repurposing use of Rational Exergy Management Model to curb actions since detailed data on construction age and primary energy consumed and CO emissions by building envelopes were accessible. Net zero district means of considering the level of crossing the quality targets are tackled for infrastructure concerning of resources (exergy) and the energy citizens’ needs waste management, transportation, soft mobility, (yearly) (Kilkis 2011). service provision apart from solving the net zero A comparison of the thermal comfort, the energy energy balance problem and enhancing load match- consumption, and the carbon emission rate in two ing capabilities of the heating and power technolo- types of neighbourhoods located in Madagascar was gies. Given that the vast majority of the building presented in (Nematchoua 2020). The study was stock consists of extremely aged construction, 588 S. KOUTRA ET AL. space heating needs would exhibit significant fact when moving to urban scale, additional factors improvements by enacting essential envelope retro- in regards to the design influence the energy perfor- fitting procedures. mance (Amaral et al. 2018). Saheb et al. explain that zero-energy initiatives are driven either by urban ‘retrofitting’ and are usually the 2.1 The zero-energy district and the RESIZED impacts of the urban metabolism by the transforma- European project tion of industrial areas into districts or the develop- ment of new agglomerations with high outcomes for In an effort to ‘translate’ the EPBD principles in dis- all residents, etc. (Saheb et al. 2019). In fact, the sus- tricts (Concentrated action: Energy Performance of tainability criteria considered by local actors are dif- Buildings 2002), we assume that: ‘a NZED is ferently ‘interpreted’ by different communities to a delimited part of a city with high energy performance assess the ‘zero energy’ concept and its applicability. and a nearly zero or very low amount of energy con- This work intends, thus, to contribute to fill this gap, sumed to a significant extent by its local production’. by establishing a knowledge base to support further Broadly speaking, the NZED adjusts the (nearly) zero- developments in urban agglomeration along with energy principles to the urban context to assess its a holistic toolkit as proposed in RESIZED European potential impacts and feasibility assuming that the project (ERA Chair Team 2015). energy requirements on districts are assessed as part of its components (public lighting, landscape, etc.). 2.1.1 The RESIZED research project Sornes et al. at the research project ZenN (Nearly In 2015, the University of Mons and the Research Zero Energy Neighbourhoods), introduce the defini - Institute for Energy proposed a multi-disciplinary tion where the global energy demand of a cluster of approach (Figure 1) in the field of NZED through the residential buildings is met by renewable energy ambitious RESIZED project aiming at: sources which are produced on site, without further details by considering the neighbourhood as a sum of Enhancing the scientific excellence around the buildings (Sornes et al. 2014). In this sense, a NZED is topic with the development of holistic approaches not a sum of NZEBs but as a group of buildings with and synergies among the Departments and the different consumptions, whose overall balance must Public Bodies and private companies. almost reach zero; nevertheless, the buildings remain Developing a toolkit to enable the process the most important consumer of the total amount of (urban planning, building design, energy pro- the energy demand (Amaral et al. 2018). duction system design, green mobility etc.) of Undeniably, one of the main challenges of going zero-energy design in urban scales. beyond the building level, is the definition of bound- Developing a project portfolio and validate the aries as it is commonly understood that enlarging the results on demonstration cases to ensure the perimeter of intervention the constraints influencing research results and spread the best practices the energy performance become stronger and the (Koutra et al. 2019). level of complexity as well. Geometry has a significant role to mitigate the factors for minimising 3 Methodological approach the consumption, while in parallel to maximise the (local) production. To this A preliminary definition for NZED, proposed by the topic, several studies in the existing literature U-ZED approach, is: search for the assessment of geometric factors to ‘NZED is the district, where the potential of the evaluate the performance, such as the aspect or the energy supply (on-site) is equal (or nearly equal) to the depth ratio (Hachem et al. 2013), compactness or final energy demand of its users. Estimating this bal- ground and floor indexes (Rodriguez-Alvarez 2016) ance is not always a straightforward process; for or site coverage and shape (Mauree et al. 2017). instance, Marique and Reiter consider factors related However, even when the methodologies propose to the space heating/cooling, ventilation, appliances, strategies to district (or even city) scale, these studies cooking etc., while a particular emphasis for calculat- still remain on the buildings’ performance ignoring ing the mobility flows is defined with the introduction more dynamic phenomena (i.e. mobility flows); in of the Energy Performance Index as INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 589 Figure 1. The toolkit of NZEDs’ approach developed in RESIZED European project. energy production annually. U-ZED process is evolved Dmifm=Ti (1) along with three pillars to achieve this equilibrium in the district in an attempt to optimise the energy where i represents the territorial unit, m the means of requirements of the district’s users/citizens and build- transportation used, Dmi the total distance travelled, ings (Pillar 1). This step is primordial for the zero- fm the consumption attributed to the means of trans- energy objective; the ‘demand’ (usually expressed in portation and Ti the number of persons in the terri- kWh) refers to the requirements in energy to fulfil the torial unit i (Marique and Reiter 2014). metabolic functions but also to ensure the operations Equation 2 provides the mathematical representa- of the existing building stock. Complementary to this, tion of this concept: the Pillar 2 proposes the energetic ‘hybridization’ X X on-site implying the balanced combination between f Demand f Offer (2) the use of the on-site resources and the installation of the diverse technologies on-site, while Pillar 3 indicates where the f Demand is calculated as the sum of the another strong feature of the interdisciplinary planning energy requirements in the districts and the offer on- of physical flows of energy, water and waste, implying site (RES potential). NZED aims at optimising (mini- the share of renewable resources and the generation of mising) the energy demand (annually) with the paral- local energy and the need for energy storage systems lel maximisation of RES’ use for the local energy (Figure 2). Some examples of these implementations are production (on-site) (Equation 3). ensuring the liveability of the concept can be: NZE Dobjective : X X (3) ● Energy: renewable fuels, biogas products, reuse min f Demand with a parallel max f Offer of waste heat coupled with efficient energy con- sumption of built environment etc. For instance, U-ZED approach is developed along with three pillars energy storage systems should be used in order of action (Figure 2). U-ZED ‘defines’ the zero-energy to maximise and use effectively the solar thermal application in districts as the balance between the energy. Indeed, the stored solar thermal energy demand and the on-site offer to maximise the local 590 S. KOUTRA ET AL. Figure 2. Description of the three pillars of action in NZEDs by the U-ZED approach. can be used to cover the peaks of the thermal Phase 2: Diagnosis and analysis demand in winter and in the transitional The second phase of the approach is the diagnostic months, while in summer the solar system can on-site analysis and the initial screening of the studied even cover the whole thermal demand