Design and supply system for emergency temporary housing by various construction methods from the perspective of environmental impact assessment: The case for the Great East Japan earthquake

Energy & Buildings 203 (2019) 109425

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Design and supply system for emergency temporary housing by various construction methods from the perspective of environmental impact assessment: The case for the Great East Japan earthquake Tsuyoshi Seike a,∗, Takayuki Isobe b, Yusuke Hosaka a, Yongsun Kim a, Shiro Watanabe c, Maito Shimura a a

Department of Socio-Cultural Environmental Studies, Graduate School of Frontier Sciences, The University of Tokyo, #621 Environ Bldg, Kashiwanoha 5-1-5, Kashiwa, Japan b Department of Environmental Systems Sciences, Faculty of Engineering, Musashino University, Ariake 3-3-3, Koto-ku, Tokyo, Japan c Housing Department, National Institute for Land and Infrastructure Management

a r t i c l e

i n f o

Article history: Received 4 August 2018 Revised 4 September 2019 Accepted 7 September 2019 Available online 8 September 2019 Keywords: Temporary housing Life Cycle Assessment (LCA) GHG emission Construction methods

a b s t r a c t Recently in Japan, a large number of emergency temporary housing (ETH) units have been supplied as great disasters occurred. In general, victims cannot use supplied ETH units for more than 2 years, as specified in the Disaster Relief Act. Nonetheless, some victims have used ETH for over 7 years, particularly after the Great East Japan earthquake (2011). ETH units were adopted with various construction methods such that ETH could be readily available after the earthquake. Today, there are various ETH supply systems, although it is generally accepted that supplying ETH units consumes large amounts of resources in a short time. The goal of this study is to clarify and quantify Greenhouse Gas (GHG) emissions from supplying ETH units using a life cycle assessment that considers the construction methods and usage life. The results indicate that for a usage time shorter than 2 years, GHG emissions are the lowest for steel frames with reused materials. For usage times longer than 5 years, GHG emissions are lowest for ETH units with high thermal performance. In summary, ETH usage time should be considered when choosing a suitable construction method for reducing GHG emission. © 2019 Elsevier B.V. All rights reserved.

1. Research background In recent years, extreme weather events have been occurring worldwide due to climate change. To address these changes, the Paris Climate Accord of 2015 set a limit on the emission of greenhouse gasses (GHG). A further level of commitment from all the nations is required [1]. Ikaga et al. reported that of all the industries in Japan, the construction industry contributed the highest percentage of total GHG emissions. The effectiveness of a lowcarbon policy is being investigated with the year 2050 as the goal [2]. The Japanese government has drafted a roadmap towards the adoption of Zero Energy Building (ZEB) and Zero Energy House (ZEH) plans to reduce GHG emissions. The adoption of the plans is making progress [3,4]. To quantitatively evaluate GHG emissions by region, a Life Cycle Assessment (LCA) evaluation is being de-

∗

Corresponding author. E-mail address: [email protected] (T. Seike).

https://doi.org/10.1016/j.enbuild.2019.109425 0378-7788/© 2019 Elsevier B.V. All rights reserved.

veloped for the construction sector. Under an international initiative, Annex 57 of the International Energy Agency (IEA) was established to develop a better understanding of evaluation methods and aid the interpretation of results on embodied energy and GHG emissions for buildings. Birgisdottir et al. (2017) analyzed the method for evaluating embodied energy and GHG emissions in many countries and showed that these vary. It is recommended that the definitions and formats of the system boundary, inventory, data quality, and other factors be unified [5]. In this way, the construction industry proceeds with the zero energy plans for reducing GHG emissions in order to mitigate climate change. LCA evaluation method for buildings are also being developed. Earthquakes occur frequently in Japan, there were some largescale disasters such as the 1995 Great Hanshin earthquake and the 2011 Great East Japan earthquake. Large-scale earthquakes cause significant damage to residential homes, making them uninhabitable. For these victims, ETH is provided in the wake of disasters under the guidance of the Japanese government and local

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T. Seike, T. Isobe and Y. Hosaka et al. / Energy & Buildings 203 (2019) 109425

authorities with cooperation from the Japan Prefabricated Construction Suppliers and Manufacturers Association (JPA). Such ETH is supplied mainly through manufacturers of prefabricated homes cooperated with the Standardized Architecture Committee (SAC) of JPA. In addition, the aforementioned manufacturers are major residential developers cooperated with the Housing Committee (HC) of the JPA and local contractors. The life span for ETH is set as two years under the Disaster Relief Act, which is a system designed to hasten the supply process for homes with an assumed short-term use. As its major feature, these homes use a wooden pile foundation typically not used in conventional homes. However, the ETH supplied by actors other than SAC used highly durable building materials, such as roof shingles and exterior wall siding, which were equivalent to the materials used for conventional housing. In addition, the structure soundness and thermal insulation quality were in compliance with the Building Standard Law and Act on Rationalizing Energy Use. Although, it is possible to extend the two-year period: After the 1995 Great Hanshin earthquake, the ETH units supplied were indeed extended to five years of use. In the case of the Great East Japan earthquake, approximately 10% of the ETH units were still in use in 2018, seven years after the disaster [6–8]. However, this is quite a short time frame compared with the 30 to 50 years of use intended for conventional normal homes. Therefore, the ETH units are assumed to have a large environmental load per year of use. The number of ETH units supplied after large-scale disaster in Japan was about 48,300 units for the 1995 Great Hanshin earthquake [9], about 53,0 0 0 units for the 2011 Great East Japan earthquake [10], and about 4300 units for the 2016 Kumamoto earthquake [11]. Thus, more than 10 0,0 0 0 ETH units were provided in total across Japan after large-scale disasters. As stated above, when Japan experiences a major natural disaster, ETH units are supplied in large numbers. In addition, these ETH units differ from conventional housing in that their period of use is shorter. Due to this, an ETH supply system that takes the characteristics of ETH into account when reducing GHG emissions could be necessary for future ETH supply. 2. Review of previous research Through LCA evaluation, this research determines the amount of GHG emissions for a typical Japanese ETH construction, for the purpose of suggesting supply methods with low GHG emissions. To this end, we have referred to related research on strategies to reduce GHG emissions from buildings, the construction characteristics of ETH, and research and surveys related to LCA for humanitarian construction. 2.1. Previous research on LCA for buildings Many studies have introduced strategies for reducing GHG emissions from buildings, both in Japan and abroad. Past studies conducted overseas include Lolli et al. who conducted LCA for GHG emission by evaluating the difference in insulation specifications of windows in apartments [12]. In addition, Kristjansdottir et al. (2017) conducted LCA for eight cases, including zero-emission buildings (ZEBs) and low-energy houses. Their results showed that the life-cycle of CO2 emissions from ZEBs was lower than those from other cases [13]. In China, Zhu et al. analyzed the reduction in energy consumption in prefabricated homes in northern and western China [14]. In Australia, Islam et al. conducted LCA and life-cycle cost (LCC) analysis for Australian homes by changing designs for the floor and the roof [15]. In Malaysia, Wen et al. performed comparative analysis of the environmental impact during the construction phase

of industrial homes and conventional homes in Iskandar, Malaysia [16]. In Turkey, Mangan et al. focused on the differences in performance of homes among areas with different weather classifications and made comparative validations of life-cycle energy and cost [17]. In Japan, Suzuki et al. conducted LCA for buildings [18]. Past studies on LCA for homes include the study by Okumura et al., who estimated CO2 emission for structural components of singlefamily homes [19]. Seike et al. conducted LCA for life-cycle carbon minus (LCCM) homes, which aims to reduce energy consumption throughout the life cycle to zero [20]. As demonstrated, the research on LCA evaluation for buildings in Japan and other countries shows that LCA evaluations are being performed on all types of buildings, from conventional buildings and housing to cutting edge housing such as LCCM.

