-
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requirements over its entire life cycle, by analyzing both
embodied and operational energy consumption in a climatically
responsive building in the
As in other industrialized countries, energy consumption
sizeable deposits of oil shale [4].
planning and design follow practices that are standard in
the
Energy and Buildings 40 (2008and CO2 emissions in Israel have
increased steadily over the countrys more temperate regions, and
particular adaptation to
local conditions is the exception rather than the rule [6].
The distribution of Israels energy use among different
sectors of the economy is representative of industrialized*
Corresponding author. Tel.: +972 8 6596875; fax: +972 8
6596881.
E-mail address: [email protected] (N. Huberman).
0378-7788/$ see front matter # 2007 Elsevier B.V. All rights
reserved.doi:10.1016/j.enbuild.2007.06.002then, that the only way
to avoid a drastic reduction in accepted
standards of living is to achieve an order-of-magnitude
improvement in energy-efficiency, defined as the ratio
between
energy services provided and energy consumed [3].
1.1. Energy in Israel
peripheral areas such as the Negev desert. The Negev
comprises
65% of Israels land area, but accommodates less than 8% of
its
population. Construction in the Negev typically requires
longer
transportation distances from Israels commercial and indus-
trial centers, increasing energy requirements for physical
development. The harshness of the desert climate also
affects
energy consumption, due to the heavy heating and cooling
loads in residential and commercial buildings. By and
large,whether such a demand trajectory can be met in an
environmentally sustainable manner [2]. It has been
proposed,Rapid population growth has resulted in overcrowding in
the
center of the country, causing a spill-over of construction
toadvances in renewable energy technology, it is
questionableembodied energy of the building accounts for some 60%
of the overall life-cycle energy consumption, which could be
reduced significantly by using
alternative wall infill materials. The cumulative energy saved
over a 50-year life cycle by this material substitution is on the
order of 20%. While the
studied wall systems (mass, insulation and finish materials)
represent a significant portion of the initial EE of the building,
the concrete structure
(columns, beams, floor and ceiling slabs) on average constitutes
about 50% of the buildings pre-use phase energy.
# 2007 Elsevier B.V. All rights reserved.
Keywords: Building materials; Energy-efficiency; Life-cycle
analysis; Embodied energy
1. Introduction
World energy demand is projected to increase by up to 71%
between 2003 and 2030 [1]. At present the vast majority of
this
energy consumption is based on fossil fuels, and despite
notable
past decades. The country obtains nearly all of its energy
from
imported fossil fuels [4], though it is unique in mandating
the
use of solar energy for water heating in all new residential
buildings. Since the 1970s Israels electrical power
generation
has been based primarily on coal [5] and the country also
hasNegev desert region of southern Israelcomparing its actual
material composition with a number of possible alternatives. It was
found that theA life-cycle energy analysis of bu
N. Huberman *
Ben-Gurion University of the Negev, Jacob Blaustein Institute
for
Sede Boqer Cam
Received 22 May 200
Abstract
Environmental quality has become increasingly affected by the
built e
consumption and resultant atmospheric emissions in many
countries. In
mainly on the energy required for a buildings ongoing use, while
the ene
led in recent years to strategies which improve a buildings
thermal perform
Although assessment methods and databases have developed in
recent ye
local technologies and transportation distances. The objective
of this stuing materials in the Negev desert
. Pearlmutter
ert Research, Albert Katz International School for Desert
Studies,
s 84990, Israel
ccepted 19 June 2007
ronmentas ultimately, buildings are responsible for the bulk of
energy
gnizing this trend, research into building energy-efficiency has
focused
embodied in its production is often overlooked. Such an approach
has
ce, but which rely on high embodied-energy (EE) materials and
products.
the actual EE intensity for a given material may be highly
dependent on
s to identify building materials which may optimize a buildings
energy
www.elsevier.com/locate/enbuild
) 837848
-
rgycountries, where buildings account for a large fraction of
the
overall consumption: in the U.S., the combined residential
and
commercial building sectors account for approximately 40% of
the total [7]. These sectors, however, only include the
energy
consumed in buildings during the period of their active
usage.
The share of energy used by buildings increases
significantly
when the energy used in their production is included as
well.
1.2. Energy-efficiency in the life cycle of buildings
Any comprehensive assessment of architectural energy
consumption must in fact consider the entire life cycle of
the
building, which can be divided into three phases: pre-use
phase
(embodied energy, EE), use phase (operational energy, OE)
and
post-use phase (demolition or possible recycling and reuse).
The intensity of energy consumption in the first of these
phases for the production of buildings and their components
has increased dramatically with industrialization. In contrast
to
traditional building practices based on locally available
raw
materials and human energy, modern methods have allowed vast
quantities of fuel energy to be harnessed in the manufacture
of
standardized, quality-controlled building products. The
high-
temperature processes used to produce steel, aluminum,
cement,
glass and expanded foam insulation are prime examples.
Industrial technologies have also led to sharp increases in
operational energy consumption, most notably with the advent
and proliferation of air-conditioning. Efforts in recent
decades
to moderate the use of non-renewable energy for heating and
cooling have led to significant savings through climatically
responsive design approaches, including technological
innova-
tions for improving the thermal efficiency of the building
envelope [8,9]. At the same time, however, technologies
yielding solutions such as super-insulated walls and windows
have contributed to operational energy-efficiency through
the
exploitation of high embodied-energy materials.
