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Accepted Manuscript

Title: Analysing the life cycle greenhouse gas emission andenergy consumption of a multi-storied commercial building in

Singapore from an extended system boundary perspective

Authors: Harn Wei Kua, Chee Long Wong

PII: S0378-7788(12)00175-2

DOI: doi:10.1016/j.enbuild.2012.03.027

Reference: ENB 3678

To appear in: ENB

Received date: 17-9-2011

Revised date: 10-3-2012

Accepted date: 13-3-2012

Please cite this article as: H.W. Kua, C.L. Wong, Analysing the life cycle greenhouse

gas emission and energy consumption of a multi-storied commercial building in

Singapore froman extended system boundary perspective,EnergyandBuildings (2010),

doi:10.1016/j.enbuild.2012.03.027

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http://dx.doi.org/doi:10.1016/j.enbuild.2012.03.027http://dx.doi.org/10.1016/j.enbuild.2012.03.027http://dx.doi.org/10.1016/j.enbuild.2012.03.027http://dx.doi.org/doi:10.1016/j.enbuild.2012.03.027


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Analysing the life cycle greenhouse gas emission and energy consumption of a multi-storied

commercial building in Singapore from an extended system boundary perspective

Harn Wei Kua1,2

, Chee Long Wong3

2Department of Building, School of Design and Environment, National University of Singapore, 4 Architecture Drive,

S117566, Singapore3Master of Science in Environment Management Program, School of Design and Environment, National University of

Singapore, 4 Architecture Drive, S117566, Singapore

ABSTRACT

Building life cycles contribute substantially to the emission of greenhouse gases and energy consumption; this

is especially true for the operation or use stage of the building. This work on a commercial building in

Singapore extends the traditional system boundary drawn for a whole-building life cycle assessment to include

the management of wastes produced during building operations. It was found that waste management

produces much more emissions than the operation stage. This reinforced the notion that waste recycling

should be further promoted in buildings, possibly through building level technological innovations and design

modifications. An integrated policy framework was proposed to explore ways by which building level strategies

can work with other strategies to holistically address the issues of waste reduction, sorting, collection and

recycling.

Keywords: life cycle assessment, integrated assessment, integrated policies, sustainable development,

embodied energy, Singapore.

1. Introduction1.1 Building industry and climate change

The building sector is a major contributor to carbon emissions. According to Ochsendorf [1],

buildings in United States of America account for nearly 39% of its nationwide carbon dioxide (CO 2)

emissions. In Singapore, the construction industry has been proclaimed as the third largest emission

sector, accounting for about 16% of Singapores overall CO2 emissions of 40,377 kilo tonnes in 2005

[2]. Most of the electricity used by buildings in Singapore is for air-conditioning (40-50%), mechanical

ventilation (about 20%) and lighting (15-20%).

Singapore has since set high environmental targets to improve its energy efficiency by 35% andincrease its waste recycling rate to 70% by 2030. In response to these targets, Singapore has

adopted the approach of greening buildings as key initiative in reducing CO2 emissions for the built

environment. Introduced in January 2005, the Building and Construction Authority (BCA)s Green

Mark Scheme (GMS) serves as the national assessment criteria system to recognize both new and

existing buildings locally which adopts environmentally friendly features such as increasing green

cover, use of energy and water efficient technologies to reduce consumption, among others. Since

April 2008, under statutory requirements all new or existing buildings above 2,000m2

in area

undergoing major retrofitting has to attain at least a Green Mark Certification. As of 1 Sept 2010, a

total of 524 buildings (existing and new) have been at least certified under the GMS [3]. Although

1Corresponding author. Email address: [email protected]. Telephone: +65 6 516 3428.

anuscript


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the GMS has attained plausible achievements since its introduction, it is not without its

shortcomings.

In the latest version (version 4 [4]) of the GMS for non-residential and residential buildings, the

computation of carbon emissions is awarded a maximum of only 2 points (out of 155 points) for

carbon footprint reporting. The reporting requires new buildings to assess their construction and

operational carbon by means of either reporting through a carbon consultant or through a simple

form in declaration of the amount of key materials, electricity and renewable energy source

consumed. Since then, BCA has received numerous feedbacks calling for more weightage to be given

to accounting for the buildings carbon footprint as an indicator of building sustainability. More

specifically, there are proposals to include a life cycle approach to the computing of energy

consumption by building stocks, and then look for ways to reduce their life cycle energy requirement

and greenhouse gas (GHG) emissions. Therefore, it is fair to say that conducting life cycle studies on

building stocks in Singapore is only beginning to catch on.