2.2. Typical construction methods for ETH and LCA for humanitarian construction Past studies on ETH include those conducted from the perspective of ETH construction methods, energy consumption and LCA. With respect to the reusable of used building parts from post used ETH, Yoshiba et al. investigated three cases of reuse in Fukushima Prefecture, whereas Haganuma et al. investigated the reuse of log house-type ETH also in Fukushima; both studies revealed the current state and challenges in reusing the housing units [21,22]. Seike et al. analyzed cases of reuse upon the removal of ETH [23]. This research demonstrates that not using adhesives and reducing the number of components can make the components of wooden frame ETH easier to re-use, by reducing the damage to the components and minimizing disassembly work. On the other hand, Sato et al. conducted a study on the temperature monitoring for room in ETH, a discussion on energy consumption was not considered [24]. Outside of Japan, Hossini et al. conducted multi-criteria LCA on the differences across eight construction methods after the 2003 Bam earthquake in Iran [25]. Researching ETH supplied in Turkey, Atmaca et al. conducted LCA and showed that the energy consumption was significant during the operating phase [26]. On the other hand, Song et al. considered differences such as wall specifications in ETH supplied in Nanjing, China, and revealed differences in energy consumption and CO2 emissions throughout the life cycle [27]. The results reported that the construction phase comprises 65% of the life cycle energy. Escamilla et al. focused on local and global procurement of ETH in past disasters and analyzed the housing in terms of environmental impact and cost based on LCA and by technical performance [28]. Kuittinen performed LCA evaluations on shelters and ETH in various countries, including Japan and Indonesia, and indicated that GHG emissions should be considered even in ETH and shelter construction [29]. Thus, ETH units outside of Japan have been assessed by LCA to discuss their supply parameters. As previously mentioned, past studies have been conducted rebuilding and reuse methods of post used building parts and temperature monitoring for room in ETH. LCA of GHG by these ETH units has not been conducted thus far in Japan. Thus, measures for reducing the environmental load of ETH can only be discuss in the limited contents. To reduce environmental load of ETH, it is necessary to grasp and discuss the comprehensive environmental load of ETH from the construction stage to the end of life stage. Therefore, this study conducted LCA through the construction, operation, and end-of-life processes for ETH units to consider the supply system for such housing from the perspective of GHG. Based on the results, this study considers the design and supply system for ETH in Japan to reduce GHG.

T. Seike, T. Isobe and Y. Hosaka et al. / Energy & Buildings 203 (2019) 109425

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Table 1 Number of ETH units supplied by construction method (JPA, 2011 [10]; GAPW, 2012 [30]). Supplier

Construction method

Number of units supplied

Resource

Standardized Architecture Committee (SAC) Housing Committee (HC)

Steel frame Steel frame Wooden Subtotal Steel frame Wooden Subtotal

28,409 8040 6506 14,546 2978 6829 9807 52,762

[10] [10,30] [30] [10] [10,30] [30] [10] [10]

Local posting systems

Total

3. Research methodology LCA is widely used for many products and homes for quantitative understanding of the environmental impact over the life cycle from manufacturing to operation and disposal. As previously discussed, ETH is built by a variety of construction methods. In addition, its period of use is defined as two years under the Disaster Relief Act. Although some homes are removed within that timeframe, the reality is such that the period for many homes is extended beyond five years under the request of the disaster victims. Thus, the expected and actual use periods vary for many of ETH units. Therefore, this study performed LCA with respect to the differences in construction methods used to build ETH units as well as their period of use. Specifically, the assessment was performed for the two-year period defined under the Disaster Relief Act; five years, which was the actual use period after the Great Hanshin earthquake; and seven years, which assumes that the homes provided after the Great East Japan earthquake are still in use. The following sections discuss the LCA method used in this study.

3.1. Assessed homes LCA was performed for ETH units built after the Great East Japan earthquake under various construction methods. According to JPA (2011) data, 28,409 units of ETH were supplied to three prefectures in Iwate, Miyagi and Fukushima by SAC, 14,546 units were supplied by HC, and 9807 units were supplied by other systems [10]. The ETH units supplied by the JPA SAC adapted all lightweight steel frame prefab structures. Thus, the JPA supplied 28,409 steel frame units. The ETH supplied by the HC involved some construction methods: steel frame and wooden frame, panel, depending on the specifications of the housing manufacturer. According to data from the General corporate judicial person Association for Promotion of Wooden building (GAPW), there were 6506 units of wooden ETH supplied by JPA. This number of units supplied is the wooden ETH supplied by HC, so the wooden ETH supplied by HC is assumed to be 6506 units. The remaining 8040 units were steel frame ETH supplied by the HC [30]. Next, most other supply was done through the local posting systems. According to the same data, there were 9807 units of ETH supplied publicly by each prefecture [10]. The breakdown of housing units shows that of the 9807 units, 6829 units consisted of wooden structures. Of these, wooden frame ETH constituted the majority, although several small and medium local contractors contributed to the supply. Moreover, parts of the construction method differed for each contractor. Although there were partial differences, the wooden frame constructions were largely the same. Therefore, wooden frame ETH units supplied by major housing manufacturers affiliated with HC were constructed in larger numbers, and can be used to represent the most typical wooden frame ETH.

The above details are summarized in Table 1. Based on this number of units supplied, we shall identify both ETH resource input and landfill disposal volume after the Great East Japan Earthquake. As shown above, steel structures by the SAC under JPA, steel structures by the HC under JPA, and wooden structure by the HC were major construction methods for ETH, which accounted for 80% of the total ETH. These three construction methods were assessed in this study. Furthermore, according to data from the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) the floor plans of the houses built by the JPA, which supplied the majority of the ETH, are divided into three types, according to area. The respective percentages of each type against the number of units supplied are 14% (19.8 m2 ), 71% (29.7 m2 ), and 15% (39.6 m2 ) [31]. In light of this information, LCA was performed for a floor plan of 29.7 m2 , which is the most commonly used area for this ETH and is close to the average area of all types of the homes. This area is for a standard plan; the actual area of the built unit varies slightly according to the construction method. In addition the SAC 19.8 m2 and 39.6 m2 plans were designed based on changing the location of the party walls in the standard 29.7 m2 plan. The standard plan for ETH provided by the HC was 29.7 m2 . Some manufacturers provided ETH units with floor plans of 19.8 m2 and 39.6 m2 ; however, due to ETH regulations regarding floor plans the majority of suppliers only provided ETH units with floor plans of 29.7 m2 . Orders for each suppliers were collected, interviews were conducted with the manufactures, and resource inputs for ETH by each construction method were identified for ETH with a floor area of 29.7m2 under the three construction methods. To confirm the parts used for ETH units by each manufacture, we obtained data that show the floor plan, elevation plan, and quantity of components used from each manufacture. For the material input of each part, we gathered data from each manufacture as weight-based resource input data on purchase orders. We checked these resource input data, floor and elevation plans, and specifications; if we discovered any inconsistencies, we contacted the manufactures and recalculated the resource input. Using this process, the resource input data for each ETH was checked and estimated by us and the manufactures. An outline of the interview survey and the information gathered is shown in Table 2. A majority of materials procured for the construction of this ETH were from domestic manufacturers. Specifications of ETH is summarized and explained in Table 3. Fig. 1 also shows the floor plans. (1) Steel structure by the SAC under JPA Wooden piles are used for the foundation of a steel structure built by the SAC under JPA. The structure features a lightweight steel frame and a sandwich panel to insulate the exterior wall, in which urethane foam is sandwiched by sheets of steel. The interior finish uses decorative gypsum boards. Windows consist of aluminum sash and single glazing. Steel-based ETH by SAC was originally designed for construction site office, where major compo-

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T. Seike, T. Isobe and Y. Hosaka et al. / Energy & Buildings 203 (2019) 109425 Table 2 Survey outline and data obtained through survey.

