Sustainable Development Scenarios for Urban Blocks: Energy Renovation and Quality of Life in the Greek City †
Laboratory of Building Construction and Building Physics, Department of Civil Engineering, Faculty of Engineering, Aristotle University of Thessaloniki, 541 24 Thessaloniki, Greece
*
Author to whom correspondence should be addressed.
†
Presented at the ICSD 2021: 9th International Conference on Sustainable Development, Virtual, 20–21 September 2021.
Environ. Sci. Proc. 2022, 15(1), 37; https://0-doi-org.brum.beds.ac.uk/10.3390/environsciproc2022015037
Published: 10 May 2022
(This article belongs to the Proceedings of The 9th International Conference on Sustainable Development)
Abstract
:SDG11–Cities and Communities aims to renew and plan cities and other human settlements so that they offer opportunities for all, while improving resource use and reducing environmental impacts. This research examines the regeneration of urban blocks as a means for improving the overall quality of life in Greek cities. The objective of the research is to determine the energy and economic efficiency of four building renovation interventions, including conventional energy upgrading—such as building shell thermal insulation—and more intensive solutions, such as phase change materials, green roofs, and passive solar system integration. The research methodology combines dynamic simulations with Energy Plus simulation software and an economic evaluation of the interventions as well. The results prove that the reduction in energy demand can vary between 55.7% and 59.1% according to the renovation scenario, while the cost of each intervention varies from 73 to 347 EUR/m2, proving that the payback period of each scenario largely depends on urban block form. The findings of the research can be useful in defining the most efficient renovation strategies at the urban block scale and to promote urban sustainability.
1. Introduction
The new EU strategy for “A Renovation Wave for Europe—Greening our buildings, creating jobs, improving lives” [1] and the European regulations, which are setting stricter energy efficiency targets for the improvement of new and existing buildings, are leading the way of cities toward a climate neutral Europe until 2050 [2]. SDG11–Cities and Communities aims to renew and plan cities and other human settlements so that they offer opportunities for all, while improving resource use and reducing environmental impacts [3].
Mediterranean cities face many challenges concerning their sustainable development. The mild Mediterranean climate compared to that of the European central or northern countries and the fact that there are longer periods of solar availability [4] favor both the lower energy demand for the heating of buildings and the higher potential for renewable energy sources installations. According to the SDG7–Affordable and Clean Energy Indicators, Greece’s share of renewable energy in 2018 (18.05%), was above the European mean [5]. However, the dependency of the country on energy imports from other countries (70.68%) is much higher than the European mean (58.19%), while 22.7% of the population still fails to keep their home warm [5].
The bad condition of the Greek building stock [6], which has not been renovated for many decades, together with the fact that passive design and renewable energy installations have not been considered for older buildings, has resulted in a high energy footprint for the building sector. At the same time, the low construction quality of buildings has negative effect on the inhabitants’ quality of life, including low standards of noise protection and low aesthetics.
However, the way to a sustainable renovation practice is cost dependent [7], as the initial capital needed for the building interventions is in many cases not affordable for the owners. On the other hand, there have been many incentives and state subsidies trying to promote building renovation, mainly in terms of the energy upgrading [8,9]. These strategies have mainly promoted building insulation and heating systems equipment replacement with more efficient ones. More intensive passive strategies have been rarely considered as the additional cost of such interventions is often considered as a barrier their construction.
In November 2021, the Commission launched a call to cities to join the European Mission on Climate-Neutral and Smart Cities. The objectives of the mission are to achieve 100 climate-neutral and smart European cities by 2030 and to ensure that these cities act as experimentation and innovation hubs to enable all European cities to follow suit by 2050 [10].
The opportunity for EU cities to participate and promote their climate neutrality by 2030 could be an ambitious target. The eight-year horizon for achieving climate neutrality means that it is necessary to set efficient strategies in order to reach the goal by 2030.
Many renovation technologies, solutions, and smart strategies have been applied at the building scale—including conventional or more innovative materials, passive solar systems, renewable energy installations, etc.—in order to improve the energy performance of buildings, as the renovation of the building stock is a major contributor toward climate neutrality. However, the building scale is a rather small scale to reach a large impact toward climate neutrality, especially in a shorter time horizon.
The consideration of larger-scale interventions can be proved an appropriate solution in terms of faster, more efficient, and better integrated renovation of the building stock. This research aims to prove that the examination of renovation interventions at the urban block scale has many advantages as it can be better oriented toward the most energy-demanding urban areas, it can provide an economy of scale including both limiting cost and renovation time and effort, and it can contribute to the regeneration of the overall image of the city as well.
