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Data collection and analysis of the building stock and its energy performance—An example for Hellenic buildings
Energy and Buildings 42 (2010) 1231–1237
Contents lists available at ScienceDirect
Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild
Data collection and analysis of the building stock and its energy performance—An example for Hellenic buildings Elena G. Dascalaki ∗ , Kaliopi Droutsa, Athina G. Gaglia, Simon Kontoyiannidis, Constantinos A. Balaras Group Energy Conservation, Institute of Environmental Research and Sustainable Development, National Observatory of Athens, I. Metaxa & Vas. Pavlou, 152 36 P. Penteli, Greece
a r t i c l e
i n f o
Article history: Received 1 December 2009 Received in revised form 12 January 2010 Accepted 17 February 2010 Keywords: Energy consumption Certificates Building stock Database
a b s t r a c t The process of building labeling and certification in accordance to the provisions of the European Directive on the Energy Performance of Buildings (EPBD) constitutes a unique opportunity for collecting information on the characteristics of the building stock and its energy performance on a national and European level. Thus, there is a need to handle data from a large stock of buildings and to be able to analyse information and extract practical trends and benchmarks. Stakeholders and technical managers who oversee a number of buildings experience similar needs in order to collect, organize and monitor the energy performance of a large pool of buildings. To facilitate these efforts, a common evaluation database and complimentary software for its exploitation have been developed in the frame of a European project. This paper presents an overview of the database and its available tools, and the main results from a case study on Hellenic buildings that reveals relevant characteristics. The Hellenic database included a sample of 250 buildings from different regions in Greece, with a breakdown that is representative of the national building stock. The main results focus on the buildings’ energy performance, thermal envelope characteristics and the exploitation of solar thermal energy. © 2010 Elsevier B.V. All rights reserved.
1. Introduction The continuous environmental deterioration and the scarcity of available natural resources have raised global concern on the exploitation of renewable energy sources and the effective application of energy conservation strategies in all energy consuming sectors. In 2006, the gross inland consumption in the European Union EU-27 member states was 1825.2 million tonnes of oil equivalent (Mtoe), of which 129.7 Mtoe or 7.1% from renewables largely made of biomass (69%), hydro (20.5%), wind (5.5%), geothermal (4.3%) and only 0.8% for solar [1]. The final energy consumption reached 1177.4 Mtoe, of which 59.7 Mtoe or 5.1% from renewables excluding consumption for electricity and delivered heat and 9.2% including consumption of the energy branch for electricity and heat generation and distribution losses [1]. The building sector consumes about 39% (455.2 Mtoe) of the total final energy consumption and emits about 35% of the total CO2 emissions in Europe. Consequently, reducing energy consumption in the building sector can constitute an important instrument in the efforts to alleviate the EU energy import dependency (currently at about 53.8% and may reach two-thirds by 2030 [2] unless some urgent additional measures and policies are adopted) and comply with the
∗ Corresponding author. Tel.: +30 210 8109143. E-mail address: [email protected] (E.G. Dascalaki). 0378-7788/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2010.02.014
Kyoto Protocol that came into effect on February 16, 2004 to reduce carbon dioxide emissions by an overall 8% in the EU compared with 1990 values, by 2012. Along these lines, the European Directive 2006/32/EC on energy end-use efficiency and energy services aims to achieve an overall national indicative energy savings target of 9% before the end of the 2020s by energy services and other cost-effective energy efficiency improvement measures in all EU member states. The adoption of well-tailored energy conservation strategies for buildings on a regional, national and European level requires knowledge of the specific characteristics of the building stock. Despite the numerous studies carried out during the past decades dealing with the assessment of various retrofit interventions on the energy performance of buildings, it is a fact that little is actually known on the state of the European building stock, its characteristics and current trends. Consequently, there is a growing need for systematic collection, classification and analysis of data from the building sector. Implementation of the European Directive 2002/91/EC on the energy performance of buildings (EPBD) with the attribution of Energy Performance Certificates (EPC) to almost all buildings in Europe has initiated the mapping process for the existing European building stock. In Greece, the national EPBD implementation follows the provisions of the national law N.3661/08 on “Measures for the reduction of energy consumption in buildings and other provisions” that was issued in May 2008 and due to several delays is expected to be enforced in 2010 with the publication of the new
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“Regulation on the Energy Assessment of Buildings—KENAK”. The EPC will attribute each building a numerical indicator for ranking purposes according to an asset rating of its energy performance, while at the same time it will be supplemented by recommendations on cost-effective energy conservation measures. The EPC will be compulsory for new constructions and existing buildings over 1000 m2 that undergo major renovations, and existing buildings with a floor area exceeding 50 m2 when they are sold, rented or transferred to other relatives of the owners. An electronic database will be established to collect the results from the building energy audits and EPCs along with the reports from the inspections of boilers, heating installations and air-conditioning systems. In addition, the new European Directive 2009/28/EC on the promotion of the use of energy from renewable sources mandates that each member state should increase its use of renewable energy sources (RES) – such as solar, wind or hydro – to reach an ambitious 20% share of energy from renewable sources by 2020. Each EU member state will have to increase its share of RES by 5.5% from 2005 levels, with the remaining increase calculated on the basis of per capita gross domestic product, for example, to reach by 2020 a share of 10% in Malta up to 49% in Sweden. While the focus of the Directive 2009/28/EC is on the promotion of large scale renewable energy installations, member states are nevertheless requested to use “minimum levels for the use of energy from renewable sources in buildings”. Architects, engineers and planners are also to benefit from member state ‘guidance’ when planning new construction projects, while local and regional administrative bodies should be recommended to “ensure equipment and systems are installed for the use of heating, cooling and electricity from RES and for district heating and cooling when planning, designing, building and refurbishing industrial or residential areas”. Under the Directive 2009/28/EC, EU member states must stipulate the “use of minimum levels of energy from renewable sources in new buildings and in existing buildings that are subject to major renovation”. This paper presents an overview of the infrastructure and tools that could facilitate the exploitation of data on the building stock and its energy performance. Elaboration of the results from a pilot application in Greece reveals the characteristics of the Hellenic building stock. A brief comparison of similar data from ten EU member states is also included.