Survey Date

Data Obtained

Steel frame/SAC

Steel frame/HC

29th Nov. 2016 5th Jan. 2017 6th Apr. 2018 Floor plan, elevation, specification, quantity by component type

7th Nov. 2016 15th Nov. 2016 28th Nov. 2016 Floor plan, elevation, specification, order quantity by component type

Wooden frame/HC 20th Oct. 2016 15th Dec. 2016 Floor plan, elevation, estimate sheet, specification, order quantity by component type

Table 3 Main specifications of ETH by each construction method.

CF sheet: Carbon fiber sheet, PB: Plaster board, GW: Glass wool, PS: Polystyrene, PU: Polyurethane, PE: Polyethylene, FRC: Fiber Reinforced Cement.

nents can be reused after the construction is finished. Based on the interviews with the manufacturers, apart from the interior materials and plastic thermal insulation foam filled under the floors, most of the materials can be re-used, with a re-use rate of 99% for steel components and 90% for wooden components. Overall, this construction method allows for a total of 75% of the mass of the resource input to be re-used. Therefore, ETH supplied after the Great

East Japan earthquake also uses reused components as a part of these homes. (2) Steel structure by the HC under JPA The foundation for steel frame ETH units by the HC under JPA consists of concrete pillar and a steel frame, and the structure uses lightweight steel frames. The exterior is finished using fiber-

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Fig. 1. General floor plan of ETH.

reinforced cement (FRC) siding, and a sheet of steel is used for the roof. The interior is finished with decorative gypsum boards. Plastic foam and glass wool are used as an insulating material. Windows consist of aluminum sash and double glazing. (3) Wooden structure by the HC under JPA The foundation for wooden ETH built by the HC under JPA uses wooden piles. The structure is mainly a wooden frame with 105 mm × 105 mm lumber. The exterior is finished with sheets of steel, and slate shingles are used for the roof. The interior is finished with decorative gypsum boards. Glass wool and cellulose fiber are used as insulating material. Windows consist of aluminum sash and double glazing. As a supplement, the foundation of each ETH is simple, and aims to provide ETH in a short construction period. Therefore, the resources input for foundation are fewer than those used in normal detached houses. The GHG emissions were estimated for the construction of ETH under each construction method using the data given above. However, supplied equipments were assumed as same items in this

study, because equipments for all ETH units were supplied as same specific. In addition, the SAC 19.8 m2 and 39.6 m2 plans were designed based on changing the location of the party walls in the standard 29.7 m2 plan. Therefore, the addition or subtraction of party walls in the 19.8 m2 and 39.6 m2 plans were calculated as part of the total resource input. 3.2. System boundary This research clarified the life cycle GHG emissions for each ETH, including the embodied CO2 emissions from product stage to end of life stage, and discussed how the results could be applied towards suggesting policies for reducing GHG emissions. The system boundary in this research is shown in Fig. 2. In the product stage, the GHG emissions required for the manufacture of construction material and the GHG emissions associated with raw material extraction are taken into account. In the construction stage, the use of heavy machinery at construction sites could not be verified in detail due to the upheaval caused by the disaster damage. Furthermore, most ETH were one-

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Fig. 2. Boundary of the system. Table 4 Cases of product and construction stage.

Type of floor plan Construction method Building materials Foundation

CASE1

CASE2

CASE3

CASE4

29.7 m2 Steel frame/SAC Not using reused materials Wooden pile

29.7 m2

29.7 m2 Steel frame/HC Not using reused materials Concrete pillar

29.7 m2 Wooden frame/HC Not using reused materials Wooden pile

Using reused materials Wooden pile

story temporary housing. Therefore, the rate of heavy machinery use during construction was low. Based on the above, this research concluded that most of the GHG emissions during the construction stage were related to the transport of the building materials. Therefore, only transport was evaluated. For the use stage, since the planned period of usage for the ETH was two years, even if it exceeded two years, repair work was generally not performed. Therefore, the major GHG emissions predicted for the use stage were from energy consumption for heating, ventilation, air conditioning, hot water, and lighting. End of life stage included transport, waste processing, and disposal between disassembly site and recycling factory or final disposal site. Although heavy machinery was used for some of the disassembly, majority of disassembly was performed manually by workers. Therefore, heavy machinery was excluded from this research. Certain processes were not included in the system boundaries for this research as shown above. However, more than 95% of the ETH life cycle GHG emissions reported in Kuittinen’s research were accounted for [29]. Therefore, the trends in GHG emissions for the ETH studied were sufficiently accounted for, even if they were on the system boundaries defined for this research. 3.3. GHG emission during product and construction stage Assessment of GHG released during product and construction stage was performed for ETH models built with a steel structure by the SAC under JPA, a steel structure by the HC, and a wooden structure by the HC. Given that reuse of components is possible for steel structures by the SAC, another model in which ETH is built with reused components during construction was also considered. We evaluated the standard 29.7 m2 plan for these four cases. Therefore, four cases were analyzed and are shown in Table 4. In addition, there are three types of floor plans for ETHs from the SAC: 19.8 m2 , 29.7 m2 and 39.6 m2 . We evaluated the ETHs provided by the SAC separately to understand the impact of the floor plans. Therefore, three cases were analyzed and are shown in Table 5. As a tool for LCA, a database relevant to LCA in Japan was classified into those developed from input–output tables and those developed by a cumulative method. Databases developed from an input–output table have a rough categorization of processes; de-

Table 5 Cases of product and construction stage per each floor plan of SAC. CASE1 Type of floor plan Construction method Building materials

CASE2

19.8 m2 29.7 m2 Steel frame/SAC Not using reused materials

CASE3 39.6 m2

tailed consideration of the processes is not possible. In contrast, although inventory data collection by a cumulative method requires time for assembling the data, it considers details of the processes. This study used an inventory database developed by a cumulative method for LCA in order to identify the environmental load of each type of ETH. In Japan, the National Institute of Advance Industrial Science and Technology has developed an inventory database, Inventory Database for Environmental Analysis (IDEA) ver. 2.2, is a hybrid of statistical and cumulative data [32]. IDEA is a database for environmental load associated with the process of manufacturing various products, based on LCA survey results on product manufacturing processes and statistical data related to energy consumption by Japanese industrial organizations. for data on some processes, the environmental load was obtained from data on physical quantities associated with the material composition in the input-output table, but the environmental load due to the ripple effect is not taken into consideration. Among these data, those on imported resources such as iron ore refer to representative process data from previous surveys. After considering the exporting countries, the power input entered into the database is divided proportionally according to the volume of trade with the exporting country and environmental load data are obtained using IEA data on the power consumption rate of each country [33]. These imports include marine transport. The power consumption rate for domestic products varies by area but the environmental load data are obtained by using the national average. In this research, most of the inventory data used were data related to building material manufacture. In IDEA, the boundaries for this inventory data include the period of building material manufacture and the resource mining boundary. Although the transport of iron ore, which is mostly imported from overseas, was included, some inputs did not include transport at the time of material procurement. However, the IDEA database indicates the quality of each item of inventory data, in addition to including

