Characterizing the essential materials and energy performance of city buildings: A case study of Macau

Journal of Cleaner Production 194 (2018) 263e276

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Characterizing the essential materials and energy performance of city buildings: A case study of Macau Qingbin Song a, *, Huabo Duan b, Danfeng Yu b, Jinhui Li c, Chao Wang d, Jian Zuo e a

Macau Environmental Research Institute, Macau University of Science and Technology, Macau Smart Cities Research Institute, College of Civil Engineering, Shenzhen University, Shenzhen 518060, China c School of Environment, Tsinghua University, Beijing 100084, China d Guangdong Provincial Key Laboratory on Functional Soft Condensed Matter, School of Materials and Energy, Guangdong University of Technology, Guangzhou 510006, China e School of Architecture & Built Environment, The University of Adelaide, Adelaide 5001, Australia b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 29 March 2018 Received in revised form 18 May 2018 Accepted 18 May 2018 Available online 19 May 2018

The lack of a clear understanding of the consumption of materials and energy in construction activities and by existing buildings has hindered sustainable urban development in Macau. This study is therefore designed to quantify the consumption of building materials and energy in Macau over past 16 years, from the perspective of life cycle analysis. The results show that there has been rapid growth in the annual consumptions of both materials and energy throughout the entire lifetime of buildings. In 2016, the construction of buildings contributed to almost all materials use during their lifetime, which in 2015 was approximately 10 times greater than in 1999, but the energy consumption of buildings only accounted for 7.8% of their total energy consumption. The amounts of material and energy consumption in the construction of buildings are about 1.375 tons/m2 and 1176.72 MJ/m2, respectively. Most energy was consumed during the operational lifetime of the buildings however, constituting 92.2% of the total energy consumption; this is particularly the case in the gaming industry. In 2016, the average energy consumption of residential buildings was 264.97 MJ/m2$year, which actually increased. However, the management and recycling of building waste in Macau is still an area that is underdeveloped. Actually, nearly all building materials and energy are imported from neighboring regions in mainland China, resulting in potential resource and energy supply risks for Macau. The findings obtained in this study will enable policy makers, designers, and building users to make more sensible judgments in promoting the development of sustainable buildings in Macau and elsewhere. © 2018 Elsevier Ltd. All rights reserved.

Keywords: Buildings Materials use Energy consumption Life cycle analysis Macau

1. Introduction Recently, the relationship between the building sector and energy consumption has been constantly discussed, due to the large energy consumption of buildings (Cubi et al., 2015). It has been calculated that globally, buildings are responsible for 40% of all energy use and one third of greenhouse gas emissions (Huovila et al., 2009). In mainland China, the energy consumed by the building sector accounted for more than 36% of the national primary energy consumption in 2014 (BECRC, 2016; Song et al., 2016). In the U.S., residential buildings only contributed to about 22.2% of the total energy consumption (primary energy consumption,

* Corresponding author. E-mail address: [email protected] (Q. Song). https://doi.org/10.1016/j.jclepro.2018.05.148 0959-6526/© 2018 Elsevier Ltd. All rights reserved.

electricity retail sales, and electrical system energy losses) (Fumo, 2014). Energy security, environmental concerns, thermal comfort, and economic matters of buildings have become the driving factors for further research and development with the aim of reducing energy consumption and the associated greenhouse gas emissions (Hong et al., 2015; Chen and Ng, 2016; Marzouk et al., 2017). Macau, a Special Administrative Region of China, is an internationally renowned city, with a burgeoning tourism industry (Song et al., 2017a). The rapid economic development and increasing population have sparked a high volume of construction activity in Macau. In 2015, there were a total 2750 building companies engaged in construction projects (1236 companies) and renovation projects (1514 companies), which is approximately 2.82 times the number of building companies that were engaged in the same activities in 2000. Currently, the energy consumption of buildings

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during their operational phase has become the dominant component of their total energy consumption, accounting for more than 70% of their final energy use in 2016 (DSEC, 2017a). The energy consumption of buildings cannot be overlooked with respect to guaranteeing Macau's energy security and addressing problems caused by climate change. Accordingly, the energy consumption associated with buildings in Macau has inevitably displayed an upward trend along with the construction of large numbers of buildings (Song et al., 2017b, 2018). Despite the improved energy-saving standards in building operation, the energy consumption of buildings in cities has been rising in recent years (Hong et al., 2016; Zhang et al., 2015). Currently, life cycle assessment (LCA) is one of the measurement instruments that is able to thoroughly assess energy consumption and environmental impact (Song et al., 2012; Song and Li, 2015; Mao et al., 2017). The LCA approach is considered to be one of the most popular methods to analyze the technical aspects of green and sustainable buildings (Duan et al., 2015; Kylili et al., 2017). Through LCA analysis, opportunities to reduce energy consumption and environmental impacts across all life cycle stages can be identified, which will help to avoid simply shifting the problem elsewhere. In recent years, many LCA studies have been carried out in the building sector, by university researchers, urban designers, architects, engineers, and consultants (Hellweg and Canals, 2014). For example, Zhang et al., 2015 identified the energy consumption of the Chinese building sector by establishing an estimation model of building energy consumption from a life cycle perspective. However, an analysis of the literature shows that a large number of researchers applied LCA to case studies of buildings’ energy systems and environmental impacts (Winther and Hestnes, 1999; Aste et al., 2010; Cellura et al., 2014). Very few studies focused on the lifecycle analysis in terms of materials and energy consumption from the perspectives of a whole city or country (Modeste et al., 2015), which will be more useful for realizing sustainable urban buildings, compared with a case study of only one or several buildings. Especially, there is no clear and comprehensive understanding about the extent of Macau's materials and energy consumption, and the corresponding energy efficiency in the building sector (Song et al., 2017b). In addition, a considerable underestimation of energy usage associated with buildings has impeded the effective implementation of measures to improve building energy efficiency. Therefore, a consolidated knowledge base is required to inform decision makers about the best course of action to suit their situation, prior to opting for detailed analysis for retrofit alternatives. This study is designed to characterize the use of materials and energy in the building sector in Macau during 1999e2016 from a lifecycle perspective. Through the use of LCA, we can gain a clear and integrated image of the overall materials and energy consumption attributable to buildings in Macau, and then uncover past changes and developing trends, from a macroscopic point of view. Furthermore, we have made some suggestions to improve building energy efficiency in Macau, and to promote sustainable urban development. 2. Materials and methods 2.1. Basic information regarding buildings in Macau 2.1.1. New buildings during the research period Table S1 lists basic information on new buildings in Macau during the research period. The amount of new building areas shows an apparent declining trend from 1999 to 2002. After that, the building industry begins to soar again, reaching a historical peak at 1.93 million m2 in 2007. Actually, at the same time as the