of the area, the identification of the problems, limitations and district, if the solar system is properly designed. opportunities. ● Water: sewage treatments and saving Kristensen studied the chains and connections of ● Waste: thoroughly sorted in practical systems, the DPSIR model starting with the ‘driving forces’ with material and energy recycling maximised through ‘pressures’ to ‘states’ and impacts on eco- wherever possible. At the same time, this evokes systems, human health, etc. leading to political the opportunity to dominate the role of storage responses. At his works, Kristensen explains the energy systems, such as battery recycling to components of the DPSIR model by using store energy, which is quite challenging due to (Kristensen 2004): the scale and the technological and financial barriers for their installation. Analysis of applying D for Driving Forces to express a ‘need’. Examples waste energy utilisation techniques in different of primary driving forces are the need for shelter, sectors of economy identifies more possibilities food, wateretc. in electricity and heat energy saving and pollu- P for Pressures. Driving forces lead by human tion prevention. activities. These human activities exert ‘pres- sures’ on the environment, as a result of pro- duction or consumption processes and 3.1 Detailed description of the methodological are mainly divided into three main types: (i) steps excessive use of environmental resources, (ii) Four phases describe the dynamic process of the changes in land use and (iii) emissions to air, U-ZED methodology water and soil. Phase 1: Strategic decision of the NZEDs’ ● S for States. As a result of pressures, the ‘state’ of installation the environment is affected; that is the quality of The first step of U-ZED’s application is the strategic the various environmental compartments in decision by planners and city stakeholders towards relation to the functions that these compart- the zero-energy district planning. This step is mainly ments fulfil. related to the political decisions and strategies to I for Impacts. The changes in the physical, eco- engage stakeholders, planners but also to empower nomic, societal or urban environment determine citizens towards the successful application of the the quality of ecosystems and the welfare of concept. human beings. INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 591 R for the expression of responses as solutions for fourth Phase of the U-ZED approach concerns the policymakers to minimise the impacts as empirical study, the validation and the monitoring of described previously. the proposed action plan. Figure 4 explains the flow of the four proposed U-ZED hereby, being inspired by the DPSIR assess- phases of the methodology. ment tool analyses in detail the potential of a district Developing the U-ZED process in four phases (2), to be designed in line within the zero-energy princi- as previously described, is a complex process requir- ples (Figure 3). ing well-defined coordination procedures, collecting Phase 3: Assessment of scenarios and analysing accurate data, managing the risks and At the previous step, we evaluated and devel- the budget, ‘adapting’ the users’ behaviour etc. oped our diagnosis to identify the studied area, its Further steps and perspectives are expected with actual problems, the on-site constraints and oppor- the involvement of local authorities and citizen par- tunities. In this Phase, planners and city stake- ticipation for the conception of the zero-energy holders assess the diagnostic study and develop planning at their district, surveys and on-site analysis a scenario analysis explaining the different possibi- are proposed, as well but also evaluation of costs and lities for the district’s re-arrangement or its concep- benefits for the suggested actions for each case- tion. Planners develop and examine diverse study. scenarios towards the achievement of the zero- energy strategy and its application in the studied district. In the case of data lack, the process returns 3.1.1 Limitations of the methodology to the previous step (loop). As previously explained, the application of the U-ZED Phase 4: Implementation approach revealed the complexity of the zero-energy Following the strategical decision for the zero- applicability in urban scale; for this study, we analyse energy planning actions and the selected scenario, basically the pillar (1) of the needs’ optimisation, which will ‘optimize’ the zero-energy strategy, the which is the first and important step of the concept. Figure 3. DPSIR approach is developed in U-ZED phase 2 analysis. 592 S. KOUTRA ET AL. Figure 4. Algorithmic description of the U-ZED process. The main limitations of our study are cited below: influencing the successful application of the zero- energy concept in districts is not exhaustive. Table 1 Ambiguous definitions regarding the zero- presents the KPIs included for the current study and as energy concept and limited real case studies a preliminary application of the U-ZED approach; the and lessons-learnt in urban scale to retrieve suc- selection is realised along with the objective of balan- cessful stories of the past; cing the annual demand and on-site offer related to the ● Limited access in open (and not confidential) data availability for each of them as a first overview of data regarding mainly the energy consumption the theoretical application of the key factors influencing per household; the energy performance in districts and the limitation of ● Social behaviour and adaptation to zero-energy this study to pillar 1. transition, need for continuous actions and mon- For this study, we focus our scope and objec- itoring actions by planners and city stakeholders; tives at: ● Limitations on costs of proposed technologies and systems to achieve the zero-energy balance; Site opportunities: the index is related to the Administrative obstacles and difficulties in poli- site’s geography, the concrete localisation, the tical engagement and related policies. specific climate conditions and the resources’ on-site potential. These components identify as well the connections of the studied area (acces- 3.2 Key performance indicators sibility/proximity) with its surroundings. KPIs are a concept originating from business adminis- Mobility: Complementary to the previous KPI, the tration with the aim to provide tools for measurement ‘mobility’ is a key index to assess with tangible and in business fields. In reality, they are quantifiable metrics more quantified methods the accessibility of the reflecting the performance of achieving wider goals and studied area; this index seeks for the assessment help in the implementation of different strategies of the integration of mild transport modes as well. (Bosch et al. 2017). For this study, we considered, as ● Functional/Social/Dwellings’ mixing: this index is key aspects of the energy performance of NZEDs, site basically significant for the first axis of our analysis opportunities and attributes. The list of the KPIs (optimisation of energy requirements by users). INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 593 Table 1. Key performance indicators (KPIs) in NZEDs. KPI Description U-ZED References Location/ RES potential City centre: 3–5 km (ARENE 2005); Τopography/ Proximity to city centre Between the ‘stops’: 200–500 m (Amaral et al. 2018) Climate conditions Mobility Offer in mild means of 1.500 m from IC/IR or less (Teller et al. 2014) transport 700 m around the perimeter (Reiter et al. 2014a), (Senel 2010), 300 m between the ‘stops’ (Marique and Reiter 2012) 30 passages/day (poles) 20passages/day (suburban) 5–10 min between the ‘passages’ Functional Mixing Mixed-use, highly dense 300 m of a commercial centre (Teller et al. 2014), (Reiter et al. 2014a) and compact 300 m of a primary school 500 m of an activity centre Social Mixing and Number of social 15% in social dwellings (Shnapp et al. 2020) Equity dwellings/surface (ha) 10% accessible to ‘middle’ revenues (Teller et al. 2014), (Laroche 2010), Affordability for the (Chouvet 2007) housing and diversity Mixing in Variety of dwellings’ 10% of studios and/or