T. Seike, T. Isobe and Y. Hosaka et al. / Energy & Buildings 203 (2019) 109425

calculations for GHG emission inputs from energy used overseas. Thus, the database is compatible with ISO14044. It is also one of the most reliable domestically available databases in Japan. In addition, LCI databases such as Ecoinvent [34] and Gabi LCA databases [35], developed outside Japan, are also available. However, as they are foreign LCA databases, their accuracy has not been sufficiently verified for use in LCA evaluation in Japan. Due to the above reasons, it was determined that for LCA evaluation in Japan, using IDEA, would give the most accurate LCA evaluation results. Therefore, the LCA evaluation was performed using IDEA. Therefore, this study performed LCA using the primary unit of GHG in IDEA to identify the differences in GHG emission by the construction of ETH in Japan. The GHG emission is calculated by using the following Eq. (1):

PCk =

all  



Qk,i × Ei / Fk

(1)

i=1

where PCk,i is the GHG emission per m2 of floor area during the construction of an ETH unit k , Qk ,i is the resource input for construction component i needed to build k, and Ei is the GHG emission in manufacturing the construction component i, Fk is floor area of an ETH unit k. For some re-used items, washing and repairs were required. Reusable parts include steel pillars and beams; exterior panels; and parts such as substrate panels, which are associated with structures. In Japanese homes, the service life of these parts is 30 years or more. Therefore, repairs mainly consist of replacing the damaged parts with new parts. In other words, repairing reusable parts can be considered an input of new parts. As such, for the maximum case for reducing GHG emissions, we considered repairs to be unnecessary for all reusable parts and gave them a value of zero. Therefore, the embodied CO2 was set at zero, and only the GHG from the collection transport were considered. Most of the

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GHG of the collection is generated by transportation from the dismantling site to the manufacture plant. Due to this, the GHG emission of reused material was set the value of transportation from the manufacture plant to the construction site. In addition, interviews with supply contractors revealed that 99% of steel materials and 90% of wood materials could be re-used. Therefore, in case of re-use, the re-use rate for steel materials was set at 99%, while that of wood materials was set at 90%. Wood is considered to be a carbon stock during its period of use. However, since wood is burned on disposal in about 2 years to 7 years, the carbon stock of wood materials was not considered. GHG emission by transportation was considered as follows. Firstly, because the Great East Japan earthquake caused significant damage over a broad area, structural components for ETH were supplied from across the country. Material procurement by each contractor after the Great East Japan Earthquake was affected by post-disaster upheaval. Therefore, the details are not completely known. Each contractor surveyed had factories nationwide. The main manufacture plants were the SAC in Tochigi Prefecture and the HC in Ibaraki Prefecture. Therefore, it was assumed that the materials were shipped from these factories. However, since the materials for ETH construction were procured from locations across Japan, three transport conditions were set: material procurement from nearby areas, material procurement from major factories in Kanto, and material procurement from farther away. Transport distance for each case was set at 100 km for procurement from nearby, while for procurement from factories in Kanto, it was set at the actual distance from each factory to the construction sites. Cases of procurement from further away were set at the 10 0 0 km range, which includes the major industrial centers of Nagoya and Osaka, which were not damaged in the Great East Japan Earthquake. The transport conditions detailed above are shown in Fig. 3.

Fig. 3. Conditions for transportation during construction.

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The construction site was set as Kamaishi City in Iwate Prefecture because ETH was supplied from each actor considered in this study in Kamaishi. Furthermore, roads in many regions in Japan are narrow. Therefore, in many cases, the materials were transported to construction sites on trucks no larger than ten tons. Thus, for this research, the weight of trucks used for transportation was 10 ton. The primary unit for GHG was assumed to be 0.161 kg-CO2 eq/ton·km, which is the primary unit for GHG when an average load ratio defined in IDEA ver. 2.2 was transported by a 10-ton truck [32]. 3.4. GHG emission during the use stage Under the Building Energy Efficiency Act, energy consumption in Japanese architecture must be calculated as the primary energy consumption at the time of design by program for calculating primary energy consumption in house [36]. The calculation method is characterized by assuming an average home in Japan and calculates the consumption by taking inputs such as the performance of the exterior walls as well as the types and performance of equipment such as the heating and cooling system, water heater, ventilation and lighting. Therefore, GHG emission during the inhabitance in ETH was calculated by determining the primary energy consumption using this program [36]. Each input item was determined through design drawings and specification documents obtained from the contractors. Thermal performance was calculated as the thermal resistance by determining the specifications for the roof, walls, and floor from design drawings and specifications. Table 3 shows the specifications for the roof, exterior walls, party walls as well as the floor of each ETH unit. Table 6 shows the specifications and thermal resistance for insulation of ETH, and Table 7 shows the conditions for the living room and the input values for insulation for the primary energy consumption calculation program obtained from Table 6. The specifications were determined from documents on equipment. Air conditioners procured were small-scale room air conditioning units capable of both heating and cooling, with a rated output of 2.8 kW and an energy consumption rate of approximately 5.0. The air circulation equipment used small-scale propeller fans. Hot water heaters were small gas-powered units of 400 kcal/min capacity, intended for one-person households. Lighting equipment used fluorescent lighting. Setting conditions for the primary energy consumption calculation program were determined based on the above specifications. Table 8 shows the configured conditions for each equipment type. By using the obtained data shown above, four areas of climate classification for Kamaishi were selected to calculate the primary energy consumption through the computing program [36]. GHG emission was calculated by using the primary energy consumption and Eq. (2). Based on IDEA ver. 2.2, the GHG primary unit for power and gas were 162 kg-CO2 eq/GJ for power and 75 kg-CO2 eq/GJ for gas [32].

Uk = (Ehk × E + Eck × E + E vk × E + Ehwk × G + Elk × E + Eotk × E ) / Fk

(2) m2

where Uk is the GHG emission released per of floor area during one year of occupancy in an ETH unit k, Ehk is the primary energy consumption by the heating system in k, Eck is the primary energy consumption by the cooling system in k, Evk is the primary energy consumption by the ventilation system in k, Ehwk is the primary energy consumption by the water heating in k, Elk is the primary energy consumption by the lighting system in k, Eotk is the primary energy consumption by other appliances k, E is the GHG emission per GJ of electricity, G is the GHG emission per GJ of LPG, and Fk is floor area of an ETH unit k.

Gas was assumed to be used for water heating, whereas electricity was assumed to be used to operate space heating and cooling, ventilation, lighting, and other appliances in the calculation.

