Available online at www.sciencedirect.com
ScienceDirect Procedia Environmental Sciences 38 (2017) 500 – 508
International Conference on Sustainable Synergies from Buildings to the Urban Scale, SBE16
Embodied CO2 Emissions in Building Construction Materials of Hellenic Dwellings Georgios Syngrosa, Constantinos A. Balarasb and Dimitrios G. Koubogiannisa,* a
Department of Energy Technology Engineering, Technological Educational Institute of Athens, Agiou Spyridonos Str, Aigaleo, GR 12210, Athens, Greece b Group Energy Conservation, Institute for Environmental Research and Sustainable Development, National Observatory of Athens, I. Metaxa & Vas. Pavlou, P. Penteli, GR 15236 Athens, Greece
Abstract As current research moves towards zero energy buildings, it is important to minimize the total energy consumption and environmental impact of a building during its lifecycle. Total energy consists of the operational energy and the embodied energy, which is related to the embodied CO2 (ECO2) emissions that contribute to the greenhouse phenomenon. This paper identifies the basic construction materials of four typical Hellenic dwellings and estimates their environmental impact in terms of ECO2. To this end, a material analysis is required. ECO2 is estimated by multiplying material masses with the corresponding ECO2 coefficients (kgCO2/kg). Due to lack of a comprehensive Hellenic database, data from an international database are utilized. The results provide practical baseline indicators for the contribution of each material in terms of mass and ECO 2. Concrete is the dominant material in terms of mass, while steel dominates in terms of ECO 2. In one case, the materials of the major electromechanical installations are also considered; their contribution in terms of ECO2 is low compared to that of the construction materials. Finally, CO2 payback time related to the replacement of building openings in order to upgrade its energy performance is demonstrated in one of the cases. © Published by Elsevier B.V. B.V. This is an open access article under the CC BY-NC-ND license © 2017 2017The TheAuthors. Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of SBE16. Peer-review under responsibility of the organizing committee of SBE16. Keywords: Lifecycle inventory; embodied CO2; building construction materials.
*
Corresponding author. Tel.: +30-210-5385728 ; fax: +30-210-538306. E-mail address:
[email protected]
1878-0296 © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of SBE16. doi:10.1016/j.proenv.2017.03.113
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1. Introduction Building energy consumption corresponds to 40% of the total energy consumption in Europe and is responsible for about 45% of the CO2 emissions in the atmosphere, which is accountable for the greenhouse effect1. From a legislative point of view, the main tool for improving the energy efficiency of the European building stock is the European Directive on the energy performance of buildings (EPBD recast Directive 2010/31/EC). Accordingly, national efforts focus towards the concept of nearly zero energy buildings by the end of the decade. On the other hand, from a scientific point of view, Life Cycle Assessment (LCA) of buildings has attracted an increasing research interest and is implemented in research studies concerning issues in building energy. LCA principles and framework are defined in the ISO14040 standard, while ISO14044 describes the relevant requirements and guidelines. Furthermore, ISO14025 prescribes the principles and procedures of Environmental Product Declaration (EPD), i.e. the standardized way of quantifying the environmental impact of a product or system based on LCA principles. Embodied energy (EE) and embodied CO2 (ECO2) of building materials are essential ingredients of LCA that could also be used to assess policies or various energy conservation measures implemented in existing buildings. EE concerns the total energy consumed in a building life-cycle. This includes the extraction of the raw materials, their transportation, manufacture and installation on-site, as well as their deconstruction or decomposition. EE is a sustainability indicator for buildings, since it is related with ECO2, material reuse and recycling, justifying the significance of the selection of appropriate construction materials in order to reduce the negative environmental impacts. EE and ECO2 values per unit mass for various materials vary not only from material to material, but also from country to country. The life cycle of any material that can is used in a building construction, generally consists of the following stages: excavation, processing, construction, operation, maintenance, demolition, waste or recycling/reuse. Each of these stages involves some kind of energy consumption and relevant CO2 emissions in order to be