2. Methodology The effort to improve the knowledge on the energy-related characteristics and major trends of the European building stock mandates the need for establishing a common database with uniform information and structure. This will offer an opportunity to exploit the information from the national EPCs and reports from building energy audits, inspection of boilers and air-conditioning systems that will be kept in nationally established electronic databases. Along the same lines, this database could be used by stakeholders and technical managers, who oversee a number of buildings, to collect, organize and analyse relevant data in order to best maintain, operate and monitor the energy performance of their buildings. In all cases, collecting and organizing the necessary data will reveal key information for accessing and improving their building stock. The database includes a total of 255 parameters covering a wide, yet realistic, range of building characteristics (Fig. 1). The data refers to: general building data (location, use, and conditioned area), building envelope data (e.g. U-values, surface areas, and construction types), electromechanical (E/M) installations including renewable energy systems that may be in operation (e.g. system information and operation parameters) and their efficiency, energy demand (heating, cooling and hot water loads), final (operational
and/or calculated) and primary energy consumption as well as CO2 emissions. Various data entries are specified according to user defined classifications (e.g. energy carrier types, heat/cold generation types) so that they are adapted according to specific needs. For practical purposes and in order to test the concept, the database is an EXCEL worksheet. The corresponding data for each building (dataset) is entered in a row. The columns of the table (255 in total) describe the building properties. Each column (data field) of the table stands for a defined quantity, which may be a number (e.g. conditioned floor area of the building in m2 ) or a string indicating special information (e.g. the name of the city where the building is located). The database is complemented by various tools for data manipulation and statistical analysis that may be used to easily analyse and process the data using different criteria. A detailed description of the database contents is available in [3]. The database structure is also available on line. The database was populated with data from 12 pilot studies in different EU member states. The following section, presents an overview of the Hellenic pilot study along with representative results. The analysis reveals the building envelope characteristics, energy performance and use of RES in Hellenic buildings. Finally, a comparative presentation of similar data from a sample of buildings from different European countries is elaborated for comparative purposes.
3. Hellenic buildings According to the Hellenic National Statistics Service, there are about 4 million buildings in Greece, with a total floor area of 552 million square meters. The residential and tertiary sectors represent 77% and 23% of the total, respectively. Most of the residential sector consists of apartment buildings the majority of which are old and have aged installations with low energy efficiency. In 2006, the final energy consumption of Hellenic buildings was about 88,400 GWh accounting for 35.4% of the total final energy consumption [4]. Data from a total of 250 buildings were incorporated in the Hellenic database. Emphasis was given on residential buildings, currently representing 76% of the Hellenic building stock. A representative number of non-residential (NR) buildings for different end-uses were also included. In total, 176 residential and 74 NR buildings located in the different national climatic zones were incorporated in the database. The residential buildings included 118 apartment buildings (high-rise buildings with more than two floors) and 58 single dwellings (low-rise buildings with one or two floors). The NR buildings included office, hospital, hotel, airport buildings as well as sports halls and swimming pools. The breakdown of the number of different end-use buildings and their average annual final thermal, electrical and total energy consumption per unit floor area, for the three national climatic zones, is summarized in Table 1. Some trends of the average energy consumption in NR buildings among the different climatic zones have fluctuations due to the different operational characteristics of the specific end-use of NR buildings included in the sample. For example, in zone A, some NR buildings have seasonal operation (e.g. hotels that operate only in summer) or limited hours of operation (e.g. airports with limited traffic and operation in winter compared with full operation during the tourist season in summer). As a result, they have low thermal energy consumption and relatively higher electrical energy consumption. The sample of the Hellenic buildings used in this analysis is composed of 70% residential buildings, 12% airports, 7% sports halls, 4% hospitals, 2% swimming pools, 2% offices, 2% educational buildings and 1% hotels. The above breakdown is considered to be repre-
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Fig. 1. Main structure of the DATAMINE database.
sentative of the Hellenic building stock. According to the Hellenic National Statistics Service the residential sector represents 77% of the entire building stock, whereas the NR building stock represents the remaining 23% (i.e. 2.7% office and commercial buildings, 0.46% educational buildings, 0.82% hotels, 0.06% hospitals and 19% other uses including airports, sports halls, etc.). The final total energy consumption in the residential buildings of the sample ranges from 43 to 348 kWh/m2 a, while for NR buildings values range from 38 to 673 kWh/m2 a. The number of buildings (250) included in the sample is rather small and it does not allow the derivation of final and specific conclusions. However, the buildings are representative of the different categories and cover different construction periods and locations throughout the country. The results of the present analysis may be
indicative and demonstrate some trends in the Hellenic building stock on a local as well as national level. The following discussion places an emphasis on the building thermal envelope and energy performance, including a closer analysis on the use of solar thermal energy, when available. Taking into account the fact that residential and NR buildings differ significantly in terms of use, size and operation, results are given separately for the two sectors.
3.1. Thermal envelope The sample of the 250 buildings originates from pilot building energy audits (40% of available data) and other short energy audit campaigns using standard questionnaires and energy audit reports
Table 1 Breakdown of the number of buildings and average annual final energy consumption (operational data) for the national climatic zones, in the Hellenic database. End-use of buildings
Climatic zones (heating degree days) A (600–1150)
B (1151–1600)
C (1601–2065)
Residential Number of buildings Average annual thermal energy consumption (kWh/m2 a) Average annual electrical energy consumption (kWh/m2 a) Average annual total energy consumption (kWh/m2 a)
15 70 38 108
117 99 38 136
44 155 34 189
Non-residential Number of buildings Average annual thermal energy consumption (kWh/m2 a) Average annual electrical energy consumption (kWh/m2 a) Average annual total energy consumption (kWh/m2 a)
19 26 141 167
45 130 96 226
10 233 138 371
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Fig. 2. Average heat transfer coefficient of external walls for different building construction periods of residential and non-residential buildings in the Hellenic database. The vertical dash line indicates the U-value of the national thermal insulation regulation (TIR).
Fig. 3. Total surface of exterior wall areas for different heat transfer coefficients of residential and non-residential buildings in the Hellenic database. The horizontal dash line indicates the U-value of the national thermal insulation regulation (TIR).