Under this perspective, this research analyzes the energy efficiency of four passive energy upgrading interventions implemented at the urban block scale aiming to, on the one hand, examine the contribution of urban block form on the energy performance before and after renovation, and, on the other hand, define the degree to which the investment of the renovation can be translated into an economic value.
As urban block form has been proved to affect the energy performance of heating and cooling of buildings [11], it is expected that it can also significantly affect the economic efficiency of the interventions.
This research aims not only to define the additional cost in comparison to the conventional renovation intervention (exterior thermal insulation), but also to define the payback period of each renovation scenario.
The results of the research can prove that some passive interventions have a short payback period, which makes them more sustainable from an economic point of view, while others have longer payback period as the cost of materials stays relatively high. This means that it is necessary to examine the energy savings together with the initial cost of the interventions and the payback period in order to define their overall efficiency and sustainability.
2. Materials and Methods
The examined cases are described in this section. First, the initial condition of the urban blocks is presented and, second, the four intervention scenarios are described.
The methodology for assessing energy demand and cost of all cases (initial condition and renovated scenarios) is analyzed.
2.1. Description of the Examined Cases
The research examines two typical residential urban blocks representing the existing form of the built environment of a Greek city (Figure 1a,b).
The first urban block has four floors while the second has seven floors. All building elements of both urban blocks are considered to be non-insulated, according to the majority of buildings that were built before 1980 in the centers of Greek cities.
Across all EU Member States, most of the floor area is composed of residential buildings. Greece has a relatively large share of residential buildings (84.21%). The share varies considerably, from around 60% in Slovakia, the Netherlands, and Austria, to more than 85% in the southern countries of Cyprus, Malta, and Italy. Moreover, the percentage of multifamily buildings (65.21%) in Greece is also one of the largest in Europe after Poland, Spain, Italy, and Estonia [12].
According to the results of the 2011 building census, 58.35% of buildings in Greece were built before 1980 and 58% of the total buildings’ main construction system is reinforced-concrete load-bearing structure and brick masonry walls. Among these buildings, 61% are attached to the neighboring buildings [13]. A more detailed study of the typical urban block in the Greek city can be found in [11,14].
The two examined urban blocks are assumed to have a typical construction system of reinforced-concrete load-bearing structure (u-value = 3.25 W/m2K) and brick masonry walls (u-value = 1.72 W/m2K). For the horizontal building elements, the u-value of the roof slab is assumed to be 2.11 W/m2K, the u-value of the concrete slab on ground is 2.65 W/m2K, and for the slabs between floors, the u-value is 2.74 W/m2K. Windows are single glazing with a u-value of 5.81 W/m2K. It should be noted that both urban blocks are examined for the climatic conditions of Zone C, which is the second coolest zone in Greece according to the national Energy Performance of Buildings Regulation [15]. The two examined urban blocks are considered to have a retail use on the ground floor, while all other floors are assumed to have a typical layout plan with residential use. Urban block 2 has a recessed last floor (by 2.5 m), resulting from the current practice required by the Building Regulation in Greece for narrow street canyons. In this study, the road width is assumed to be 10 m.
2.2. Renovation Strategies
Four renovation scenarios were considered for the assessment of energy and economic efficiency of the interventions.
The first includes the typical insulation of the building shell by adding a thermal insulation layer at all the exterior surfaces and all surfaces facing non-heated spaces (Figure 2b). Windows are also replaced with new double-glazed ones. It should be noted that the other three scenarios are also considered to have been upgraded according to scenario 1, and the interventions described next are additional interventions to already thermally insulated buildings.
The second scenario includes improvement of the thermal mass of the building shell by adding a 3 cm PCM board with a melting point at 25 °C in the interior side of all exterior walls and ceilings (Figure 2c).
The third scenario includes the construction of a green roof on the last floor slab of all buildings (Figure 2d).
The fourth scenario includes the addition of sunspaces and shading on building facades. Sunspaces are added on the balconies of the last floor of the first urban block and the last two floors of the second urban block. Sunspaces are deactivated during the summer by sliding the glazing parts on the sides. Shading includes horizontal blinds in the exterior shell, outside of all sunspaces (Figure 2e).
All the construction details of the existing and the renovated building shell scenarios are presented in Figure 2a–e for urban block 1. Figure 3a,b presents the existing (base-case) and the renovation scenario 4 (passive solar and shading) for urban block 2. Scenarios 1–3 are not presented for urban block 2 as the construction details are similar to the details of urban block 1, except for the geometry of the section.