Therefore, strategies which reduce a buildings energy needs
for maintaining thermal comfort do not necessarily lower
energy demand in the production phase, or in the overall
life
cycle. While reducing operational energy consumption has
been a goal of designers for many years, embodied energy has
received much less attention. There are several reasons for
this,
among them the lack of a clear assessment methodology and
the
data required to implement it, as well as a common
assumption
that the initial energy needed for production of a building
is
minor compared to its long-term operational needs. Some
studies have indicated that this is indeed the case, citing
figures
in the range of 80% running energy to 20% embodied energy
[10]. It is clear, however, that as operational energy use
becomes lower, the role of embodied energy in minimizing
overall consumption becomes increasingly prominent [1013].
In recent years the methodologies for embodied-energy
assessment have improved, as have the reliability and
availability of data. One recent report [9] indicated that
the
embodied energy in an office building may be as much as 67
times its annual operational energy, though most studies
show
more modest ratios. Depending on the expected lifetime of
the
N. Huberman, D. Pearlmutter / Ene838building and its
energy-efficiency level for operation, theembodied energy typically
represents between 10% and 60% of
the total energy used during the lifetime of the building
[2,14,15].
The choice of a given building material can have multiple
effects on a buildings energy consumption over the different
phases of its life cycle, and as suggested previously, these
effects can be contradictorysince properties such as high
insulation value may yield relative savings in operational
energy together with higher embodied-energy costs. The
balance of these factors is especially significant since a
buildings external structure and envelope (roof, floor,
walls
and windows) tend to account for the greatest portion of its
EE
[16].
Often a range of different materials can be found to fulfill
the
same function in a building, and since their
energy-efficiency
may vary significantly, savings can be achieved through
substitution. In some cases these savings arise from the use
of
renewable energy in the production process, and in others
from
the reuse or recycling of existing products.
Materials which incorporate industrial and consumer wastes
(such as fly-ash concrete, recycled plastic lumber, etc.)
can
reduce both the depletion of natural resources and the
pollution
generated by disposal. These environmentally friendly
materials are becoming more widespread [9], though it is
crucial that their benefit be gauged within the larger
life-cycle
context.
To obtain a comprehensive picture of a products whole-life
environmental costs, a number of guidelines and draft
standards
have been developed in recent years. The process whereby the
component and overall environmental flows in a system are
quantified and evaluated is known as life-cycle assessment
(LCA) [9]. It treats the life cycle of any product as a series
of
stagesfrom cradle (raw material extraction and harvest-
ing), through manufacturing, packaging, transportation and
use, to grave (disposal). While energy-related building
regulations have begun to proliferate, life-cycle
environmental
assessments are still voluntary in almost all countries
[17].
LCA studies generally consist of four phases, as set out in
ISO Standard 14040 [18]: goal and scope definition,
life-cycle
inventory, impact assessment and interpretation.
These four steps of the LCA methodology can be applied
specifically for life-cycle energy analysis (LCEA), which
uses
energy as the only measure of environmental impact. This
does
not replace the broader LCA environmental assessment
method, but facilitates decision-making concerning energy-
efficiency as an indicator of a buildings overall resource
efficiency [11,19].
1.3. Previous studies
Several recent studies have attempted to evaluate the
environmental impacts of buildings in an integrated fashion
over the entire life cycle. Adalberth [20] suggested an
organized LCEA methodology, and showed an example of
its application [21] in three prefabricated single-unit
dwellings
in Sweden. The LCEA methodology was applied in a variety of
and Buildings 40 (2008) 837848cases for evaluating energy flows
in residential buildings, such
-
rgyas the green house in Melbourne, Australia [11]. A
detailed
study [22] analyzed the life-cycle energy consumption of a
residential building in Michigan, including energy costs,
different impact categories and the influence of future
energy
cost scenarios.
In the context of LCEA, a number of studies have evaluated
the potential for reducing the pre-use energy in buildings
through material substitution. An Indian study presented a
comparison of EE requirements for three residential
buildings
using different structural systems [23], and a Canadian
research
[24] examined the EE and greenhouse gas emissions associated
with the on-site construction of a number of structural
systems.
A study by Pierquet et al. [25] analyzed both the thermal
performance and embodied energy of wall systems in a cold
climate in the U.S.
Substantial net savings in the pre-use phase have been found
for buildings constructed in India with local materials, due
to
reductions in transportation distances [26]. Two other
Indian
studies presented a comparison of energy embodied in
building
materials, one for both common and alternative materials and
building systems [27] and the other for a wide range of wall
elements [28].
Meanwhile, the accuracy of methods to assess EE data as
part of LCA studies is still questioned. Pullen [29]
compared
diverse EE values from different origins and evaluated the
influence of the methodology used on the results obtained,
concluding that LCEA practitioners should be aware of the
imprecision of EE data. In response, Treloar et al. [30]
presented methods for assessing and improving the
reliability
of EE calculations for making decisions in the context of
LCEA. A broad overview of previous LCEA studies was
recently compiled [31], in which the importance of ongoing
thermal efficiency in life-cycle energy use was
re-emphasized.
In addition, different LCA applications have been proposed
to address a broader list of environmental impacts and
improve
accuracy, even analyzing re-use [32,33] and recycling
methods
in the context of LCA [34]. Tools for improved LCA in
buildings have also begun to proliferate, as summarized by
Erlandsson [35].