1.2 Applying life cycle assessment (LCA) to analyse energy consumptions of entire buildings

LCA is a process whereby the material and energy flows of a system are quantified and evaluated

according to their life cycle stages, which, for a typical building, normally include the material

extraction, production, transportation, construction, use (also known widely as operation),

renovation, deconstruction and/or demolition, and recycling stages. According to international

organisation for standardisation (specifically, ISO14040) [5], LCA studies generally consist of four

phases: goal and scope definition, life cycle inventory (LCI), impact assessment and interpretation of

results. The goal and scope defines the objectives, assumptions and system boundaries of the

studies. The LCI involves data collection and calculations to quantify material and energy inputs and

outputs of the defined system. Impact assessment evaluates the significance of potential

environmental impacts based on the LCI. Finally, these impacts, which may be expressed in the form

of global warming, are calculated for environmental assessments. As a whole, LCA allows for

comparative evaluations of impacts of different processes and building materials on the

environment.

There were LCA studies done specifically on quantifying energy consumption during the different

life cycle stages; this approach is known as life cycle energy analysis (LCEA). Ramesh et al. [6] divided

the energy uses in the various life cycle stages into initial embodied energy (EE), recurring embodied

energy (EEr), operating energy and demolition energy. During periodic building maintenance, energy

is used to refurbish the building, whereby materials are either repaired or removed and then

replaced with new ones. The EEr used for such maintenance is the sum of the embodied energy of

the material and the energy used for working on these materials. The sum of these energy

components is known as life cycle energy. Their definitions are concurred by most of the studies in

the current literature.

Many LCEA have been conducted. Studies such as [7], [8], [9] and [10] showed that as much as

85% of the total energy consumption throughout a building life cycle was used in the operation

phase, whereas the manufacturing of construction materials, erection and renovation of buildings

collectively account for around 15% of the total energy use. Citherlet and Defaux [11] found that by

reducing operation energy by 20%, through the improvement of thermal insulation of envelope, the

total life cycle energy can be reduced by about 16%. Furthermore, they found that by further


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increasing the insulation with technologies such as 3-paned windows with low-e coatings, the

operation energy can be reduced by 54%, thereby resulting in an overall reduction of 49% in the life

cycle energy.

However, there were also studies showing that 40-60% of the life cycle energy is used in the

production and construction stages [12]. Specifically, Thormark [13] showed for Swedish low-energy

houses that material substitution could reduce the share of energy use in the material production

phase by 17% for a row house and by 15% for an apartment building. Even if the EE constitutes a

comparatively low fraction of the total life cycle energy than operation energy, opportunities to

reduce EE should never be ignored. In fact, in certain cases, materials with high thermal insulation

capability have lower EE (for example, cases considered in [14] and [15]). In these cases, a switch to

these materials will result in reductions in both embodied and operation energies. In other words,

when prescribing energy reduction solutions, one should not independently focus on the operation

phase.

In the majority of the whole-building LCEA and life cycle GHG analysis (LCGA) in the current

literature, processes that are considered under the operation phase comprise of cooling, heating,

ventilation, lighting, supply of water, heating or cooling of water, and operating of other electrical

appliances. The end-of-life options in these whole-building LCA are usually confined to the

demolition or recycling of building materials. Although wastes including waste heat, used water

and solid wastes are produced from a buildings operations, management of these wastes are

usually neither considered in the operation nor end-of-life phase; only construction and demolition

(C&D) wastes are usually included. Put in another way, these LCA typically restricted the system

boundary of their analyses to the building scale. However, Dodoo et al. [16] considered the role

played by district heating from a combined cycle heat and power (CHP) plant in their LCA of the

primary energy consumption of a wooden apartment building designed to meet the Swedish

building code. This exemplifies an effort to integrate a district-level condition/factor into a building-

scale analytical framework, and hence extending the system boundary. To a lesser degree, this

observation was also made by Sartori and Hestnes [17]. If the objective of a LCA is to fully

understand how the life cycle of a building creates an environmental impact on its immediate

environment through creating a demand for resources and production of wastes that have to be

assimilated into its environment then extending the conventional system boundary is necessary.

The authors called this approach an extended system boundary perspective.

