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Construction Research Congress 2014 ©ASCE 2014 A Framework for Assessing Environmental Implications of an Urban Area Seyed Mostafa BATOULI1 and Yimin ZHU2 1 2 PhD student, Department of Civil and Environmental Engineering, Graduate Assistant, OHL School of Construction, Florida International University, 10555 West Flagler Street, Miami, FL, USA, email: [email protected] Associate Professor, OHL School of Construction, Florida International University,10555 West Flagler Street, Miami, FL, USA, email: [email protected] ABSTRACT Increased consciousness of the environment progressively put more pressure on policy makers and urban planners to ensure sustainability of built environment. The single biggest obstacle to devise environmentally sound urban development plans is the insufficient understanding of the urban system. The interactions between various components of urban environment as well as the large number of factors affecting its’ environmental performance, makes it impossible to model todays metropolitans in every detail. Therefore some sort of simplification is inevitable for urban environmental modeling. However, in order to avoid subjective assessment of impact factors, it is necessary to define appropriate quantitative cut-off rules based on needs and available resources. This study proposes a framework for assessing the environmental impacts of an urban area based on the concept of statistical “parameter variation and scenario analysis”. The method is capable of considering any sector in an urban development with desired level of details, and provides information about the significance of environmental impacts of that sector as well as uncertainty of the results. A case study is also provided to elaborate the capabilities of the framework. INTRODUCTION A huge proportion of energy and resources is depleted in cities and hence they are a major contributor to environmental harm (Ramaswami et al. 2008). Today urban areas consume about 70% of energy and produce about 80% of Greenhouse Gas (GHG) emissions (Russo and Comi 2012). Considering the fact that urban to rural population is steadily increasing and it is estimated that 70% of people will live in cities by 2050 (Khare et al. 2011); the impact of urban development on the environment could be even more severe in future. On the other hand, increased consciousness of the environment progressively put more pressure on policy makers and urban planners to ensure sustainability of new built environment. Factors such as urban density (Norman et al. 2006), energy requirements of the buildings operation (Al-Homoud 2005), embodied energy of building materials (Junnila and Horvath 2003), and transportation (Kennedy et al. 2010) are claimed to be the most influential factors contributing to environmental impacts of communities. OBJECTIVES It is often stated that the single biggest obstacle to devise environmentally sound urban development plans is the insufficient understanding of the urban system (Zellner et al. 2008). Ideally it would be desirable to model an urban development 2365 Construction Research Congress 2014 ©ASCE 2014 with all processes, energy flows and releases to the nature in a unique system to have an accurate estimate of the implications associated with each entity within the city region. However, it is believed that the complexity of such a system is far beyond the existing resources (Wiek and Binder 2005). Therefore some sort of simplification is inevitable for urban environmental assessment modeling. One essential requirement for such simplification is to determine whether a specific segment of the built environment has significant impact or not. The sector which has received the most attention is the “building sector”. The most detailed life cycle assessment studies to date are those related to the “building design and materials” (Norman et al. 2006). There have been a few examples of studies on environmental impacts of complete buildings (example: (Ochoa et al. 2002) and (Junnila et al. 2006)); however a complete building contains thousands of components and hundreds of different materials and therefore carrying out an LCA for a complete building is costly and time consuming and the worst is even if a full study is done, it would be very difficult, if not impossible, to validate the results. Moreover, focusing on measuring the absolute environmental impacts of one sector is associated with problems related to justifying the study boundaries (Reap et al. 2008) and hence usually a comparative study is preferred (Horvath 2004). That explains why comparative studies by far outnumber those focusing on one material. This study, proposes a method based on the concept of statistical “parameter variation and scenario analysis” (Finnveden et al. 2009) to overcome the mentioned problems. The method is capable of considering any sector in an urban development with desired level of details, and provides information about the significance of environmental impacts of that sector as well as uncertainty of the results. The rest of the paper describes the proposed framework followed by an application example. FRAMEWORK FOR ASSESSING ENVIRONMENTAL IMPACTS The proposed framework includes nine major processes as shown in figure1. The first process is to divide an urban area into a number of categories