The validity of using single point indicators such as energy
to assess overall environmental impact has also been
scrutinized. Grant [36] posited that single indicators do
not
represent all environmental aspects, but are more tangible
than
complex models and therefore easier to understand. A report
by
Peuportier et al. [37] noted that complete LCA is more
appropriate for evaluating environmental impacts than for
prescribing particular materials, though it was subsequently
concluded that LCA can also be useful for determining
suitable
technologies [38,39]. Decisions concerning the relative
importance of different indicators also reflects current
environmental pressures, and LCA weighting has even been
characterized as a political rather than a scientific act,
subject to
changing political agendas in the future [40].
The ongoing challenge of evaluating environmental impacts
generated by buildings is addressed in the present study,
which
aims to fill several perceived voids. First is a lack of
building
N. Huberman, D. Pearlmutter / EneLCA studies conducted in
Israel, particularly for desertbuildings. While most of the
literature on LCEA uses existing
EE coefficients from different countries when local values
are
not found, this study introduces the peculiarities of the
Negev
desert of southern Israel into the calculation of local EE
values,
which are then compared with values from different sources.
In
order to evaluate the net savings of different building
systems
during the whole life cycle of a climatically responsive
building in the Negev desert, the obtained EE values of
building materials are then applied in diverse configurations
to
calculate the EE of a building as part of the complete LCEA
study.
2. Methods
2.1. LCEAgoal and scope definition
This study evaluates the influence of different building
material configurations on the energy-efficiency of a desert
building in Israel. For that purpose, the total energy budget of
a
particular building is assessed by applying the LCEA
methodology.
Following the methodological stages of the LCA detailed
above, the heart of the LCEA process consists of a life
cycle
inventory, in which the essential quantification of energy
flows
is conducted, and an impact assessment for converting energy
consumption into observable impacts such as CO2 emissions
[11]. The LCEA consists of an analysis of the principal
energy
flows during the pre-use and use phases of the buildings
life
cycle, for the purpose of identifying material
configurations
with minimal cumulative energy consumption over these
phases. (Energy consumption in the post-use phase, as well
as
recurring embodied energy in the use phase, are excluded
from
the analysis due to the high level of uncertainty and
variability
involved in their estimation.)
Emphasis is placed on comparing traditional materials with
more commonly used industrial materials, and gauging their
relative influence on life-cycle energy consumption. An
additional aim of the study is to quantify the payback
period of a given alternative, or to quantify the time
required
for an operational energy advantage (or disadvantage) to
counterbalance an initial investment (or savings) in EE.
2.1.1. Studied system
An existing building served as a base case for the analysis.
The building is located at the Sede-Boqer campus of Ben-
Gurion University, in the arid Negev region of Israel at
30.88Nlatitude, at approximately 480 m above sea level (Fig. 1).
The
climate of the region is characterized by sharp daily and
seasonal thermal fluctuations, dry air and clear skies with
intense solar radiation. Summers are hot and dry, with a
mean
daily maximum temperature of 32 8C, while nights are cool(daily
minimum of 17 8C). Global radiation is intense,averaging 7.7 kWh/m2
per day during June and July. Winter
days are typically sunny but cool, with a mean daily maximum
temperature of 14.9 8C and a nightly minimum of 3.8 8C
inJanuary. Prevailing winds are northwesterly and consistently
and Buildings 40 (2008) 837848 839strong during the late
afternoon and evening [6,41].
-
rgyN. Huberman, D. Pearlmutter / Ene840The analysis
intentionally focuses on a modern building, in
which a conscious attempt was made in the design stages to
minimize operational energy costs, thus amplifying the
relative importance of its embodied-production energy. To
evaluate the actual energy-savings and the potential for
additional reductions in the cumulative energy consumption
over the life span of the building, different envelope
configurations were evaluated by hypothetically substitut-
ing particular building materials.
The building selected is part of a student dormitory complex
(Fig. 2), and was designed with a number of passive heating
and
cooling featuresincluding south facing windows to capture
solar radiation in winter, cross ventilation for summer
nocturnal
cooling, double-glazing and insulated shutters, and massive
insulated walls. The complex includes 24 individual
apartment
block buildings, and the building type used as a model for
the
case study consists of eight single-storey apartments
arranged
symmetrically over two storeys. All calculations were based
on
a half block, ensuring a realistic representation of internal
and
external walls. The four apartments in this half-block
module
comprise 112 m2 of floor area, with approximately 21 m2 of
south-facing glazed openings and 14 m2 facing north. All
openings are treated with operable insulated aluminum roller
shutters.
Fig. 1. Location of the case study site (Sede-Boqer, at 30.88N
latitude), in theNegev region of southern Israel. The locations of
raw materials are shown
relative to a 50-km radius of the city of Beer-Sheva, the
assumed manufacturing
site.For the building selected as a base case, the functional
unit is
the service provided by four student apartments of 28 m2
each,
Fig. 2. The case study building, as shown in elevation from the
south (empha-
sizing the selected half-block, with four one-storey apartments)
and the first
floor plan.
and Buildings 40 (2008) 837848over 50 years (the buildings
assumed life span).