building industry, the gaming industry also started to expand rapidly after the opening of gambling rights in 2002, leading to the construction of commercial buildings associated with this industry. However, since 2008, the global economic crisis has resulted in another declining trend in the building industry. Up until 2012 and 2013, the building industry gradually returned to an increasing trend due to economic development. Overall, the building industry experienced fast growth during the period of 1999e2015. Fig. S1 presents the distribution of the different types of new buildings constructed from 1999 to 2015. Residential buildings accounted for 46.02% and 63.25% of the total building areas in 1999 and 2003, respectively. However, they only accounted for 13.77% in 2007, 11.06% in 2011 and 25.17% in 2015. “Other buildings” mainly refers to those associated with the gaming industry, which indicates that the gaming industry has become the most significant driver for new buildings, reaching a peak value of about 84.64% of all of the new building areas in 2007.

2.1.2. Buildings in use Fig. S2 presents the average residential floor space per capita in Macau, which varies within a narrow range between 23.0 and 24.2 m2. Though a great number of new buildings have been built in the past 10 years, the average residential floor space per capita has only increased by 1.2 m2, and still there has been no great improvement. This is possibly a result of the fast population growth (increasing from 531.8 thousand in 2007, to 652.5 thousand in 2016) and the large ratio of new buildings being for other industries (more than 70% of all the new building areas). In comparison with the other countries and regions in Fig. S2, the average residential floor space per capita in Macau is also much lower, and is only higher than that of Hong Kong. According to Fig. S3, due to the small area of Macau, building units of less than 50 m2 in size occupy about 39.41% of all the building units in Macau, especially on Coloane Island (67.27%). Meanwhile the building units with areas of 50e99 m2 constitute the majority (44.58%) of all building units.

2.2. LCA goals and scope This study sought first to review and evaluate the life cycle materials and energy consumptions of the whole building sector in Macau, and then to provide some effective suggestions to promote and improve the energy efficiency of buildings in Macau. For the LCA research, the system boundary determines which processes should be included within the LCA which should be consistent with the goal of the study. From the life cycle perspective, all of the related activities throughout the building's life cycle should be encompassed, including the production of building materials, building construction, building operation and building demolition. Due to the small area and the lack of various resources, almost all building materials and most of the energy required in Macau were imported from other countries and region, especially Mainland China and Hong Kong. Therefore, in this study, we will mainly refer to the three stages of building construction, building operation and building demolition, as shown in Fig. 1. The boundaries of this study are restricted to the area of Macau, thus the transportation of the materials and energy from the import countries or regions into Macau will be excluded from our study. For the research period, we will consider the time from 1999 to 2016, which represents the potential materials and energy consumption trend of building sectors since Sovereignty over Macau was transferred back to China on 20 December 1999.

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Fig. 1. Life cycle boundaries of the buildings.

2.3. Calculations and assumptions 2.3.1. Construction and decoration phase Because the erection of new buildings, repair and maintenance of old buildings, and renovation or destruction of vacated buildings are closely connected with the activities of construction enterprises, it is appropriate to employ the materials and energy consumptions of the construction industry to represent the consumption of materials and energy associated with these activities. It is noted that the materials and energy consumptions resulting from decoration processes have been considered in the construction industry. In addition, considering the fact that there are hardly any local building material production activities, the material use will be calculated based on import and export data, and can be expressed as shown in Equation (1). At the same time, the construction energy consumptions of the buildings will be analyzed using Equation (2).

CM ¼

X  CMji  CMje

(1)

j

CE ¼

X

CEl  hl

(2)

l

CEu ¼ CE=a

(4)

c

where CMu and CEu refer to the amounts of construction materials (tons/m2) and energy consumption (TJ/m2), respectively; ac is the floor space for building construction (m2).

2.3.2. Operation phase For the building operation phase, only the energy consumption was considered in this study, and other materials and energy consumptions related to maintenance and repair processes of buildings were ignored, due to their small relative proportion. According to the Macau statistics and census bureau, Macau's building operation energy consumption can be divided into three categories: (1) residential buildings, (2) commercial buildings, and (3) buildings of other industries (mainly referring to those of the gaming industry). The energy consumptions can be calculated as shown in Equation (5).

UE ¼

X X X UErl  hl þ UEbl  hl þ UEol  hl l

where CM and CE refer to the annual amounts of construction materials used (tons) and the corresponding energy consumption (TJ), respectively; j and l represent the types of construction materials and energy, respectively; CMji refers to the import volume of material j (tons); CMje is the export volume of material j (tons); CEl refers to the energy consumption (electricity: million kWh; diesel: 1000 L); hl is the unit heat values of energy (electricity: TJ/million kWh; diesel: TJ/1000 L, shown in Table 1). In order to make comparisons with the building construction activities in other cities or regions, the unit material and energy consumptions per unit area will be very important, and can be expressed as shown in Equations (3) and (4).

CMu ¼ CM=a

l

(5)

l

where UE refers to the energy consumption of building operation in Macau (TJ); l represents the type of energy; UErl ; UEbl and UEol represent the energy consumption volume from commercial buildings, and buildings of other industries (electricity: million kWh; common kerosene and diesel: 1000 L; oil gas: tons; natural gas: 1000 m3); hl is the heat value of unit energy (electricity: TJ/ million kWh; common kerosene and diesel: TJ/1000 L; oil gas: TJ/ ton; natural gas: TJ/1000 m3). The unit energy consumption for building use can be calculated according to Equation (6).

UEu ¼ UE=a

(6)

o

(3)

c

where UEu refers to the annual unit energy consumption (TJ/ m2$year) for building operation; ao is the building area (m2) in use.