(60% of available data) from different regions in Greece. Quality checks were performed before the data was incorporated in the database. About 40% of the available data (72 buildings) included information from asset rating, while for the remaining 178 buildings available data was from operational rating, with additional data on energy performance and thermal envelope characteristics. A detailed analysis of the energy-related building properties of the sample was carried out including the U-values of the different building elements, the different types of heat supply systems and the energy balance-including measured and calculated energy consumption. The residential and NR building sectors differ significantly in terms of building use, size, operating hours, heating/cooling systems and set-points. In order to draw more representative conclusions data from buildings belonging to the two sectors were analysed separately. This permits an in-depth analysis of the data taking into account the particular characteristics of each sector. The small number of different end-use buildings within the sample of the NR buildings did not allow for a meaningful analysis of the specific NR categories, although this would be possible in the future once the database is populated with additional data. Fig. 2 illustrates the dependence of the average heat transfer coefficient (U-value) of walls with the building’s age (year of construction). This is based on the total number of residential and 50% of the NR buildings of the Hellenic data sample. The U-value of the walls in the analysed residential buildings varied from 0.84 to 1.93 W/m2 K. The average value before 1980 (a total of 99 buildings) was 1.54 W/m2 K, while a reduction of 32% was achieved after the implementation of the existing national Thermal Insulation Regulation (TIR) which was introduced after 1980 (averaging a U-value of 1.04 W/m2 K). The lowest values correspond to buildings constructed after 2000. However, the mean U-value even for the buildings recently erected remains higher than the one mandated by the national TIR (0.7 W/m2 K). This indicates that there are still some problems with its implementation. The average U-value for the NR buildings sample before 1980 (a total of 18 buildings) was 2.56 W/m2 K, while a reduction of 69% was achieved following the implementation of the national TIR after 1980 (averaging a Uvalue of 0.80 W/m2 K). The fact that the buildings with the smaller wall U-value have been erected after 1980 and represent 47% of the sample, is an indication that the new NR buildings are constructed in line with the specifications of the national TIR, indicated in the graphs by the vertical dashed line. The average U-value for external windows in the residential and NR buildings of the sample is 4.4 and 4.6 W/m2 K, respectively. No clear trend can be observed in the evolution of the coefficient over the years. This can be attributed to the fact that the replacement of single glazing with double ones is very often incorporated in the
process of a routine building refurbishment as it is recognised as a technique to achieve both thermal and acoustical comfort. This is the reason why very slight differences in the U-value of windows are observed among buildings of various ages. Despite the fact that the mean values of the coefficient are within the limits foreseen by the national TIR, the fact that its value remains higher than 3.26 W/m2 K (indicative mean U-value for double glazing) indicates that single glazing can be found even in recent constructions. The U-value of roofs in the analysed sample of residential buildings varied from 0.94 to 2.46 W/m2 K. The average value before 1980 (a total of 99 buildings) was 1.91 W/m2 K, while a reduction of 50% was achieved after the implementation of the national TIR after 1980. The lowest values correspond to buildings constructed after 2000. However, the mean U-value even for the residential buildings erected recently remains higher than the one mandated by the TIR (0.7 W/m2 K). This indicates that there are still some problems in its implementation. In the analysed NR buildings the coefficient varied from 0.46 to 1.01 W/m2 K. The average value of the coefficient before 1980 (a total of 18 buildings) was 1.00 W/m2 K, while a reduction of 53% was achieved after the implementation of the national TIR after 1980. The average value in the decades after 1980 is within the limits foreseen by the national TIR, which indicates that the new NR buildings are constructed in line with the specifications of the Regulation. The analysis of the whole sample revealed that improvement of the roof insulation is required in all the residential buildings and in 62% of the NR buildings in order to satisfy the limits foreseen by the national TIR. The addition of roof insulation is very often implemented in the process of a routine building refurbishment. However, the impact of such an intervention is limited to improving the thermal comfort conditions in the last floor in winter and summer, but it does not have a major impact on the energy consumption of the whole building. Fig. 3 illustrates the distribution of the buildings’ exterior wall area to the different U-value classes. Thermal insulation in the majority of the analysed buildings is not in line even with the provisions of the 1980 national TIR, indicated in the graphs by the horizontal line. Accordingly, 61% of the total exposed wall fac¸ade areas of residential buildings and 70% of NR buildings will have to be refurbished with additional thermal insulation. Fig. 4 illustrates the distribution of the buildings’ external window area to the different U-value classes. Accordingly, the U-value exceeds the upper limits of the national TIR (indicated in the graph by the horizontal line) in 22% and 7% of the total glazing area for the analysed residential and NR buildings, respectively. Overall, about 75% of the total transparent facade areas of the buildings will have to be replaced with double glazing. Fig. 5 illustrates to what extent the construction of the buildings in the Hellenic data sample is in line with the requirements of the 1980 national TIR. The U-value of a building is calculated
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Fig. 4. Total window area for different heat transfer coefficients of residential and non-residential buildings in the Hellenic database. The horizontal dash line indicates the U-value of the 1980 national thermal insulation regulation (TIR).
as the sum of the products of the U-values for each of the building elements (e.g. walls, roof, glazing, etc.) and the corresponding area of each building element, divided by the sum of the building’s envelope areas. For each of the three climatic zones defined in the Regulation, the buildings with U-value above the corresponding theoretical curve f/V = f (U-value), defined as a function of the building’s external thermal envelope area (f) to the building’s volume (V), do not comply with the 1980 national TIR. As shown in Fig. 5, the U-value exceeds the limits set in the Regulation in 87%, 84% and 98% of the residential buildings in the sample for climatic zones A, B and C, respectively. 3.2. Solar thermal energy Final energy consumed for household space heating accounts for 66% of total energy used in residential buildings, cooling for less than 1%, but is projected to grow at a fast pace in the future, water heating and cooking for 22%, electrical appliances for 6%, and lighting for 5%. For NR buildings, space heating accounts for 50.5% and other heat uses (sanitary hot water and cooking) for 22.5%, electrical appliances for 16.5%, lighting for 4% and cooling for 6.5%. The most common solar energy thermal application is for sanitary hot water (SHW) production. Greece has a well developed market of small systems for SHW production using natural flow systems (thermosyphon) without any need for pumps or control stations, that are widely used in residential buildings and small hotels, with an electric heat resistance in the SHW storage tank as
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a back-up. A small number of large central systems with central hot water storage and forced circulation systems are installed in large hotels. Solar cooling is an emerging market with a huge growth potential [5], but to this date there are only a handful of installations in Greece (e.g. two hotels in Crete, a couple of office buildings in Athens and the largest solar field installation in a cosmetics factory near Athens). The use of solar thermal energy for SHW was identified for the buildings included in the sample Hellenic database. Fig. 6 illustrates the variation of electrical energy consumption which is the common backup energy source for SHW, in the sample of residential buildings used in this analysis. Results are given for the three national climatic zones for single dwellings and apartment buildings with solar collectors for SHW and the corresponding values for other types of systems (e.g. electric water heaters). Given the available data, it was not possible to derive the exact contribution of the SHW production system to the total electrical energy consumption. However, the analysis clearly illustrates a trend for buildings using solar collectors to consume less electricity than those using conventional systems for SHW production. The total electrical energy consumption in the sample of dwellings is reduced by 27–37% depending on the climatic zone, while in the sample of apartment buildings the reduction ranges between 36% and 57%.