based on expert knowledge with regards to readily available data. Criteria to be used for categorization are those which are expected to have the greatest impact on the environmental performance of elements of the built environment. Example criteria to evaluate environmental impacts of the construction phase of residential buildings could be “structure of the building”, “square footage” and “location and topography of the land”. It should be noted that the initial categories are only the starting point of the algorithm and if necessary, will be later modified in an iterative process as shown in figure 1. When the urban environment is broken down into a desired number of categories, the algorithm starts with the first category. At this stage, data about additional parameters is acquired to enhance accuracy of the assessment within the category. An “enhancement parameter” is a set of additional information about the buildings within a single category which should be acquired with reasonable effort to make the environmental assessment of the category more accurate. In fact these “enhancement parameters” are defined so that they can minimize possible discrepancies within a single category. Examples of “enhancement parameters” include “major structure of the building” or “number of residents of the building”. This information is not used for the categorization of the city and is not readily 2366 Construction Research Congress 2014 ©ASCE 2014 2367 available to the urban planner. Therefore the cost of acquiring these types of data is only justifiable if they can significantly improve the accuracy of the model. “Enhancement parameters” are sorted based on the simplicity, i.e. the one which requires the least amount of effort and cost is parameter 1 and as the process goes forward, the more effort intensive parameters are chosen. Purpose of the fifth process (defining scenarios) is to delimit maximum variations in environmental impacts of the current enhanced category. One merit of the model is that it could be supported by prospective LCA. Prospective LCA or “LCA modeling the effects of changes” (Tillman 2000) has an advantage over retrospective LCA in that it is not dependent on parts of the system which are not affected by the changes. This is an important quality for the purpose of assessing a metropolitan because, as mentioned before, the complexity of the system is one of the most important obstacles in environmental assessment of an urban area. After scenarios are evaluated quantitatively, the decision makers choose the best and the worst case scenarios and finally based on the size of category and desired level of accuracy, decide whether the uncertainties are acceptable or not. The process iteratively continues for all categories and final reports are prepared. Start 1. Categorize the urban area 6. Apply prospective LCA to scenarios 2. Go to next category 3. Defining enhancement parameters 5. Defining scenarios within enhanced category 4. Go to next parameter 7. Select scenarios with lowest and highest impacts 8. Apply the highest and lowest scenarios to the category No Last category? No Yes Met accuracy objectives? No Last alternative? Yes Yes 9. Report End Figure 1. Proposed framework for assessing the environmental impacts of an urban area Construction Research Congress 2014 ©ASCE 2014 2368 CASE STUDY This section provides a case study to elaborate the functionality of the proposed framework. Consider the metropolitan area of Miami-Dade with more than 550000 land parcels. Figure 2 (a) and (b) show respectively the building square footage frequencies and number of building floors. Figure 3 (a) and (b) depicts data related to year of construction of the buildings and the frequencies of the ratio of total building area in a land parcel to the size of the land (Data is provided by Miami-Dade County). Since all these four factors are considered relevant to the environmental performance of a building, characterization of the city could be done based on them. For instance one initial category could be “two story buildings between 3000 and 5000 square feet which have been built after year 2000 and are built with building to lot ratio in range of 0.4-0.5. We will name this category the “Initial category”. (a) (b) Figure 2. (a) Building square footage frequency, and (b) Number of building floors (a) (b) Figure 3: (a) Building year built frequency, and (b) Building to lot fraction After all categories are defined and the first category is selected, the next step as depicted in figure 1 is to define enhancement parameters. The simplest parameter is to treat all the buildings in initial category as if they are the same. To assess if this Construction Research Congress 2014 ©ASCE 2014 assumption is good enough or not we need to define a number of scenarios which can show all discrepancies within the category with the constraint of the current enhancement parameter. This could be a comparison between a sample building with 3000 square feet, the environmentally friendliest materials and construction methods, the least number of residents and so on from one limit, and a 5000 square feet building with maximum number of tenants and worst materials and construction methods in the other extent. Most probably such a wide category does not meet the desired level of accuracy and hence the algorithm moves to the