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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
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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
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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
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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
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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
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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
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Exterior Siding
flooring and wood flooring
Stucco
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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.
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