For all four scenarios, the u-values of all building elements after the renovation are considered to be equal to the maximum permitted values given by the Greek Energy Performance of Buildings Regulation (KENAK) [15]. According to the regulation’s limits, the u-values for the exterior walls should not exceed 0.45 W/m2K. For the horizontal building elements, the u-value of the roof slab should be no larger than 0.40 W/m2K. The u-value of the concrete slab on ground should be up to 0.75 W/m2K. Windows should be double glazed with a u-value no larger than 2.80 W/m2K.
2.3. Assessment Methodology
For the energy efficiency assessment of the urban blocks, dynamic simulations with the Energy Plus 9.1.2 software were performed. First, the total load demand for the heating and cooling of buildings was calculated for the base-case scenario, representing the existing situation of the buildings, and then three renovation scenarios were also simulated to define the improvement of the energy performance during the whole year period.
For the assessment of the economic cost of the interventions, all the surfaces of all building elements used in each renovation scenario were calculated. Then, the value—including material and construction cost of each building element—was set according to Greek market values from well-known companies. The economic cost values were also verified through relevant literature [16,17]. Table 1 and Table 2 present the calculated surface areas of each element included in each intervention scenario and the cost in EUR/m2, including material and constructional cost for both urban blocks.
Next, the payback period of each intervention was assessed by taking into account the savings resulting from energy demand in each renovation scenario and the current price per KWh in Greece.
3. Results
For the assessment of the economic efficiency of each intervention it is necessary to define the improvement in terms of the energy savings it can provide. The total energy demand for heating and cooling was calculated for both urban blocks through simulations and is presented in Table 3. It should be clarified that the simulations at this stage of the research include only the thermal demand (heating and cooling) per m2 on a yearly basis and not electricity consumption. It is remarked that in all cases urban block 2 performs better in terms of energy consumption as the total energy demand is lower for the base-case and the renovation scenario as well. It should also be noted that scenario 2 (PCM) is the most efficient in terms of energy demand for urban block 1, while scenario 4 (passive solar and shading) is the most efficient intervention for urban block 2. However, to determine which intervention is more efficient on an economic basis as well, it is necessary to calculate the cost in each case for constructing each scenario.
The economic evaluation of each intervention scenario for both urban blocks is presented in Table 4 and Table 5. It is obvious that the cost of renovation for both examined cases is higher in scenario 2 (PCM). This is because this renovation scenario includes the most extensive interventions (in terms of surface), as PCMs are applied in all exterior walls and all ceilings (exterior and interior).
Moreover, as expected, the total renovation cost for all scenarios is higher in urban block 2 due to its larger size. However, if the cost is calculated per m2, it is obvious that urban block 2 has a significantly lower cost for the construction of all scenarios (Table 6). The cost of all interventions is between 36% (scenario 2) and 52% (scenario 4) lower for urban block 2.
To assess the economic sustainability of the renovation scenarios, the payback period was calculated assuming that the cost of energy stays unchanged during the years (Table 7) and equal to 0.11 EUR/KWh, which is the cost of electric energy given by the national energy provider (DEI). In both cases, the first renovation scenario (thermal insulation) has the shortest payback period compared to the other three renovation scenarios. It should also be noted that PCM scenario (2) has the longest payback period, which can be explained by the fact that it is the most extensive intervention because it is applied in all floors (walls and ceilings). Moreover, buildings are characterized by heavyweight construction in their initial situation as they are constructed by reinforced-concrete load-bearing structure and brick masonry walls, which means that the additional thermal mass provided by the PCM may not be as efficient as other interventions.
The comparison of the examined urban blocks shows that urban block 2 has a significantly shorter payback period in all scenarios. Especially for scenario 4 (sunspaces and shading), the payback period is halved for urban block 2. This can be explained considering that this urban block has a different geometry in the last floor (recession) that favors the integration and efficiency of sunspaces.
4. Discussion
This research investigated the energy upgrading interventions at the urban block scale. The environmental efficiency (in terms of energy consumption) and the economic effectiveness of the interventions were assessed.
The results of the research showed that urban form can significantly affect not only the energy efficiency but also the economic effectiveness of renovation. Therefore, urban block form is an important parameter to consider before planning any renovation strategy. Among the two urban blocks examined, the one with the larger size and the more compact form was proved to be more efficient in terms of energy, demanding less energy for heating and cooling. Moreover, it was proved that in this urban block all renovation interventions present better economic effectiveness because initial capital depreciation occurs significantly earlier, from 5 to 7 years, depending on the renovation scenario.
