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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: norah@bgu.ac.il (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