dwellings of ‘one-room’ (Teller and Marique 2014), Dwellings functions, number of 10% of dwellings of ‘two rooms’ (Schulz 2006), (ARCEA 2016), rooms/floors etc. 10% of ‘three rooms’ or more (Ministère du logement, de l’égalité, 10% of public dwellings des territoires et de la ruralité 2014) R + 1 to R + 5 (max) Low energy Buildings’ low energy Heating: ≤60 kWh/m /y (Yepez-Salmon 2011), consumption standards Electricity: ≤20 kWh/m /y (Service Public de Wallonie -DGO4, 2010) The three cases are related to a diversity on func- to maximise or minimise the objectives of the city tions, populations and a mixed built stock, which planning (Chuvieco 1993). For the current analysis, will enable and promote the autonomy. QGIS is used for the cartographical analysis of the Standards of low energy consumption: quantified representative attributes of the built and urban to define the consumption on low energy build- environment of the diagnostic study of the ing design. Cuesmes district. As a toolbox, GIS allow planners and architects to perform a spatial analysis with Figure 5 represents the KPIs’ selection along with the use of different actions and the integration of the three pillars of action in the U-ZED approach. diverse factors (Chuvieco 1993). Interest for the current manuscript provides the first pillar regarding the optimisation of the energy require- 3.3.2 HOMER ments of the users in the studied districts. In this figure, Bahramara et al. claim HOMER is a powerful tool for we analyse the key parameters to explain the three energy planning in cities with the aim of determining proposed pillars in figure 5. the optimal size of specific system elements through a techno-economic analysis considering the compo- nents in grid-connected or autonomous implementa- 3.3 Methods and tools tions (Bahramara et al. 2016). HOMER requires six As analysed above, at the second phase of the U-ZED types of data including the: meteorological data; the method, we developed a roadmap towards the zero- load profiles; the attributes of the selected compo- energy transition in districts within the use of different nents; the space; the economic and other technical software explained briefly below: data and can be adjusted to simulate or optimise an examined grid configuration. Energy system design 3.3.1 QGIS tool and optimisation with the use of HOMER software Chuvieco argues that the association of the spatial has been reported in (Rahman et al. 2016) assessing optimisation models with the use of GIS formulates the implementation of a hybrid energy system for the and develops the planning options in an attempt off-grid Sandy Lake community in Canada while 594 S. KOUTRA ET AL. Figure 5. Representation of KPIs’ selected in U-ZED approach. proposing the hybrid energy resource combination 3.3.3 The Method of Degree Days which could serve the electricity demand. Seven Day and Karayiannis explain that the method of Degree energy scenarios were developed from 0 to 100% Days is mainly used for estimating the heating energy renewable energy shares. A process for modelling demand in buildings for nearly 70 years (Day and electricity generation based on multiple configura - Karayiannins 1998). Moreover, attempts have been tions of hybrid renewable energy sources was pre- made to formalise the energy consumption monitoring sented and tested on an identified off-grid village targeting in buildings. The way in which the method of location in India. In addition, Shahzad et al. proposed Degree Days is applied involves assumptions and an economical and optimised design for electricity approximations introducing the uncertainties into the generation using hybrid energy source PV/Biomass problem. It is expected that the method of Degree Days for an agricultural farm and a residential community provides the smallest contribution to errors and it is centred in a small village of district Layyah in the important to quantify this contribution; for this study, Punjab province of Pakistan (Shahzad et al. 2017). the Method is used in its simplified application for the Last, He et al. employed HOMER in order to evaluate rough estimation of the current demand in district. the techno-economic performance of renewable energy-based microgrid scenarios in residential com- 4 Case-study analysis munities in Beijing (He et al. 2018). In this study, HOMER is utilised for the energy The validation of the toolkit developed is materialised analysis of the district’s power requirements under along with two main demonstration cases at the sur- two scenarios integrating rooftop PV on the build- roundings of the city of Mons. As explained in Koutra ings (a) without and (b) with a coupled battery et al. the district of Epinlieu constitutes of the first energy storage component (detailed results pre- experiment of empirical analysis for the RESIZED tool- sented in the Annexe). box (Koutra et al. 2019). The common attribute of the INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 595 two pilot analyses (Epinlieu and Cuesmes) is their ‘social mobility flows, the functional and social mixing, etc. project’ character and the fact that their location pre- An important component of the diagnostic study sents similarities. Nonetheless, the urban context of the completing the analysis of its profile is undoubtably (non)-built environment differentiates; some prominent the demographic data and the population profile. comparative results are presented in this section. Exploring the potentialities for the ‘zero-energy’ Cuesmes is a district close to the city of Mons (4 km spatial ‘re-structure’, we studied the opportunities from the city centre) (Fig. 6) with an old building stock and the constraints on-site and we defined the and high energy requirements (despite the renovation attributes of the demographic profile of the stu- strategies); however, with interesting site opportunities. died cases. The district selected is basically comprised of social hous- In 2018, the district counted 1202 citizens with ing with poor quality and unfavourable living conditions a significant number of non-active residents (City for its population. In this section we will present the Population – Cuesmes 2018). Indeed, the district of application of the four U-ZED steps in Cuesmes district. Cuesmes is considered as the district where a lowest rate of people has a high educational level Table 3; (only 15% of the local population 4.1 Phase 1. Strategic decision of the NZEDs’ has a university degree); the unemployment rate installation is high (~10%) and the average income is relatively low (app. 1300€/month). Compared to Cuesmes, The diagnosis of the district’s dysfunctions along with the district of Epinlieu has similarities in terms of the site opportunities are the motivations for the zero- its demographical analysis. energy transition towards the ‘zero-energy’ planning. 4.2.1 KPI. Site opportunities (Location/ 4.2 Phase 2. Diagnosis and analysis Topography) Formerly agricultural land, the district of Cuesmes The main criteria considered for the phase of diagno- was created during the years ‘50–‘60 to accommo- sis are summarised in Table 2; among them, the ana- date low-income populations due to its urban lysis of the built and non-built environment, the Figure 6. Geographical location of selected case-study (perimeter of analysis). 