Table 1 Unit heat values of the used energy in Macau. Type

Oil gas (TJ/ton)

Diesel (TJ/1000 L)

Common kerosene (TJ/1000 L)

Natural gas (TJ/1000 m3)

Electricity (TJ/million kWh)

Heat value

0.0456

0.0370

0.0350

0.0390

3.6000

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2.3.3. End-of-life phase As mentioned above, the renovation activities of vacated buildings or their demolition and subsequent transportation activities were often carried out by construction enterprises, therefore, the material use and energy consumption of the destruction of vacated buildings has been included in the statistical data of the construction phase in Macau. Herein, the end-of-life phase will mainly refer to the waste disposal processes. 2.4. Data sources Several sources were utilized to obtain the primary lifecycle materials and energy data compiled in this study. These include the “Construction Statistics” (DSEC, 2017c), “Construction Sector Survey” (DSEC, 2017b), “Private Sector Construction and Real Estate Transactions” (DSEC, 2017d), “Macau Energy Statistics” (DSEC, 2017e), “Research report abstracts on Macau energy efficiency” (ODES, 2014), “Macau Statistics Yearbook” (DSEC, 2017a), “Macau Environmental Status Reports” (EPU, 2016), and “External Merchandise Trade Database” from the Statistics and Census Service of Macau (DSEC, 2017f). For more details, the primary data sources used in this study are shown in Table 2.

materials consumption of the building industry from 1999 to 2015 is presented in Table 3. It can be clearly seen that the trend of building materials consumption has been highly consistent with the increase of building floor areas (Table S1). It can be seen from Table 3 that the non-metal materials are the primary component of material consumption of the total materials. For the non-metal materials, the materials for the building structure (e.g. sands, gravels, raw cement, clinker cements, and bricks) contribute to more than 98% of the non-metal materials consumption, especially the sands and clinker cements, in comparison with the decorating and renovating materials (e.g. ceramic tile and tesserae, paints, and glasses). For the metal materials, steel is the most important material consumption, and its consumption volume increases from 42666 tons in 1999e424292 tons in 2015, representing an approximately 10-fold increase. Due to the changes of building structure and type in Macau resulting from technical innovation, the ratio of the materials consumption to the total building material consumption has exhibited several variations. For example, during the period of 1999e2015, the ratio of raw cements used increased from 0.28% to 9.55%, while the ratio of clinker cements decreased from 66.19% to 26.97%; more importantly, the usage ratio of steel in the buildings maintains a fast increasing trend from 7.44% to 27.12% of the total materials consumption.

3. Results 3.1. Construction phase 3.1.1. Material consumption Building materials, referring to over 2000 kinds of products and materials, generally fall into two categories: metal materials, including steel, aluminum, copper, etc., and non-metal materials, such as cement, glass, architectural ceramic, stone, lime, cement, and so on (Vilches et al., 2017). In this study, considering the importance of different building materials and data availability, metals only refer to the steel and wires used for building construction, while the non-metal materials include sands, gravels, cements, bricks, ceramic tiles and tesserae, sanitary appliances, woods, paints, and glasses. The

3.1.2. Energy consumption Primary energy consumption during the construction stage of buildings in Macau mainly includes diesel used in the building machinery and transportation vehicles, and electricity for electrical equipment. Fig. 2 shows the diesel and electricity consumption for building construction in Macau. For the diesel consumption, there is a general tendency towards rising consumption during the period of 2000e2016, accompanied with the some fluctuation during the periods of 2007e2009 and 2013e2016. The diesel consumption of the building industry increases from 4 million L in 2000 to the first peak values (30 million L) in 2007, followed by a short-term decline to 12 million L in 2009 and a long-term increase to the second peak value in 2014 (34 million L, also the largest

Table 2 Data sources. Life-cycle stage

Data sources

Construction and decoration phase Construction areas Construction Statistics; Macau Statistics Yearbook Material use Construction Sector Survey; Macau Statistics Yearbook Energy consumption Macau Energy Statistics Building use phase Building use Private Sector Construction and Real Estate Transactions Energy consumption Macau Energy Statistics Energy-unit consumption per Research report abstracts on Macau energy economic value added efficiency End-of-life phase Material and energy Macau Energy Statistics consumption Building waste generation and Macau Environmental Status Reports; Macau composition Environmental Statistics Building waste recycling and Macau Environmental Status Reports disposal General data Material import Macau Statistics Yearbook; External Merchandise Trade Database Energy import External Merchandise Trade Database Local electricity CEM Annual Report; Macau Statistics Yearbook

Covered time range

Departments

1999e2016

Statistics and Census Service of Macau

1999e2015 2000e2016 2000e2016

Statistics and Census Service of Macau

2000e2016 2005, 2007, 2009, 2011, 2013

Office for Development of the Energy Sector

2000e2016

Statistics and Census Service of Macau

2000e2015

Environmental Protection Bureau of Macau

2007e2015

1999e2015 2000e2015 1999e2015

Statistics and Census Service of Macau

Macau power plant; Statistics and Census Service of Macau

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Table 3 Material consumptions of new buildings from 1999 to 2015 (tons). Year

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015

Non-metal materials

Metal materials

Sands

Gravel

Raw cement

Clinker cements

Bricks

Ceramic tile and tessera

Sanitary appliance

Wood

Paint

Glass

PVC plastics

Steel

Wire

119380 133,214 328818 446605 269180 362770 465005 840630 1060798 1013019 405133 350675 397952 567802 415097 375864 438545

16857 29,525 29595 26836 90336 28622 21525 45673 18294 22915 546 1436 9060 3816 36215 33039 72897

1606 9367 11650 10361 26203 54121 36102 214659 243603 106458 57122 13449 41134 111478 161699 172744 149418

378800 278,905 314000 142500 270085 182819 432404 521908 526054 417239 174730 222500 350000 481219 506412 522694 421965

2034 14,964 16877 21187 35017 67578 45907 62185 59294 52082 38268 22608 17557 16745 13717 15919 12283

9248 12050 9225 11295 12997 24259 33192 27874 28001 34729 28230 27410 21350 54775 26201 28907 29095

336 430 410 463 636 884 1556 1538 1414 1978 1261 1282 1186 1412 1085 1599 1977

821 1490 1410 1241 3518 4892 8367 12052 14710 9972 9106 6260 8372 11931 8146 10131 14772