accomplished. The embodied energy of a building comprises of two components, namely the direct EE and the indirect EE. Direct EE is the energy consumed for the transportation and installation of building materials and products to the construction site. Indirect is the EE consumed to acquire, process and manufacture the building materials, including any transportation related to these activities. Indirect EE can be further divided in initial and recurring EE. Initial EE is the energy consumed for the acquisition, transportation and processing of raw materials to create a product. The recurring EE is related to the energy consumed in the maintenance, repair and replacement of a product during its service life2. Unfortunately, EE databases suffer from problems of variation and incompatibility. According to Dixit et al.2, most of the previous studies either followed the International LCA standards, or they did not follow any standards. The authors referred to the necessity of the development of a global database and compiled a list of parameters, mostly local, that are responsible for the lack of a global database, such as the methods of EE estimation, the building design, the construction methods, the kind and quantity of the construction materials, the system boundaries or the geographical locations. The basic methods for the calculation of EE are the process method, the input-output method and hybrid analysis methods that combine the characteristics of both other approaches to facilitate more comprehensive and accurate analysis3. In order to estimate the total EE and the related ECO2 emissions of a building, a good material analysis, i.e. breakdown of the various building components to their constitutive materials is required. Various studies are available in the literature, concerning the calculation of EE and ECO2 in buildings, some of which are indicatively referred herein. Venkatarama et al.4, estimated the energy consumed for the production, transportation and installation on-site of a number of traditional construction materials and concluded that an important amount of energy is spent for their manufacture and transportation. Shams et al.5 focused on a typical, five-floor residence in Bangladesh and examined the associated CO2 emissions for different construction materials. They showed that a reduction of almost 52% of the total EE and about 45% of the total ECO 2 of the building could be achieved only by replacing the principal materials (cement concrete, mortar) with other like fly-ash or blast furnace slag. They emphasized that aluminum and steel have high ECO2 and EE values compared to glass, timber or recycled products, while the use of bricks instead of ceramics reduced CO2 emission by one third. EE of the building was estimated 4,273.90 MJ/m2 and the embodied emissions 343.55 kgCO/m2. Xing et al.6 compared steel and aluminum with concrete, mostly in residential buildings in terms of EE and environmental emissions and concluded that concrete exhibits lower energy consumption than steel or aluminum in the entire building life-cycle. All of their case studies revealed the same results, i.e. that concrete dominates in terms of mass, while steel and aluminum
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dominates in terms of ECO2 due to the high values of ECO2 per material mass. Monahan et al.7 compared different building practices, in terms of ECO2 and EE impact. They studied a timber framed low energy building of 83 m2 in UK, exhibiting for ECO2 a value of 405 kgCO2/m2 and 5962 MJ/m2 for EE. A second scenario using timber framed with brick cladding, exhibited 535kgCO2/m2 and 7700MJ/m2, i.e. an increase of 32% in ECO2 and 35% in EE compared to the first scenario. Finally, they considered the building to be timber framed with conventional cavity walls and found 612kgCO2/m2 and 8200MJ/m2, i.e. an increase of 51% for ECO2 and 35% for EE, compared to the first scenario. To estimate EE and ECO2 of Hellenic residential buildings, Koubogiannis and Balaras8 grouped the basic materials, as belonging to the set of Construction Materials (CM) or the set of Electromechanical Installations (EMI). Based on previous works9,10,11 of the same research group, they studied two typical Hellenic buildings, namely a Multi-Family Dwelling (MFD) and a Single-Family Dwelling (SFD), both located in Athens and of the same construction period (2000-2010), estimated the EE and ECO2 impact of the materials comprising the EMI set and compared the results between the two buildings8. The main materials used for space heating, hydraulic and hot water installations were first identified and their mass contribution was calculated. For the estimation of the initial EE and ECO2 contribution of each material to the EMI set, appropriate EE and ECO2 coefficients were required. In the absence of any