next enhancement parameter. Other parameters could narrow the predefined category on items such as “structure of the building”. Moving forward to the next enhancement parameter increases the accuracy, but it also is costly. For the above example, the cost includes acquiring data about the structure of the buildings within Initial category and conducting separate LCAs for each type of structure. If any of enhancement parameter does not meet the needs or they are all too costly, the next step is to divide the predefined “Initial category” to smaller parts. Assume that the “New category” has the same characteristics as the “Initial category” except for that it only includes buildings between 4000 and 5000 square feet. The process continues with defining enhancement parameters. Here we provide an example to illustrate how the prospective LCA can help to get rid of costly calculations while still providing reliable results. In order to evaluate the “New category”, as described earlier and depicted in figure 1, “enhancement parameters” should be defined. The first step is to define a sample building which falls into “New category”. Data from a sample building is studied here to elaborate the model. The sample building called “USA Future house” is a two-story residential with an approximate total living area of 4500 square feet built by a number of US sponsors in Beijing, China (Zhu and Tao 2009). Among thousands of construction activities, only fourteen major construction activities related to the building envelope are considered. This considerably reduces the cost and time consumption of the analysis. The quantity take-off’s for the activities are done. Several alternative construction procedures and/or building materials are investigated for each activity as shown in Table 1. The choice of alternatives is so that the activity requirements are fulfilled but no other constrains (such as time or cost) is considered. For instance the activity “Excavation” can be accomplished using either a cubic yard excavator or manually. Due to the scope of study, the fact that the cost of manual excavation is more than 5 times higher than using and CY machines respectively) has equipment ($1055 vs. $189 and $150 for not been considered. Similarly “cut and chip trees” in activity “site clearing” can be done either with a crew of one 130 HP brush chipper, one 3 CY crawler loader and one chain saw or alternatively with a 1.5 CY hydraulic excavator and a 12 CY dump truck. In both cases the grading is assumed to be executed with a 30000 lb. grader. Another example for the choice of alternatives is when different building materials could be used for the same purpose. The four alternatives for the activity “Subgrade Insulation” are in fact differentiated based on the insulation material used (expanded polystyrene, extruded polystyrene, foam polyisocyanurate board and blown cellulose board). Likewise, the concrete used in different alternatives for activities “footing 2369 Construction Research Congress 2014 ©ASCE 2014 construction”, “stem wall” and “slab on grade construction” are different in concrete mixture and flyash content. For other activities, a combination of material and construction procedure is changed in each alternative. Exterior and interior wall constructions are of the latter type were a wide range of alternatives including SIP and wood or steel stud construction is considered. Only one alternative is considered for activities “backfill” and “roof truss”. The crew needed for each activity is taken from (RS Means 2013). In order to have a good understanding of environmental impacts of construction activities, the life cycle assessment (LCA) framework of (ISO 14040 2006) is followed. LCA is a widely accepted environmental assessment tool which monitors and evaluates the environmental impacts of a product system through a holistic approach. All forms of energy and material inputs as well as any type of waste product or emission to the environment are quantified to provide a basis for a realistic environmental assessment. A complete LCA consists of four phases namely “goal and scope definition”, “inventory analysis”, “impact assessment” and “interpretation”. Table 1. Brief description of construction activities Number of Activity Brief Description Alternatives Cut & chip trees to 12" (Total area of 0.23 acre) Site Clearing 3 Grading of 1111 Sq.Yd. Excavation 3 Excavation of 36.38 BCY soil Footing 6 47.98 CY footing with 0.97 ton reinforcement Construction Stem Wall 6 42.33 CY with 0.86 ton reinforcement Construction Subgrade 4 572.02 SF Insulation Insulation Backfill 1 27.56 LCY backfill Slab-on-Grade 12 43.87 CY with reinforcing Construction Exterior Wall 49 5011.49 SF Construction 2410.97 SF Light Frame Wood Truss Roof, Roof Truss 1 span 24' to 29' and 1496.32 SF Light Frame Wood Truss Roof, span 30' to 33' Roof 6 Quantities depend on alternatives Construction Interior Wall 72 Quantities depend on alternatives Construction Roofing 6 64.40 Sq roofing Flooring 2 3020.60 SF flooring Exterior Siding 8 5011.49 SF siding 2370 Construction Research Congress 2014 ©ASCE 2014 In goal and scope definition, the study domain and the intended audience of the study are explicitly specified and initial data quality requirements are determined. Inventory analysis is the process in which inputs and outputs from and to the