505 544 745 548 611 956 1273 1432 1951 1658 1897 1430 1358 1286 1231 1370 1379

236 862 136 507 324 547 1582 630 379 635 804 341 235 490 165 356 305

29 39 64 66 244 391 677 115 429 286 250 210 202 314 361 856 883

42566 18,922 22025 30166 105897 117379 329137 388520 475510 311608 78106 73415 120105 201959 377402 478304 424292

1429 1155 1598 889 1550 2214 4325 11867 9690 11683 6873 4547 5093 5434 6299 14539 14193

Total

436004 329361 366490 208862 430879 401919 858420 1028121 1117432 841870 339525 360003 525458 775565 941019 1074675 921144

Fig. 2. Diesel and electricity consumption of building industry in Macau Ratios to final energy consumption of all Macau (%) Building energy consumption (TJ).

value). In recent years, due to the depression of the gaming industry, the diesel consumption during the building construction stage has exhibited a slight decline. With respect to electricity consumption, only one obvious fluctuation period during 2008e2010 can be observed, potentially as a result of the global financial crisis. When it comes to 2007, the highest electricity consumption is equal to 534 million kWh, which is 35.6 times that in the year 2000. After that, the electricity consumption exhibits a steep decline to 37 million kWh in 2011, and then maintains a steady trend. Fig. 3 presents the total energy consumption of the construction stage. The total energy consumption of the building industry was about 1117 TJ in 2016, and varied from 197 to 2550 TJ. On the whole, the changes in the total energy consumption during 2000e2016 are more closely correlated with the trends of diesel usage, due to diesel's high overall contribution (mean value 74.42%) of the total energy use in building construction. Two obvious periods of fluctuation during 2008e2010 and 2014e2016 can be seen, similar to the case of diesel consumption. Fig. 3 also indicates the ratio of the energy use by the building industry relative to the final energy consumption of all Macau. Similar to the trends for energy use, the ratios increase from 1.5% in 2000 to 11.6% in 2007, followed by a

three year decline to 3.0% in 2010. Upon reaching 2013, there is a small peak value (5.4%), and then the ratios decrease slightly. Overall, the energy consumption of the building industry has a general rising tendency from 1.5% in 2000 to 3.9% in 2016. 3.1.3. Materials and energy consumption per unit floor area Considering that the construction time of buildings often lasts several years, the new building areas do not necessarily represent the building materials and energy consumptions in that year. Therefore, we consider the total 16 years’ data as the research object in order to understand the unit material and energy consumptions. Fig. 4 presents the unit material consumption of the construction stage for the buildings constricted during 1999e2015. The total unit material consumption is 1.375 tons/m2. For the non-metal materials, the sands (0.527 tons/m2) and clinker cements (0.405 tons/m2) are two primary building materials, and raw cement, bricks, gravel, and ceramic tile and tesserae are also important components. The unit steel consumption is as high as 0.237 tons/ m2, and is the most significant component of the overall metal consumption. In comparison with the consumption of building materials in Shenzhen city (residential buildings: 0.91 tons/m2 and

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Fig. 3. Total energy consumption and its ratios of construction stage.

Fig. 4. Unit materials consumption of the building construction (tons/m2).

commercial buildings: 1.22 tons/m2, survey data), the construction of buildings in Macau consumed a greater amount of building materials. Based on the building areas and the energy consumption, the unit energy consumption is also calculated in this study. It is calculated that the unit energy consumption is 1176.72 MJ/m2, which is also equal to 21.32 L/m2 diesel consumption and 107.73 kWh/m2 electricity consumption. According to the research results from Zhang et al. (2015), the energy consumption per unit building area in mainland China decreased from 350.79 MJ/m2 in 2001 to 165.87 MJ/m2 in 2013, which is only 14e30% of the energy consumption in Macau. 3.2. Operation phase 3.2.1. Energy consumption 3.2.1.1. Residential buildings. Table 4 describes the energy consumption of residential buildings in Macau, which includes common kerosene for lighting, oil gas (also called liquefied petroleum gas) and natural gas for cooking and hot water, and electricity for

lighting and household appliances. On the whole, the energy consumption of residential buildings has maintained a long-term growth trend, increasing from 2100 TJ in 2000e4139 TJ in 2016, with a 4.39% annual increase. Only in 2006 and 2010 did energy consumption experience a slight decline, mainly caused by the sharp drops of common kerosene consumption. For the four types of energy, electricity contributes the most to the total energy consumption, accounting for about 77.14% (mean value), followed by oil gas (22.23%). In further detail, there are some differences for the different types of energy consumptions. For common kerosene, its usage has faced a continuous decline from 1.52 million L to zero, due to its substitution by the wide use of electricity. Leading up to 2014, considering environmental protection and safety, natural gas begins to be introduced into Macau households, and its usage increased fast from 250 thousand m3 in 2014 to 819 thousand m3 in 2016. Natural gas can be seen as an effective supplement of oil gas in Macau. Due to the wide application of household appliances, electricity use has maintained a long-term increasing trend from 412 million kWh in 2000 to 958 million kWh in 2016. In

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Table 4 Energy consumption of residential buildings in Macau. Year

Common kerosene (1000 L)

Oil gas (tons)

Natural gas (1000 m3)

Electricity (million kWh)

Total energy (TJ)

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016

1515 1210 810 672 560 578 161 136 132 214 0 0 0 1 0 0 0

12358 11938 13182 14637 15774 17393 15675 15193 15652 14951 13543 12535 13034 13536 12253 12954 14445