2.1.2. Building materials
The actual building used as the base case for the analysis
was
built with reinforced concrete, cast in place for external walls
as
well as for floor and ceiling slabs. These concrete walls
(and
roof) are covered with extruded polystyrene (XPS), a rigid
foam
with closed cells that is produced in a continuous extrusion
process and marketed locally as Rondopan. This external wall
insulation layer has a thermal resistance value (R) of 1.82
km2/
W (approximately double that required by Israel Standard
1045), and is protected by a stone veneer approximately 5 cm
thick as the exterior finish material. Exterior insulation on
the
roof provides a resistance of R = 3.0.
For all of the alternative (hypothetical) envelope
configura-
tions, a reinforced concrete skeleton was taken as a
constant
including roof and floor slabs, as well as necessary
vertical
structural elements estimated to cover 33% of the original
wall
area. The remaining concrete (67% of wall area) was then
substituted by different infill masonry block types (using a
wall thickness of 20 cm for external walls and 10 cm for
internal
partitions). The totalwallR-value (1.96 km2/W) and finish
layers
were kept constant (identical to the base case) in all
configurations, by adjusting the insulation thickness
depending
on the insulating value of the particular mass material.
Windows,
floors and roof systems were also maintained constant for
all
configurations. Lightweight construction was not considered
since, in addition to being uncommon for residential buildings
in
-
rgythe region, it has been found to be climatically
inappropriate for
the Negev [42].
When considering different masonry blocks to be compared,
two principal groups of materials were considered. The first
group includes standard materials which are commonly
available in the Israeli market and in general usage for
residential construction. The first of these is the standard
hollow
concrete block (HCB), with dimensions of 40 cm 20 cm 20 cm, with
four cavities in two rows. These blocks areordinarily manufactured
using 1012% Portland cement.
Another common infill material that was chosen for
comparison
is the autoclaved aerated concrete (AAC) block, marketed
in Israel as Ytong or Ashkalit and which is lighter in
weight
(400500 kg/m3) and higher in thermal resistance than
ordinary concrete blocks. The process of their manufacture
is characterized by the high rates of EE necessary for
manufacturing of lime and Portland cement, for the grinding
of these materials and of sand, as well as for autoclaving.
The second group of materials considered includes
alternative masonry block types which are not currently
manufactured and marketed on a large scale, but that could
potentially fulfill the same function as the standard block
types.
These materials have been found in laboratory testing to
meet
the requirements of the Israeli construction industry for
compressive strength, durability and water absorption [43].
The following alternative materials were chosen for the
analysis: stabilized soil blocks (SSB) and fly-ash blocks
(FAB).
SSB: In many desert regions, adobe bricks can be produced
on-site from local soil and dried in the sun, with a very
low
investment of non-renewable energy. However, the loess soils
in
the Negev have a high percentage of montmorillonite clay,
which
experiences large volumetric changes with varying moisture
content that lead to cracking of the material. The durability
of
blocks made with this type of clay may be improved, and
their
compressive strength nearly doubled, with the addition of 4%
lime and 2% cement to the mixture [44]. The strength of
montmorillonite-based materials may further increased by
using
mechanical compaction [45]. While in Israel this material
has
only been used in individual initiatives, the industrialization
of
earth block manufacture in some locations, such as parts of
the
U.S. and Australia (where labor is relatively expensive),
has
made the material economically competitive [26].
FAB: Research carried out in the Negev has shown that
durable masonry blocks can be produced entirely without
cement which is highly energy-intensive in its production by
replacing it with two types of locally produced fly-ash
(based
respectively on low-calcium coal and oil shale). Both types
of
ash are industrial waste materials, produced as by-products
in
power-generation plants, and since a large portion (estimated
at
close to 1 million tonnes per year) of this waste is not
currently
recycled, it constitutes a potentially large-scale source of
pollution [46]. Given that the two-types of fly-ash are
available
waste materials, the products EE was assumed to include only
transportation (in various stages of the process) and final
block
manufacture. The composition of mixed fly-ash blocks (FABm)
used for the present analysis was 50% sand, 35% oil shale
fly-
N. Huberman, D. Pearlmutter / Eneash and 15% coal fly-ash, with
20% mixing water.The energy needed for production of FAB can be
reduced even
further more by substituting local soil for sand, which in fact
must
be transported from outside the Negev region. While this
configuration may reduce transportation energy, the extent of
the
reduction is dependent on the location of the manufacturing
plant
in which the final product is produced and its distance from
the
source of soil. This type of soil/fly-ash block (FABs), based on
a
composition of 70% loess soil and 30% oil shale fly-ash
(with
15% mixing water), has also been tested for compressive
strength
and durability with promising results.
2.2. LCEAinventory methodology
The LCEA inventory involves the actual quantification of
energy inputs to the system in the different life-cycle phases.
All
energy values are expressed in primary energy terms, using
the
common unit of GJ (109 joules) in order to allow comparisons
and additions between them. The particular methodology
utilized to calculate energy flows in each phase is as
follows:
2.2.1. Pre-use phase
Energy flows in the pre-use phase were quantified so as to
account for all direct energy inputs, whereas only a part of
the
indirect energy was included. The level of analysis was thus
limited to IFIAS level II, which is intended to capture most
(on
the order of 90%) of the energy inputs to the system [47].
Per-
unit embodied-energy values were derived for individual
building components (including major finish materials as
well
as bulk and insulation materials in the envelope) and then
multiplied by their quantities within the building as
designed.