3.5. GHG emission at the end-of-life stage Ida et al. investigated the process at the end-of-life phase of an ETH unit [37]. Although some special cases have been reported such as reuse of the building, the ETH was treated in a manner similar to that for normal construction waste. Kobayashi et al. performed LCA for construction waste in Japan [38]. Using these two past studies as references, this study identified the GHG emission at the end-of-life phase of ETH units. This study performed LCA at the end-of-life phase of ETH units according to the construction method. For steel structures by SAC, two cases were developed. The first was concerned with a normal waste treatment method, and the second dealt with a reuse case given that structures and exterior wall panels in steel structures can be reused. LCA at the end-of-life phase for ETH is detailed below. As with the construction phase, the IDEA database was used for LCA. Table 9 shows the treatment method for recycling per material and the associated environmental load. If supplemented, steel and non-metals can be purchased as conventional valuables. Therefore, steel and non-metals were counted towards the production process for recycled goods, and the GHG emissions associated with this recycling included only the GHG from transport to an intermediate disposal facility. Using Q GIS ver. 2.1.8 [39], which is a geographic information system (GIS) provided under the GNU General Public License, and the location data for industrial waste disposal facilities, as provided by the Ministry of Land, Infrastructure and Transportation(MLIT) [40], the transportation distance was determined by the following method. Firstly, the distance from the construction sites to intermediate disposal facilities and landfills were considered to be the distance from the nearest facility to the construction site based on the waste disposal facility GIS data provided by MLIT [41]. The distance for scrap PVC was assumed to be the distance to the nearest facility with a recycling system operated by the Japan PVC Pipe and Fitting Association (JPPFA) [42]. Secondly, for thermally recycled items, transport from the interim processing facility to disposal at the thermal recycling facility was also necessary. Therefore, the distance to the nearest thermal recycling facility was added to the distance from the construction site to the intermediate disposal facility. Fig. 4 shows the conditions for transportation. The transportation distances are shown in Table 9. Transport trucks were set as large-scale trucks based on their transport efficiency. Thus, 10-ton trucks were selected to meet the transport conditions on Japanese roads. However, in some cases, 4-ton trucks were used if the amount of waste was small. For this, the evaluation of the 4-ton truck was performed concurrently. The primary unit for GHG was assumed to be 0.294 kg-CO2 eq/ton·km or 0.161 kg-CO2 eq/ton·km, which is the primary unit for GHG when an average load ratio defined in IDEA ver. 2.2 [32] was transported by 4-ton or 10-ton truck. By using the data above, the GHG emission at the end-of-life phase was assessed by Eq. (3):

E Lk =

all  



Qk,i × (Di + T Ri × T E ) / Fk

(3)

i=1

where ELk is the GHG emission per m2 of floor area at the endof-life phase for an ETH unit k , Qk ,i is the GHG emission of the construction component i generated by dismantling k, Di is the GHG primary unit for waste treatment for i, TRi is the transportation distance to the waste disposal facility for i, TE is the GHG pri-

Table 6 Specifications and thermal resistance based on insulating performance in each construction method. Window

Steel frame/SAC

Steel frame/HC

Wooden/HC

Door

Single glazing + Aluminum sash

Double glazing + Aluminum sash

Double glazing + Aluminum sash

Floor

Exterior wall

Party wall

Ceiling and roof

Metal door

Metal door

Material

Thickness (m)

TC (W/(m·k))

TR (m ·K/W)

Material

Thickness (m)

TC (W/(m·k))

TR (m ·K/W)

Material

Thickness (m)

TC (W/(m·k))

TR (m2 ·K/W)

Carpet Timber board Plastic foam (PS) Ris Ros Steel sheet

0.0019 0.004 0.05

0.08 0.16 0.028

0.19 0.16 0.04

0.35

0.00003 0.00124 0.00003

55 0.038 55

0.0343 0.00035 0.05 0.0095

0.038 55 0.05 0.22

0.90 0.00 1.00 0.04 0.11 0.04 0.10 1.00 0.10 0.11 0.11 0.00 0.13 0.07 2.22 0.04 0.09 0.04

Air GW 16kg PB

0.089 0.0095

0.07 0.045 0.22

0.07 1.98 0.04

0.012 0.1 0.0125

0.16 0.038 0.22

0.11 0.04 0.10 1.00 0.10 0.11 0.11 0.00 0.07 2.00 0.10

CF sheet Timber board Plastic foam (PS) Ris Ros Steel sheet Plastic foam (PU) Steel sheet Air Timber board GW 24kg PB Ris Ros PB GW 10kg PB Ris Ris Asphalt sheet Air Cellulose fiber PB

0.19 0.16 0.04

0.035

0.01 0.02 1.88 0.15 0.15 0.10

0.002 0.012 0.055

55

CF sheet Timber board Plastic foam (PS) Ris Ros FRC siding

0.002 0.0036 0.075

0.00035

0.02 0.03 1.79 0.15 0.15 0.00

0.022 0.100 0.022

0.22 0.038 0.22

0.002

0.11

0.120 0.022

0.040 0.22

0.01 0.08 1.38 0.15 0.15 0.00 0.90 0.00 0.07 0.08 2.63 0.06 0.11 0.04 0.10 2.63 0.10 0.11 0.11 0.02 0.07 3.00 0.10

0.09 0.04

Ris Ros

Plastic form (PU) Steel sheet GW 10kg PB Ris Ros PB GW 10kg PB Ris Ris Steel sheet Plastic foam (PE) Air GW 16kg PB Ris Ros

0.022 0.050 0.022

0.22 0.050 0.22

0.006 0.004

55 0.03

0.100 0.0095

0.045 0.22

2

Ris Ros PB GW 10kg PB Ris Ris Steel sheet Air GW 10kg PB Ris Ros

0.022 0.050 0.022

0.22 0.050 0.22

0.006

55

0.100 0.022

0.05 0.22

2

T. Seike, T. Isobe and Y. Hosaka et al. / Energy & Buildings 203 (2019) 109425

Metal door

0.09 0.04

CF sheet: Carbon fiber sheet, GW: Glass wool, PB: Plaster board, PE: Polyethylene, PS: Polystyrene, PU: Polyurethane, Ros: Outside surface resistance, Ris: Inside surface resistance, TC: Thermal Conductivity, TR: Thermal resistance, FRC: Fiber Reinforced Cement.

9

10

T. Seike, T. Isobe and Y. Hosaka et al. / Energy & Buildings 203 (2019) 109425 Table 7 Input data for insulation in each construction method.

Floor area Envelope Climate area UA (W/(m2 ·k)) ηac/ah Heat transmission coefficient (W/(m2 /k))

Steel frame/SAC

Steel frame/HC

Wooden/HC

Main habitable room 23.90 m2 Sum floor area 29.16 m2 Total area 110.27 m2 Zone 4 UA = 0.79 ηac = 1.6 ηah = 3.1 W:6.51 D:4.07 F:0.47 EW:0.48 PW:0.70 CR:0.38

Main habitable room 21.98 m2 Sum floor area 28.21 m2 Total area 114.22 m2 Zone 4 UA = 0.58 ηac = 1.4 ηah = 2.6 W:4.65 D:4.07 F:0.45 EW:0.44 PW:0.70 CR:0.45

Main habitable room 23.60 m2 Sum floor area 29.81 m2 Total area 112.66 m2 Zone 4 UA = 0.64 ηac = 1.8ηah = 3.4 W:4.65 D:4.07 F:0.57 EW:0.35 PW:0.32 CR:0.30

UA : Average outer shell heat transmission coefficient (W/(m2 ·k)), ηac/ah : Average solar heat gain coefficient during cooling/heating period, W:window. D:Door, F:Floor, EW:Exterior wall, PW:Party wall, CR:Ceiling and roof. Table 8 Configured conditions for equipment by construction method. Types of equipment Heating and Cooling Main/Other habitable room area Ventilation

Hot water

Lighting Main/Other habitable room area

Heating and Cooling mode Type of heating/cooling equipment radiator

Heat and cool only habitable room Room air conditioner

Adaptation of energy saving technique Select type of ventilation Air change Adaptation of energy saving technique Hot water supply Types of hot water heater Type of heat source for hot water Type of bath function Installed/not installed Install incandescent lamps Distributed multiple-light arrangement Dimming control