Among all the examined interventions, the PCM was less efficient due to the prohibitive cost of construction and the exceedingly long payback period. Therefore, it is not a recommended strategy in a Mediterranean climate, a result that has also been shown by other researchers [18]. However, in this study, the PCM chosen was targeted to improve the heating load demand during winter according to the melting point temperature chosen, as this solution was calculated to contribute more to the overall yearly energy demand. Other researchers, investigating PCM integration during the cooling period for the Mediterranean climate, reached mixed results [19], as it depends on appropriate design of the PCM integration and the building’s inertia.
Green roofs have been calculated to be a very efficient scenario (after the conventional building shell insulation scenario 1), as it has a short payback period, mainly due to its relatively limited initial investment cost.
Passive solar systems have also been proved a very efficient renovation strategy for the Greek climate, as the systems can provide significant energy savings, a result also supported by other research in a similar climate [20], while at the same time they can also foster the quality of life in cities by providing improved indoor sound quality, and the ability to improve building aesthetics.
The work proposed could be further expanded by examining more typologies of urban blocks to be able to generalize the results for larger urban areas, while at the same time it could also include RES system installation at the urban scale in order to assess renovation strategies targeted toward nearly zero energy buildings (nZEBs). The results of the research are useful for defining large renovation priorities at the city scale and for introducing specific solutions for the retrofit of buildings.
Author Contributions
Conceptualization, D.T.; methodology, D.T.; software, D.Z. and D.T.; writing—original draft preparation, D.T.; writing—review and editing, D.T., D.Z. and D.B.; supervision, D.B.; project administration, D.B. and D.T.; funding acquisition, D.B. and D.T. All authors have read and agreed to the published version of the manuscript.
Funding
This research is co-funded by Greece and the European Union (European Social Fund—ESF) through the Operational Program “Human Resources Development, Education and Lifelong Learning 2014–2020” in the context of the project “Sustainable interventions for the energy and aesthetic improvement of the city” (MIS 5047805).
Conflicts of Interest
The authors declare no conflict of interest.
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Figure 1.
(a) Perspective view of urban block 1 and (b) perspective view of urban block 2.
Figure 2.
Construction details of the base-case scenario and of the renovation scenarios: (a) initial condition of buildings (base-case scenario); (b) intervention scenario 1: thermal insulation; (c) intervention scenario 2: PCM; (d) intervention scenario 3: green roof; (e) intervention scenario 4: passive solar and shading.
Figure 2.
Construction details of the base-case scenario and of the renovation scenarios: (a) initial condition of buildings (base-case scenario); (b) intervention scenario 1: thermal insulation; (c) intervention scenario 2: PCM; (d) intervention scenario 3: green roof; (e) intervention scenario 4: passive solar and shading.
Figure 3.
Construction details of the (a) base-case scenario and (b) renovation scenario 4 (passive solar and shading).
Figure 3.
Construction details of the (a) base-case scenario and (b) renovation scenario 4 (passive solar and shading).
Table 1.
Building element quantities for urban block 1 and cost per m2 for each intervention.
| Zone | Building Element | Interventions | Net Area | Renovation Scenario | |||
|---|---|---|---|---|---|---|---|
| m2 | 1 | 2 | 3 | 4 | |||
| EUR/m2 | |||||||
| Residential, Retail | External Brick Wall | Insulation, PCM | 5495 | 55 | 40 | - | - |
| External Ceiling | Insulation, PCM, Green Roof | 1152 | 40 | 40 | 50 | - | |
| Ground Floor | Insulation | 1152 | 40 | - | - | ||
| Internal Ceiling | PCM | 3343 | - | 40 | - | - | |
| Staircase 1 | Internal Concrete Wall | Insulation, PCM | 1411 | 20 | 40 | - | - |
| External Ceiling | - | 148 | - | - | - | - | |
| External Concrete Wall | - | 269 | - | - | - | - | |
| Entrance 1 | Internal Brick Wall | Insulation, PCM | 150 | 20 | 40 | - | - |
| Elements in all zones | Windows | Windows | 1187 | 180 | - | - | - |
| Sunspace | Sunspace and Shadings | 735 | - | - | - | 180 | |
| Shadings | Sunspace and Shadings | 818 | - | - | - | 220 | |
1 non-heated space.
Table 2.