While ranges of various raw material EE values were obtained
from published studies [27,28,4850], the embodied energy of
major components was calculated for the local situation by
combining the average of available data for raw materials
(e.g.
cement) with actual manufacturing processes (e.g. for the
production of concrete) and transportation energy
requirements
according to resource locations within the region.
In most cases EE values are based on the process analysis
method, which considers hierarchically the actual processes
responsible for producing the materialfrom the level of raw
material extraction, to building materials and element
produc-
tion, to construction of the entire building [47,51]. In cases
for
which raw material data were unavailable (such as expanded
polystyrene), the EE of the final product was obtained
directly
from literature.
For transportation energy, it was assumed that all final
product manufacturing took place in the city of Beer-Sheva,
within a 50 km radius of which most of the resources are
located (see Fig. 1). A common energy intensity factor of
1.57 MJ/(tonnes km) was adopted for all transportation of
materials, based on typical fuel consumption and related
energy
costs of trucking [52].
Energy required for on-site construction of the building
itself was estimated as a percentage of the overall material
embodied energy. The figure of 8% of initial EE was adopted
as
an intermediate rate, based on different approaches found in
the
and Buildings 40 (2008) 837848 841literature [11,32,53].
-
2.2.2. Use phase
Energy required for the provision of thermal comfort was
quantified on a yearly basis for heating and cooling seasons
and
assumed to be constant over the 50-year life span of the
building.
An active thermal simulation employing Quick II software
(TEMMI, Ltd.) was performed to quantify the operational
energy requirements of the building system for heating and
cooling. Loads were calculated by establishing a seasonal
comfort temperature set point (20 8C for winter days and 24
8Cfor summer days, with 50% humidity and infiltration rates
typical for local construction), and quantifying the thermal
energy required to maintain this interior temperature. A
ventilation rate of six air changes per hour (ACH) was
introduced during summer night time hours. To quantify the
yearly energy requirement, typical hot (July) and cold
(January)
energy-related carbon dioxide emissions. A direct translation
of
primary energy values to CO2 emissions was made by applying
a conversion factor [47].
2.3. LCEAimpact assessment
Results obtained in the LCEA inventory from the different
phases were summed over the assumed life span of the
building
for further evaluation. These primary energy values were
then
translated into quantities of CO2, a prime indicator of
environmental impact due to its role in global warming
[36,40,55].
Two different analyses were performed in order to evaluate
the inventory results. The first one was the calculation of
the
cumulative energy expenditure, measuring the energy
life-cycle
impacts of a given configuration by adding its overall
embodied
9]
(MJ
,852
,230
,216
,536
938
184
179
,890
,710
,766
,180
,420
N. Huberman, D. Pearlmutter / Energy and Buildings 40 (2008)
837848842daily cycles were simulated and the resulting daily
energy
requirements were multiplied by statistical factors
representing
the length of the respective cooling and heating seasons
(120
days for summer and 100 for winter). Thermal loads were
converted to delivered energy using the appropriate
efficiency
factors (COP = 2.9 for electrical air-conditioning in
summer,
and 0.7 for gas-fired heating in winter).
Physical properties of the various building materials
(density, conductivity and specific heat) were input to the
QUICK II software based on values from the software
database,
supplemented by local values [54] when appropriate.
It should be noted that numerous elements and factors were
acknowledged and considered outside the scope of the
analysis.
These include the EE of detailed features such as furniture,
appliances, infrastructure, and landscaping, as well as use-
phase energy for lighting, cooking, water heating, etc. As
mentioned previously, the analysis did not include upstream
indirect EE, recurring EE or post-use energy, and does not
address actual economic costs or aesthetic and social image
factorsany of which could be crucial for decision-making in
an actual design process.
Aside from energy consumption itself, global warming was
the only impact category studied in this LCA, as expressed
by
Table 1
Embodied-energy values of building materials in the Negev.
Sources: [4446,5
Material EE (MJ kg1) EE
Concrete 1.15 2
Reinforced concrete 2.60 6
Hollow concrete block 1.08 1
Autoclaved aerated concrete block 3.27 1
Stabilized soil block 0.49
Fly-ash block (mixed) 0.23
Fly-ash block (soil) 0.21
Stonec 0.79 1
Expanded polystyrenec 116 2
Glassc 18 46
Reinforcing steelc 35 273
Aluminumc 211 570
a Base case.b Alternative cases.
c Calculated as average of published values.energy and its total
operational energy over a 50-year life span
(both values given in terms of equivalent primary energy),
yielding energy consumption totals. The second one was the
payback period which in a general sense represents a break-
even point between various configurations, after which a
use-
phase advantage difference outweighs an opposite difference
in
the pre-use phase.
Since the energy results are shown here as a total primary
energy value without listing the details of fuels used, the
conversion factor adopted for CO2 emissions quantification
represents an average value of different energy sources and
their related emissions. However, based on the published
coefficients and the differences in the type of energy used in
the
analyzed phases it was decided to use different approximate
values for each phase (100 kg of CO2 produced per GJ of EE,
and 50 kg/GJ for OE).
3. Results
3.1. Pre-use phase: embodied energy
In Table 1 the derived embodied-energy values are shown for
the various building products considered in the analysis.