Not adopted Wall – mounted exhaust only ventilation unit 0.5 air change per year Not adapted Hot water supply with bathroom Water heater specifically designed for hot water supply Gas water heater Water heater for bath (with reheating) Installed Using instead of incandescent lamp in all equipment Not adapted Not adapted

Table 9 Recycling methods of each construction material. Material

Methods

kg-CO2 eq/kg

Distance(km)

Source

Wood Plaster board Glass Plastic foam PVC Other plastics FRC Glass wool Steel Non – Ferrous metals Equipment Other materials

Chip and Thermal recycling Material recycling Landfill Thermal Recycling Material recycling(Crushing) Thermal Recycling Landfill Landfill Scrap Recycling Scrap Recycling Material recycling (Separating and crushing) Landfill

0.029 0.001 0.007 2.704 0.063 2.704 0.007 0.007 0.000 0.000 0.096 0.007

27+9km 27km 29km 27+9km 27+53km 27+9km 29km 29km 27km 27km 27km 27+9km

IDEA ver. 2.2 [32] Kobayashi et al. [38] IDEA ver. 2.2 [32] IDEA ver. 2.2 [32] IDEA ver. 2.2 [32] IDEA ver. 2.2 [32] IDEA ver. 2.2 [32] IDEA ver. 2.2 [32] – – IDEA ver. 2.2 [32] IDEA ver. 2.2 [32]

mary unit for transportation to the waste disposal facility (kg-CO2 eq/ton·km) and Fk is floor area of an ETH unit k. 3.6. Assessment of GHG emission over the entire life cycle for ETH Fig. 5 shows a diagram for the assessment of GHG emission across the life cycle of ETH. These values were determined by evaluating the emissions over the product, construction, use, and endof-life stage. GHG emission in "1) production and construction stage" was calculated from material inputs and transportation distances for ETH according to the construction method. GHG emission in "2) use stage" was calculated from external walls and the performance of equipment in ETH according to the construction method. The period of use was assumed to be two years, as defined by the Disaster Relief Act; five years, which is the maximum extension applied for homes built after the Great Hanshin earthquake; or seven years for homes built after the Great East Japan earthquake and currently remain in use. GHG emission in "3) end-of-life stage" was

calculated from emissions by the construction material and transportation distance for ETH according to the construction method. GHG emissions across the entire life cycle of ETH were determined by adding GHG emissions for product and construction, use, and end-of-life processes. Eq. (4) shows the calculation method for ETH according to the construction method:

LCGHGk = PCk + Uk × T + ELk

(4)

where LCGHGk is the GHG emission per m2 of floor area across the entire life cycle of an ETH unit k; PCk is the GHG emission during product and construction of k; Uk is the GHG emission during the use of k over one year; T is the period of use from 1 to 7 years; and ELk is the GHG emission for the end-of-life stage of k. The supply system for ETH in Japan is subsequently discussed on the basis of the results. In addition to the Japanese domestic LCA evaluation database discussed above, a program was also used to calculate the energy consumed in transport. Therefore, the LCA evaluation results obtained by this research reflect the GHG emis-

T. Seike, T. Isobe and Y. Hosaka et al. / Energy & Buildings 203 (2019) 109425

11

Fig. 4. Transportation conditions for the end-of-life stage.

Fig. 5. Diagram of GHG emission involving all life cycle processes.

sions from the energy consumed in Japanese manufacturing to the highest degree possible. 4. Results 4.1. GHG emission during product and construction GHG emission during the product and construction of ETH was calculated according to the construction method. For steel structures by SAC, where three floor plans and some components are reusable, four cases were assumed. The three cases in the four assumed cases of each construction method exclusively used new components, and the fourth case used reused components for the frame and exterior walls. Therefore, normal steel structures by SAC, steel structures with reused components by SAC, steel structures by HC, and wooden structures by HC were considered for a total of four cases. Fig. 6 and Table 10 show the resource inputs and GHG emissions for these cases. The results of each case are described below.

The GHG emission for normal steel structures of 29.7 m2 type by SAC was 330 kg-CO2 eq/m2 , which is nearly equal to that of the steel structures by HC. The breakdown of the GHG emission showed that plastic foam was the greatest contributor to the emission followed by steel. The former is attributed to the use of insulating material for exterior walls using plastic foam, which has a significant GHG emission during its manufacturing. PVC was another significant contributor to the emission compared with other construction methods because of its major use in interior materials such as flooring. GHG emission for steel-structured ETH units by SAC with reused components was 153 kg-CO2 eq/m2 , which is approximately 45% that of the results of normal steel structures by SAC using all new materials. Steel was the major contributor to this reduction, owing to the reuse of steel components such as pillars and beams in the frame and to the steel sandwich panels. In steel structures by HC, GHG emission was significant for steel used for components such as the structural frame. In particular, steel accounted for half of the GHG emission in

12

T. Seike, T. Isobe and Y. Hosaka et al. / Energy & Buildings 203 (2019) 109425

Fig. 6. Resource input and GHG emissions for ETH (29.7 m2 type) per each construction method.

Table 10 Resource input and GHG emissions for ETH (29.7 m2 type) per each construction method. Construction method

Steel frame/SAC

Steel frame/SAC with reused materials

Steel frame/HC

Floor plan

29.7 m2

29.7 m2

29.7 m2

2

2

2

2

29.7 m2

Unit

(kg/m )

(kg-CO2 eq/m )

(kg/m )

(kg-CO2 eq/m )

(kg/m )

(kg-CO2 eq/m )

(kg/m2 )

Wood Plaster board Glass Plastic foam PVC Other plastics FRC Glass wool Steel Non-ferrous metal Equipment Other Reused materials Actual plant Transport Actual plant Total

22 5 1 17 7 1 0 0 54 1 11 2 – – 123

9 2 2 123 31 5 0 1 98 13 37 1 – 8 330

2 5 0 15 1 1 0 0 3 0 11 2 82 – 123

2 2 0 83 6 5 0 0 5 0 37 1 5 8 153

24 42 1 2 1 2 7 2 85 5 12 2 – – 185

18 13 2 8 3 9 34 6 166 44 39 7 – 11 362

111 37 4 5 2 1 0 7 4 4 11 23 – – 209

ETH by HC. However, steel structures by HC used glass wool as the main insulator, which resulted in a lower GHG emission by plastics compared with other construction methods. The GHG emission was highest for this construction method, at 362 kg-CO2 eq/m2 . GHG emission for wooden structures by HC was 299 kg-CO2 eq/m2 . That for lumber used in structures was not significant and made up only 10% of the total. Plastic was the greatest contributor to GHG emission, accounting for 30% of the total. This occurred because the plastic foam used as the insulator releases a significant amount of GHG during its manufacturing. The next largest contributor was nonferrous metal, including aluminum used in the sash windows. Subsequently, the resource inputs and GHG emissions for the ETH per square meter for each SAC floor plan is shown in Fig. 7, Table 11. The GHG emission for normal steel structures of 29.7 m2 type by SAC was 330 kg-CO2 eq/m2 , which is nearly equal to that of the steel structures by HC. under other floor types, GHG emission for