4. Characteristics of European buildings Relevant information from ten EU member states (i.e. Austria, Belgium, Bulgaria, Germany, Greece, Ireland, Italy, Netherlands, Poland, Slovenia, Spain and UK) were used to populate the database with data from 19000 residential and NR buildings [3]. Analysis of this larger sample permits a cross-country comparison of the energy characteristics for specific building types. Fig. 7 illustrates the distribution of the average U-value for representative buildings in different construction periods from ten EU member states. For each construction period, an “average” building type is defined for every country by averaging the corresponding U-values. This example demonstrates how the available data and tools may also be used to derive cross-national comparisons. The distribution of the average U-value indicates a continuous improvement of the thermal characteristics of the building envelope over the past 100 years. A drastic reduction of the U-value coefficient for external walls and roofs is illustrated in Fig. 7. This trend was less observed for the U-value of basement walls. For glaz-
Fig. 5. Compliance of existing residential building constructions (symbols) in the three national climatic zones with the 1980 national thermal insulation regulation (TIR) requirements (solid lines) as a function of the building’s external thermal envelope area (f) to the building’s volume (V).
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Fig. 6. Total annual electrical final energy consumption in the Hellenic residential sample of dwellings (left) and apartment buildings (right), with solar collectors and other types of systems for service hot water production.
Fig. 7. Cross-country comparison of the total heat transfer coefficient of (a) exterior walls and (b) roofs for a sample of residential buildings from ten European countries [3].
ings, the U-value variations with the construction year were very limited. This may be attributed to the fact that the replacement of single with double-glazing has been a very common refurbishment intervention over the past few decades in most countries. 5. Conclusions The building sector consumes about 40% of the total energy consumption and emits about 35% of the total CO2 emissions in Europe. Current knowledge on the specific characteristics and trends of the building stock is rather limited, which impedes the adoption of effective energy conservation measures for the building sector. Consequently, there is a growing need for systematic collection, classification and analysis of data from the building sector. The process of building labeling and certification in accordance to the provisions of the EPBD constitutes a unique opportunity for collecting information on the characteristics of the building stock and its energy performance on a national and European level. Taking into account the great variety of buildings, as well as certificate types in the European member states and the very different status of national EPBD implementation efforts, the creation of a harmonized data monitoring platform is imperative. In response to these needs a common European effort developed the necessary infrastructure for the exploitation of the information from the national energy performance certificates and reports for building energy audits, inspection of boilers and air-conditioning systems that will be kept in nationally established electronic databases. The deliverables of this effort include a harmonized database and a set of analysis tools for organizing and monitoring the data, as well as processing it using different criteria.
The methodology was assessed during twelve pilot studies in different European countries. Overall, it was viewed as a very useful tool for organizing and processing national data on the building stock and extract information on its characteristics and major trends. The representative analysis performed using the available Hellenic data included results on the characteristics of the Hellenic building stock in terms of the building’s thermal envelope characteristics, final energy consumption, and the use of solar energy collectors. These results were used to illustrate some characteristics of the Hellenic building stock and the concept of how to use the DATAMINE database and analysis tool. Similar analysis may also be performed using any of the 255 parameters to derive relevant conclusions provided that there is sufficient available data. Accordingly, representative results from the analysis of the sample Hellenic residential and non-residential buildings revealed that the annual average thermal energy consumption (operational data) of the Hellenic buildings ranges from 70 to 155 kWh/m2 a in residential buildings and from 26 to 233 kWh/m2 a in NR buildings, depending on the different climatic zones. Similarly, the average total energy consumption ranges from 108 to 189 kWh/m2 a in residential buildings and from 167 to 371 kWh/m2 a in NR buildings. Follow-up analysis showed that over time there is a trend of decreasing U-values of the building’s thermal envelope (e.g. walls, roof, glazing, etc.), although the great majority of Hellenic buildings is either not thermally insulated or poorly insulated. Even according to the 1980 national TIR, which is currently under revision in the frame of the ongoing national work for EPBD implementation that will introduce even more strict thermal insulation regula-
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tions for the building’s envelope, over 60% of exterior walls and 80% of windows of the existing building stock do not meet minimum code requirements. On a positive note, further analysis of the available Hellenic data, reveals that the use of solar thermal collectors for sanitary hot water production reduces the total electrical energy consumption by 27–37% in single dwellings and 36–57% in apartment buildings. Finally, the database was also populated with relevant data from 10 European countries in a pilot exercise in order to make cross-country comparisons and draw conclusions on the characteristics of the European building stock as a whole [3]. Overall, the methodology (database and tools) is flexible enough to be used by building managers who are responsible for a number of buildings for collecting and analyzing relevant data in order to monitor the energy performance of their building stock and rank their priorities regarding energy-related measures. For example, compare the impact on the energy performance of the buildings from the use of different heating, cooling or ventilation systems, equipment efficiency, controls, temperature settings, distribution losses, or lighting installed power and controls. In all cases, collecting and organizing the necessary data is the first step in order to reveal key information that can be used to access and improve a given building stock.
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Acknowledgments This work is based on the results of the European project DATAMINE that was partly financed by the European Commission, DG XVII in the framework of the Energy Intelligent Europe under the coordination of the Institut Wohnen und Umwelt GmbH, Germany and the collaboration of twelve (12) partners from the corresponding European member states (http://env.meteo.noa.gr/datamine/). References [1] EC, European Union Energy & Transport in Figures—2009 edition, Office for the Official Publications of the European Communities, Luxembourg, 2009, 228 pp. [2] P. Capros, L. Mantzos, V. Papandreou, N. Tasios, European Energy and Transport, Trends to 2030—Update 2007, in: Directorate-General for Energy and Transport, European Commission, Brussels, April, 2008, p. 156. [3] T. Loga, N. Diefenbach (eds.), DATAMINE—Collecting Data From Energy Certification To Monitor Performance Indicators for New and Existing Buildings, Final report, 197 p., January 2009. Available on line: http://env.meteo. noa.gr/datamine/DATAMINE Final Report.pdf. [4] EU Energy & Transport in Figures, Part 2: Energy, Statistical Pocket Book, Directorate General for Energy and Transport, Office for Official Publications of the European Communities, Luxembourg, 2009, 232 pp. [5] C.A. Balaras, G. Grossman, H.-M. Henning, C.A.I. Ferreira, E. Podesser, L. Wang, E. Wiemken, Solar air conditioning in Europe—an overview, Renewable & Sustainable Energy Reviews 11 (2) (2007) 299–314.
Contents lists available at ScienceDirect
Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild
Data collection and analysis of the building stock and its energy performance—An example for Hellenic buildings Elena G. Dascalaki ∗ , Kaliopi Droutsa, Athina G. Gaglia, Simon Kontoyiannidis, Constantinos A. Balaras Group Energy Conservation, Institute of Environmental Research and Sustainable Development, National Observatory of Athens, I. Metaxa & Vas. Pavlou, 152 36 P. Penteli, Greece
a r t i c l e
i n f o
Article history: Received 1 December 2009 Received in revised form 12 January 2010 Accepted 17 February 2010 Keywords: Energy consumption Certificates Building stock Database
a b s t r a c t The process of building labeling and certification in accordance to the provisions of the European Directive on the Energy Performance of Buildings (EPBD) constitutes a unique opportunity for collecting information on the characteristics of the building stock and its energy performance on a national and European level. Thus, there is a need to handle data from a large stock of buildings and to be able to analyse information and extract practical trends and benchmarks. Stakeholders and technical managers who oversee a number of buildings experience similar needs in order to collect, organize and monitor the energy performance of a large pool of buildings. To facilitate these efforts, a common evaluation database and complimentary software for its exploitation have been developed in the frame of a European project. This paper presents an overview of the database and its available tools, and the main results from a case study on Hellenic buildings that reveals relevant characteristics. The Hellenic database included a sample of 250 buildings from different regions in Greece, with a breakdown that is representative of the national building stock. The main results focus on the buildings’ energy performance, thermal envelope characteristics and the exploitation of solar thermal energy. © 2010 Elsevier B.V. All rights reserved.
1. Introduction The continuous environmental deterioration and the scarcity of available natural resources have raised global concern on the exploitation of renewable energy sources and the effective application of energy conservation strategies in all energy consuming sectors. In 2006, the gross inland consumption in the European Union EU-27 member states was 1825.2 million tonnes of oil equivalent (Mtoe), of which 129.7 Mtoe or 7.1% from renewables largely made of biomass (69%), hydro (20.5%), wind (5.5%), geothermal (4.3%) and only 0.8% for solar [1]. The final energy consumption reached 1177.4 Mtoe, of which 59.7 Mtoe or 5.1% from renewables excluding consumption for electricity and delivered heat and 9.2% including consumption of the energy branch for electricity and heat generation and distribution losses [1]. The building sector consumes about 39% (455.2 Mtoe) of the total final energy consumption and emits about 35% of the total CO2 emissions in Europe. Consequently, reducing energy consumption in the building sector can constitute an important instrument in the efforts to alleviate the EU energy import dependency (currently at about 53.8% and may reach two-thirds by 2030 [2] unless some urgent additional measures and policies are adopted) and comply with the
∗ Corresponding author. Tel.: +30 210 8109143. E-mail address: [email protected] (E.G. Dascalaki). 0378-7788/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2010.02.014
Kyoto Protocol that came into effect on February 16, 2004 to reduce carbon dioxide emissions by an overall 8% in the EU compared with 1990 values, by 2012. Along these lines, the European Directive 2006/32/EC on energy end-use efficiency and energy services aims to achieve an overall national indicative energy savings target of 9% before the end of the 2020s by energy services and other cost-effective energy efficiency improvement measures in all EU member states. The adoption of well-tailored energy conservation strategies for buildings on a regional, national and European level requires knowledge of the specific characteristics of the building stock. Despite the numerous studies carried out during the past decades dealing with the assessment of various retrofit interventions on the energy performance of buildings, it is a fact that little is actually known on the state of the European building stock, its characteristics and current trends. Consequently, there is a growing need for systematic collection, classification and analysis of data from the building sector. Implementation of the European Directive 2002/91/EC on the energy performance of buildings (EPBD) with the attribution of Energy Performance Certificates (EPC) to almost all buildings in Europe has initiated the mapping process for the existing European building stock. In Greece, the national EPBD implementation follows the provisions of the national law N.3661/08 on “Measures for the reduction of energy consumption in buildings and other provisions” that was issued in May 2008 and due to several delays is expected to be enforced in 2010 with the publication of the new
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“Regulation on the Energy Assessment of Buildings—KENAK”. The EPC will attribute each building a numerical indicator for ranking purposes according to an asset rating of its energy performance, while at the same time it will be supplemented by recommendations on cost-effective energy conservation measures. The EPC will be compulsory for new constructions and existing buildings over 1000 m2 that undergo major renovations, and existing buildings with a floor area exceeding 50 m2 when they are sold, rented or transferred to other relatives of the owners. An electronic database will be established to collect the results from the building energy audits and EPCs along with the reports from the inspections of boilers, heating installations and air-conditioning systems. In addition, the new European Directive 2009/28/EC on the promotion of the use of energy from renewable sources mandates that each member state should increase its use of renewable energy sources (RES) – such as solar, wind or hydro – to reach an ambitious 20% share of energy from renewable sources by 2020. Each EU member state will have to increase its share of RES by 5.5% from 2005 levels, with the remaining increase calculated on the basis of per capita gross domestic product, for example, to reach by 2020 a share of 10% in Malta up to 49% in Sweden. While the focus of the Directive 2009/28/EC is on the promotion of large scale renewable energy installations, member states are nevertheless requested to use “minimum levels for the use of energy from renewable sources in buildings”. Architects, engineers and planners are also to benefit from member state ‘guidance’ when planning new construction projects, while local and regional administrative bodies should be recommended to “ensure equipment and systems are installed for the use of heating, cooling and electricity from RES and for district heating and cooling when planning, designing, building and refurbishing industrial or residential areas”. Under the Directive 2009/28/EC, EU member states must stipulate the “use of minimum levels of energy from renewable sources in new buildings and in existing buildings that are subject to major renovation”. This paper presents an overview of the infrastructure and tools that could facilitate the exploitation of data on the building stock and its energy performance. Elaboration of the results from a pilot application in Greece reveals the characteristics of the Hellenic building stock. A brief comparison of similar data from ten EU member states is also included.
