Life Cycle Ecological Footprint Reduction for a Tropical Building

Rapid urbanization signicantly impacts natural resource demands and waste management in the construction sector. In this study, a novel methodology has been developed that could assess the overall environmental impact of a building during its lifespan by considering resources such as building materials, energy use, emissions, water, manpower, and wastes. e proposed method can estimate the life cycle ecological footprint (EFT) of a building. e result indicates that 957.07 global hectares (gha) of bioproductive land are required during the lifespan of the case building. e CO2 absorption land is the most signicant bioproductive land in the EFT of the building. e low environmental impact of building materials may reduce the ecological footprint (EF) of buildings, and using renewable energy can also reduce the operational EF of a building. e proposed building materials and solar PV systems have the potential to reduce the building’s life cycle environmental impact by up to two-thirds.e EF assessment of all existing and proposed buildings may be examined in order to execute strategies for a sustainable construction sector.


Introduction
Rapid urbanization in uences natural resource demand and energy use as well as greenhouse gas (GHG) emissions [1,2]. e construction industry is accountable for 40% of the global materials demand [3], 32% of the global energy consumption, and 19% of the global energy-related GHG emissions [4]. e Indian construction industry is expected to grow annually at 5.6% during 2016-20, and it may grow annually up to 7.1% by 2025 [5]. However, one-quarter of the total consumed primary energy and one-third of the total generated electricity are consumed in Indian buildings [6,7].
In the entire lifespan of a building, energy, construction materials, manpower, construction and demolition (C&D) waste, water, transportation, and GHG emission are considered to be the major factors that have an ecological impact [8][9][10][11]. Many studies on life cycle energy [12,13], emissions [14], C&D waste [15], transportation [16], and water consumption [17] in buildings have been reported. e estimated material use in India is projected to be nearly 15 billion tonnes by 2030, and it will further increase up to 25 billion tonnes by 2050 [18], while total C&D waste generated in the country in 2015 was about 716 million tonnes [19]. Bardhan analyzed that the building material production and building construction phase required water up to 27 kilolitres/m 2 of the oor area [17]. Waste is generated in every phase of the building, while the maximum C&D waste is generated when the building is demolished [15]. e energy consumption and CO 2 emissions by the transportation of building materials and C&D waste are signi cantly low as compared to the total life cycle energy consumption and emissions of the building [16]. Ding examined the energy consumption pattern during the di erent life stages of case study buildings; the study suggested that the operational phase and the construction phase of the building are responsible for 62% and 38% of the total life cycle energy consumption, respectively [20]. Suresh et al. assessed that the total annual GHG emissions of TERI University, Delhi, is approximately 0.72 tCO 2e per capita of the campus [21]. us, the building sector has the potential to achieve local and global environmental objectives (i.e., United Nations, Sustainable Development Goals) [22].

Ecological Footprint (EF).
e EF indicator can measure the rate of resource consumption and waste generation, and it compares with the resource production and waste assimilation rate of the planet [23]. e indicator comprises all resources/activities as input and converts them into a single output (i.e., global hectare) unit. e unit of EF is defined as "One global hectare (gha) is equivalent to one hectare of bioproductive land with world average productivity" [24].
Only a few studies have been reported for the EF assessment of buildings [25][26][27][28][29][30]. Kumar et al. reported that the life cycle ecological footprint of the Indian houses is in the range of 242-401 gha [25]. Jiaying and Xianguo examined the eco-efficiency and eco-footprint of a building; however, various assumptions such as demolition energy factors and construction, and destruction time of building are considered to estimate the environmental impact of each phase of the building [26]. Lui et al. reported that the life cycle ecological footprint of the multi-layer residential building is 0.859 ghm 2 [27]. Martínez-Rocamora et al. examined the annual EF of the Hernando Colón Hall of Residence is about 79.4 gha, while the maximum contributor was carbon absorption land (96.6% of the total bioproductive land) [28]. Gottlieb et al. had estimated that the EF of a selected school building is about 314 gha per year; the school building annually consumed bioproductive land of 160 folds of the total constructed area of the building [29]. Husain and Prakash reported the annual ecological footprint of a tropical building as 73.8 gha (i.e., the consumed bioproductive land was nearly 101 folds of the total constructed area of the case building [30].