596 S. KOUTRA ET AL. Table 2. Calculations of energy requirements for apartment blocks non-renovated. Degree Losses UAmin One building Total (D ) UAmax One building Total (D ) tmin tmax 2 2 Month days (m ) U (W/m K) (W/K) (D ) (kWh) (kWh) (W/K) (D ) (kWh) (kWh) 1min 1max J 436 2,079 2,2 3.659,04 38.288,19 153.152,78 5.488,56 57.432,29 229.729,17 F 544 47.772,43 191.089,70 71.658,64 286.634,56 M 457 40.132,35 160.529,40 60.198,53 240.794,10 A 228 20.022,27 80.089,07 30.033,40 120.133,60 M 149 13.084,73 52.338,91 19.627,09 78.508,36 J 96 8.430,43 33.721,71 12.645,64 50.582,57 J 78 6.849,72 27.398,89 10.274,58 41.098,34 A 85 7.464,44 29.857,77 11.196,66 44.786,65 S 185 16.246,14 64.984,55 24.369,21 97.476,83 O 214 18.792,83 75.171,32 28.189,24 112.756,98 N 397 34.863,33 139.453,33 52.295,00 209.180,00 D 474 38.288,19 153.152,78 62.437,86 249.751,43 Total 290.235,1 1.160.940,21 440.357,7 1.761.432,59 growth. At the time being, RES conversion technol- 4.2.3 KPI. mixing ogies remain undeveloped in the district, however 4.2.3.1 Functional mixing. The district has a total a potential biomass energy production facility sup- surface of 46,17 ha and 1.245 buildings and Table 5, it plied by organic waste has been planned. Another is an ancient and highly energy consumer district option examined is connecting to the geothermal principally composed of residential land-use without inventory in the city of Mons. The meteorological mixed-use attributes. data provided by the IRM (2013) (IRM 2020) related to the solar radiation per year as well as the direc- 4.2.3.2 Social mixing. Regarding the criterion of tion and the average velocity of the wind attest ‘social mixing’, we observe a mixed district in terms Cuesmes’ potential towards an energetic retrofit - of age categories and a diversity of nationalities (50% ting suiting net-zero energy district objectives. As of the local population in the Community of Mons are for the previous analysis in the case of Epinlieu, the French and Italian and the rest comprises of diverse ‘geothermal’ opportunity remains still nationalities, Germans, Spanish, Greek) (Wallonie underexplored. Familles 2018). 4.2.3.3 Mixing of dwellings and built environ- 4.2.2 KPI. Mobility and public means of transport ment. Regarding the diversity in building morpholo- During the ‘on-site’ analysis in the district (16–31/ gies in Cuesmes, the current building stock consists of 3/2019), we observed that citizens are ‘car depen- completely terraced housing. However, the buildings dent’ for their daily movements inside and around consist of a R + 1 (64%), constructions on the ground the district. The district is not well-connected by floor, at 20%, constructions in R + 2 (10%) Table 6 and the public means of transport; nonetheless, it is constructions in R + 3 (6%). The built stock of the situated close to the city of Mons and surrounded district is dated basically before 1850 (more than 70% by other cities, as well (5 km far from Mons, of the existing dwellings) with the terraced form to be 56 min walk or 25 min by bike from Jemappes, predominant (Fig. 8). The district has low mixed-use 1h15walk or 16 min by bike from Frameries, etc.). attributes including basically residential activities, while The district is not well-served by public means of the land use is occupied partially by public and socio- transport Table 4: the only railway stations at cultural equipment as well as commercial centres. 5 km around the district are in Quaregnon, The built inventory for Epinlieu district has Frameries, and Mons between 4 and 5 km of the analogous characteristics of a ‘social housing’ Table district’s surroundings (Fig. 7). Similar to these 7 project of the Hainaut area with renovated dwell- findings, in Epinlieu the analysis proves a well- ings of moderate construction quality and important served district by bus and in a walkable distance deficiencies in terms of energy losses and heating from the city centre (2.5 km distance). (cooling) requirements, as visualised in Fig. 9 INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 597 Figure 7. Walkability analysis in the Cuesmes district and educational infrastructure to surroundings. Figure 8. Analysis of the built environment in regard to the criterion of ‘construction age’ (Cuesmes). 4.2.4 Estimation of energy requirements After the first estimations and the outcomes, we It is expected that the corresponding space heating encoded the U-values using the calculation tool of the needs of the majority of the district’s building stock buildings’ thermal requirements provided by the would present a high value as it is concluded by Belgian Building Research Institute (BBRI). More infor- examining the age of construction data (4). mation can be retrieved regarding the calculation tool 598 S. KOUTRA ET AL. Figure 9. Analysis of the built environment in regard to the criterion of ‘construction age’ (Epinlieu). Figure 10. Energy consumption per building typology in the selected case study. INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 599 provided by BBRI in (CSTC 2020). An illustration of the UA = 0,8 * U*S min energy requirements is provided in Fig. 10, while the UA = 1,2 * U*S max detailed calculations of the annual heating energy D = (UA X Degree Days * 24)/1000 1min min requirements are explained in tables below D = Number of units * D 1tmin 1min Explanations for the calculations D = (UA *Degree Days * 24)/1000 1max max Table 3. Calculations of energy requirements for apartment blocks non-renovated. Degree Losses UAmin One building Total (D ) One building Total (D ) tmin tmax 2 2 Month days (m ) U (W/m K) (W/K) (D ) (kWh) (kWh) UAmax (W/K) (D ) (kWh) (kWh) 1min 1max J 436 2,079 1,1 1.829,52 19.144,10 134.008,68 2.744,28 28.716,15 201.013,02 F 544 23.886,21 167.203,49 35.829,32 250.805,24 M 457 20.066,18 140.463,23 30.099,26 210.694,84 A 228 10.011,13 70.077,93 15.016,70 105.116,90 M 149 6.542,36 45.796,54 9.813,55 68.694,82 J 96 4.215,21 29.506,50 6.322,82 44.259,75 J 78 3.424,86 23.974,03 5.137,29 35.961,05 A 85 3.732,22 26.125,55 5.598,33 39.188,32 S 185 8.123,07 56.861,48 12.184,60 85.292,22 O 214 9.396,41 65.774,90 14.094,62 98.662,35 N 397 17.431,67 122.021,67 26.147,50 183.032,50 D 474 20.812,62 145.688,34 31.218,93 218.532,50 Total 146.786,05 1.027.502,34 220.179,07 1.541.253,51 Table 4. Calculations of energy requirements for single-family houses non-renovated. Degree Losses UAmin One building Total (D ) One building Total (D ) tmin tmax 2 2 Month days (m ) U (W/m K) (W/K) (D ) (kWh) (kWh) UAmax (W/K) (D ) (kWh) (kWh) 1min 1max J 436 269,86 1,4 302,24 3.162,67 2.030.435,97 453,36 4.744,01 3.045.653,95 F 544 3.946,09 2.533.387,99 5.919,13 3.800.081,99 M 457 3.315,00 2.128.232,19 4.972,51 3.192.348,29 A 228 1.653,87 1.061.787,62 2.480,81 1.592.681,42 M 149 1.080,82 693.887,52 1.621,23 1.040.831,28 J 96 696,37 447.068,47 1.044,55 670.602,70 J 78 565,80 363.243,13 848,70 544.864,70 A 85 616,58 395.841,87 924,86 593.762,81 S 185 1.341,96 861.538,20 2.012,94 1.292.307,30 O 214 1.552,32 996.590,13 2.328,48 1.494.885,20 N 397 2.879,77 1.848.814,40 4.319,66 2.773.221,60 D 474 3.438,32 2.207.400,57 5.157,48 3.311.100,85 Total 24.249,58 15.568.228,06 36.374,36 23.352.342,09 Table 5. Calculations of energy requirements for social houses non-renovated. Degree Losses UAmin One building Total (D ) One building Total (D ) tmin tmax 2 2 Month days (m ) U (W/m K) (W/K) (D ) (kWh) (kWh) UAmax (W/K) (D ) (kWh) (kWh) 1min 1max J 436 175,36 1,60 224,46 2.348,76 575.445,66 336,69 3.523,14 863.168,50 F 544 2.930,56 717.987,25 4.395,84 1.076.980,88 M 457 2.461,89 603.162,08 3.692,83 904.743,12 A 228 1.228,25 300.921,13 1.842,37 451.381,69 M 149 802,67 196.654,60 1.204,01 294.981,89 J 96 517,16 126.703,63 775,74 190.055,45 J 78 420,19 102.946,70 630,29 154.420,05 A 85 457,90 112.185,51 686,85 168.278,26 S 185 996,61 244.168,46 1.494,91 366.252,69 O 214 1.152,83 282.443,51 1.729,25 423.665,27 N 397 2.138,66 523.972,31 3.207,99 785.958,47 D 474 2.553,47 625.599,18 3.830,20 938.398,78 Total 18.008,94 4.412.190,03 27.013,41 6.618.285,05 600 S. KOUTRA ET AL. Table 6. Calculations of energy requirements for social houses renovated. Degree UAmin One building Total (D ) One building Total (D ) tmin tmax 2 2 Month days Losses (m ) U (W/m K) (W/K) (D ) (kWh) (kWh) UAmax (W/K) (D ) (kWh) (kWh) 1min 1max J 436 175,36 0,7 98,20 1.027,58 251.757,48 147,30 1.541,37 377.636,22 F 544 1.282,12 314.119,42 1.923,18 471.179,13 M 457 1.077,08 263.883,41 1.615,61 395.825,12 A 228 537,36 131.652,99 806,04 197.479,49 M 149 351,17 86.036,39 526,75 129.054,58 J 96 226,26 55.432,84 339,38 83.149,26 J 78 183,83 45.039,18 275,75 67.558,77 A 85 200,33 49.081,16 300,50 73.621,74 S 185 436,02 106.823,70 654,02 160.235,55 O 214 504.36 123.569,04 756,55 185.353,56 N 397 935.66 229.237,89 1.403,50 343.856,83 D 474 1.117,14 273.699,64 1.675,71 410.549,47 Total 7.878,91 1.930.333,14 11.818,37 2.895.499,71 Table 7. Calculations of energy requirements for social