These
m3) EE (MJ m2 element) EE (MJ m2 floor area)
466548 1486a, 1024b
10591246 3378a, 2328b
243 241b
338 335b
138 136b
38 38b
36 36b
95 140
54271 376a, 216336b
374 96
593698 1891a, 1303b
6845 326
-
coefficients are listed in terms of energy per unit mass
(MJ/kg)
of the given material, as well as per unit volume (MJ/m3) to
account for varying material density. Calculated material EE
values are also shown per unit area of the given vertical or
horizontal element to account for its thickness, and per
unit
floor area to account for actual material quantities in the
case
study building (in both its actual and alternative
configura-
tions). It can be seen that the volumetric EE coefficients
of
secondary materials like glass and aluminum are higher by
an order of magnitude than those of mass materials like
reinforced concrete. When the relative volume of these
materials is taken into consideration, however, it is clear
that
the latter account for the bulk of the buildings total
embodied
energy (see also Fig. 4).
The EE coefficients calculated for these mass materials are
3.2. Use phase: operational energy
As can be seen in Fig. 5, the system with autoclaved aerated
concrete (and considerably less supplemental insulation) had
the highest OE requirements for both heating and cooling. As
all the wall configurations in this step are equivalent in
their
overall thermal resistance, it is clear that the higher
energy
requirement for this configuration is due to the relatively
low
heat capacity of the lightweight AAC block, and its relative
inability to store available energy (particularly absorbed
solar
energy in winter, as well as excess heat on summer days) and
to
reduce loads during the critical hours. Among the different
configurations, the lowest OE consumption is seen for those
configurations which combine a highly resistant external
insulation layer with an internal mass material of high
density
(and high heat storage capacity)such as reinforced concrete
N. Huberman, D. Pearlmutter / Energygeographically specific to
the Negev site in Israel, but were
found to fall within the range of published values from
various
studies in other countries. This can be seen in Fig. 3,
which
shows the Negev data in relation to the maximum values found
in the published range (from an Australian study [50]) and
to
the minimum values (from India [28]).
Fig. 4 shows a breakdown of embodied energy by material,
in the entire building as designed and with the hypothetical
substitution of non-structural concrete by various masonry
infill
materials. In each of these alternatives the insulation
thickness
is adjusted to maintain a constant overall wall resistance
(R-
value), and the finish material is held constant. These
substitutions result in substantial reductions in overall EE,
as
all of the different block types are at least 50% less
energy-
intensive in their production as reinforced concrete. These
reductions are in the range of 3040% for the entire
building,
and the lowest values are obtained with alternative (soil
and
fly-ash) blocks.
It is interesting to note that even though the
configurations
with reinforced concrete and hollow concrete blocks are both
based on cement (with its high embodied energy per unit
volume), the building constructed with concrete blocks
consumes more than 25% less total initial energy than the
base case (a reduction of over 150 GJ). This is due to the
large
quantity of cement in the solid cast-concrete relative to
the
Fig. 3. Comparison of EE coefficients of mass materials, as
calculated for theNegev and as published in studies from Australia
[50] and India [28].hollow block, as well as to the additional
reinforcing steel,
whose high EE coefficient of 275 GJ/m3 [48] makes it
particularly energy-intensive.
The alternative configuration incorporating AAC (Ytong)
blocks reaches a slightly lower EE total than the building
with
ordinary concrete blocks, despite the relatively high EE
coefficient of the AAC itself. This is because its higher
thermal
resistance allows an equivalent wall R-value to be achieved
with thinner layer of EXP insulation, which is far more EE-
intensive per unit volume than either type of block.
The EE results expressed in Fig. 4 are in total GJ for the
entire building system of a given floor area. In order to
evaluate
the scale of these values with respect to data from other
studies,
however, they may be better expressed in EE per unit floor
area,
and in this case the values reported here range from 3.28 to
4.91 GJ/m2. The literature on initial EE of entire buildings
has
produced a wide array of results, depending on the
methodology used, the country analyzed, the system bound-
aries, the construction technology, types of transportation,
etc.
but many of these identify ranges similar to the results
found
here. Some examples include 310 GJ/m2 [27], 412 GJ/m2
[12], and up to 11 GJ/m2 [56,57].
Fig. 4. Comparison of embodied energy by building configuration
(not includ-
ing on-site construction), with constant total wall R-value.
and Buildings 40 (2008) 837848 843(RC) and stabilized soil
blocks (SSB).
-
3.3. Life-cycle energy/impact
In Fig. 6, the cumulative energy consumption over an
assumed 50-year life span is shown for building
configurations
with different wall mass materials. Values at year zero thus
Fig. 5. Comparison of annual operational energy by building
configuration,
with constant total wall R-value.
N. Huberman, D. Pearlmutter / Energy844represent the embodied
energy of the given configuration
(including on-site construction as well as material EE), and
values at year 50 represent the total life-cycle energy
requirement including both production and operational
primary
energy consumption.
The most prominent difference seen between these
configurations is the relatively high life-cycle energy con-
sumption of the reinforced concrete base case building,
which
exceeds that of a concrete block building by over 150 GJ and
of
any other option by at least 200 GJand the source of this
difference is the concretes excess energy in production. TheFig.
6. Cumulative energy consumption by building configuration over a
50-
year life-cycle. Values at year zero represent pre-use embodied
energy
(including on-site construction)which for the base case building
exceeds
that of the concrete block alternative by an amount equivalent
to 25 years of
operational energy.savings yielded by these options relative to
the base case
amount to between 27 and 33% in terms of embodied energy,
and after 50 years of OE consumption up to 20% in terms of
cumulative life-cycle energy. Thus the scale of energy
required
for producing the building and its materials, and the
potential
for reducing it through simple material substitution, are in
this
case significant in life cycle terms.
The consumption of the AAC configuration has a higher
cumulative energy requirement than any of the other masonry
block options. While its embodied energy is slightly lower
than
the configuration with regular concrete block, its higher
operational needs become significant over a 50-year period.
As
emphasized previously, this difference is a direct expression
of
the walls thermal mass deficiency in a desert climate, since
its
total thermal resistance is equivalent in this case to all
other
options. At the same time, this lack of thermal mass does
not
increase the cumulative consumption of the AAC building
(within its 50-year life span) to the level of the base case
whose massive concrete walls are thermally advantageous, but
are produced with a large initial investment of embodied
energy.
Another interesting result is the lifetime consumption of
the
stabilized soil block (SSB) configuration, whose enhanced
thermal performance leads to the lowest cumulative energy
total of any configuration. This further demonstrates the
significance, here in life cycle terms, of utilizing both
internal
mass and external insulation in desert buildings.
An informative way of gauging the differences between
configurations is to quantify the embodied-energy savings of
a
given option relative to the base case, in terms of the
equivalent
number of years worth of operational energy. Under the
circumstance of the present analysis, the production energy
saved by substituting alternative materials in place of
poured
concrete is equivalent to the buildings heating and cooling
requirements over a period of 2330 years, depending on
particular type of masonry block. Although the SSB config-
urations initial EE is higher than either of the options using
fly-
ash, the SSB buildings lower operational requirements lead
to
a payback after less than 20 years, thus, constituting the
preferable mass material within the analyzed configurations.
Using the conversion factors detailed in Section 2.3 above,
the life-cycle carbon emissions may be estimated for this
best
case (SSB) relative to the base case configuration. The base
case was found to have a lifetime emission total of 76 tonnes
of
CO2, while the stabilized soil configuration totals 58
tonnes
(Table 2). Therefore the substitution of stabilized soil block
for
the non-structural concrete in the actual building is
responsible
for an estimated reduction of 24% in total CO2 emissions
during the life of the building.
4. Discussion
Underlying this analysis was the notion that in a modern,
climatically responsive desert building constructed with
industry-standard methods and materials, the energy required
for the buildings production could be just as significant as
the
and Buildings 40 (2008) 837848energy required to maintain
thermal comfort in it over its entire
-
useful life. This was indeed found to be the case, with
embodied
energy accounting for some 60% of the buildings overall
life-
cycle consumptiona relation which is consistent with
Table 2
Comparison of energy and related CO2 emissions by building
configuration
EE
Energy (GJ) CO2 (tones)
Reinforced concrete 615 61
Autoclaved aerated concrete block 445 44
Hollow concrete block 445 45
Fly-ash block (soil) 410 41
Fly-ash block (mixed) 411 41
Stabilized soil block 427 43
N. Huberman, D. Pearlmutter / Energyprevious statements that
production accounts for 4060% of
the total energy use in low-energy houses [14].
It was further found that this embodied energy could be
reduced significantly through design decisions involving
simple
material substitutions in its wall construction. When the scale
of
these reductions is evaluated in life cycle terms, it is seen
that they
may be equivalent to decades worth of operational energy
expenditures, and that they represent considerable
proportional
savings in total consumption even after the accumulation of
such
expenditures over a 50-year life span.
The greatest reductions, as expected, are obtained from
alternative materials using recycled waste and other local
resources, which have inherent benefits in terms of the
energy
intensity of their manufacture and transportation. What was
less
expected is the large scale of savings that can be obtained
from
standard materials i.e. conventional hollow concrete blocks
when compared to a structure built with full poured-concrete
walls.
An overview of energy consumption by life-cycle phase for
different mass material configurations is shown in Fig. 7,
as
normalized for the floor area of the building. This summary
shows that the base case building has a cumulative lifetime
energy consumption equaling just over 8 GJ/m2 of floor area,
and that this total may be reduced to 6.57 GJ/m2 by
substituting alternative wall materials.Fig. 7. Energy
consumption by mass material and life-cycle phase, per unit
floor area (over a 50-year life-cycle).Other studies that have
analyzed the life-cycle energy use in
residential buildings for a 50-year period have typically
shown
cumulative values of at least 15 GJ/m2 [11,14,57], with
great
differences in maximum values depending on the
methodologies,
system boundaries, geographical location, materials and
building
design. The relatively low values in this study may be
attributed
to a combination of low EE coefficients (relative to values used
in
the Australian studies cited above) and low operating
require-
ments, due to the buildings thermally efficient design. Also
the
analysis does not include operational energy that is not
connected
to heating and cooling requirements (appliances, recurrent
embodied energy, etc.), nor does it account for the post-use
phasewhich could noticeably increase the final values when
comparing with other studies.