Research Gap.
Various studies attempt to evaluate the environmental impact of buildings, considering energy [7], emissions [21], or a combination of such factors [31]. Some studies also used the ecological footprint indicator to estimate the environmental impact of the entire building's lifespan [26,30]. However, all the input resources (see Figure 1) have not been measured simultaneously to evaluate the life cycle ecological footprint of a building.  2 Advances in Civil Engineering

Research Goal.
e objective of the research work is to develop a method that can estimate the environmental impact of a building during its whole lifespan. e proposed method evaluates the building's eco-imprint on the Earth through the ecological footprint indicator. e research goal has been carried out according to the methodological flow diagram shown in Figure 2.

Advantages and Disadvantages.
e research study presents a novel method for the life cycle ecological footprint assessment of a building. It integrates resource limitations (i.e., available biocapacity of the planet) and sustainability aspects over the entire lifespan of a building. e life cycle ecological footprint provides a more comprehensive assessment than the energy analysis and emission analysis [32,33]. e study does not consider the future degradation of bioproductive land during the calculations [24]. e assumption in calculating the life cycle ecological footprint is the uniformity of bioproductivity of various types of lands, for example, forest land and cropland [34]. us, it provides only a general estimate of bioproductive land use.
is study emphasizes the environmental impact assessment of buildings located in tropical countries. e study is also significant for the policy makers because of very huge infrastructural enhancement, which will be required in the near future due to rapid urbanization. e study can be helpful to estimate the overall impact of the building sector in India. e natural resource stresses in India are high, and it has already exceeded the country's existing biocapacity. e total biocapacity deficit of the country is about 0.7 gha/ capita [34]. A comprehensive assessment of the natural resource demand in the building sector can be facilitated by this study.

Methodology
A methodology has been developed that could assess the overall environmental impact of a building by considering resources such as materials, energy, emissions, water,

Advances in Civil Engineering
A b � the total area of occupied land of building (ha) manpower, wastes, and so on. Simultaneously, some sustainable features have been examined that can reduce the ecological impact of buildings. In this case study, it computes the life cycle ecological footprint (EF T ) of a building, and its potential reduction is explained below:

Life Cycle Ecological Footprint (EF T ).
e EF T of a building takes into account the natural resource consumption, direct land use, transportation, manpower, and construction and demolition waste. In order to evaluate EF T , the direct and indirect utilities in the building are transformed into their corresponding bioproductive land categories. e EF T e system boundary of a building's lifespan is depicted in Figure 1. e principle of assessment of the EF T is shown in Figure 2. e assessment of EF T is calculated by the equation that is listed in Table 1. EF e&m , EF t , EF m , EF we , EF w , and EF land represent the ecological footprint of energy and materials use, transportation, labour/manpower, waste assimilation, water use, and direct land use during the building lifespan, respectively. e all-listed parameters cumulatively assess the EF T of a building.

Energy and Materials Use (EF e&m ).
e EF e&m has been determined by the addition of the total energy-related emission and natural material used during the life cycle of a building. e EF e&m of a building is calculated by using the equation that is provided in Table 1.

