Thermal Mass and Insulation: Domestic Buildings in the Mediterranean Climate

THERMAL MASS AND INSULATION: DOMESTIC BUILDINGS IN THE MEDITERRANEAN CLIMATE Olga Tsagkalidou

Architectural Association School of Architecture | Graduate School AA SED MSc + MArch Sustainable Environmental Design 2014 - 2015 | Research Paper 1 | January 2015

Thermal Mass & Insulation: Domestic Buildings in the Mediterranean Climate

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Architectural Association School of Architecture Research Paper 1 | MSc + MArch Sustainable Environmental Design 2014 - 2015

Thermal Mass & Insulation: Domestic Buildings in the Mediterranean Climate

AUTHORSHIP DECLARATION FORM

Research Paper 1

TITLE: Thermal Mass and Insulation: Domestic Buildings in the Mediterranean Climate

NUMBER OF WORDS: 3367

STUDENT NAME: Olga Tsagkalidou

DECLARATION: “I certify that the contents of this document are entirely my own work and that any quotation or paraphrase from the published or unpublished work of others is duly acknowledged.”

Signature:

Date: 16 January 2015

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Thermal Mass & Insulation: Domestic Buildings in the Mediterranean Climate

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Architectural Association School of Architecture Research Paper 1 | MSc + MArch Sustainable Environmental Design 2014 - 2015

Thermal Mass & Insulation: Domestic Buildings in the Mediterranean Climate

TABLE OF CONTENTS Abstract.....................................................................................................07 1. Introduction............................................................................................07 2. Climate Analysis....................................................................................07 3. Domestic Buildings in Greece...............................................................07

3.1. Classification of the residential building stock.......................07

3.2. Construction and characteristics of domestic buildings.........08 4. Thermal Mass and Insulation................................................................09 5. Precedent Studies.................................................................................10

5.1. Recommendations of the EPCs............................................10

5.2. Measures for efficient energy saving and CO2 reduction.......11 6.Conclusions............................................................................................12 Acknowledgements...................................................................................12 References................................................................................................13

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Architectural Association School of Architecture Research Paper 1 | MSc + MArch Sustainable Environmental Design 2014 - 2015

Thermal Mass & Insulation: Domestic Buildings in the Mediterranean Climate

ABSTRACT The latest worldwide trend to reduce the carbon footprint puts European Union in the road of setting new energy efficiency targets for its Member States. In Greece the recently adopted legislation has triggered a renovation plan of the national building stock. This paper examines the characteristics of the domestic building stock, highlighting the existent thermal mass structure and the lack of thermal insulation. Finally, the effectiveness of the currently proposed measures and of alternative ones that focus the improvement of the building envelope’s energy performance, is also analyzed.

Keywords: energy efficiency, domestic buildings, mediterranean climate, building fabric, thermal mass, insulation, Energy Performance Certificate, legislation, building stock, night-ventilation, renovation measures 1. INTRODUCTION

Under the pressure of the forthcoming climate change and the urgent necessity for smart and sustainable growth and energy security, policy makers in the European Commission have established a set of goals regarding energy efficiency measures to be achieved from the Member States by 2020. The purpose of the Europe 2020 Strategy is to create 20% of the energy consumption from renewable energy sources (RES) and increase energy efficiency by 20%. The building sector is going to play a paramount role in the outcome of the desired result. The existing building stock in European countries constitute over the 40% of final energy consumption, of which the 63% comes from the residential building stock (Balaras et al, 2005).

The status quo of the domestic building sector in Greece is identical, accounting for the 24% of the country’s total energy consumption. In order to alleviate the CO2 emissions and meet the EU 2020 targets, the Greek State adopted in 2008 the European Directive 2002/91/ EC for the Energy Performance of Buildings (EPBD). The scheme is in use since 2010, incorporating a certification process, through which Energy Performance Certificates (EPCs) are issued. The process firstly aims to categorize the performance of buildings to energy classes and secondly to propose recommendations for improvement in case the building is classified in class B or lower (Gelegenis et al, 2013).

Having in mind the Greek residential building stock, its constructional characteristics and its building envelope’s poor performance, as well as the unpromising outcomes of recent studies carried out regarding the efficiency of the recently issued EPCs (Gelegenis et al, 2013), a concern remains on whether Greece is on the right side of the road towards achieving the 20% carbon emissions’ reduction or would fall short of the targets for 2020 set by the European Union.

ern Greece, whereas temperatures in the summer period could rise higher than 36°C in both cities. It is obvious that energy conservation measures should take into account the cold winters as well as hot summers that could lead in overheating risks. Temperatures differences during each month can exceed 10°K, giving an indication of possible passive cooling strategies, especially during the summer period.

2. CLIMATE ANALYSIS

In general Greece has a Mediterranean climate.

In order to capture a more specific range of the climate, weather data from two different cities, Athens (Lat. 37.967) and Thessaloniki (Lat. 40.517) are presented (Figures 01 and 02). The annual cycle can be divided into three seasons, summer (June – August), a mid-season (March – May & September – October) and winter (November – February). Lower temperatures occur during the winter season reaching -7°C in Thessaloniki located in North-

3. DOMESTIC BUILDINGS IN GREECE

Figure 01: Monthly Temperature of Athens (Source: Meteonorm)

Figure 02: Monthly Temperature of Thessaloniki (Source: Meteonorm)

According to the Technical Guidelines issued by the Technical Chamber of Greece and used for the EPCs assessment (TOTEE 20701-1/2010), the Greek landscape is divided into four different climatic zones based on the latitude, local climate and altitude of each county (Figure 03). This classification is important because it gives the energy performance standards according to which the building’s energy class is calculated.

3.1. Classification of the residential building stock

Recent studies have focused on categorizing based on age and usage criteria - the existing urban building stock in Greece, since identifying a vast field of interest in relation to promoting energy conservation and CO2 emissions reduction (Figures 04 and 05). In particular, domestic buildings constitute the 75% of the total building stock in Greece and are responsible for the 73.6% of the energy consumed by the whole building sector (Balaras et

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Thermal Mass & Insulation: Domestic Buildings in the Mediterranean Climate

al, 2005).

Based on a typology-usage classification, residential buildings constitute the majority of the building stock of the Greek cities, reaching a percentage of 79%. Usually the residential buildings in Greece are mono-functional multi-storey apartment blocks (Figures 06 and 07), what is also known with the term “Poly-katoikia” (translated from Greek: many-dwelling) (Theodoridou et al, 2011).

The classification of the building stock according to the age of their construction is valuable because it gives indications about the constructional characteristics of the buildings. Figure 04 represents the percentage of residential buildings for different periods of construction.

The year 1979 could be considered as a pivotal moment in the construction field, due to the enactment of the Thermal Insulation Regulation (TIR). According to a more detailed study which was based on statistical data from the Hellenic Statistical authority (Theodoridou et al, 2011), the buildings built in urban areas of Greece before 1980 are 1,496,102 corresponding to the 74.6% the total building stock, whereas the ones built after 1980 are only 507,712.

Consequently, it is evident that the majority of the existing building stock is uninsulated, representing a low quality building fabric and giving indications of poor energy performance.

Higher insulation standards were adopted by Greek policy makers only since 2010 with the application of the European Directive 2002/91/EC to all new building permits. However, due to economic and political reasons and the economic crisis of 2008, a large drop in permits has been observed for newly constructed buildings since 2007 (Theodoridou et al, 2011), making the problem of low quality building stock more intense.

3.2. Construction and characteristics of domestic buildings

The strong seismogenic activity that takes place quite often in Greece is one of the environmental factors that has an impact on the building construction. In order to follow the seismic regulations, buildings should have a very strong bearing structure. As stated in a recent works (Papamanolis, 2004; Theodoridou et al, 2011), focusing on the analysis of the constructional characteristics of domestic buildings, the bearing structure of most of the buildings in Greece is of reinforced concrete. In relation with the strict standards obliged by the Greek Seismic Code, the result is constructions of high thermal mass.

Ceramic bricks and plaster are the main materials used in the construction of walls. The external walls usually consist of double rows of bricks 9 cm thick with a minimum 7 cm cavity between them. In contemporary constructions this cavity if filled with a 5 cm insulation boards, usually extruded polystyrene insulation (EPS) or expanded polystyrene (XPS). A layer of 2 mm of plaster is usually applied on both sides of the wall, resulting in an overall thickness of 25 – 30 cm. Internal walls within apartments consist of a single 9 cm brick row. An EPS or XPS layer, usually around 3 mm, is used onto the external surface of the bearing structure (Papamanolis, 2004).

The majority of the building stock in Greece, due to the oldness of the construction, has single glazed windows. Only recently national energy improvement programmes – “Saving at Home”, 2011 - took place in order to improve the performance of the building envelope (Gelegenis et al, 2013). One of most popular measures applied was to replace single glazed windows with double glazed ones. In newly constructed apartment buildings the appli-

Figure 04: Breakdown of Hellenic building stock for different periods of construction (Source: Balaras et al, 2005)

Figure 03: Climatic Zones of Greece (Source: Technical Chamber of Greece - T.O.T.E.E. 20701-1/2010)

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Figure 05: Breakdown of Hellenic building stock according to the end use of the buildings for 1990 (Source: Balaras et al, 2005)

Architectural Association School of Architecture Research Paper 1 | MSc + MArch Sustainable Environmental Design 2014 - 2015

Thermal Mass & Insulation: Domestic Buildings in the Mediterranean Climate

cation of double glazed windows is in a way mandatory in order to achieve the regulation standards.

4. THERMAL MASS AND INSULATION

As it is previously presented, the two main highlights of the Greek domestic building stock is on one hand the lack of insulation and on the other the existence of high thermal mass. Consequently, the condition and the physical characteristics of the building fabric undertake a fundamental role affecting the energy performance of the construction. The building envelope takes the role of a “filter”, being the part that deals with and manages the interchanges between the internal and external conditions (Jones, 2008).

Thermal insulation as defined by Szokolay is one of the most important techniques for controlling the heat transfer. Its main role is to de-couple the interior spaces from the exterior ones by radically mitigating the heat flow from warmer towards colder spaces through the building envelope. In climates that cold winter periods are followed by hot summers, the role of insulation is beneficial for all year long (Zold, Szokolay, 1997).

Insulation can be found as external, internal or cavity one and it is usually applied to all the surfaces that are exposed to the exterior environment. Insulating materials are characterized by the heat transfer mechanisms.

Conductivity is very important because normally applies to heat transfer through solids. The rate of the heat transfer depends on its thermal conductivity or k-value, which is generally related to the density of the material. High-density materials with high k-values, like concrete and metals, allows heat to pass through them, whereas low-density

Figure 06: Multi-storey apartment building in Thessaloniki from 1980s (Source: Author)

materials (insulating materials) can almost eliminate the heat transfer (Jones, 2008). Depending on climatic conditions, excessive insulation may lead to overheating during hot summer periods.

Thermal mass is called the part of the building which is able to store heat during the daytime and release it back in the space when the sun is no longer present (Baker, 2007). Thermal mass can also be considered as the building’s thermal battery. The ability of the material to store heat from its environment as defined by Jones (2008) can be calculated from the formula: Thermal capacity (J/K·m3) = Volume (m3) x Density (kg/m3) x Specific Heat (J/kg·K)

Diurnal temperatures cycles usually affects only the first thickness of the material, because the deeper into the material, the less heat flows into it in a short period of time (Baker, 2007). This gives indications on the effectiveness of thermal mass distribution inside a space (Figure 08). In order for the thermal mass to be useful and efficient, the surface that is coupled with the interior environment should be large. Interior, finishings like suspended ceilings and floorings with carpets, compromises its efficiency.

Another important characteristic of thermal mass is the response of the building to the outdoor conditions and the variations of temperature (Figure 09). The differences between heavyweight and lightweight structures are found in the fluctuation/stabilization and the respectively peaks of indoor temperature within a diurnal cycle and in the warm-up and cool-down rate (Yannas, 1994).

During the winter period a better use of the solar and internal gains can be made, as the space heats up gradually throughout the day and is able to release back

Figure 07: Multi-storey apartment building in Thessaloniki from 2000s (Source: Author)

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Thermal Mass & Insulation: Domestic Buildings in the Mediterranean Climate

the absorbed heat later during the night when is actually needed. Hence, the period when the mechanical heating system is desired can be decreased. During summer the process is quite similar. During daytime excessive heat is stored into the structure of the building, keeping as low as possible the indoor temperatures. Later in the night, this heat must be taken out by using passive cooling techniques (Baker, 2007).

The solar control and the protection from heat gains using shading devices, the cooling process of the surfaces by the means of natural ventilation and the moderation of heat flows and daily swings in the indoor temperature by the thermal mass can be considered as passive cooling techniques (Santamouris, 2003). In particular, night-ventilation can be really efficient for buildings with high thermal capacity (Santamouris, 2007). As stated, night-ventilation can mitigate not only the peak indoor temperatures, but also the temperature within a diurnal cycle, helping the building, especially during morning hours, to have a lower temperature kickstart. A time lag between the peak indoor and outdoor temperature is also observed.

Night-ventilation can be effective in cases where there is an adequate temperature difference and sufficient exposure of thermal mass.

(a) concentrated thermal mass

5. PRECEDENT STUDIES 5.1. Recommendations of the EPCs

As it is already stated and also presented by Gelegenis et al. (2013), the Energy Performance Certification process may have up to two phases. During the first phase the overall performance of the building is being assessed based on its usage and the calculation of the primary energy consumption and the respectively CO2 emissions.

In case the building is categorized in a lower class than class B, then at a second phase improvement measures are proposed by independent energy inspectors. The proposed measures could concentrate on (a) the improvement of the building envelope, in an attempt of mitigating the heat-exchanges between the interior and the exterior environment, (b) upgrading the existing heating and cooling mechanical equipment as nowadays more efficient systems are out in the market, (c) the use of renewable energy sources in order to decrease the fuel consumption and electricity and (d) building management systems.

In line with the study, only the 33% of the issued EPCs are dealing with the improvement of the building fabric, a measure that is broadly known for its cost-effectiveness and its retrofitting efficiency. Figure 10 presents the usual improvement recommendations and their frequency of appearance. The most dominant measure, accounting for the 67.2% by itself, focuses on the installation or replacement of SWH systems. As part of the broader category of the exploitation of renewable energy sources, such measures seem to be the easy solution as they can easily upgrade the energy class of the building, since it is based on the substitution of electricity with solar energy and therefore primary energy consumption is significant-

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(b) most effective thermal mass

(c) least effective thermal mass Figure 08: Alternative thermal mass distribution (Source: Baker, 2007)

Figure 09: Heavyweight and lightweight building response (Source: Baker, 2007)

Architectural Association School of Architecture Research Paper 1 | MSc + MArch Sustainable Environmental Design 2014 - 2015

Thermal Mass & Insulation: Domestic Buildings in the Mediterranean Climate

ly reduced (Gelegenis et al, 2013). The insulation of the exterior walls, which is a vital, less expensive and more efficient measure, accounts only for the 20.6%, while the thermal insulation of the roofs for the 10.3%.

Figure 10: Detailed analysis of the frequency of appearance of the most often recommended measures in obligatory EPCs (Source: Gelegenis et al, 2013)

However, sometimes the external insulation configuration cannot be applied and therefore an internal one must be considered. The side on which the insulation panels would be placed can completely change the final performance of the space.

Recent analysis has been carried out concerning the comparative assessment between external (ETI) and internal (ITI) insulation configuration (Figure 11) for domestic building refurbishments in climatic regions both in northern Greece as well as in the southern part of the country (Kolaitis et al, 2012). The study also takes into consideration a different behavioral occupancy pattern, an ‘active’ occupant behavior (ACT) that the occupants intervene in their environment and a passive one (PAS).

Generally, it is found that the performance of the ETI is better than the ITI. In specific, during the winter period the heating loads are reduced significantly in both cases compared to an uninsulated building, with the ETI configuration having slightly better overall results as it allows also the use of the thermal mass of the structure. The interesting outcomes are found during the summer period, when the cooling loads after the installation of either ETI or ITI are increasing (Table 01). Here is the point where the behavior of the occupants becomes essential, as it is obvious that the ‘active’ occupants are able to reduce significantly the energy consumption and prevent overheating risks during the hot summer periods.

It can be assumed that the EPCs direction is strongly affected by the construction industry and its administrative processes affects its fundamental goals. Instead of promoting high-cost measures, attention should be given to the improvement of the existing, poor-quality building fabric through simpler and noteworthy interventions.

5.2. Measures for efficient energy saving and CO2 reduction

The improvement of the envelope of the buildings, which acts as the “modifier”, should be a first-come-to-mind measure in order to control the heat-exchanges, increase the energy savings thoughout the year and minimize the CO2 emissions (Jones, 2008). Taking into account the poor condition of the fabric of the majority of the Greek dwellings the application of insulation is the first intervention that should be implemented. In reference with evaluations of various energy saving methods, the insulation of the walls, especially of the external facades of the building, is the most effective one with energy savings reaching 3360% of the energy consumption for heating (Balaras et al, 2005).

In general, the external thermal insulation is the most preferable one due to the forthright deal with constructional details such as thermal bridges, the preservation of the useful thermal mass of the bearing structure and the avoidance of possible condensation within the walls.