comprehensive Hellenic database, available values from the international literature12 were used. Although not being a rigorous approach, since these coefficients are nationally dependent parameters, the results provided first practical indicative values for the energy and environmental impact for the case studies under consideration. The present work applies a similar methodology to identify and calculate the mass of the basic items of the set of construction materials in typical Hellenic dwellings, focusing on the estimation of their initial ECO2. Four case studies have been selected, all located in Athens and of the same construction decade (2000-2010). Mass and ECO2 values of the dominant construction materials per unit building floor area are presented and compared. Massdominant materials are identified that can be used to prioritize future needs for developing national databases. The availability of such databases could contribute to the sustainable design of the future building, since they will provide the capability of selecting, assessing and using environmentally friendly materials during the design or refurbishment stage of a building. In what follows, the methodology and the case studies are presented, followed by the analysis and the results. For one of the case studies, the results for the CM set are merged with the corresponding ones concerning its EMI set and the relative importance of each set is assessed. Finally, an indicative example of how such an analysis can be used to assess energy conservation measures is presented; this concerns the estimation of ECO2 payback time in a case where timber frames in the openings (windows and doors) of a building are replaced by aluminum ones. 2. Methodology A three-step (bottom-up) process analysis was implemented for the CM set. Accordingly, a detailed material analysis is performed first, followed by mass analysis and then by the EE and/or ECO2 analysis, as described below. Step 1 - Material analysis: This concerns the breakdown of a given Set of materials and equipment into their constitutive materials. At first, the Set is divided in distinct Groups of major components in the form of a tree. Then, each Group is segregated to its constitutive main Items. In this task, the major Items of the Group are identified and continuously split into sub-items till reaching the lower level of Basic Items, i.e. entities that cannot be further split into sub-items. The material analysis is accomplished by identifying and recording the constitutive single materials of the Basic Items. In the present study, the CM Set for Hellenic dwellings was divided into the following Groups13 concerning: load bearing structure, masonry and coatings, insulation, flooring and covering, material integration. The identification of materials in each group was based on the final building drawings of each case study. Step 2 - Mass analysis: For each material recorded in the previous step, its mass (in kg) was calculated. The required data were again extracted from the final building drawings. Step 3 - ECO2 analysis: The mass values obtained in the previous step, were transformed to ECO2 (kgCO2) after multiplying them by the corresponding ECO2 coefficients (denoted herein by CECO2 and expressed in kgCO2/kg of material). Although it is well known that these coefficients are nationally dependent parameters, in the absence of a comprehensive relevant database in Greece, available values from the Inventory of Carbon and Energy (ICE) 12 were used. The boundaries involved within the ICE database are cradle-to-gate. The required quantities of the forms of
Georgios Syngros et al. / Procedia Environmental Sciences 38 (2017) 500 – 508
energy for the various materials, contained in the database, concern energy converted to primary equivalent. Accordingly, ECO2 coefficients correspond to these primary energy values. One has to be aware that such a processbased analysis suffers from truncation errors3. 3. Case studies Four case studies of typical Hellenic dwellings were selected; two Multi-Family Dwellings (MFD) and two Single-Family Dwellings (SFD), all located in Attica (climatic zone B of Greece) and constructed in the same period (2000-2010). Case A (Fig. 1-left) is a three storey MFD (2008) with basement and tilted roof. Each floor (87.30 m2) has an apartment (70.48 m2) and common staircase (16.82 m2). Case B (Fig. 1-right) is a three storey MFD (2010). Each floor (82.25 m2) has an apartment (70.00 m2) and common staircase (12.25 m2). Case C (Fig. 2-left) is a SFD (2010) with a floor area of 112.35 m2 and a basement (112.35 m2). Case D (Fig. 2-right) is a two level (maisonette) SFD (2009) with a ground floor area of 83.00 m2, an upper level (53.00 m2) with an internal wooden stair and a basement (52.50 m2). Details for the four case studies are available in13.