This work contributes to the literature in two important ways: it provides the first ever LCEA and

LCGA on a commercial building in Singapore, and adopts an extended system boundary perspective

to fully assess the environmental impacts of the case study building. The main research objective is,

through a comparison of the energy consumption and GHG emissions from the different life cycle

stages, provides a guide for integrated policymaking to reduce the total life cycle energy

consumption and GHG emissions of this building.

2. MethodologyThe case study is an industrial project that is a six-storey ramped up food-factory in Singapore. It

was constructed in Year 2003 at a cost of about 47 million Singapore Dollars (SGD; this is equivalent

to USD 36.2 million), and occupies a land area of 27,029 m2

and has a total gross floor area of 52,094


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m2. The net tenable space is 35,262m

2and presently it houses a total of 204 food tenants and 1 food

court. The building has a total common area of 16,832m2. With operations round the clock, the food

factory sells food products for the mass market, which includes the selling of basic food such as salt

and rice, production of foods such as soy bean products, cakes and pastries, providing catering

service for functions and events. Equipped with various green features, including daylighting

technologies, it is poised to be exemplary for green design for multi-storied commercial buildings in

Singapore, it is chosen as the main subject of this study.

The facilities managers who are in-charged of the monitoring of its building performance

frequently collect and collate reports on, for example, utilities consumption and waste volume

collection reports. In addition, the volume of construction materials used for routine maintenance

were also measured and recorded within payment systems for audit purposes. These data sets were

shared with us during this study.

However, due to the lack of reliable data, GHG emissions and energy usage arising from the

transportation of individual building users and delivery vehicles, and sewage discharge were

excluded from the study. Carbon offset potential from existing onsite greenery was also excluded. In

determining what types of emissions to consider for each of these life cycle stages, we followed the

guidelines of the World Resource Institute (WRI) and World Business Council for Sustainable

Development (WBCSD) [18], which categorizes emissions into 3 scopes: scope 1 refers to all direct

onsite emissions; scope 2 refers to the embodied emissions in purchased energy; and scope 3 refers

to all indirect emissions. Table 1 shows the system boundary considered for the LCEA and LCGA and

the different types of emissions that were considered for each of the life cycle stages.

Data for the LCIs was obtained using two approaches. Process analysis was applied to find out the

energy use and emissions for every detailed process in each of the life cycle stages considered. In the

absence of reliable process data, macroscopic industry-wide data extracted from economic input-

output (EIO) tables was used. This hybrid method is widely known as the EIO-LCA methodology. The

detailed methodologies and source of data and information are described in the following sub-

sections.

2.1 Production and transportation of building materials

Table 2 shows the quantity of different types of building materials utilized in the building. This

distribution is similar to the case study on a building in Thailand [19], in which the authors found that

steel and concrete together accounted for 77.8% of all EE. Only the EE and EEm (embodied

emissions) contributions by concrete (Ordinary Portland Cement (OPC), gravel, sand) and steel were

considered in this study. This data is derived using the process analysis approach. Singapore imports

most of its OPC from Taiwan. The energy consumption data associated with the stages from

secondary raw materials to OPC production were obtained from companies based in Hualian, Taiwan

[20]. The fuel consumption data from transportation of manufactured OPC from Hualian to

Singapore was also obtained by Teo et al. [20]. Diesel consumption for transportation within

Singapore and associated emission data were based on an average distance of 20km from port to

cement company and then from cement company to the location of the building. Assuming that to

produce 1kg of OPC, 0.063kg of gypsum and 2kg of limestone are needed; the LCI of gypsum andlimestone were obtained from [21]. Furthermore, 1kg of concrete block is assumed to be composed


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of 0.5 parts (by mass) water, 1 part OPC, 2 parts sand, and 3 parts gravel. The LCIs (including

uncertainties in the readings) for all these constituents were taken from the study by Kua [21].

Maghimai and Kua [22] derived the LCIs for the production of primary and secondary steel.

Within Singapore, the production of secondary steel via the Electric Arc Furnace (EAF) method was

considered. Singapore does not produce its own supplies of primary steel and it obtains much of its

primary supplies from China. Therefore, LCIs for the extraction of iron ore, sintering and pelletizing,

production via the Basic Oxygen Furnace (BOF) method and continuous casting were derived for

China. Finally, the LCIs for the transportation of the finished steel products to Singapore were also

estimated. The EE and EEm data for steel was taken from their work.

2.2 Building construction

To find the energy required for, and the resultant emissions from, construction activities in

Singapore, the economic input-output tables of Singapore were used [23]. