Methodological approach

2.3.1 Bottom-up methodology

The struggle towards sustainable development and the need for holistic energy policies have concerned researchers since the early 70s, leading to the establishment of various techno-economic energy assessment models often with focus on the residential sector ((67), (68), (69), (70), (71), (72), (73), (74), (75)), such as the top-down and bottom-up approaches; according to Sathaye et al.

bottom-up modelling approach concerns the comparison of energy and environmental consequences between various energy conservation scenarios, leading to economic conclusions (76).

While top-down approaches are based on macroeconomic features, bottom-up modelling is rather based on disaggregation, also taking into consideration various technical issues and parameters (77);

in short top-down and bottom-up terms stand for aggregate and disaggregate models (78).

Moreover, bottom-up methodologies usually deal with the implementation of specific energy technologies applied in various combinations (77).

Furthermore, researchers distinguish between bottom-up statistical techniques and bottom-up engineering techniques also for the residential building stock (79). In the first case, occupation plays a strong role on the energy consumption data, whereas in the case of engineering techniques the focus is on specific buildings’ typologies and the effect of interventions on the energy behaviour as regards the buildings’ envelope and HVAC systems. The proposed methodology is aiming at a combination of these two bottom-up approaches (Fig. 2.5). Thus, based on a survey and the statistical analysis of the collected data, important features of the residential stock will be highlighted, based on their typology, occupancy, energy behaviour as well as their built-up environment. Afterwards, the implementation of various interventions will be studied in terms of energy conservation and their economic feasibility.

A similar bottom-up, building physics based, feasibility study was presented in 2002 by Papadopoulos et al.. The research concerned 90 buildings in Northern Greece and showed that basic intervention measures, such as insulation of the buildings’ envelope and replacement of old windows with new ones, can lead to a payback period of 8 years in 62% of the examined stock, whilst this percentage rises up to 81% if the pay-back time concerns 1/3 of the buildings’ life cycle (80). These interventions were proposed based on the 2002 standards, thus an insulation of 3-5 cm for the vertical construction elements and 5-8 cm on the roofs, with double-glazed openings and U-Values less than 3.2 W/m²K. Hence, according to the current legislative framework regarding the Energy Performance of Buildings, these values are rather low (18). Thus, the calculated payback periods are now expected to be more favourable, also given the fact that energy pricing is 18% higher as regards heating oil. Beyond the economic feasibility study based on sensitivity and parametric analysis of the methodological framework, a life cycle analysis (LCA) will be carried out as suggested by Anastaselos et al. (81).

An analogous approach was introduced by Pfeiffer et al. (82) based on the vision of the 2 kW society proposed by Kesselring and Winter (83); under the three main aspects of sustainability, namely economy, ecology and society, they approach the problem of residential energy reduction in Switzerland by analysing the existing housing stock as well as the future buildings according to the existing building standards and the expected technological development. A series of state of the art and future building technologies are then implemented in order to evaluate possible energy-savings in the residential building sector.

Overall, numerous bottom-up residential stock models have been introduced over the past years differing in various aspects of their methodological approach. However, the majority of these models use a typological classification for the buildings under study. In this framework the North Karelia Finland (84) model as well as other models compared by Kavgic et al., seem to have various

similarities to the proposed methodology (85). Top-down models applied in Greece are very few compared to the rest of the scientific community. Lately, Hatzigeorgiou et al. presented a thorough analysis of the rather poor state of the art concerning the relation of CO2 emissions and economic development, highlighting the apparent bi-directional causality between energy intensity and CO2

emissions (86).

As regards household energy modelling, bottom-up models are mostly based on conventional end-use technologies, referring to the HVAC systems and the buildings’ envelope, without taking into consideration the income of the inhabitants or the GDP, like the top-down models do. Consequently, these two methods are based on different economic feasibility approaches and may therefore lead to significantly diverse results. Therefore, hybrid models have been introduced by numerous researches ((87), (88), (89), (90), (91)), in order to ensure maximum accuracy and flexibility for the development energy efficiency intervention scenarios (77). According to Jacobsen, hybrid models use the energy efficiency rates calculated by the bottom-up methodology in order to quantify the exogenous energy efficiency in the top-down methodology; therefore, building’s physics based results determine the energy demand exogenous factors of the macroeconomic model (77).

Böhringer also studied various aspects of integrated models ((78), (92), (93), (94), (95)); he argues that the balance of such models is very vulnerable and distinguishes three different types, namely (a) the combined large scale existing bottom-up and top-down models, (b) the usage of mainly energy based data in the macroeconomic relation, thus a targeted and limited contribution of the bottom-up model in the integrated model and (c) a single mathematical format that combines technical and buildings’ physics data with the macroeconomic features (78). Regardless the nature of the hybrid model, they all intend to combine the technological features of the bottom-up models and the economic diversity of top-down approaches. A simplified scheme of such integration regarding the residential stock for regional and national level was presented by Swan et al. (79), whereas Kavgic et al. offer a top-down bottom-up general modelling approach diagram (85). A simplified combination of these two schemes is considered to be characteristic for this methodological approach as depicted in Fig. 2.5.

Fig. 2.5 Simplified representation of the general integration model in which the bottom-up methodological approach is being depicted

In this framework, the methodological approach is based on a combined engineering and statistical bottom-up model, providing data that can enhance a hybrid model, concerning Greek macroeconomic features and residential buildings’ state of the art, thus a field for further research.

2.3.2 Facts and problems - Case study

Many studies dealt with the feasibility of refurbishment based on housing stock policies, especially in the UK ((96), (97), (98), (99)), also focusing on indoor air quality (100). More specifically, Atkinson et al. point out the need for rectification regarding the limitations set by the market, the low standard of information concerning the consumers as well as the unbalanced landlord/tenant relationship, which determines the responsible authority that will undertake the retrofitting works (99). These problems are also met in Greece and are difficult to manage. It is characteristic that the first National Grant Program regarding subsidies for energy-upgrading measures in multi-family buildings, issued in 2011, will be reorganised in order to better adjust to the Greek reality; in multi-family buildings the apartment owners are often more than ten, leading to a mosaic of opinions, rarely converging,

according to individual beliefs and interests. Consequently, a common strategy on the energy upgrading measures for the whole building is rarely the case.

Moreover, funding issue becomes a major drawback due to the current economic crisis of Greece, leading to limited state subsidies, banks’ low willingness to provide loans and poor loan capability of private investors. These are matters that strongly affect energy policies concerning the building sector.

A further parameter with strong influence on energy refurbishment policies is the low level of awareness as regards the environmental, economical and energy efficiency benefits. Energy conservation and sustainability are still not strongly endorsed by the Greek society. The social unawareness and scepticism against new efficient of still unknown technologies and the ignorance of energy conservation’s benefits along with restricted financial inducements, are acting as a barrier for the broad implementation of such measures.

Last but not least, a very important aspect is the tenure status. As depicted in Fig. 2.6, Greece has a very large tenure quota, which mainly refers to apartments. In particular, ownership status in large MF – buildings, such as the Greek Polykatoikia, can influence the implementation of retrofit measures to great extents. As already described earlier issues concerning multiple ownerships and respective disagreements on matters of energy refurbishment measures are often the reason for their slow implementation as well as their rejection. More specifically, Athanassaki analyses this issue underlining the following aspects (55); unlike in the case of the Energy Building Certificate, the owners of a MF – building’s apartment are not legally bind to implement any kind of retrofit measures. Furthermore, if such interventions are being implemented partially, i.e. the retrospective thermal insulation of flat roofs or the Pilotis floor, the concerned party/owner can act on its will. In any other case, where retrofitting measures refer to the whole building, the legal framework is not as clear as expected. Namely, according to the statute a reinforced or simple majority could be demanded. In addition, if one or more owners disagree to contribute to the respective costs, the legal procedure for the “res judicata” could last even up to 3 years. This is the reason why many owners avoid investing in energy upgrade related works. It is important to note that the respective legal framework goes back to 1929 with the Regulation on the “horizontal property” (N. 3741/1929), where the terms of jointly owned and shared parts of the building were introduced. Hence, the need to revise this legal framework is imperative, whilst it could be used for the link of the configuration of property pricing according to energy performance characteristics, within a specific legal framework.

Fig. 2.6 Tenure status of households in EU for the year 2009 (101)

*The data regarding Germany refer to year 2005 (most recent available data)