Figure 11: Wall assemblies: no insulation (left), external thermal insulation (middle) and internal thermal insulation (right) (Source: Kolaitis et al, 2012)

It is proven that the Greek behavioral patterns are in favor of the ‘active’ occupant attitude. Occupants in their residences are used to interact with their environment and more specific with windows and shading devices (Drakou, Tsangrassoulis, 2012). Among the surveyed occupants, the 60% open the windows in summers in order to improve the air quality, while the 35% are also aware of the prevention of the overheating. The percentages of the occupants that interact in a daily basis with the windows and consider the option of cross-ventilation and night-ventilation possible are also very high.

As mentioned by Santamouris et al, (2010), night ventilation is in general one of the most effective passive cooling techniques and may decrease up to 40 KWh/m2 the annual cooling load in residential buildings. It is proven that up to a 3°K reduction of the peak indoor temperature can be observed, if the previous night a night-ventilation

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Thermal Mass & Insulation: Domestic Buildings in the Mediterranean Climate

Table 01: Normalized annual energy demand for all the examined test cases (Source: Kolaitis et al, 2012)

technique had occurred. Nevertheless, night-ventilation is strongly based on the exploitation of the available useful thermal mass of a building, the temperature difference between the interior space and the exterior environment, and the temperature difference of the external air within a diurnal cycle. Consequently, the potential of this technique might be compromised by the heat island effect which is apparent in the dense urban areas of the Greek cities.

Even in situations when natural ventilation techniques are not very efficient the thermal mass of the building can counterbalance to some extent the overheating risks. Heavyweight structures have the ability to store the heat inside their fabric, keeping in this way the indoor temperatures lower. Sakka et al (2012) analyzed the performance of free-running low-income houses in Athens during the extreme heat wave of the summer of 2007. It was found that buildings of high thermal mass have a kind of “climatic memory�. Their performance depends on a broader period of time and they are not significantly affected by short-term climate changes, such as the first days of heat waves.

6. CONCLUSIONS

During the last years a worldwide interest in reducing the carbon footprint of cities is being shown. Among the global community, the European Union has set a forthcoming target accompanied by a Directive towards all the Member States, with the intention to decrease the levels of the CO2 emissions and the greenhouse gases. In Greece, the current energy efficiency legislation focuses on the categorization both of the existing building stock, as well as of any possible new constructions to energy classes. In case the buildings do not meet the minimum standards, improvement measurements are being proposed.

The existing domestic building stock of Greece is characterized by its old age and poor quality of the building envelope. The majority of the apartment blocks are structures of high thermal capacity and no insulation. Only recently constructed buildings have sufficient levels of thermal insulation.

It is widely accepted that the role of the building fabric is very significant for the ultimate energy performance of the building. The building envelope is the intermediate between the interior and the exterior environment, and consequently it is responsible for the thermal comfort of the occupants. The combination of a high thermal ca12

pacity bearing structure and well applied thermal insulation can lead to a substantial reduction of the dependence on auxiliary heating and cooling systems.

However, recent studies present that the current energy efficiency procedures that occur in Greece do not have the desired results. Proposed improvement measures do not focuses on the condition of the building fabric, but tend to be market driven, promoting the profit of the high technology industry. This puts Greece in the wrong way and the risk of failing to fulfill the 2020 goals is evident. Simpler and more efficient measures that deal with the core of the problem and focus on the improvement of the building envelope must be considered.

A more straightforward adoption of the proposed guidelines and legislation must occur in order to start discussing about a smart and sustainable growth in the country.

ACKNOWLEDGEMENTS

I would like to thank all the AA SED teaching staff and visiting lecturers (Simos Yannas, Paula Cadima, Gustavo Brunelli, Jorge Rodriquez, Nick Baker and Joana Gonçalves), who were very supportive and encouraging throughout the term. I would also like to offer my special thanks to my tutor, Mariam Kapsali for her help and guidance through the RP1 tutorials.

Architectural Association School of Architecture Research Paper 1 | MSc + MArch Sustainable Environmental Design 2014 - 2015

Thermal Mass & Insulation: Domestic Buildings in the Mediterranean Climate

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Drakou, A., A. Tsangrassoulis. (2012). Analysis of the Greek Behavioural Pattern in Residences and its Effect on Thermal Simulation Estimates. PLEA 2012, Lima.

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Tools: Meteonorm V7.1.2.15160

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