houses for elderly people non-renovated. UAmin One building Total (D ) One building Total (D ) tmin tmax 2 2 Month Degree days Losses(m ) U (W/m K) (W/K) (D ) (kWh) (kWh) UAmax (W/K) (D ) (kWh) (kWh) 1min 1max J 436 175,36 0,70 98,20 1.027,58 251.757,48 147,30 1.541,37 377.636,22 F 544 1.282,12 314.119,42 1.923,18 471.179,13 M 457 1.077,08 263.883,41 1.615,61 395.825,12 A 228 537,36 131.652,99 806,04 197.479,49 M 149 351,17 86.036,39 526,75 129.054,58 J 96 226,26 55.432,84 339,38 83.149,26 J 78 183,83 45.039,18 275,75 67.558,77 A 85 200,33 49.081,16 300,50 73.621,74 S 185 436,02 106.823,70 654,02 160.235,55 O 214 504,36 123.569,04 756,55 185.353,56 N 397 935,66 229.237,89 1.403,50 343.856,83 D 474 1.117.14 273.699,64 1.675,71 410.549,47 Total 7.878,91 1.930.333,14 11.818,37 2.895.499,71 D = Number of units * D itineraries and mild transportation systems. The pro- 1tmax 1max Combining the above, it can be supported that the posed action plan introduces the idea of a more com- district presents numerous problems related to con- pact, mixed-use and dense district with more struction, the building typologies, structures and forms infrastructure responding to the daily citizens’ as well as a low grade of renewable energy resource requirements and less ‘car dependent’. Inspired by integration. Rogers’ planning theory (Urban Task Force 1999). In comparison with the case of Cuesmes, the urban Pillar 2: Maximisation of local energy production, context of Epinlieu district consists of terraced houses enhancement of RES. The analysis considers the solar with gabled, flat or mansard roofs or gabled roofs with potential and we proposed the PVs’ installation as parking. The energy (annual) profile is presented in a preliminary step; similar was the case for the case Fig. 11 (Koutra et al. 2019). of Epinlieu after the diagnostic phase. In the scope of sizing (the solar panel installation per typology), the study included indicators, such as the temperature 4.3 Phase 3. Assessment of the scenarios and solar irradiance. Three types of annual loads In particular, the proposed actions are: were calculated per typology based on the average Pillar 1: Emphasis on actions in the KPIs of: mobility consumption. Energy flow data were provided on an and mixing. The implemented scenario focuses its hourly basis for an average year. Specifically, terraced analysis on the expansion of the existing bus network houses with flat roofs and houses with double- and the passages per day with complementary pitched roofs were considered as a common typology INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 601 Figure 11. Average energy requirements in the diverse typo-morphologies of the district of Epinlieu. with respective 5566 kWh/yr consumptions. For types by a Cost-Benefit Analysis to investigate the possible 3 and 46,123 kWh/yr, and finally the large apartment profits of this installation (Ioakimidis and Ferrao 2010). blocks had 22,264 kWh/yr. (Koutra et al. 2019). What is important for the biomass scenario, which was Pillar 3: Energy storage PV electric storage: hardly to assess at our current analysis in Cuesmes, is Balancing from the one side the dysfunctions and the estimation of the demand for the installation of the problems described at the diagnostic phase of the technology and the carriers needed to serve the the analysis, as mentioned previously, we analysed requirements. Modelling tools are proposed at the the scenario of PVs’ installations. The HOMER micro- same work for this analysis, such as TIMES (a dynamic grid optimisation tool was used for the study of the model) as a further analysis. optimised integration of rooftop PV panel installa- tions on the district’s building stock related to the 4.4 Phase 4. Implementation maximisation of locally available RES exploitation as part of the second pillar of the U-ZED approach (ener- Following the analysis carried out in previous sections getic hybridisation). of the manuscript, we note that the district has var- The energetic and financial analysis in HOMER ious dysfunctions related to mobility, social equity, demonstrated that the region of Mons offers a good a high energy consumption, a strong dependency by solar irradiance potential with an annual average of car, etc. It, therefore, appears important in this work to 2.91 kWh/m /day. Consequently, as a more affordable propose solutions to match the citizens’ expectations and accessible renewable energy conversion technol- and to achieve the NZED’s objectives. In this section, ogy, in line with the intended zero-energy application we will establish a general situation in which we will in the district, we proposed the scenario of PVs’ instal- deal with the problems mentioned at the diagnostic lation as an initial energy retrofitting intervention. study Table 8. In a projected situation, we propose the Nonetheless, as explained already, the district appears analysis of the energy criterion with regard to the interesting agricultural activity, therefore, the scenario energy potential/inventory of the region to see how of the energetic hybridisation could be the subse- to make the district autonomous in renewable ener- quent step of the U-ZED application on-site. gies, the possible energy hybridisations and what Ioakimidis and Ferrao at their works explain the ben- would be the solutions allowing to reach and main- efits of the biomass on the influence of local electric tain this autonomy in the future. power production and fuel consumption; however, an In order to better meet the population needs, the analytical methodological and holistic approach is requirements towards the NZED transition and bring required to assure the application of the data and attractiveness to the district, we propose the use of the implementation of the strategy ‘on-site’ followed Rogers’ theory to allocate the functions in relation to 602 S. KOUTRA ET AL. the diverse distances. By living in closer proximity to In the proposed scenario, we studied the possi- each other, we can accommodate far more of the bility of energy production by PVs. As a reminder, world’s population, use less energy, concentrate the region of Mons has a good solar irradiance goods and services and move from one place to potential allowing an interesting rate of its exploita- another more efficiently. For instance, building at 50 tion. The availability of solar irradiation at the desig- homes to the hectare and above has created all the nated location is calculated from the global solar attractive spaces we like best. At below 50 homes per irradiation incident on the surface of the PV array. hectare, it is hard to keep shops, buses, doctors, nur- Fig. 13 presents the monthly averages of daily inci- series and schools within walking distance; the less dent solar radiation throughout a year for the stu- dense cities are, the further they sprawl, the worse the died location. In addition, the buildings on-site are traffic problems are. Phase 4 and U-ZED’s contribution suitable for PV application as, firstly, the size and at the re-arrangement of a highly dense and compact distance of the buildings do not cast shade on their district is inspired by the graphs provided below. respective rooftops, and, secondly, their east west Addressing the problem of infrastructure and ser- orientation allows to capture solar radiation vices’ proximity, we recommended actions such as: throughout the day. the establishment of new services to handle the In the case of placing the panels required to ‘mono-functional’ attributes appeared in the district match the district’s annual electric demand on (2,3 Fig. 12), educational activities (1 and 4, Fig. 12) a single location, this would yield a total area of and the re-arrangement of green and public spaces (5, 25 ha, equivalent to almost half of the total land 6 and 7, Fig. 12). In terms of accessibility, we recom- area of the studied district. A solution promoting mended the expansion of the existing bus network a large-scale centralised solar power plant, or with additional itineraries (streets of Ciply and a photovoltaic power plant is therefore not feasible Espinette) and the reinforcement