N
Fig. 1. Floor plans for Case A (left) and Case B (right).
N
Fig. 2. Floor plans for Case C (left) and Case D (right).
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Table 1 summarizes the envelope areas for cases A and B and Table 2 for cases C and D, respectively. For all the case studies, the same (five) Groups mentioned in section 2 (material analysis) were considered to consist the CM Set. The main materials contained in each Group (for cases A, B, C, D) are: bearing structure (steel, concrete), masonry-coatings (bricks, mortar (cement, sand, lime), senaz, plaster), insulation (extruded polystyrene), flooringcovering (ceramic tiles, lime, marble, concrete, waterproofing materials - asphalt bitumen), material integration (paints, timber (kitchen, cabinets, pergolas), timber (MDF) for internal openings, aluminum frames (cases A, B) or MDF (cases C, D) for external openings, aluminum frames for basement doors (case D)). Table 1. Areas of walls and openings for cases A and B. Case A Orientation
Case B
North
South
East
West
North
South
East
West
2
External walls area [m ] Basement
30.10
30.50
30.00
30.00
30.00
19.25
30.00
19.25
Ground floor
36.15
36.30
30.00
30.00
10.50
20.00
10.50
20.00
st
36.15
36.30
30.00
30.00
36.00
22.50
36.00
22.50
Ground floor
4.40
9.00
3.60
21.90
24.50
2.20
1st, 2nd, 3rd floor (x3)
5.40
7.90
4.30
6.40
6.20
1.80
nd
rd
1 ,2 ,3
floor
External openings area [m2] Basement
2.00
Table 2. Areas of walls and openings for cases C and D. Case C Orientation
Case D
North
South
East
West
North
South
East
West
Basement
23.75
23.75
33.75
33.75
20.00
20.00
10.00
10.00
Ground floor
23.75
23.75
33.75
33.75
31.50
31.50
30.60
30.60
20.00
20.00
10.00
10.00
1.00
1.05
External walls area [m2]
1st floor
There is no 1st floor 2
External openings area [m ] Basement
6.90
Ground floor
5.60
1st floor
4.16
3.76
6.10
2.35
7.00
4.20
5.52
6.00
3.15
5.65
3.36
3.68
6.10
1.68
1.68
There is no 1st floor
4. Results and discussion For each case study, the value and the percentage contribution of the main construction materials in terms of their mass and ECO2 are presented in Tables 3-5. Table 3 summarizes the area, total mass, ECO2 values, as well as the mass intensity and ECO2 intensity values, i.e. values normalized per unit floor area. The specific ECO2 value, i.e. value per unit mass of the total CM set is also presented. According to this Table, total mass values in cases A and B are greater than those of cases C and D, since the former buildings are MFD with relatively larger areas and volumes and thus contain higher amounts of construction materials. In terms of mass intensity, A and B exhibit comparable values, since they MFD of similar size. The same is true for C and D that are SFD. The specific ECO2 value is about 25% in all cases. The results provide baseline indicators for a rough estimation of the ECO2 impact of Hellenic dwellings (with similar characteristics as the ones described herein) due to their construction materials, by knowing the total mass value of CM for any other building. As anticipated, the ECO2 impact of MFD buildings is greater than
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that of the SFD ones, since their CM mass is higher. On the other hand, their intensity values per unit floor area are lower, due to the relatively larger floor area. Table 4 summarizes for each case study, the mass percentage and mass intensity for the top-eight CM materials (in terms of their contribution to the total CM mass), as well as the average quantities. Table 5 summarizes similar information in terms of ECO2 contribution to the total ECO2 value of the construction materials. In all cases, the basic construction materials are concrete, bricks, plaster, steel, lime, ceramic tiles, wood and aluminum, both in terms of mass and ECO2, representing about 90% of the total. The first three materials (i.e. concrete, bricks, plaster) account for about 83% of the total mass, while the first five materials account for about 82% of the total ECO2. The ranked list for the two quantities examined (mass and