Building element quantities for urban block 2 and cost per m2 for each intervention.
| Zone | Building Element | Interventions | Net Area | Renovation Scenario | |||
|---|---|---|---|---|---|---|---|
| m2 | 1 | 2 | 3 | 4 | |||
| EUR/m2 | |||||||
| Residential, Retail | External Brick Wall | Insulation, PCM | 18,278 | 55 | 40 | - | - |
| External Ceiling | Insulation, PCM, Green Roof | 4503 | 40 | 40 | 50 | - | |
| Ground Floor | Insulation | 4235 | 40 | - | - | - | |
| Internal Ceiling | PCM | 19,705 | - | 40 | - | - | |
| Internal Brick Wall | PCM | 9565 | - | - | - | - | |
| Staircase 1 | Internal Concrete Wall | Insulation, PCM | 3921 | 20 | 40 | - | - |
| Entrance 1 | Internal Brick Wall | Insulation, PCM | 986 | 20 | 40 | - | - |
| Elements in all zones | Windows | Windows | 4233 | 180 | - | - | - |
| Sunspace | Sunspace and Shadings | 1989 | - | - | - | 180 | |
| Shadings | Sunspace and Shadings | 2358 | - | - | - | 220 | |
1 non-heated space.
Table 3.
Total energy demand (in KWh/m2) for the heating and cooling of the base-case and the renovation scenarios for the two urban blocks.
Table 3.
Total energy demand (in KWh/m2) for the heating and cooling of the base-case and the renovation scenarios for the two urban blocks.
| Urban Block | Base-Case | Renovation Scenario | |||
|---|---|---|---|---|---|
| Total Energy Demand (KWh/m2) | |||||
| 1 | 2 | 3 | 4 | ||
| 1 | 214.54 | 95.01 | 91.20 | 93.40 | 92.10 |
| 2 | 185.39 | 79.35 | 76.58 | 78.79 | 75.90 |
Table 4.
Total cost of the renovation scenarios for urban block 1.
| Scenario | Renovation | Net Area | Renovation Cost | Total Scenario Cost |
|---|---|---|---|---|
| (m2) | (EUR) | (EUR) | ||
| 1 | Insulation | 9361 | 425,625 | - |
| Windows | 1187 | 213,660 | - | |
| 639,285 | ||||
| 2 | PCM | 23,103 | 924,138 | 1,563,422 |
| 3 | Green Roof | 1152 | 57,595 | 696,880 |
| 4 | Sunspaces | 735 | 132,300 | - |
| Shadings | 818 | 179,960 | - | |
| 951,545 |
Table 5.
Total cost of the renovation scenarios for urban block 2.
| Scenario | Renovation | Net Area | Renovation Cost | Total Scenario Cost |
|---|---|---|---|---|
| (m2) | (EUR) | (EUR) | ||
| 1 | Insulation | 31,923 | 145,2950 | - |
| Windows | 4233 | 761,940 | - | |
| 2,214,890 | ||||
| 2 | PCM | 11,3916 | 4,556,640 | 6,771,530 |
| 3 | Green Roof | 4503 | 225,150 | 2,440,040 |
| 4 | Sunspaces | 1989 | 358,020 | - |
| Shadings | 2358 | 518,760 | - | |
| 3,091,670 |
Table 6.
Cost per m2 for all renovation scenarios for the two examined urban blocks and percent difference between the two cases.
Table 6.
Cost per m2 for all renovation scenarios for the two examined urban blocks and percent difference between the two cases.
| Renovation Scenario | Cost (EUR)/m2 | ||
|---|---|---|---|
| Urban Block 1 | Urban Block 2 | Percent Difference (%) | |
| 1 | 142 | 73 | 49 |
| 2 | 347 | 223 | 36 |
| 3 | 154 | 80 | 48 |
| 4 | 211 | 102 | 52 |
Table 7.
Payback period of each intervention scenario for the two urban blocks.
| Urban Block | Payback Period (years) | |||
|---|---|---|---|---|
| Renovation Scenario 1 | Renovation Scenario 2 | Renovation Scenario 3 | Renovation Scenario 4 | |
| 1 | 11 | 25 | 12 | 16 |
| 2 | 6 | 18 | 7 | 8 |
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Tsirigoti, D.; Zenginis, D.; Bikas, D. Sustainable Development Scenarios for Urban Blocks: Energy Renovation and Quality of Life in the Greek City. Environ. Sci. Proc. 2022, 15, 37. https://0-doi-org.brum.beds.ac.uk/10.3390/environsciproc2022015037
AMA Style
Tsirigoti D, Zenginis D, Bikas D. Sustainable Development Scenarios for Urban Blocks: Energy Renovation and Quality of Life in the Greek City. Environmental Sciences Proceedings. 2022; 15(1):37. https://0-doi-org.brum.beds.ac.uk/10.3390/environsciproc2022015037
Chicago/Turabian StyleTsirigoti, Dimitra, Dimitrios Zenginis, and Dimitrios Bikas. 2022. "Sustainable Development Scenarios for Urban Blocks: Energy Renovation and Quality of Life in the Greek City" Environmental Sciences Proceedings 15, no. 1: 37. https://0-doi-org.brum.beds.ac.uk/10.3390/environsciproc2022015037