of mild transporta- due to space limitations. Moreover, this solution is tion networks with cycling secure lanes connected to not to be preferred since it entails a significant the existing Ravel and the Vélib system for bike rental, alteration on the environment and infers constraints (8, Fig. 12). on land use. Hence, an applicable solution would be Figure 12. Proposal for the district’s re-arrangement towards the transition of the zero-energy concept in Cuesmes. INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 603 Figure 13. Annual profile of average daily incident solar radiation (kWh/m2/day) with monthly resolution for the area of Cuesmes. Table 8. Results of the rooftop PV installation optimisation run. Estimated annual electricity Net present Calculated PV Levelized cost of Annual energy Scenario consumption (kWh/yr) cost (€) output (kWh/yr) energy (€/kWh) savings (%) Including storage 3.300 € 19.942 5.434 € 0.273 77.3 Without storage 3.300 € 5.843 5.434 € 0.065 42.8 placing PV rooftop installations on the buildings, rooftop, which can be placed on a 3 × 5 array. The taking into account that the average available roof- electricity tariffs were imported from the Eurostat top surface area was estimated at 25 m per build- database and were defined at 0,275 €/kWh for grid ing according to the findings of the diagnosis phase purchase and 0.15€/kWh as an indicative feed-in-tariff on the built environment. Following the proposed resulting from the Qualiwatt established averages scenario, an optimal rooftop PV-electrical storage (Eurostat 2018). system for buildings located in the Cuesmes district It is important to mention that PV installations in has been sized and optimised with the use of the the Wallonia region are subsidised through green HOMER software tool on a 15-year project lifetime. certificate programmes and net metering, however Furthermore, the panels’ optimal rooftop orienta- they have been inactive since the end of June 2018, tion (slope and azimuth) was calculated with the when the Qualiwatt programme expired. Error! online tool PV-GIS (European Commission 2019a) Reference source not found. presents the key findings enabling increased efficiency on the conversion of of the optimisation study, distinguishing between an incident solar irradiance. Although HOMER optimises installation including an electrical storage unit and the installation subject to the minimisation of its one without any storage provisions. The purpose of respective Net Present Cost, the component capacity introducing subcases is two-fold: (a) to highlight the search space is configurable, offering an option for advantages of coupling the PV array mainly reflected setting an upper boundary on each component’s on the percentage of annual energy savings and (b) to parameter search space. Acknowledging the total contrast the trade-off between system costs and rooftop installed capacity limitations applying in potential energy savings. Regarding energy consump- Belgium (max. PV capacity <10 kW), an upper bound- tion, a synthetic annual electric load profile (3.300 ary value was placed on the PV module capacity kWh/yr) was compiled and inserted as the occupant optimisation search space. The equivalent peak usage pattern on which the energy dispatch algo- power capacity to a 25 m total array area is approxi- rithm would size the PV-system, based on energy mately 4.95 kW, in this case 15 PV modules per provider data for multiple categories of residential 604 S. KOUTRA ET AL. Figure 14. Annual daily hourly means of the power flows corresponding to each rooftop PV system configuration. electricity consumers (Lepage 2019). Annual energy 4.1 GWh, the 3.2 GWh can be supplied from rooftop savings are calculated as the percentage of the reduc- integrated PV-storage systems or 1.8 GWh directly tion on the purchased energy from the grid over the generated from rooftop mounted PV arrays. These assumed annual energy consumption. The LCOE is values are comparable to the maximum achievable defined as the average cost per kWh of useful elec- annual PV contribution towards diminishing the trical energy produced by the system, hence this fig - energy consumption on district scale, which is fixed ure also accounts the total injected energy to the on 3.6 GWh for the first configuration and 2.0 GWh for power grid. The values of annual cashflows use dis- the second configuration due to the imposed capacity count and inflation rates evaluated at 2% and 1%, limitations mentioned above. The geometric footprint respectively, accounting for a 0,99% real discount of each rooftop system is equivalent to 24.9 m . The rate, influencing the calculated net present cost. total cost of implementing subcase (a) is € 18.951.390 Fig. 14 depicts the annual daily hourly means of and (b) € 5.534.025 corresponding to a 1.11 k to CO the power flows corresponding to each rooftop PV and 2.0 k to CO emissions reduction attributed solely system configuration with and without the inclusion to reduced grid energy purchases. In the Appendix B, of a battery energy storage component against the we provide the key results from the HOMER analysis synthesised household demand. The benefits of cou- performed for a generic building located at the district pling PV generation with battery electric storage are of Cuesmes. reflected upon the reduction of grid purchases during day intervals with scarcity of solar resources, which under battery discharging demonstrate finer 5 Conclusions load matching capabilities than the PV only config - uration. In addition, the evening peak demand can be Rapidly growing world energy use and urban growth served with the charged energy driven to the battery in modern ‘mega-cities’ have already created con- from excess PV generation during daylight, leading to cerns regarding the RES’ exhaustion and the impacts an overall reduction in grid sales compared to the of the climate change. Undoubtably, increasing system without a storage unit. energy efficiency is commonly assumed as If the results for the rooftop installation of one a ‘difficult’ process in complex systems and living building are extrapolated to the district level as laboratories, as the cities are. In this current context a proxy for the calculation of the costs and benefits of rising uncertainties, prioritising the efforts towards of this intervention, it can be supported that from the reduction of the energy consumption among the a hypothetical cumulative annual consumption of European and national policies. INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 605 All these issues due to the uncontrolled urban Through three pillars of action: (1) the optimisation sprawl are well documented, while the energy con- of the energy requirements, (2) the energetic hybridisa- sumption derived from the built environment and the tion and (3) the organisation of energy storage, we transportation represents a significant problem to introduce a check-list of key performance indexes, consider. Although, some research is being developed which have a significant impact to the decision of the for more autonomous and optimised urban patterns, zero-energy district planning. Inspired by the DPSIR specific evaluation tools and methods to evaluate the model, we developed an algorithmic process of the urban strategic planning towards this direction are U-ZED application in districts with the introduction of still missing, while the existing ones basically focus four (4) phases of planning: (1) the strategic planning on individual buildings neglecting the complex phe- decision (derived mainly by the city stakeholders and nomena occurred in urban scale, for instance the the decision to the zero-energy transition), (2) the diag- mobility flows etc. nosis and the analysis of the current situation in the In this manuscript, and to reply to this gap, district (including the typo-morphological analysis of its assuming a strong correlation between the factors built and non-built environment as well as the calcula- of the energy consumption and the typo- tion of the actual energy requirements of its users and morphological structure of an agglomeration, we