ECO2) is not the same. The cases of aluminum and steel are also characteristic examples. The contribution of each material in terms of mass and ECO2 is different. Concrete and steel are characteristic examples of the influence of ECO 2 per unit material mass. Concrete dominates in terms of mass in all cases (60% in average). However, steel is the dominant material in terms of ECO2 (average 30%), due to its high ECO2 content (CECO2 coefficient). Concrete follows next with a small difference due to its high mass value. Table 3. Summary of the calculation results for the construction materials in the four cases studies. Case
Area
Mass
ECO2
Mass intensity
ECO2 intensity
Specific ECO2
Study
[m2]
[kg]
[kg CO2]
[kg/ m2]
[kg CO2/ m2]
[kg CO2/kgCM]
A
438.0
1,209,211
327,538
2,761
748
0.27
B
410.5
1,005,142
252,388
2,449
615
0.25
C
231.6
886,674
202,934
3,828
876
0.23
D
188.0
679,085
163,740
3,612
871
0.24
Average
3,162
777
0.25
Std-dev
663
124
0.017
Table 4. Mass intensity contribution of the top-eight dominant materials of the CM set (mass contribution). Mass intensity [kg/m2]
Percentage mass [%] Material
A
B
C
D
Average
A
B
C
D
Average
Concrete Bricks
59.7
57
65.5
54.6
59.2
1648
1396
2507
1972
1881
17.5
18.2
11.6
18.4
16.4
483
446
444
665
509
Plaster
7.2
8.1
5.4
7.3
7.0
199
198
207
264
217
Steel
3.5
2.4
3.0
2.4
2.8
97
59
115
87
89
Lime
2.4
2.5
1.6
2.8
2.3
66
61
61
101
72
Tiles
1.7
2.0
2.2
2.9
2.2
47
49
84
105
71
Wood Aluminum (Total)
0
1.6
1.9
0.7
1.1
0
39
73
25
34
0.2
0.2
0
0.05
0.1
6
5
0
2
3
(92.2)
(92.2)
(91.2)
(89.2)
(91.1)
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Georgios Syngros et al. / Procedia Environmental Sciences 38 (2017) 500 – 508 Table 5. ECO2 intensity contribution of the top-eight dominant construction material (ECO2 impact). ECO2 intensity [kgCO2/m2]
Percentage ECO2 [%]
Material
A
B
C
D
Average
A
B
C
Average
D
CECO217
Steel
33.3
24.5
33.7
25.5
29.3
919
600
1290
921
933
2.29
Concrete
22.8
23.4
28.6
22.7
24.4
630
573
1095
820
779
0.14
Brick
14.9
16.5
11.3
17.5
15.1
411
404
433
632
470
0.23
Lime
6.9
7.5
5
8.8
7.1
191
184
191
318
221
0.76
Tiles
4.6
4.3
7.4
6.5
5.7
127
105
283
235
188
0.74
Wood
0
4.7
4.9
8.1
4.4
0
115
188
293
149
0.72
Aluminum
5.7
7.3
0
1.5
3.6
157
179
0
54
98
8.16
Plaster
3.2
3.9
2.8
3.6
3.4
88
96
107
130
105
0.12
(Total)
(91.4)
(92.1)
(93.7)
(94.2)
(92.9)
Furthermore, the distribution in terms of mass values is more homogeneous than the one for ECO2, due to the fact that even if some materials are encountered in small quantities they have larger C ECO2 coefficients. Finally, materials like marble, iron, insulation and glass are not included in the tables containing the dominant materials, due to their small mass quantity and their low CECO2 coefficient. The contribution of each material to the overall construction is similar for all cases, due to the similar architectural design and construction practices (i.e. similar location and period of construction). The quantities of steel used in the load bearing structure of the buildings exhibit significant variations for the case studies that in turn affect the estimated ECO2 values (e.g. MFD cases A and B). The value corresponding to case B (600 kgCO2/m2) is 37% lower than that of A (919 kgCO 2/m2) since the quantities of steel used in the two cases are different (97 kg/m2 and 59 kg/m2, respectively). Table 6 summarizes the results for the CM and for some major groups of EMI materials (e.g. equipment and components used for space heating, domestic hot water, hydraulic system) for case A9. A total number of 22 different materials were identified13, in particular 14 materials in the CM set and 11 in the EMI set (some materials are common). The contribution of the EMI set to the building total in terms of mass is negligible, i.e. less than 2% in terms of ECO2 compared to the impact of the CM set. These preliminary results for the role of EMI in the total embodied energy underline the importance of the design in the initial selection of building materials. Table 6. Total contribution of the CM set and the EMI set for case A.