2. Methodology The effort to improve the knowledge on the energy-related characteristics and major trends of the European building stock mandates the need for establishing a common database with uniform information and structure. This will offer an opportunity to exploit the information from the national EPCs and reports from building energy audits, inspection of boilers and air-conditioning systems that will be kept in nationally established electronic databases. Along the same lines, this database could be used by stakeholders and technical managers, who oversee a number of buildings, to collect, organize and analyse relevant data in order to best maintain, operate and monitor the energy performance of their buildings. In all cases, collecting and organizing the necessary data will reveal key information for accessing and improving their building stock. The database includes a total of 255 parameters covering a wide, yet realistic, range of building characteristics (Fig. 1). The data refers to: general building data (location, use, and conditioned area), building envelope data (e.g. U-values, surface areas, and construction types), electromechanical (E/M) installations including renewable energy systems that may be in operation (e.g. system information and operation parameters) and their efficiency, energy demand (heating, cooling and hot water loads), final (operational
and/or calculated) and primary energy consumption as well as CO2 emissions. Various data entries are specified according to user defined classifications (e.g. energy carrier types, heat/cold generation types) so that they are adapted according to specific needs. For practical purposes and in order to test the concept, the database is an EXCEL worksheet. The corresponding data for each building (dataset) is entered in a row. The columns of the table (255 in total) describe the building properties. Each column (data field) of the table stands for a defined quantity, which may be a number (e.g. conditioned floor area of the building in m2 ) or a string indicating special information (e.g. the name of the city where the building is located). The database is complemented by various tools for data manipulation and statistical analysis that may be used to easily analyse and process the data using different criteria. A detailed description of the database contents is available in [3]. The database structure is also available on line. The database was populated with data from 12 pilot studies in different EU member states. The following section, presents an overview of the Hellenic pilot study along with representative results. The analysis reveals the building envelope characteristics, energy performance and use of RES in Hellenic buildings. Finally, a comparative presentation of similar data from a sample of buildings from different European countries is elaborated for comparative purposes.
3. Hellenic buildings According to the Hellenic National Statistics Service, there are about 4 million buildings in Greece, with a total floor area of 552 million square meters. The residential and tertiary sectors represent 77% and 23% of the total, respectively. Most of the residential sector consists of apartment buildings the majority of which are old and have aged installations with low energy efficiency. In 2006, the final energy consumption of Hellenic buildings was about 88,400 GWh accounting for 35.4% of the total final energy consumption [4]. Data from a total of 250 buildings were incorporated in the Hellenic database. Emphasis was given on residential buildings, currently representing 76% of the Hellenic building stock. A representative number of non-residential (NR) buildings for different end-uses were also included. In total, 176 residential and 74 NR buildings located in the different national climatic zones were incorporated in the database. The residential buildings included 118 apartment buildings (high-rise buildings with more than two floors) and 58 single dwellings (low-rise buildings with one or two floors). The NR buildings included office, hospital, hotel, airport buildings as well as sports halls and swimming pools. The breakdown of the number of different end-use buildings and their average annual final thermal, electrical and total energy consumption per unit floor area, for the three national climatic zones, is summarized in Table 1. Some trends of the average energy consumption in NR buildings among the different climatic zones have fluctuations due to the different operational characteristics of the specific end-use of NR buildings included in the sample. For example, in zone A, some NR buildings have seasonal operation (e.g. hotels that operate only in summer) or limited hours of operation (e.g. airports with limited traffic and operation in winter compared with full operation during the tourist season in summer). As a result, they have low thermal energy consumption and relatively higher electrical energy consumption. The sample of the Hellenic buildings used in this analysis is composed of 70% residential buildings, 12% airports, 7% sports halls, 4% hospitals, 2% swimming pools, 2% offices, 2% educational buildings and 1% hotels. The above breakdown is considered to be repre-
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Fig. 1. Main structure of the DATAMINE database.
sentative of the Hellenic building stock. According to the Hellenic National Statistics Service the residential sector represents 77% of the entire building stock, whereas the NR building stock represents the remaining 23% (i.e. 2.7% office and commercial buildings, 0.46% educational buildings, 0.82% hotels, 0.06% hospitals and 19% other uses including airports, sports halls, etc.). The final total energy consumption in the residential buildings of the sample ranges from 43 to 348 kWh/m2 a, while for NR buildings values range from 38 to 673 kWh/m2 a. The number of buildings (250) included in the sample is rather small and it does not allow the derivation of final and specific conclusions. However, the buildings are representative of the different categories and cover different construction periods and locations throughout the country. The results of the present analysis may be
indicative and demonstrate some trends in the Hellenic building stock on a local as well as national level. The following discussion places an emphasis on the building thermal envelope and energy performance, including a closer analysis on the use of solar thermal energy, when available. Taking into account the fact that residential and NR buildings differ significantly in terms of use, size and operation, results are given separately for the two sectors.
3.1. Thermal envelope The sample of the 250 buildings originates from pilot building energy audits (40% of available data) and other short energy audit campaigns using standard questionnaires and energy audit reports
Table 1 Breakdown of the number of buildings and average annual final energy consumption (operational data) for the national climatic zones, in the Hellenic database. End-use of buildings
Climatic zones (heating degree days) A (600–1150)
B (1151–1600)
C (1601–2065)
Residential Number of buildings Average annual thermal energy consumption (kWh/m2 a) Average annual electrical energy consumption (kWh/m2 a) Average annual total energy consumption (kWh/m2 a)
15 70 38 108
117 99 38 136
44 155 34 189
Non-residential Number of buildings Average annual thermal energy consumption (kWh/m2 a) Average annual electrical energy consumption (kWh/m2 a) Average annual total energy consumption (kWh/m2 a)
19 26 141 167
45 130 96 226
10 233 138 371
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Fig. 2. Average heat transfer coefficient of external walls for different building construction periods of residential and non-residential buildings in the Hellenic database. The vertical dash line indicates the U-value of the national thermal insulation regulation (TIR).
Fig. 3. Total surface of exterior wall areas for different heat transfer coefficients of residential and non-residential buildings in the Hellenic database. The horizontal dash line indicates the U-value of the national thermal insulation regulation (TIR).