0 0 0 0 0 0 0 0 0 0 0 0 0 0 258 469 819

412 421 443 453 485 549 565 617 637 682 697 766 792 797 913 943 958

2100 2102 2224 2322 2485 2790 2754 2919 3012 3144 3127 3329 3446 3486 3856 4004 4139

comparison with other types of energy, the usage of oil gas experienced more fluctuations during 2000e2016. In 2000, the oil gas consumption was 12358 tons and reached a peak value of 17393 tons in 2005. However, the oil gas consumption has dropped since 2005. When it comes to 2014, only 12253 tons of oil gas (minimum value) was consumed, which increased slightly from then on. The residential sector constitutes the third largest major energy consumer in the world, representing 27% of total energy consumption (Nejat et al., 2015). In Cameroon, the residential sector even constitutes the largest major energy consumer, constituting 66% total energy use in 2010 (Modeste et al., 2015). However, the mean contribution ratio of residential consumption to the total energy consumption in Macau is only 14.82%, which is much less than that of global energy use. 3.2.1.2. Commercial buildings. Here, the commercial buildings will mainly include offices, catering businesses, hotels, etc., but will not contain those buildings related to the gaming industry. The energy consumption of commercial buildings in Macau is given in Table 5. It can be seen that the total energy consumption has experienced a fast growth trend from 2174 TJ in 2000e4211 TJ in 2016, which is similar with the trend of energy consumption for residential buildings. The electricity consumption by office equipment and other electronic products is the largest contributor to the total energy consumption of commercial buildings, about 71.75% (mean

value), followed by oil gas (27.86%). Oil gas and natural gas are mainly used for cooking and heating water in the catering businesses and in hotels. Due to the fast economic development in Macau, the demands of oil gas maintain a long-term increasing trend from 10646 tons in 2000e30162 tons in 2016. In 2000, the oil gas usage of commercial buildings was a little lower than that of residential buildings, but by 2016, it had become 2.09 times of that of residential buildings. In contrast, the electricity use was higher than that of residential buildings in 2000, but one-third lower in 2016. The consumption of natural gas was 5.88 million m3 in 2016, accounting for 5.33% of the total energy consumption of commercial buildings. 3.2.1.3. Other industries. Here, the other industries will mainly refer to the power and gaming industries. Currently, due to the boom of the gaming industry, its energy consumption can basically represent the total energy use from the buildings of all other industries, as its overall contribution is more than 99%. As described in Table 6, the total energy consumption from other industries increased from 1778 TJ in 2000e11043 TJ, with 6.21 times growth. Currently, “other industries” has become the most significant energy consumer, in comparison with residential and commercial buildings. Out of the four types of energy, electricity is still the most significantly used form of energy, and its contribution ratio was 98.95% (mean value) in 2016. During 2000e2016, the

Table 5 Energy consumption of commercial buildings in Macau. Commercial buildings

Oil gas (tons)

Natural gas (1000 m3)

Electricity (million kWh)

Total energy (TJ)

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016

10,646 11,777 12,457 12,640 12,298 12,056 15,108 18,179 22,915 24,474 26,956 29,819 29,719 # # # 30,162

0 0 0 0 0 0 0 0 0 0 0 0 0 # # # 5878

469 477 503 526 565 631 659 641 595 617 660 668 626 # # # 724

2174 2254 2379 2470 2595 2821 3061 3137 3187 3337 3605 3765 3609 # # # 4211

# means that the data is confidential and unpublished.

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Table 6 Energy consumption of buildings from other industries. Year

Oil gas (tons)

Natural gas (1000 m3)

Electricity (million kWh)

Total energy (TJ)

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016

938 587 612 590 1045 1406 1708 # # 315 244 554 # # # # 0

0 0 0 0 0 0 0 0 0 0 0 0 0 # # # 146

482 496 518 549 593 676 864 1053 1282 1769 2031 2167 2519 # # # 3066

1778 1812 1893 2003 2182 2498 3188 3791 4615 6383 7323 7826 9068 # # # 11043

# means that the data is confidential and unpublished.

electricity use by other industries increased by 6.36 times. The use of oil gas had decreased to zero by 2016, but the natural gas consumption in 2016 was 146 thousand m3.

3.2.2. Total energy consumption of building operation Fig. 5 presents the total energy consumption of buildings operation and its ratio to total final energy consumption in Macau. It can be seen that the energy consumption from building use in Macau maintains a fast growth trend, and varies from 6447 to 19487 TJ during the period of 2000e2016. For the three kinds of building sectors, their individual energy consumptions also exhibits increasing trends, especially “other industries”. Due to the tremendous boom of the gaming industry, the contribution from “other industries” has become the most significant source of energy consumption, its ratio increasing from 27.8% of the total energy use by buildings in 2000 to 55.7% in 2016, which highlights that the application of energy-saving strategies for building use in the gaming industry should be a primary focus. As can be seen from Fig. 5, the energy consumption of buildings use in Macau is the most significant component of final energy use, maintaining a long-term increasing trend from 47.3% to 68.3%, which is much higher than that of the associated construction phase.

3.2.3. Unit energy consumption of building operation Due to a lack of data on the building areas containing nonresidential buildings, here only unit energy consumption for residential buildings is calculated, as shown in Fig. 6. In 2016, the unit energy consumption of residential buildings was 264.97 MJ/ m2$year, which has not decreased, but actually increased in comparison with previous years’ data. This trend may be attributable to the increasing number of home appliances and the rise in living standards. Zhang et al., 2015 reported that the unit energy consumption of residential buildings in mainland China was about 263.57 MJ/m2$year during the period of 2001e2013, which is comparable with that of the buildings in Macau. Goggins et al., 2016 indicated that, based on Irish Building Regulations, the unit energy consumption of new residential buildings in 2008, 2011, and 2016e2020 were 324, 216, and 162 (nearly zero energy buildings) MJ/m2$year, respectively. In residential buildings worldwide, energy efficiency improvements of 26% were made during the period 2000e2015 (IEA, 2016a). In Macau, the unit energy consumption of residential buildings is equivalent to the levels during 2008e2011 in Ireland, and it has not shown any improvements. There is still a long road if we want the buildings in Macau to reach nearly zero energy consumption in the future. As shown in Fig. 6, the unit electricity consumption of residential buildings also increased from 48.34 kWh/m2$year in 2007 to 61.33 kWh/m2$year in 2016. The Macau Office for Development of the Energy Sector

Fig. 5. Total energy consumption and its ratios of buildings use in Macau.

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Fig. 6. Unit energy consumption of residential buildings.

published some data on the unit energy consumption per unit economic value added for non-residential buildings. From this can be known that the unit energy consumption per unit economic value added shows an obvious decline, especially in the retail business (from 305.1 MJ/thousand MOP in 2005 to 41.9 MJ/thousand MOP in 2013) (Song et al., 2017b). In non-residential buildings, a 37% improvement was achieved globally in terms of energy consumption per square meter during the period 2000e2015 (IEA, 2016a). According to our experiences, the energy improvement per unit area in Macau should be lower than the global level.