CM set EMI set Total
Mass
Mass intensity
Mass
ECO2
ECO2 intensity
[kg]
[kg/m2]
[%]
[kg CO2]
[kgCO2/m2]
1,207,530
2756.00
99.85
327,538
748
ECO2 [%] 98.4
1680
3.83
0.15
5,104
12
1.6
1,209,210
2760.00
100.00
332,642
760
100.0
For a preliminary assessment of the environmental impact resulting from the implementation of popular energy conservation measures, this work considered the replacement of the external wooden frame single-glaze openings in case D by aluminum frame double-glazing, with thermal breaks. This is a popular refurbishment measure in old buildings, not only as an energy upgrade, but also for aesthetic purposes, safety, air tightness, etc. The ECO2 impact as a result of this action is 6,006 kgCO2 (Table 7). In order to estimate the CO 2 savings due to the lower operational energy consumption from this measure, the official national software TEE/KENAK was used to calculate the annual primary energy use of the building and its energy class, for both scenarios. The building uses a central heating system with an oil-fired boiler and electrical heat pumps for cooling. In its original state, the building energy class
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was F (low performance), while in the refurbished state it was improved to an energy class-D. The annual final energy savings were calculated at 7,670 kWhth and 508 kWhe. Using the national conversion factors of 0.264 kgCO2/kWh for heating oil and 0.989 kgCO2/kWh for electricity, the annual CO2 savings were 2,527 kgCO2. Accounting for the ECO2 of the old- and new-openings (i.e. 6,006 kgCO2 from Table 7), the associated ECO2 payback time is 2.4 years. Table 7. Mass and ECO2 contribution of different types of openings for case D. Scenario
Mass [kg]
Mass (kg/m2)
ECO2 [kgCO2]
ECO2 intensity [kgCO2/m2]
Wooden frame,single-glazing
568
3.0
409
2.2
Aluminum frame, double-glazing
2100
11.2
5,597
29.8
5. Conclusions – Future work Initial embodied CO2 emissions corresponding to construction materials were evaluated for four typical Hellenic dwellings, all intentionally located in the same climatic zone and of the same construction period, in order to seek for possible correlations in the results. A three-step procedure consisting of material, mass and ECO2 analysis was performed for each case. In the absence of national ECO2 coefficients, available values from the open literature were used. For one of the cases, the materials involved in the major electro-mechanical installations were also considered. The main construction materials of the case studies were identified (i.e. concrete, bricks, plaster, steel, lime, ceramic tiles, wood, aluminum). Baseline indicators were calculated for each material. For example, concrete was found to dominate in terms of mass (~60%), while steel dominated in terms of ECO2 (~30%). An approximate value of 0.25 was found to correlate the total mass to the total initial embodied CO2 emissions. Preliminary results indicate that the contribution of the materials for major electro-mechanical installations in terms of mass is negligible and in terms of ECO2 is low (