the offer by RES on-site), (3) the development of introduce a simplified methodological decision a scenario analysis towards the ‘optimal’ combination approach, the U-ZED, aiming at conceptualising and (4) the implementation. the zero-energy balance in larger territorial scales The first attempts to validate and experiment the as part of a holistic and interdisciplinary approach proposed methodology have been realised and of a toolkit introduced in the RESIZED European experimented in the various districts in Belgium, for project by the Faculties of the University of Mons. instance in Cuesmes, but also in previous attempts – The literature revealed the weaknesses of develop- district of Epinlieu; both pilot projects are of social ing methodologies for district scales to estimate housing character, close to the city of Mons with the overall consumption but mainly to assess prop- previous tentative of being renovated, but still are erly the factors influencing the zero-energy considered as low-quality housing areas. The main objectives. comparative attributes of both analyses are explained For this study, we consider the ‘district’ as an at the manuscript; nonetheless, among the perspec- urban block and a micrograph of a city. The analysis tives has been the continuity of the RESIZED project prioritised the review of several aspects for the and the involvement to the validation of the theore- understanding and the evolution of the concept tical findings of more case applications with different and the identification of the aspects that influence urban attributes and context (i.e. weather conditions, the energy performance from a design and opera- typologies etc.). At the same time, functional and tion insight. To do so, several indicators, namely social mixing are low; however, the district has inter- climatic or morphological, are discussed to develop esting possibilities towards its future transition to the a NZED strategy. Nonetheless, the variety of existing application of the zero-energy concept on-site. In the variables and indexes reveals that there is no spe- relevant section we provide the diverse scenarios fol- cific and standardised or broadly accepted checklist lowing our analysis as well as the cartographical simu- of indicators for energy efficiency and performance lations of the current and the projected situation with to NZED design. the implementation of the U-ZED approach. 606 S. KOUTRA ET AL. INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 607 Although the zero-energy idea can be conceptua- EPRES Energy Primary from Renewable Energy Sources PV Photovoltaic(s) lised in a district with an approach like individual build- NREL National Renewable Energy Laboratory ings by articulating the main energy uses, the concept LCA Life Cycle Assessment remains complicated and challenging for contempor- CBA Cost-Benefit Analysis ary cities because of various constraints and limitations GIS Geographical Information Systems in different levels of action. This implies innovative DPSIR Drivers-Pressures-States-Impacts-Responses KPIs Key performance indicators approaches to interdisciplinary planning that highlight HOMER Hybrid Optimization Model for Electric the importance of the zero-energy concept and aid city Renewables stakeholders and planners to define these structures. PEB Performance Energetique des Batiments Indeed, the interrelation between urban structure and BBRI Belgian Building Research Institute energy is a key aspect of this path. Related to this, IRM Royal Meteorological Institute of Belgium (Institut Royal Météorologique) a ‘well-structured’ area is a key point that increases LCOE Levelized Cost of Energy sustainable transport and the share of renewable resources. This study contributes to the scientific discussion on Acknowledgements the linkage between energy and urban structure to This research was funded by the European Commission increase the energy efficiency in districts. One of the under the RESIZED (Research Excellence for Solutions and main challenges around this topic resides on the com- Implementation of Net Zero Energy City Districts) project, plexity of the urban scale. Studies focussing on this as part of Grant Agreement no 621408, as well as by the problematic are still few and further analysis should be European Regional Development Fund and Wallonia Region, conducted to understand and identify in-depth the con- project reference FEDER C3E2D–Wal-e-cities. cept in an attempt to enable its feasibility in practice. The human factor but also the user (occupant) behaviour Disclosure statement and public awareness are significant for successful poli- cies and for the zero-energy concept in districts. Further No potential conflict of interest was reported by the author(s). research and works can contribute on extending the presented approach and applying it on diverse case Funding studies with diverse contexts, climate conditions, living standards and constraints with respect to the longevity This work was supported by the RESIZED european FP7 project of modern cities and the achievement of their sustain- (grant agreement: ID: 621408); European Regional Development Fund and Wallonia Region [C3E2D (UE+RW / FEDER)]. able objectives. The study reveals the need for more comprehensive and complementary approaches to embrace correctly all the dimensions of the zero- Notes on contributors energy concept and prioritise it in the forthcoming urban strategies of modern city planning. Sesil Koutra Sesil KOUTRA is an Engineer of Urban Planning and Design (2009) graduated from the Faculty of Engineering of Aristotle University of Thessaloniki (Greece). She holds a Master in Project and Construction Management from the Nomenclature Faculty of Civil Engineering of Aristotle University of EU European Union Thessaloniki (Greece) (2011). She began her professional career U-ZED Urban zero-energy district in 2009 as a Junior Urban Consultant for studies and urban GHGs (emissions) projects and the management and realisation of European pro- Greenhouse gases (emissions) jects. Since April 2015, she has been carrying out a doctoral MS Member state thesis at the Faculty of Architecture and Town Planning, under NZED Net-zero-energy district the supervision of Professor Vincent BECUE and defended her EPBD Energy Performance of Buildings’ Directive thesis in May 2020. (2002/91/EC) Sesil KOUTRA performed her thesis under the European FP7 NZEB(s) Net-zero-energy building research project RE-SIZED (Research Excellence for Solutions IEA International Energy Agency and Implementation of net Zero Energy City Districts). This RES Renewable Energy Sources work concerns the typo-morphological analysis of the autono- DHW Domestic Hot Water mous district in energy and the development of an assessment RE Renewable Energy tool on a parametric basis towards the territorial adaptation to EPGP Energy Primary Green Purchased the zero-energy concept and define the typo-morphology of the 608 S. KOUTRA ET AL. net-zero energy district. Since November 2019, she participates making it possible to optimise resilient projects according to in the research project ‘CoMod’, which he proposes to study this territorial vulnerabilities. notion of ‘compact city’ using graph theory in collaboration with Vincent Becue has a PhD in building art and urban planning, the Research Institute for Complex Systems of UMons and since applied research around the city and technical and environmen- February 2020, she is charged with the course on sustainable tal issues related to urban planning and, in particular for improv- urban planning in the Erasmus Mundus SMACCs (Smart Cities ing the spatial quality. Spatial organisation is an additional and Communities) program. dimension to the economic, environmental and social pillars and makes it possible to define the quality of sustainable Noémie Denayer Noémie is an Architect graduated in 2019 from urban planning and mainly the composition of urban places the Faculty of Architecture and Urban Planning of the University according to interrelations functional. This therefore requires of Mons performing her professional internship at the time