3.3. End-of-life phase When these buildings reach the end of their lifetime, a huge amount of building waste is produced. In addition, some building waste is also created as a result of new construction activities, in addition to maintenance and repair processes of old buildings. As shown in Fig. 7, the amount of building waste generated exhibits two obvious fluctuation periods of 2007e2012 and 2014e2015. From 2000 to 2007, the generation of building waste increases from about 0.30 million m3 or 0.50 million tons, to 3.12 million m3 or 5.30 million tons. However, due to the global economic crisis in 2008, the demolition of buildings and the construction of new

buildings showed a declining trend up to the year 2012. Then, the generation of building waste increased slightly from 2012 to 2014, but decreased again in 2015, to about 1.63 million m3 or 2.77 million tons. Noticed that in Macau, according to the Macau Statistics and Census Service, the building waste will not only include the building demolition waste, but also the excavated stones and soils during building construction. Even some excavated sea mud and some other inert waste are also involved in the building waste. Especially, the weight of excavated stones and soils during building construction are very large. Therefore, the statistical building waste volume will be much larger than the building materials consumption in recent years. Currently, only part of the total metals in a building are recycled upon its demolition, but it represents less than 10% (by weight) of building waste generated (Duan et al., 2015). More than 90% of concrete and masonry waste is removed from building sites but has no associated recycling strategies, which indicates a huge gap between Macau and some developed countries such as Germany (87%) and Japan (97%) (Zhang and Fei, 2010). According to the Macau Environmental Protection Bureau, the composition of the building waste from Macau which was transported to building waste landfill, is presented in Fig. 8. It can be seen that the cements, bricks, stone, tile and soil are the most important components,

Fig. 7. Building waste generation amount in Macau.

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Fig. 8. Building waste composition in Macau.

accounting for about 63%, followed by wood (11%), plastics (4%) and asphalt (4%). In addition, the furniture and large goods from household decoration contribute to about 3% of the total building waste. However, because this building waste landfill is simple landfill and very close to the sea, actually, the treatment and disposal of building waste can be seen as sea disposal. Though most of the building waste constitutes inert waste, it still has a large potential to cause environmental harm, due to the release of hazardous substances, such as heavy metals and persistent organic pollutants (POPs) in paints and plastics (Duan et al., 2016).

3.4. Building energy structure Fig. 9 presents the change in the energy use of buildings throughout their whole lifecycle from the period of 2000e2016. The building energy consumption in Macau mainly refers to five types of energy, including common kerosene, diesel, oil gas, electricity, and natural gas. From 2000 to 2016, diesel, oil gas and electricity are always used. Especially, electricity contributes to the most of the energy consumption, and its ratio to the total building energy consumption has the fastest growth from 79.41% to 84.24%,

Fig. 9. Building energy structure changes in Macau: (A) 2000; (B) 2005; (C) 2010; (D) 2016.

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while the oil gas consumption exhibits a 7.56% decrease, due to its substitution with electricity and natural gas. The ratio of diesel consumption firstly increases from 2.27% in 2000 to 7.12% in 2005, then exhibits a 3.57% decline in 2010, and finally contributes about 4.55% in 2016. As mentioned above, common kerosene only contributes the smallest amount of energy consumption, and has not been used since 2010. In order to reduce the carbon emissions from energy consumption, natural gas has begun to be used in Macau, and accounted for about 1.30% of total building energy consumption in 2016. In the future, the current trends could continue: increasing electricity consumption; stable diesel consumption; decreasing oil gas consumption; and increasing natural gas consumption. Cleaner sources of electricity will be the great opportunity for greener buildings to reduce their potential environmental impacts. 3.5. Import sources of materials and energy 3.5.1. Import sources of building materials As mentioned above, almost all building materials are imported from other countries and regions. Here, most of the non-metal materials (cements, including raw cements and clinker cements) and metal materials (steel) are taken as the typical materials from which to understand Macau's import sources, as shown in Fig. 10. It can be seen from Fig. 10(A) and (A’), that mainland China was the most significant import source of cements in 1999 and 2015, accounting for more than 90% of the total import volume. In 1999, Hong Kong was also an important import source of cements, contributing to about 7.87% of the imported cements. However, the imported cements from all other countries and regions, except

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mainland China, were less than 1% of the total imported cements in 2015. Similar to the case of cements, steel are also mainly imported from mainland China, accounting for about 67.71% in 1999 and 98.15% in 2015, respectively. The sources of imported steel in 1999 were more diversified, e.g. Hong Kong, Malaysia, Europe, Japan, and Taiwan were the important import sources. By 2015, the absolute majority of imported steel were coming from mainland China. As a Special Administrative Region of China, due to the relatively close distances and cheaper prices, Macau's largest import source of building materials and energy has become mainland China. All of these results indicate that since returning to mainland China, Macau has depended increasingly on mainland China. 3.5.2. Energy import Almost all kinds of energy in Macau are imported from other countries and regions. However, not all of the data regarding energy import over the years can be obtained, therefore we only present the newest data, as shown in Fig. 11. In comparison with the building material imports, it can be noticed that the sources of energy import are more diversified. According to Fig. 11 (A), it can be seen that common kerosene is mainly imported from Singapore, accounting for 54.18% of all imported volume, followed by the UK (30.95%) and mainland China (7.08%) in 2008. For diesel import, mainland China is the most significant import source (55.70%), and Singapore is also an important source (38.23%). When considering the import of oil gas, Saudi Arabia, mainland China, and United Arab Emirates are more important, accounting for about 43.42%, 26.70%, and 18.48%, respectively. In order to meet its soaring electricity requirements, Macau has purchased electricity from mainland China in ever-increasing quantities since 2005, and electricity

Fig. 10. Import sources of building materials in Macau: (A) Cements in 1999; (A0 ) Cements in 2015; (B) Steels in 1999; (B0 ) Steels in 2015.