2

Wooden frame/HC

2

(kg-CO2 eq/m2 ) 36 12 6 96 9 2 0 20 8 49 37 13 – 12 299

19.8 m2 type of ETH was 350 kg-CO2 eq/m2 and 39.6 m2 type of ETH was 320 kg-CO2 eq/m2 . The smaller the floor area, the higher the amount of GHG emissions per square meter at the time of construction. On the flip side, the larger the floor area, the smaller the GHG emissions per square meter at the time of construction. This is because the percentage of housing area accounted for by the equipments has a large impact. Namely, the smaller the floor area, the larger the ratio of housing space present in the equipments, while the larger the floor area, the smaller the ratio of housing space present in the equipments. However, the scope of this is limited, with the impact peaking at approximately 5%. Next, since there is a variation in the distance that each ETH must be transported before construction, we assumed 100 km to be the minimum and 10 0 0 km as the maximum distance to understand the impact of this variable. The results are shown in Fig. 8 and Table 12. When it was assumed that the transportation distance was 100 km, which is shorter than the actual distance to the plant, GHG

T. Seike, T. Isobe and Y. Hosaka et al. / Energy & Buildings 203 (2019) 109425

13

Table 11 Resource input and GHG emissions for ETH per each floor plan of SAC. Construction method

Steel frame/SAC

Floor plan

19.8 m2

Unit

(kg/m2 )

(kg-CO2 eq/m2 )

(kg/m2 )

(kg-CO2 eq/m2 )

(kg/m2 )

(kg-CO2 eq/m2 )

Wood Plaster board Glass Plastic foam PVC Other plastics FRC Glass wool Steel Non-ferrous metal Equipment Other Transport Actual plant Total

23 6 1 17 7 1 0 0 54 1 17 2 – 130

10 2 2 123 31 5 0 1 98 13 56 1 8 350

22 5 1 17 7 1 0 0 54 1 11 2 – 123

9 2 2 123 31 5 0 1 98 13 37 1 8 330

22 4 1 17 7 1 0 0 54 1 8 2 – 120

9 2 2 123 31 5 0 1 98 13 28 1 8 320

29.7 m2

39.6 m2

Fig. 7. Resource input and GHG emissions for ETH per each floor plan of SAC.

Fig. 8. GHG emissions for each transport for each ETH (29.7 m2 type).

287 34 321 351 30 381 153 20 173 29.7 m2 (kg-CO2 eq/m2 ) 322 322 2 8 324 330 Floor plan Unit Products Transport Total

322 20 342

Actual plant

29.7 m2 (kg-CO2 eq/m2 ) 287 287 3 12 290 299

Wooden frame/HC

100km Actual plant

10 0 0km Steel frame/HC

100km 10 0 0km Actual plant

Steel frame/SAC with reused materials

100km 10 0 0km 100km transportation distance

Actual plant

Steel frame/SAC Construction method

Table 12 Resource input and GHG emissions for ETH per each construction method.

emissions associated with the transportation/construction of ETH decreased, to about 1% of the product. On the other hand, when the distance was 10 0 0 km, GHG associated with transportation increased to about 5% of the product. However, if the materials were procured domestically, GHG associated with transportation was not high relative to the total GHG emissions associated with the construction of ETH.

4.2. GHG emission during use stage

29.7 m2 (kg-CO2 eq/m2 ) 351 351 3 11 354 362

10 0 0km

T. Seike, T. Isobe and Y. Hosaka et al. / Energy & Buildings 203 (2019) 109425

29.7 m2 (kg-CO2 eq/m2 ) 141 145 3 8 144 153

14

Fig. 9 and Table 13 show the GHG emissions during the use stage of ETH units according to the construction method. According to the computing program for primary energy consumption, GHG emission during the use stage according to the construction method was 214 kg-CO2 eq/m2 ·year to 251 kg-CO2 eq/m2 ·year, where the difference in GHG emission from primary energy consumption by home specifications varied by about 10%. Space heating was the greatest contributor to the GHG emission followed by hot water and lighting. A significant difference was also observed for GHG emission by heating owing to differences in insulation performance in the exterior wall. The GHG emission by other appliance was essentially the same.

4.3. GHG emission during the end-of-life stage Fig. 10 and Table 14 show the GHG emission during the endof-life stage of ETH units according to the construction method. GHG emission owing to the disposal of plastics was significant in steel structures by both SAC and HC. GHG emission was also lower by approximately 10% when the frame and exterior walls were reused compared with that using only new materials. In the case of wooden structures by HC, disposal of lumber and plastics contributed significantly to GHG emission. The load by transportation was not as high as that from the end-of-life stage. Glass, glass wool, and plaster board are products that constitute specific amounts of resource investment in addition to the main structure. However, their disposal does not involve incineration. Due to this, the GHG emission input units are between 1/500th and 1/1000th of that required for disposal by incineration of plastic form or plastic. Therefore, the GHG emission value associated with the disposal of each material was extremely small.

4.4. GHG emission across entire life cycle Fig. 11 shows the evaluation results for GHG emission across the entire life cycle of ETH units according to the construction method, and Table 15 shows the results for ETH periods of two, five, and seven years. Fig. 12 shows the change in GHG emission across the entire life cycle from construction to the end of the seventh year of use for ETH according to the construction method. The impact of reusable components in steel structures by SAC during construction was relatively large, so following four types of construction method were analyzed; normal steel structures by SAC, steel structures featuring reused components by SAC, steel structures by HC, and wooden structures by HC. One factor relating to this is that GHG emissions from the use of the ETH is 80% to 90% of the total. This means that the use phase has a high GHG emissions factor compared to others. This shows that using the SAC-provided ETHs led to high GHG emissions. The impact

T. Seike, T. Isobe and Y. Hosaka et al. / Energy & Buildings 203 (2019) 109425

15

Table 13 GHG emission during annual use stage for ETH (29.7 m2 type) according to construction method. Resource

Space heating Space cooling Ventilation Hot water Lighting Other appliances Total

Electricity Electricity Electricity LPG Electricity Electricity

Steel frame/SAC

Steel frame/HC

Wooden frame/HC

(MJ/m2 ·year)

(kg-CO2 eq/m2 ·year)

(MJ/m2 ·year)

(kg-CO2 eq/m2 ·year)

(MJ/m2 ·year)

(kg-CO2 eq/m2 ·year)

838 34 37 407 44 411 1771

136 5 6 31 7 66 251

606 37 37 407 44 411 1542

98 6 6 31 7 66 214

630 44 37 407 44 411 1572

102 7 6 31 7 66 219

Fig. 9. GHG emissions during annual use stage of ETH (29.7 m2 type) according to construction method.

Fig. 10. GHG emission during the end-of-life stage of ETH (29.7 m2 type) according to construction method.

16

T. Seike, T. Isobe and Y. Hosaka et al. / Energy & Buildings 203 (2019) 109425 Table 14 GHG emission during the end-of-life stage of ETH (29.7 m2 type) according to construction method. Steel frame/SAC

Wood Plaster board Glass Plastic foam PVC Other plastics FRC Glass wool Steel Non-ferrous metals Equipment Other Transport 10-ton truck 4-ton truck Total 10-ton truck 4-ton truck

Usual case (kg-CO2 eq/m2 )

Reuse case (kg-CO2 eq/m2 )

0.8 0.0 0.0 51.4 1.3 3.4 – 0.0 0.0 0.0 1.1 0.0 0.5 0.9 58.5 58.9

0.7 0.0 0.0 45.8 0.1 3.3 – 0.0 0.0 0.0 1.1 0.0 0.5 0.9 51.5 52.0

Steel frame/HC

Wooden frame/HC

(kg-CO2 eq/m2 )

(kg-CO2 eq/m2 )

0.8 0.0 0.0 5.0 0.1 5.4 0.0 0.0 0.0 0.0 1.1 0.0 0.8 1.5 13.5 14.1

4.0 0.0 0.0 13.7 0.4 1.5 – 0.1 0.0 0.0 1.1 0.2 1.2 2.1 22.2 23.1

※ - : none.