Transportation (EF t ).
e EF t of a building mainly depends on three factors: (1) building materials transportation, (2) waste transportation, and (3) manpower transportation. e assessment of the EF t of building materials, labour/manpower, and C&D waste is completed by equations that are listed in Table 1. Some assumptions are considered to estimate the impact of transportation; it is based on the survey and data collection from the local construction industry. e assumptions are as follows: (1) Heavy-duty vehicles (HDV) are used to transport building materials and C&D waste (2) Vehicle (i.e., HDV) capacity is about 3.5 tonnes, and the average distance covered is 10-15 km (3) Labourers use diesel-fuelled buses (capacity of 50 passengers) (4) Distance travelled by manpower is around 5-10 km

Labour/Manpower (EF m ).
e manpower requirement during different types of construction work is shown in Table 2. e Central Public Works Department, Government of India [41] report, is used to estimate the total number of labour-day requirements during the building lifespan. In this study, the metabolic calories required are used to determine any construction activities by manpower [28]. Construction labour burnt approximately 1,400 metabolic kcal (i.e., the rate of 175 kcal/hr [42]) during one work-day (8 hrs.). It is 0.6 times the metabolic calories (i.e., 2,400 kcal/day of an Indian person [43]) burnt during the daily work-hours by labour.
e main food items consumed in Indian conditions are presented in Table 3. e EF m is determined by the equation that is provided in Table 1.

Waste Assimilation (EF we ).
e C&D waste assimilation of a building is mainly depending on: (1) landfill disposal and (2) transportation. However, waste transportation is already included in Section 2.1.2. e EF we is determined by the equation that is provided in Table 1.

Water Use (EF w ).
Water use in the building during the life cycle (except for water used by occupants) is very essential nowadays because of the high water stress in the country. Groundwater is commonly used for building construction in India. In this study, the electricity consumed for uplifting underground water is considered to estimate the impact of water use. e EF w of the building is determined by the equation that is mentioned in Table 1.

Direct Land Use (EF land ).
is section emphasizes only the direct land occupied by a building.
e EF land of a building is determined by the equation that is provided in Table 1.

Measures for EF Reduction.
Some possible measures are suggested in the section that may reduce the EF T of the case building.

Sustainable Building Materials.
Building construction materials are responsible for a significant amount of ecological impact on the planet [47,48]. is section focuses on the assessment of environmental impact reduction of building by use of some selected sustainable materials. e details of some selected sustainable materials are given in Table 5.

Renewable Energy Use.
Renewable energy systemssolar, wind, geothermal, small hydro, and so on are generally considered a clean source of energy; however, it consumes some amount of energy (i.e., associated with materials, transportation, installation, etc.) and resources. It is accountable for the small amount of GHG emissions as well as bioproductive land consumption [55,56]. In this study, a grid-connected rooftop solar photovoltaic (RSPV) system has been discussed. Various studies have been reported on the LCA of the different types of solar PV systems [57][58][59][60]. ey suggest that the environmental impact of the solar PV system depends on various factors, which are listed as follows: (i) Type of solar photovoltaic modules (ii) Climatic conditions (iii) Installation (grid-connected, stand-alone, groundor rooftop-mounted, etc.) e details of different types of modules and the balance of system of solar PV system are listed in Table 6.  Table 7.

Results
e EF T and their reduction potential assessment have been done for the case building. e obtained results are explained below.

Life Cycle Ecological Footprint (EF T ).
e EF T of the case building is calculated by summing all their components (EF e&m , EF t , EF m , EF we , EF w , and EF land ). e EF T of the case building is 957.07 gha, while the annual average EF T of the case building is 15.95 gha/yr (assuming the building's lifespan of 60 years). e EF T per unit floor area of the building is 0.10 gha/m 2 .

Energy and Materials (EF e&m ).
e total consumption of building materials and their EF have been obtained from Table 8. e building materials and resource usage during construction in India are taken from Table 2 in Annexure, which has been used in the study. Due to lack of data, maintenance (refurbishment) impact is assumed 6.4% [63] of the total building's life cycle impact in this study. Details of machinery use such as concrete mixer, electric pump, and electric vibrator are mentioned in Table 9. e EF e&m of the case building as calculated by using the equation is 911.68 gha and their components (i.e., operational energy, building materials, construction energy, and demolition energy) have been shown in Figure 4.
Operational energy of the building contributes 52% share of the total EF e&m of the building, while embodied energy of materials contributes about 47.5%. However, the combined environmental impact of the other two   6 Advances in Civil Engineering components (i.e., EF of construction energy and demolition energy) of the EF e&m is less than 1%. Figure 5 clearly shows that bricks contribute nearly half (52%) of the total materialrelated environmental impact (EF); while cement and steel account for 33.5% and 12.2% of the total material-related EF, respectively.