One of the distinctions revealed by the analysis is the
specific
dependence of the results on local circumstances in the
desert
climate. For example, when lightweight AAC blocks (which are
generally assumed to be energy-efficient) are used in a wall
section whose overall thermal resistance is no higher than in
the
other options, the resulting cumulative consumption is
higher
than that of any other block walldue to the relative lack of
thermal mass as a basic quality of the material. The importance
of
thermal mass was also demonstrated by the life-cycle energy
advantage found for stabilized soil blocks, which have a
higher
heat capacity than those made from fly-ash.
It was found in a sensitivity analysis that the importance
of
this thermal mass would be further increased if the
buildings
detailed design allowed the potential for solar gain to be
better
realized, modifying the life-cycle energy consumption values
of the configurations and the relationship between them. In
this
and other ways, the results of the analysis are in fact
dependent
on the specific design details of the building examined, and
on
OE Cumulative energy
Energy (GJ) CO2 (tones) Energy (GJ) CO2 (tonnes)
309 15 923 77
375 19 820 63
336 17 782 61
358 18 768 59
358 18 769 59
314 16 741 58
and Buildings 40 (2008) 837848 845the subjective criteria
adopted. In this sense the study is not an
optimization exercise per se, but rather a comparative
analysis using a selected set of realistic alternatives.
The results of the analysis also highlight the importance of
several other methodological issues. Since LCA software
tools
are still of limited usefulness due to the extent of
available
databases, site-dependence, etc., the identification of
mean-
ingful relationships necessitated a detailed local analysis
of
material energy properties for each building phase studied.
In
the absence of EE coefficients for Israel, and particularly for
the
Negev, this required an in-depth process analysis (in this
case
was conducted up to IFIAS level II), accounting for energy
flows from the stage of raw material extraction all the way to
the
-
rgyconstruction site. It is again stressed that there are
numerous
types of upstream indirect energy inputs which are beyond
the scope of this analysis.
Life-cycle energy results demonstrated the importance of
evaluating EE values of basic building materials when used
in
realistic quantities in an entire building, rather than
simply
comparing their embodied-energy intensity per unit volume or
weight. One illustration of this is the comparison of hollow
concrete block and reinforced concrete (RC) as wall infill
materials. Per unit wall volume, solid poured concrete has
high
concentration of cement and also contains reinforcing steel
leading to a material EE coefficient which is 500% higher
than
hollow concrete block. When placed in the whole building,
however, the total embodied energy of the RC configuration
is
only 37% higher than the building with HCB. Another example
is
the configuration with wall blocks based on fly-ash: while the
ash
itself is considered a zero production-energy industrial by-
product (which if not reused represents a potential pollutant),
it is
part of a building whose overall EE is nevertheless
considerable.
It should also be emphasized that the actual life span of a
building is dependent on the durability of its materials and
construction. In the present study, the materials selected and
the
options considered were limited to those which could be
assumed to have a useful life span of 50 years, without
significant energy expenditures for maintenance or
renovation
(recurrent EE). In addition, all the building systems include
a
reinforced concrete structure in order to meet the
requirements
of local standards (for seismic resistance, etc.). However,
this
assumption of a 50-year useful life span for all of the
material
configurations is based on limited data, and it is not possible
to
quantify the actual amounts of energy which would be
required
for their maintenance over this period. This is especially true
for
alternative materials such as stabilized soil brick, which
has
been shown to meet durability requirements in laboratory
testing [44,45,58], but is not commonly found in the
existing
local building stock.
While the studied wall systems (mass, insulation and finish
materials) represent a significant portion of the initial EE of
the
building, the concrete structure (columns, beams, floor and
ceiling slabs) on average constitutes about 50% of the
buildings pre-use phase energy. This proportion could
diminish to some extent if recurrent EE were included in the
analysis (given that walls generally need maintenance and
the
structure is assumed to last for the duration of the
buildings
life), but there can be no doubt that the energy-efficiency
of
structural systems is an issue which has not been
sufficiently
addressed in the LCA literature. It is also a crucial
determinant
which, if improved upon significantly, could lead to vast
reductions in building energy consumption and environmental
impact (for instance by considering roof forms such as
vaults
and domes which, through their structural efficiency, can
make
use of alternative materials whose strength is insufficient for
flat
slabs). Alternative materials for insulation represent still
another possibility for life-cycle energy reduction.
Operational energy needs, at least for heating and cooling,
are quite commonly calculated by applying existing tools and
N. Huberman, D. Pearlmutter / Ene846assuming currently realistic
temperature set points, patterns ofin AAC becomes more apparent and
makes its life-cycle
energy prospects less desirable.
These findings offer evidence that alternative materials
using waste or local resources can be utilized in the creation
of
more sustainable desert architecture, minimizing energy
demand while enhancing the quality of the built environment.
Acknowledgements
The authors are grateful to the Albert Katz International
School for Desert Studies of the J. Blaustein Institute for
Desert
Research, Ben-Gurion University of the Negev, for making
this
study possible.
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N. Huberman, D. Pearlmutter / Energy and Buildings 40 (2008)
837848848
A life-cycle energy analysis of building materials in the Negev
desertIntroductionEnergy in IsraelEnergy-efficiency in the life
cycle of buildingsPrevious studies
MethodsLCEA-goal and scope definitionStudied systemBuilding
materials
LCEA-inventory methodologyPre-use phaseUse phase
LCEA-impact assessment
ResultsPre-use phase: embodied energyUse phase: operational
energyLife-cycle energy/impact
DiscussionConclusionsAcknowledgementsReferences