Fig. 11. GHG emission across the entire life cycle for ETH (29.7 m2 type) according to the construction method.

of reused components in steel structures by SAC at the end-oflife phase was relatively small and was therefore not considered here. GHG emission during product and construction, at 145 kg-CO2 eq/m2 was the lowest in steel-based ETH units by SAC that used reusable components. Other ETH yielded a nearly equal level of GHG emissions. The results show that GHG emission during the use stage was high, considering the period of use. Steel-based ETH units by SAC using reusable components, which reduced GHG emission during product and construction, yielded a higher GHG emission than steel and wooden ETH units by HC during the fifth year.

During the second year, which is the limit set by law, normal steel structures, with exclusively new materials, by SAC had the highest GHG emission followed by steel structures by HC, wooden structures by HC, and steel structures by SAC using reused components. During the fifth year, GHG emission was the highest for normal steel structures, with exclusively new materials, by SAC followed by steel structures by SAC using reused components, steel structures by HC, and wooden structures by HC. After the fifth year, it does not change order in GHG emission was observed among ETH units according to the construction method.

T. Seike, T. Isobe and Y. Hosaka et al. / Energy & Buildings 203 (2019) 109425

17

1856 1875 1970

1

1417

1

1447

2148

1 1 1

21 13

1

21 13 58

1096 1071

58

1534 1500 1759

12

1759

12 11 8

287

11

8

1468 760 804

1645

1 1 1

1

58 21 13

58

1257 438 429

1257

8 12 11

8

Space heating occupied the greatest ratio of the GHG emission during the use stage followed by hot water and lighting. GHG emission by heating was the largest because Kamaishi City, where the buildings analyzed by this study were located, is situated in northern Japan at latitude N 39°16 33 . The average temperature during the coldest time of the year is 0.8 °C. Therefore cool conditions of the area contributed to the results. The differences in GHG emission during the use stage of ETH units according to the construction method showed a large difference in energy consumption by heating owing to differences in specifications for insulation among the units. Thus, the insulation performance needs to be improved to reduce GHG emission during the use stage.

S: steel frame, W: wooden frame.

S/HC

351 145

S/SAC with reused material

287 351

S/SAC W/HC S/HC S/SAC with reused material

145 322 287 351

S/SAC W/HC S/HC

145

8

503

58

1

714

8

503

58

1

891

S/SAC with reused material

GHG emission for the product and construction stage of ETH was relatively small for wooden structures by HC at 299 kg-CO2 eq/m2 . The level was highest for steel structures by the HC at 362 kg-CO2 eq/m2 . GHG emission for steel structures by SAC in a normal case was 330 kg-CO2 eq/m2 , which is nearly equivalent to the level released for steel structures by HC. In this way, the GHG emission trends for ETH constructed by various methods can be assessed. However, discrepancies were found from the input units for each construction material reported in the research by Kobayashi et al. [43]. Therefore, it must be noted that within the scale of the results obtained by this research, smaller or larger values may be substituted. The results show that GHG emission was lower for wooden ETH than for steel-based units when the components used for the construction were entirely new. On the other hand, some components can be reused for steel structure ETH by SAC; in such a case, the GHG emission was 153 kg-CO2 eq/m2 . This result shows that the reuse case reduced GHG emission by 45% compared with steel structures by SAC in which all components were new. These results indicate differences in GHG emission during the product and construction stage between steel and wooden structures. Additionally, GHG emission was reduced significantly during the product and construction stage by using reused components.

5.3. End-of-life stage

322

S/SAC

5.1. Product and construction stage

5.2. Use stage

Product and construction (kg-CO2 eq/m2 ) Transport: actual plant (Construction) (kg-CO2 eq/m2 ) Use (kg-CO2 eq/m2 ) End-of-life (kg-CO2 eq/m2 ) Transport: 10-ton truck (End-of-life) (kg-CO2 eq/m2 ) Total (kg-CO2 eq/m2 )

7 years 5 years 2 years

Table 15 GHG emission across the entire life cycle for ETH (29.7 m2 type) according to the construction method.

322

W/HC

5. Discussion

GHG emission during the end-of-life stage was the highest for steel structures by SAC. This occurred because a certain amount of plastic foams is used inside the panels, which produces a large amount of GHG emission when they are incinerated during the waste disposal phase. However, these plastic foams are also inside panels that can be reused, and GHG emission can be reduced by roughly 10% through reuse. However, such an impact may be limited.

5.4. GHG emission across the entire life cycle Figs. 13 and 14 show the ratio of GHG emissions during “product and construction stage” and “use stage”, respectively, in emission across the entire life cycle of ETH. GHG emission during the product and construction of ETH covered 20% to 50% of the total when the period of use was two years, as defined by the law. Therefore, GHG emission across the entire life cycle was the lowest for steel structures by SAC using reused

18

T. Seike, T. Isobe and Y. Hosaka et al. / Energy & Buildings 203 (2019) 109425

Fig. 12. LCGHG emission across the entire life cycle of ETH (29.7 m2 type) according to construction method.

Fig. 13. Ratio of GHG emission during the product and construction stage against emission across the entire life cycle of ETH (29.7 m2 type).

components, which releases the lowest amount of GHGs. On the other hand, GHG emission during the use stage covered 75% to 85% of the entire life cycle when the period of use was five years, which resulted in lower GHG emission across the life cycle for steel and wooden structures by HC compared with that for steel structures by SAC. A large part of this result can be attributed to differences in GHG emission during the use stage caused by the performance of the insulation. These results indicate that the period of use needs to be considered to realize lower GHG emission when supplying ETH units.

If ETH is to be used for two years, as defined by the Disaster Relief Act, the use of reused components is important for reducing GHG emission across the entire life cycle of the unit. GHG emission during the product and construction stage is a significant factor. Next, if ETH is to be used beyond the period defined by law for five years or longer, supplying emergency units that consider GHG emission during the use stage is important. The use stage occupies a large ratio of the emission across the entire life cycle of the unit; therefore, measures such as improvements in insulation performance are necessary to lower the emission rate.

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Fig. 14. Ratio of GHG emission during the use stage against emission across the entire life cycle of ETH (29.7 m2 type).

6. Conclusion

Supplementary materials

Future approaches to ETH supplied after the disastrous earthquakes were organized in the study from an environmental impact based on the results of LCA for the ETH units supplied after the Great East Japan earthquake. The ratio of GHG emission of ETH for the use stage is smaller in terms of the life cycle when the ETH is used for two years as defined by the Disaster Relief Act. Therefore, the results indicate that the emission can be suppressed to a low level by supplying ETH units built with reused components. On the other hand, ETH is often used for periods longer than five years in the recent disasters. Therefore, GHG emission during the use stage would account for a significant portion of the emission across the entire life cycle. Insulation performance is a significant factor. Therefore, when suppression of GHG emission during the use stage is considered, it is more desirable to supply ETH units with superior insulation performance than those in which reused components are used in case long-term use is required. Considering the supply system for ETH with a small environmental load across the entire life cycle of the home, the construction method that minimizes GHG emission across the entire life cycle for ETH is different between cases in which the homes are used for two and five years. As a recommendation for future supply of environmentally friendly ETH, units that minimize the overall environmental load can be supplied by determining the properties of each construction method for such housing and by establishing a system in which such homes can be supplied by classification of less than two years and more than five years of use.

Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.enbuild.2019.109425.

Acknowledgment The authors would like to thank all who assisted in the survey for this study. This work was supported by JSPS KAKENHI grant number JP15K14081.

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