Transportation (EF t ).
By using equation, the estimated EF t of the building is 20.44 gha. Details of transportation vehicle capacity, fuel consumption, and emission factor of fuel are listed in Table 9.

Labour/Manpower (EF m ).
Food intake by the construction labour has been considered to evaluate the EF m of the case building. By using equation, the estimated EF m of the case building is 20.85 gha. e environmental impact of labour/manpower for the case building is 2.2% of the EF T of the building. Bioproductive land distribution in the EF m of the building is shown in Figure 6.

Water Use (EF w ).
Water consumption is mostly involved in the construction phase of the building (27 kilolitres of water per m 2 floor area [17]). e construction phase is more dominating than the other phase of building in terms of water use because refurbishment (during operation phase) and demolition (end of life) use a comparatively low amount of water. erefore, water consumed during the maintenance and demolition phases has been neglected in this study. e EF w is about 11.38 gha for the building (i.e., 1.2% of the EF T ).

Direct Land Use (EF land )
. By using equation, the estimated EF land of the case building is about 8 gha (i.e., 0.84% of the EF T ). e bioproductive lands contribution is depicted in Table 11 and the percentage fraction is depicted in Figure 7. e significant land type involved in the EF T is CO 2 absorption land (i.e., 95.25% of the total bioproductive land) because the case building consumed direct and indirect energy during the lifespan. In EF analysis, all the energy consumption and emissions are represented in CO 2 absorption land. e EF T distribution of different life cycle phases of the building is shown in Table 12. It clearly represents that the environmental impact of the construction and operation phases are 49.78% and 47.90% of the total impact of the building, respectively. In general, the operation phase is more dominant compared to the rest of the life phases in terms of energy use [12]. However, in the case study building, the embodied impact is almost half of the buildings' overall impact. It is because the building is not equipped with any HVAC systems. e electricity    consumption is very low during building operation, mainly meant for lights and fans. erefore, operational environmental impact is nearly equal to the embodied environmental impact of the building (see Table 12).

Reduction Potential in EF T .
Reduction potential in the EF T of the case building is estimated in two ways: first, sustainable building materials, and second, renewable power (solar PV) system.

Sustainable Building Materials.
e EF T reduction potential of the case building by use of different sustainable materials and their combinations has been assessed in this section. For such estimation, the required material properties are taken from Table 5. e estimated value of the EF T by using alternative materials (individually or in combination) in the building is shown in Figure 8. e EF T of the building may reduce up to 22.2% (Table 13) if construction materials such as fired clay brick (FCB) and Portland Pozzolana cement (PPC) are replaced with sustainable materials (i.e., FAB, HCB, AAC, and LC 3 ). Husain and Prakash reported the constructional EF of the FAB consist wall as nearly 50% lower than the conventional wall (i.e., consisting of FCB) [66]. e ecological footprint of FCB, FAB, HCB, AAC, PPC, and LC 3 is calculated as 0.001 gha/ brick, 0.00004 gha/brick, 0.0002 gha/block, 0.0006 gha/ block, 0.00009 gha/kg, and 0.00006 gha/kg, respectively.