environment are quantified and allocated to the related processes or products. Most of the required Life cycle inventory data in this study are acquired from Ecoinvent and USLCI libraries within Simapro7.2. For some equipment, the fuel consumption is directly calculated based on nominal productivity of the machine. Third stage of LCA is life cycle impact assessment in which data collected in inventory analysis are reorganized and aggregated in a set of environmental impact categories. In this study, the impact assessment is based on 12 impact categories as defined in “Building for Environmental and Economic Sustainability” (BEES). Final stage of an LCA study is interpretation in which the results from previous stages are communicated to the research audience and recommendations are provided for decision makers. Table 2. Lowest and highest impact alternatives for all activities Activity Least impact alternative Highest impact alternative Site clearing with a 1.5 CY Hand removal of the trees/ hydraulic excavator and 12 CY, Site Clearing grading with a 30000 lb. 400HP dump truck/ grading with grader a 30000 lb. grader Excavation Manual excavation Excavation with ½ CY excavator Concrete exacting with 375 kg Footing 3000 psi concrete with cement content in each cubic Construction 30% flyash pumped meter (2440 kg) Concrete exacting with 375 kg Stem Wall 3000 psi concrete with cement content in each cubic Construction 30% flyash pumped meter (2440 kg) Subgrade Blown cellulose board Extruded Polystyrene Board Insulation Slab-on-Grade 4", 3000 psi, 35% flyash, 8" Concrete exacting Construction direct chute Wood Stud Kiln Dried 24 Steel Stud (20 GA) 16 o.c., 1 5/8 Exterior Wall o.c., 2x4, Blown Cellulose x 3 5/8, Expanded Polystyrene Construction Board, 1/2" Regular Board, 5/8" WR Drywall, 3/8" Drywall, 3/8" Plywood Plywood Blown Cellulose Board Roof and 3/8" Plywood (deck SIP with 5.5" thickness Construction and truss) Wood Stud Kiln Dried 24 Steel Stud (25 GA) 16 o.c., 1 5/8 Interior Wall o.c., 2x4, 1/2" Regular x 3 5/8, Expanded Polystyrene Construction Drywall Board, 5/8" WR Drywall Steel Roof Panel 30 GA Roofing Concrete tiles (Residential) No significant difference No significant difference seen Flooring seen between Bamboo between Bamboo flooring and 2371 Construction Research Congress 2014 ©ASCE 2014 Exterior Siding flooring and wood flooring Stucco 2372 wood flooring Fiber Cement Full LCA, which is usually referred to as “cradle to grave” study, estimates environmental effects of a product system from raw material extraction to use and finally disposal or recycle. Life cycle assessment is highly regarded for its capability to assess the environmental implications throughout all stages of a product’s life, but it also has the flexibility to be used in studies with more limited scopes. As mentioned earlier this study uses a prospective approach toward LCA, which means only the impacts of those parts of the product system that has changed are compared. The study conducts a well-known partial LCA called “gate-to-gate life cycle impact assessment (LCIA)”. According to (ISO 14044 2006), LCIA is defined as “phase of Life Cycle Assessment aimed at understanding and evaluating the magnitude and significance of the potential environmental impacts of a product system”. Gate-togate LCA focuses only on one part (or process) of the entire life of product system. RESULTS OF THE CASE STUDY The environmental implications of all alternatives for each activity are analyzed and compared. A list of alternatives with maximum and minimum impacts is provided in table 2. In the few cases were none of alternatives performed the best (or worst) regarding all impact categories, the priority is given to “global warming impact”. Two hypothetical projects are defined with the minimum and maximum environmental impact. Each project consists of fourteen activities were for the minimum impact project all activities are done with the “least impact alternative” while in case of maximum impact project, the alternatives with highest impacts are chosen. The two projects are then compared with regards to environmental implications. Figure 4 shows the results. It is seen that alterations of materials and construction procedures can result in between 5 to 85 percent change with regards to different environmental implications. This is now up to the decision maker to decide whether this much variation in different impact categories worth to get real data for all the buildings in “new category” or not. Figure 4. Comparison of the projects with highest and lowest implications Construction Research Congress 2014 ©ASCE 2014 CONCLUSION This study proposes a framework for assessing the environmental impacts of a large metropolitan area. The framework has the capability of evaluating the environmental impacts of the urban area with desired level of accuracy based on the needs and available resources. A case study is provided to elaborate the capabilities of the model. A gate-to-gate LCIA study is conducted for the construction phase of a sample building to show how a simple prospective LCA study can help urban planners to identify the most significant contributors to the environmental implication. A future study could be to implement the model in an urban area. REFERENCES Al-Homoud, D. M. S. (2005). 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