a set of urban information in order to understand the distribu- being. tion of the different elements that make up the building, the Nikolaos-Fivos Galatoulas Nikolaos-Fivos Galatoulas is city, the territory and the landscape: forecasts for the whole city, a Research Assistant at the Department of Thermodynamics its future form, the distribution of activities and their many and Mathematical Physics of the Research Institute of Energy/ relationships. This is why he has chosen to favour research in UMONS, Mons, Belgium born in Patras, Greece. He served 3 the field of decision-aid systems based on space and allowing years as a Research Assistant at the ERA-Chair Net-Zero Energy the optimisation of projects and in particular the mix of urban Efficiency Unit (RESIZED project), hosted at the University of functions. He is interested in the development and use of such Mons, Belgium. He holds a Dip. Eng. in Applied Mathematics methods to provide project stakeholders with solutions to and Physical Sciences and a MSc in Microsystems and improve urban quality. This research has several key objectives Nanodevices both obtained from the National Technical which, put end to end, must allow the development of concepts, University of Athens (2013 and 2015). His MSc thesis was carried models and tools for the evaluation of sustainable urbanisation out in collaboration with the Institute of Nanoscience and (district level), integrating the content of the city (populations, Nanotechnology of the National Centre for Scientific Research activities and urban places). (NCSR) Demokritos. In addition, his experience includes 2 years Christos S. Ioakimidis University Professor with teaching on as a research student on e-tongue sensors (NCSR, Greece) and numerous under/post graduate courses related to energy, trans- 2-year employment in the renewable energy industry (Greece). port and Nanotechnology materials applied on energy issues. His current interests are related to microgrids, distributed Entrepreneur on cutting-edge technologies/services in the energy resources, combined energy studies (thermal/power), energy/transport sectors. data analysis and sustainable mobility. Experienced Researcher with extensive research portfolio on Nikolaos-Fivos Galatoulas’ work as a research assistant has cutting-edge research-driven projects on energy system analysis focused on developing data-driven methods for net-zero energy and modelling and Nanotechnology materials applied to energy district (NZED) planning. The main applications investigated issues. were on performance energy metrics of various hybrid renew- Engineer and Manager with large experience on Keys-in- able district energy system designs (power supply and heating), hands projects related with energy/renewable sectors (wind, sustainable mobility technology integration and air pollution solar PV/CSP, biomass, CHP, energy storage via batteries/ monitoring. Since the temporal profile of renewable power pumped, electro-mobility). generation is intermittent, the successful integration of renew- Specialities: (In general the new field of Integrated Large/ able resources into the NZED grid is dependent on the quality of Small Scale Complex Smart Energy and Transport Dynamic input (e.g. climate data, 24-hour forecasts, system component Systems towards a Sustainable District/City) on topics such as: characteristics etc.) for the unit commitment analysis, the opti- Energy management (HEMS,BEMS), modelling and energy/ mal operation of grid connected RES plants and the control of transport policy, demand side management, energy efficiency coupled energy storage systems. To this end, promoting the use on buildings (Smart Buildings), energy and electricity markets, of innovative quantitative methods and analysing urban data smart grids, energy/transport systems integration (RES, mRES, can contribute to informed decision-making within the scope of CCS, EVs, storage), Intelligent Transportation Systems (V2I, V2V, sustainable development. M2M, autonomous driving, etc), sustainable mobility (e-mobi- Vincent Becue Head of service for the Projects, City and lity), innovation/green economy and Nanomaterials on energy/ Territories, Vincent Becue is an architect and research professor transport problems. at the School of Engineers of the City of Paris (EIVP). He is also spokesperson for the doctoral school in architecture, urban planning and urban engineering in FNRS in Belgium. 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HOMER Analysis and Simulations Total Net Present Cost: €19.941,90 Levelized Cost of Energy (€/kWh): €0,273 System Simulation Report Location: Rue Louis Caty 196, 7033 Mons, Belgium (50°26.5ʹN, 3° 54.5ʹE) System Architecture Component Name Size Unit PV CanadianSolar All-Black CS6U-330P 4,95 kW Storage Sonnen Batterie 4 kW-6 kW eco 6 1 Strings System converter Studer Xtender XTM 4000–48 3,34 kW Grid Grid 999.999 kW Dispatch strategy HOMER Load Following Net Present Costs Name Capital Operating Replacement Salvage Total CanadianSolar €2.400 €1.933 €0 €717 €3.616 MaxPower CS6U-330P Studer Xtender €1.337 €0 €1.101 -€499 €1.938 XTM 4000–48 sonnenBatterie €10.785 €0 €8.853 -€4.017 €15.621 4 kW-6kWh eco Grid €0,00 -€1.933,00 €0,00 €0,00 -€1.933,00 Other €700,00 €0,00 €0,00 €0,00 €700,00 System €15.056,00 -€1.659,00 €5.393,00 -€6.700,00 €19.942,00 Annualised Costs Name Capital Operating Replacement Salvage Total CanadianSolar €186,23 €150,00 €0,00 -€55,67 €280,56 MaxPower CS6U-330P Studer Xtender €103,72 €50,00 €85,42 -€38,76 €150,38 XTM 4000–48 sonnenBatterie €836,89 €0,00 €686,95 -€311,69 €1.212,00 4 kW-6kWh eco Grid €0,00 -€149,97 €0,00 €0,00 -€149,97 Other €54,32 €0,00 €0,00 €0,00 €54,32 System €1.181,00 €0,03 €772,36 -€406,12 €1.547,00 612 S. KOUTRA ET AL. Electrical Summary Quantity Value Units Excess Electricity 118 kWh/yr Unmet Electric Load 0 kWh/yr Capacity Shortage 0 kWh/yr Production Summary Component Production (kWh/yr) Percent (%) CanadianSolar MaxPowerCS6U-330P 5.434 87,9 Grid Purchases 750 12,1 Total 6.184 100 Consumption Summary Component Production (kWh/yr) Percent (%) AC Primary Load 3.300 58,2 Grid Sales 2.374 41,8 Total 5.674 100 PV: CanadianSolar MaxPower CS6U-330P CanadianSolar MaxPower CS6U-330P Electrical Summary Quantity Value Units Minimum Output 0,00 kW Maximum Output 4,87 kW PV Penetration 165 % Hours of Operation 4.385 hrs/yr Levelized Cost 0,0516 €/kWh CanadianSolar MaxPower CS6U-330P Statistics Quantity Value Units Rated Capacity 4,95 kW Mean Output 0,20 kW Mean Output 14,90 kWh/d Capacity Factor 12,50 % Total Production 5.434,00 kWh/yr Storage: sonnenBatterie 4 kW-6kWh eco 6 sonnenBatterie 4 kW-6kWh eco 6 Properties Quantity Value Units Batteries 1 qty. String Size 1 batteries Strings in Parallel 1 strings Bus Voltage 240 V INTERNATIONAL JOURNAL OF URBAN SUSTAINABLE DEVELOPMENT 613 sonnenBatterie 4 kW-6kWh eco 6 Result Data Quantity Value Units Energy In 1.373 kWh/yr Energy Out 1.186 kWh/yr Storage Depletion 6 kWh/yr Losses 193 kWh/yr Annual Throughput 1.279 kWh/yr Converter: Studer Xtender XTM 4000–48 Studer Xtender XTM 4000–48 Electrical Summary Quantity Value Units Hours of Operation 7.238 hrs/yr Energy Out 4.924 kWh/yr Energy In 5.129 kWh/yr Losses 205 kWh/yr Studer Xtender XTM 4000–48 Statistics Quantity Value Units Capacity 3,34 kW Mean Output 0,56 kW Minimum Output 0,00 kW Maximum Output 3,34 kW Capacity Factor 16,80 % Grid Grid Transactions: Month Energy purchased (kWh) Energy sold (kWh) Net energy purchased (kWh) Energy charge January 157,00 74,50 82,80 €32.,09 February 94,40 105,00 −10,60 €10,20 March 63,30 176,00 −113,00 -€8,98 April 14,90 251,00 −236,00 -€33,56 May 7,51 338,00 −331,00 -€48,69 June 5,15 332,00 −327,00 -€48,34 July 0,00 350,00 −350,00 -€52,54 August 6,01 322,00 −316,00 -€46,62 September 32,80 221,00 −188,00 -€24,12 October 50,30 103,00 −52,20 -€1,54 November 132,00 76,80 55,30 €24,79 December 186,00 25,60 160,00 €47,33

Journal

International Journal of Urban Sustainable Development – Taylor & Francis

Published: Sep 2, 2021

Keywords: Case-study analysis; energy transition; holistic approach; zero-energy district

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