Renewable System.
e database of RETScreen software is used to assess the capacity of five different types of PV module systems that can meet the annual electricity demand of the building (Table 14). e life cycle ecological footprint of solar PV modules (tropical climatic zone) is shown in Figure 9. e thin film (i.e., a-Si, CdTe, and CIS) solar PV modules have comparatively lower EF values than mono-Si and multi-Si modules. However, the thin film-based PV module systems are not used for large-scale power production because of their low efficiency and high degradation rate. In India, multi-Si PV modules are generally used for power production. e average life cycle EF of mono-Si, multi-Si, a-Si, CdTe, and CIS-based solar PV systems were evaluated as 0.0694, 0.0605, 0.0297, 0.0250, and 0.0305 gha/m 2 , respectively. In Table 14, the electricity generation from the different types of modules is 0.56-2.65 × 10 −5 gha/kWh. In India, the emission factor of grid electricity is about 0.82 tCO 2 /MWh [35], and the estimated EF of grid electricity is 2.72 × 10 −4 gha/kWh while ignoring factors other than emissions. Hence, the EF reduction potential by the solar PV systems is in the range of 10 folds to 50 folds. e potential reductions of the EF T through the different solar PV systems are shown in Figure 10. e grid-connected rooftop solar PV systems can probably reduce the EF T in the range of 507.6-519.7 gha (i.e., 45.76-47% of the existing building). e maximum reduction in the EF T has been estimated for CdTe modules; it is because of the lowest EF of such modules.

Combined Effect of Building Materials and Renewable
Systems. If both the reduction measures are incorporated simultaneously into the building, it has the potential to reduce the EF T by up to 69% of the existing building. EF T with all possible combinations of building materials and solar PV modules is depicted in Table 15. e lowest EF T of the case building has been estimated for the combination of HCB + LC 3 +CdTe (i.e., 295 gha). Due to the material constraints, hazardous waste disposal, and high degradation rate of the thin film module; the multi-Si-based systems have the largest market share in the world (i.e., 51% of the total installed capacity) [67]. erefore, the combination of HCB + LC 3 +multi-Si is best suited for the building in the Indian context.   Energy-efficient retrofitting in buildings has great potential to reduce GHG emissions [68,69]. For tropical climatic buildings, green roof designs and reflective roofs (reflective coatings on roof surface) can be installed to reduce the ecological footprint of the building [47,66]. Solar tubes for daylighting can significantly reduce the artificial lighting demand of a building and may also reduce the building's ecological footprint. Hence, the ecological footprint can be reduced by using additional sustainable measures in buildings.

Conclusions
is study focuses on assessing the life cycle ecological footprint of the case building. e proposed methodology may help estimate the building impact as well as restrict to use of resources within the planetary limit. Two important measures have been investigated for the reduction in EF T of the building, that is, the use of sustainable materials and     renewable power (solar PV) system. ese two measures provide a significant reduction (maximum 69%) in EF T for the building examined. With the installation of rooftop solar PV alone, the EF T reduces by 47%. e EF T of the case building is about 957 gha (for 60 years of building life). e annual average ecological footprint of the case building is 15.95 gha, and the EF T per m 2 floor area of the building is 0.10 gha/m 2 . e major contributor to the EF T of the building is CO 2 land that is 95.25% of the total bioproductive land needed for the building.
Such a comparison shows that EF for the built environment varies with regard to architectural and constructional features, climatic conditions, level of thermal comfort, and so on. Hence, a local assessment of EF is important in order to execute strategies for EF reduction.

Abbreviations
AAC: Autoclaved aerated concrete block A f : CO 2 absorption factor of forests A oc : Percentage of CO 2 absorption in oceans C&D: Construction and demolition EF: Ecological footprint e i : Equivalence factor of bioproductive land FAB: Fly ash brick FCB: Fired clay brick GHG: Greenhouse gas HCB: Hollow concrete block HDV: Heavy-duty vehicle LC 3 : Limestone calcined clay cement LCA: Life cycle assessment LCE: Life cycle energy PPC: Pozzolana portland cement PV: Photovoltaic.

Data Availability
All the data used in this research work are cited in the manuscript.

Conflicts of Interest
e authors declare no conflicts of interest.