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Fig. 11. Energy import sources in Macau: (A) Common kerosene in 2008; (B) Diesel in 2015; (C) Oil gas in 2015; (D) Electricity composition in 2015.

consumption has dominated since 2007. Unlike the previously discussed three types of energy, all of the imported electricity is from mainland China, and its import ratio reached up to 81.65% of all the electricity consumption in Macau in 2015. Currently, no import data for natural gas is published. 4. Discussion and policy implications Rapid economic development has sparked a high volume of construction activity, and combined with the population's increasing desire for comfortable housing and conditions in Macau, this challenges its energy security and the sustainable development of buildings. The lifecycle material and energy consumption of buildings is expected to play a significant role in realizing sustainable urban development in Macau. However, the ambiguous understanding of Macau's building material and energy consumption has impeded the effective promotion and implementation of attempts to improve its building material and energy efficiency. In Macau, the building material consumption has shown a fast increasing trend, with approximately 10 times growth during the period of 1999e2015. Due to the high ratios of buildings belonging to the gaming industry, the new buildings have a trend towards greater material consumption in addition to the use of rare and expensive materials. Thus, the building design and material selection will be essential for the development of sustainable buildings in Macau. Firstly, the building design must reduce the consumption of resources and improve the resource utilization efficiency (Poon et al., 2013), which will be the controlling factors regarding material consumption. In the selection of building materials, the total environmental impacts during production, influence towards total energy consumption in the use phase and its potential for recycling or reuse must be considered. The recycling potential of building materials can reduce their overall energy use and environmental

impacts (Song et al., 2013, 2015). Therefore, choosing green building materials with low initial environmental impacts and higher recycling potential will benefit sustainable urban buildings. Currently, the recycling facilities and the capacity for building waste in Macau is insufficient. Sorted steel can be recycled, but this represents less than 10% (by weight) of generated building waste. In addition, the direct disposal of waste in the sea has some potential environmental risks. The source separation of building waste and preventative measures regarding building waste disposal will be highly necessary for future building waste management and recycling. The effective use of energy in buildings is crucial due to the continually depleting energy resources, especially for countries or regions which are currently experiencing rapid economic and population growth, but lack the required energy resources. As shown in Fig. S4, the whole lifecycle energy consumption of buildings increased from 6249 TJ in 2000 to 20 510 TJ in 2016, and its contribution has also become the absolute majority of Macau's total final energy consumption, accounting for about 72.51% in 2016. This indicates that the energy-saving activities and policies in Macau should focus on the key points of buildings and related energy consumptions, especially during the building operation phase. The unit energy consumption of the building construction is much higher than that in mainland China, which implies that the energy efficiency needs to be further improved. In general, the use of residential buildings is often the primary source of energy consumption relative to the total building energy use in the world, e.g. 57% in the US; 86% in mainland China; 92% in India; 66% in Germany; 65% in France; and 75% in Russia, as reported in 2010 by the International Energy Agency (IEA, 2016b). However, the energy consumption of residential buildings in Macau only contributed about 34.70% in 2000, furthermore decreasing to 21.34% in 2016. This can be attributed to the prosperity of the gaming industry. It is

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noted that the buildings associated with the gaming industry are very luxurious, and their energy consumption is also very high. The 10 large gaming groups, including about 36 casinos in 2016, contribute to about 56.67% of the building energy use in Macau. In future, the building energy efficiency of the gaming industry could be a key point for energy saving. Within the building energy structure in Macau, the electricity consumption ratio to the total building energy consumption has exhibited the fastest growth from 79.41% in 2000 to 84.24% in 2016. A greater utilization of clean electricity will be essential for the energy sustainability of buildings in Macau. Currently, the electricity from Municipal Solid Waste (MSW) incineration plants in Macau would be a good choice. An MSW electricity plant, also known as a waste-to-energy plant, is designed to dispose of MSW and to produce electricity as a byproduct. The proportion of local electricity generated from waste incineration had increased to 23.6% in 2013. In addition, though a natural gas-fired power station with a capacity of 136.4 MW was introduced to Macau in 2002, its electricity production is still very small, even zero in some years, due to the shortage of natural gas. In order to address this problem, the Macau government could provide subsidies for natural gasfired electricity, and help to obtain more economical and reliable sources of natural gas. Almost all building materials and fossil energy has been sourced from other countries and regions into Macau to meet its soaring building requirements, which results in potential resource and energy safety risks. The recycling of building waste is the only way to ease the large dependences on building materials from other countries and regions. In future, the Macau government should encourage the environmentally sound management and recycling of building waste. Given Macau's dearth of indigenous fossil energy resources and high import dependences, it needs to turn its gaze toward renewable energy sources, especially solar, if it hopes to alleviate the pressure of energy shortages and realize the goal of a more energy-efficient city (Zambrana-Vasquez et al., 2015), yet this will not happen without government support. Even though the Office for the Development of the Energy Sector formulated its “Safety and installation regulations on solar grid-connected photovoltaic systems” in 2015, real progress in the use of solar energy has been slow. Additional encouragement, such as tax incentives, could be given to commercial investors for using solar power. Promoting improvements in building energy efficiency is considered to play an important role in achieving these targets, because it reduces energy consumption without curtailing social welfare (Kenichi et al., 2012; Alwan et al., 2017). Building energy standards and strategies are essential because of many invaluable benefits including ensuring the energy-efficient design and sustained operations of buildings. In the European Union's Energy Performance of Buildings Directive (EPBD), it is specified that by the end of 2020, all new buildings shall be “nearly zero energy buildings” (Sartori et al., 2012). In mainland China, the current standard (GB50189-2015) is less stringent, stating that the energy consumption of new public commercial buildings should be 75% of that of comparable buildings from the 1980s (Huang et al., 2016). The UK government revised Building Regulations in 2002, 2006, and 2010, towards higher energy efficiency standards with the ultimate target of “zero carbon” new homes from 2016 (Levinson, 2014; Pan and Garmston, 2012). However, the current policies on the construction of new buildings in Macau only include two policies: “Energysaving Commitments and Advice: Internal Guidelines for public sector” and “Techniques for Building-Energy Consumption Optimization in Macau”. The energy efficiency standards and policies of buildings have still not been drawn up. In future, the Macau government should also formulate detailed building energy-saving

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Table 7 Energy-unit consumption per economic value added. Year

2005

2009

2011

2013

Retail businesses (MJ/thousand MOP) Catering business (MJ/thousand MOP) Hotels (MJ/thousand MOP)

305.1 1430.8 1010.4

120.3 1030.8 552.8

70.3 402.2 519.6

41.9 282.2 528.6

policies and energy efficiency standards to promote sustainable buildings. As effective energy-saving measures, personal energy-saving behaviors in addition to those of commercial enterprises, such as purchasing green electronic products and developing energysaving habits, are a crucial driver of energy conservation for both residential buildings and business buildings in Macau. Simple changes in consumer behavior can quickly lead to significant energy savings, but such changes will only occur if people have an awareness of the degree of control which they have over their energy consumption. Currently, many cities and countries are identifying energy-saving awareness and behaviors as a top priority for sustainable energy consumption in urban settings(See Table 7).