(60% of available data) from different regions in Greece. Quality checks were performed before the data was incorporated in the database. About 40% of the available data (72 buildings) included information from asset rating, while for the remaining 178 buildings available data was from operational rating, with additional data on energy performance and thermal envelope characteristics. A detailed analysis of the energy-related building properties of the sample was carried out including the U-values of the different building elements, the different types of heat supply systems and the energy balance-including measured and calculated energy consumption. The residential and NR building sectors differ significantly in terms of building use, size, operating hours, heating/cooling systems and set-points. In order to draw more representative conclusions data from buildings belonging to the two sectors were analysed separately. This permits an in-depth analysis of the data taking into account the particular characteristics of each sector. The small number of different end-use buildings within the sample of the NR buildings did not allow for a meaningful analysis of the specific NR categories, although this would be possible in the future once the database is populated with additional data. Fig. 2 illustrates the dependence of the average heat transfer coefficient (U-value) of walls with the building’s age (year of construction). This is based on the total number of residential and 50% of the NR buildings of the Hellenic data sample. The U-value of the walls in the analysed residential buildings varied from 0.84 to 1.93 W/m2 K. The average value before 1980 (a total of 99 buildings) was 1.54 W/m2 K, while a reduction of 32% was achieved after the implementation of the existing national Thermal Insulation Regulation (TIR) which was introduced after 1980 (averaging a U-value of 1.04 W/m2 K). The lowest values correspond to buildings constructed after 2000. However, the mean U-value even for the buildings recently erected remains higher than the one mandated by the national TIR (0.7 W/m2 K). This indicates that there are still some problems with its implementation. The average U-value for the NR buildings sample before 1980 (a total of 18 buildings) was 2.56 W/m2 K, while a reduction of 69% was achieved following the implementation of the national TIR after 1980 (averaging a Uvalue of 0.80 W/m2 K). The fact that the buildings with the smaller wall U-value have been erected after 1980 and represent 47% of the sample, is an indication that the new NR buildings are constructed in line with the specifications of the national TIR, indicated in the graphs by the vertical dashed line. The average U-value for external windows in the residential and NR buildings of the sample is 4.4 and 4.6 W/m2 K, respectively. No clear trend can be observed in the evolution of the coefficient over the years. This can be attributed to the fact that the replacement of single glazing with double ones is very often incorporated in the
process of a routine building refurbishment as it is recognised as a technique to achieve both thermal and acoustical comfort. This is the reason why very slight differences in the U-value of windows are observed among buildings of various ages. Despite the fact that the mean values of the coefficient are within the limits foreseen by the national TIR, the fact that its value remains higher than 3.26 W/m2 K (indicative mean U-value for double glazing) indicates that single glazing can be found even in recent constructions. The U-value of roofs in the analysed sample of residential buildings varied from 0.94 to 2.46 W/m2 K. The average value before 1980 (a total of 99 buildings) was 1.91 W/m2 K, while a reduction of 50% was achieved after the implementation of the national TIR after 1980. The lowest values correspond to buildings constructed after 2000. However, the mean U-value even for the residential buildings erected recently remains higher than the one mandated by the TIR (0.7 W/m2 K). This indicates that there are still some problems in its implementation. In the analysed NR buildings the coefficient varied from 0.46 to 1.01 W/m2 K. The average value of the coefficient before 1980 (a total of 18 buildings) was 1.00 W/m2 K, while a reduction of 53% was achieved after the implementation of the national TIR after 1980. The average value in the decades after 1980 is within the limits foreseen by the national TIR, which indicates that the new NR buildings are constructed in line with the specifications of the Regulation. The analysis of the whole sample revealed that improvement of the roof insulation is required in all the residential buildings and in 62% of the NR buildings in order to satisfy the limits foreseen by the national TIR. The addition of roof insulation is very often implemented in the process of a routine building refurbishment. However, the impact of such an intervention is limited to improving the thermal comfort conditions in the last floor in winter and summer, but it does not have a major impact on the energy consumption of the whole building. Fig. 3 illustrates the distribution of the buildings’ exterior wall area to the different U-value classes. Thermal insulation in the majority of the analysed buildings is not in line even with the provisions of the 1980 national TIR, indicated in the graphs by the horizontal line. Accordingly, 61% of the total exposed wall fac¸ade areas of residential buildings and 70% of NR buildings will have to be refurbished with additional thermal insulation. Fig. 4 illustrates the distribution of the buildings’ external window area to the different U-value classes. Accordingly, the U-value exceeds the upper limits of the national TIR (indicated in the graph by the horizontal line) in 22% and 7% of the total glazing area for the analysed residential and NR buildings, respectively. Overall, about 75% of the total transparent facade areas of the buildings will have to be replaced with double glazing. Fig. 5 illustrates to what extent the construction of the buildings in the Hellenic data sample is in line with the requirements of the 1980 national TIR. The U-value of a building is calculated
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Fig. 4. Total window area for different heat transfer coefficients of residential and non-residential buildings in the Hellenic database. The horizontal dash line indicates the U-value of the 1980 national thermal insulation regulation (TIR).
as the sum of the products of the U-values for each of the building elements (e.g. walls, roof, glazing, etc.) and the corresponding area of each building element, divided by the sum of the building’s envelope areas. For each of the three climatic zones defined in the Regulation, the buildings with U-value above the corresponding theoretical curve f/V = f (U-value), defined as a function of the building’s external thermal envelope area (f) to the building’s volume (V), do not comply with the 1980 national TIR. As shown in Fig. 5, the U-value exceeds the limits set in the Regulation in 87%, 84% and 98% of the residential buildings in the sample for climatic zones A, B and C, respectively. 3.2. Solar thermal energy Final energy consumed for household space heating accounts for 66% of total energy used in residential buildings, cooling for less than 1%, but is projected to grow at a fast pace in the future, water heating and cooking for 22%, electrical appliances for 6%, and lighting for 5%. For NR buildings, space heating accounts for 50.5% and other heat uses (sanitary hot water and cooking) for 22.5%, electrical appliances for 16.5%, lighting for 4% and cooling for 6.5%. The most common solar energy thermal application is for sanitary hot water (SHW) production. Greece has a well developed market of small systems for SHW production using natural flow systems (thermosyphon) without any need for pumps or control stations, that are widely used in residential buildings and small hotels, with an electric heat resistance in the SHW storage tank as
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a back-up. A small number of large central systems with central hot water storage and forced circulation systems are installed in large hotels. Solar cooling is an emerging market with a huge growth potential [5], but to this date there are only a handful of installations in Greece (e.g. two hotels in Crete, a couple of office buildings in Athens and the largest solar field installation in a cosmetics factory near Athens). The use of solar thermal energy for SHW was identified for the buildings included in the sample Hellenic database. Fig. 6 illustrates the variation of electrical energy consumption which is the common backup energy source for SHW, in the sample of residential buildings used in this analysis. Results are given for the three national climatic zones for single dwellings and apartment buildings with solar collectors for SHW and the corresponding values for other types of systems (e.g. electric water heaters). Given the available data, it was not possible to derive the exact contribution of the SHW production system to the total electrical energy consumption. However, the analysis clearly illustrates a trend for buildings using solar collectors to consume less electricity than those using conventional systems for SHW production. The total electrical energy consumption in the sample of dwellings is reduced by 27–37% depending on the climatic zone, while in the sample of apartment buildings the reduction ranges between 36% and 57%.