5. Conclusions Understanding the current materials and energy consumption of buildings is a primary requirement for formulating successful sustainable management strategies. This paper characterizes the current status and trends of the overall lifecycle material and energy consumption of urban buildings in Macau: (1) The building lifecycle energy consumption in Macau increased from 6249 TJ to 20510 TJ over the period of 2000e2016 at an approximately 9% average annual growth rate. To control the rapidly increasing energy demand of buildings, a wide range of policies regarding building energy conservation and efficiency should be deployed. Particularly, the government can give economic incentives to ensure the effective implementation of building energy strategies. (2) The energy consumption of buildings during their lifecycles accounted for about 72.51% of the final energy consumption in Macau in 2016. The building sector is of great significance to the achievement of targets for energy conservation and emission reduction in Macau. A comprehensive and elaborate information system of building energy consumption is desirable for better understanding the components of energy consumption in addition to government decision-making related to building energy efficiency. (3) The unit materials and energy consumption for building construction in Macau are higher than those in mainland China, especially for energy consumption. Hence, it is imperative that the government enacts related policy and regulation to encourage green design and effective energysaving strategies during the construction process. (4) The energy consumption of building operation (92%) occupies a significant role in the building lifecycle energy use in Macau, still exhibiting fast increasing trends, especially within the gaming industry. Energy efficient policies and measures for the gaming industry and electrical appliances could be prioritized in order to reduce the operating energy consumption of buildings. (5) The recycling facilities and the capacity for building waste in Macau are far from sufficient. In future, more building waste management and recycling policies should be implemented,

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and the recycling and safe disposal of building waste should be paid more attention. (6) Currently, in order to ease the large energy dependences on other countries and regions, Macau needs to turn its gaze toward renewable energy sources, especially solar, if it hopes to alleviate the pressure of energy shortages and realize the goal of a more energy-efficient city. Considering the large contribution of electricity in the overall energy structure, cleaner forms of electricity (such as solar energy) will be a great opportunity for green buildings and reducing their potential environmental impacts. (7) Further research activities should include revealing the primary energy consumption sources in Macau, especially during the building operation stage, quantifying the environmental impacts (e.g. greenhouse gas emissions) resulting from the overall building lifecycle, and introducing green building concepts to promote eco-design in building construction, use, and waste recycling. Appendix A. Supplementary data Supplementary data related to this article can be found at https://doi.org/10.1016/j.jclepro.2018.05.148. References Aste, N., Adhikari, R.S., Buzzetti, M., 2010. Beyond the EPBD: the low energy residential settlement Borgo Solare. Appl. Energy 87, 629e642. Alwan, Z., Jones, P., Holgate, P., 2017. Strategic sustainable development in the UK construction industry, through the framework for strategic sustainable development, using Building Information Modelling. J. Clean. Prod. 140, 349e358. BECRC (Building energy conservation research center, Tsinghua University), 2016. Annual Report on China Building Energy Efficiency. China Architecture and Building Press. Cellura, M., Guarino, F., Longo, S., Mistretta, M., 2014. Energy life-cycle approach in Net zero energy buildings balance: operation and embodied energy of an Italian case study. Energy Build. 72, 371e381. Chen, Y., Ng, S.T., 2016. Factoring in embodied GHG emissions when assessing the environmental performance of building. Sustain. Cities Soc. 27, 244e252. Cubi, E., Doluweera, G., Bergerson, J., 2015. Incorporation of electricity GHG emissions intensity variability into building environmental assessment. Appl. Energy 159, 62e69. Duan, H., Wang, J., Huang, Q., 2015. Encouraging the environmentally sound management of C&D waste in China: an integrative review and research agenda. Renew. Sustain. Energy Rev. 43, 611e620. Duan, H., Yu, D., Zuo, J., Yang, B., Zhang, Y., Niu, Y., 2016. Characterization of brominated flame retardants in construction and demolition waste components: HBCD and PBDEs. Sci. Total Environ. 572, 77e85. DSEC, 2017a. Yearbook of Statistics 1999-2015. Macau Statistics and Census Service, Macau. DSEC, 2017b. Construction Sector Survey 2000-2015. Macau Statistics and Census Service, Macau. DSEC, 2017c. Construction Statistics 2000-2012. Macau Statistics and Census Service, Macau. DSEC, 2017d. Private Sector Construction and Real Estate Transactions 2000-2016. Macau Statistics and Census Service, Macau. DSEC, 2017e. Energy Statistics 2000-2016. Macau Statistics and Census Service, Macau. DSEC, 2017f. Macao External Merchandise Trade Statistics Database. Macau Statistics and Census Service, Macau. EPU, 2016. Macau environmental Status Reports 2007-2015. Environmental Protection Bureau of Macau, Macau. Fumo, N., 2014. A review on the basics of building energy estimation. Renew. Sustain. Energy Rev. 31, 53e60. Goggins, J., Moran, P., Armstrong, A., Hajdukiewicz, M., 2016. Lifecycle environmental and economic performance of nearly zero energy buildings (NZEB) in Ireland. Energy Build. 116, 622e637. Hellweg, S.I., Canals, L.M., 2014. Emerging approaches, challenges and opportunities in life cycle assessment. Science 344 (6188), 1109e1113. Hong, J., Shen, G.Q., Feng, Y., Lau, W.S.T., Mao, C., 2015. Greenhouse gas emissions

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