4. Characteristics of European buildings Relevant information from ten EU member states (i.e. Austria, Belgium, Bulgaria, Germany, Greece, Ireland, Italy, Netherlands, Poland, Slovenia, Spain and UK) were used to populate the database with data from 19000 residential and NR buildings [3]. Analysis of this larger sample permits a cross-country comparison of the energy characteristics for specific building types. Fig. 7 illustrates the distribution of the average U-value for representative buildings in different construction periods from ten EU member states. For each construction period, an “average” building type is defined for every country by averaging the corresponding U-values. This example demonstrates how the available data and tools may also be used to derive cross-national comparisons. The distribution of the average U-value indicates a continuous improvement of the thermal characteristics of the building envelope over the past 100 years. A drastic reduction of the U-value coefficient for external walls and roofs is illustrated in Fig. 7. This trend was less observed for the U-value of basement walls. For glaz-
Fig. 5. Compliance of existing residential building constructions (symbols) in the three national climatic zones with the 1980 national thermal insulation regulation (TIR) requirements (solid lines) as a function of the building’s external thermal envelope area (f) to the building’s volume (V).
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Fig. 6. Total annual electrical final energy consumption in the Hellenic residential sample of dwellings (left) and apartment buildings (right), with solar collectors and other types of systems for service hot water production.
Fig. 7. Cross-country comparison of the total heat transfer coefficient of (a) exterior walls and (b) roofs for a sample of residential buildings from ten European countries [3].
ings, the U-value variations with the construction year were very limited. This may be attributed to the fact that the replacement of single with double-glazing has been a very common refurbishment intervention over the past few decades in most countries. 5. Conclusions The building sector consumes about 40% of the total energy consumption and emits about 35% of the total CO2 emissions in Europe. Current knowledge on the specific characteristics and trends of the building stock is rather limited, which impedes the adoption of effective energy conservation measures for the building sector. Consequently, there is a growing need for systematic collection, classification and analysis of data from the building sector. The process of building labeling and certification in accordance to the provisions of the EPBD constitutes a unique opportunity for collecting information on the characteristics of the building stock and its energy performance on a national and European level. Taking into account the great variety of buildings, as well as certificate types in the European member states and the very different status of national EPBD implementation efforts, the creation of a harmonized data monitoring platform is imperative. In response to these needs a common European effort developed the necessary infrastructure for the exploitation of the information from the national energy performance certificates and reports for building energy audits, inspection of boilers and air-conditioning systems that will be kept in nationally established electronic databases. The deliverables of this effort include a harmonized database and a set of analysis tools for organizing and monitoring the data, as well as processing it using different criteria.
The methodology was assessed during twelve pilot studies in different European countries. Overall, it was viewed as a very useful tool for organizing and processing national data on the building stock and extract information on its characteristics and major trends. The representative analysis performed using the available Hellenic data included results on the characteristics of the Hellenic building stock in terms of the building’s thermal envelope characteristics, final energy consumption, and the use of solar energy collectors. These results were used to illustrate some characteristics of the Hellenic building stock and the concept of how to use the DATAMINE database and analysis tool. Similar analysis may also be performed using any of the 255 parameters to derive relevant conclusions provided that there is sufficient available data. Accordingly, representative results from the analysis of the sample Hellenic residential and non-residential buildings revealed that the annual average thermal energy consumption (operational data) of the Hellenic buildings ranges from 70 to 155 kWh/m2 a in residential buildings and from 26 to 233 kWh/m2 a in NR buildings, depending on the different climatic zones. Similarly, the average total energy consumption ranges from 108 to 189 kWh/m2 a in residential buildings and from 167 to 371 kWh/m2 a in NR buildings. Follow-up analysis showed that over time there is a trend of decreasing U-values of the building’s thermal envelope (e.g. walls, roof, glazing, etc.), although the great majority of Hellenic buildings is either not thermally insulated or poorly insulated. Even according to the 1980 national TIR, which is currently under revision in the frame of the ongoing national work for EPBD implementation that will introduce even more strict thermal insulation regula-
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tions for the building’s envelope, over 60% of exterior walls and 80% of windows of the existing building stock do not meet minimum code requirements. On a positive note, further analysis of the available Hellenic data, reveals that the use of solar thermal collectors for sanitary hot water production reduces the total electrical energy consumption by 27–37% in single dwellings and 36–57% in apartment buildings. Finally, the database was also populated with relevant data from 10 European countries in a pilot exercise in order to make cross-country comparisons and draw conclusions on the characteristics of the European building stock as a whole [3]. Overall, the methodology (database and tools) is flexible enough to be used by building managers who are responsible for a number of buildings for collecting and analyzing relevant data in order to monitor the energy performance of their building stock and rank their priorities regarding energy-related measures. For example, compare the impact on the energy performance of the buildings from the use of different heating, cooling or ventilation systems, equipment efficiency, controls, temperature settings, distribution losses, or lighting installed power and controls. In all cases, collecting and organizing the necessary data is the first step in order to reveal key information that can be used to access and improve a given building stock.
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Acknowledgments This work is based on the results of the European project DATAMINE that was partly financed by the European Commission, DG XVII in the framework of the Energy Intelligent Europe under the coordination of the Institut Wohnen und Umwelt GmbH, Germany and the collaboration of twelve (12) partners from the corresponding European member states (http://env.meteo.noa.gr/datamine/). References [1] EC, European Union Energy & Transport in Figures—2009 edition, Office for the Official Publications of the European Communities, Luxembourg, 2009, 228 pp. [2] P. Capros, L. Mantzos, V. Papandreou, N. Tasios, European Energy and Transport, Trends to 2030—Update 2007, in: Directorate-General for Energy and Transport, European Commission, Brussels, April, 2008, p. 156. [3] T. Loga, N. Diefenbach (eds.), DATAMINE—Collecting Data From Energy Certification To Monitor Performance Indicators for New and Existing Buildings, Final report, 197 p., January 2009. Available on line: http://env.meteo. noa.gr/datamine/DATAMINE Final Report.pdf. [4] EU Energy & Transport in Figures, Part 2: Energy, Statistical Pocket Book, Directorate General for Energy and Transport, Office for Official Publications of the European Communities, Luxembourg, 2009, 232 pp. [5] C.A. Balaras, G. Grossman, H.-M. Henning, C.A.I. Ferreira, E. Podesser, L. Wang, E. Wiemken, Solar air conditioning in Europe—an overview, Renewable & Sustainable Energy Reviews 11 (2) (2007) 299–314.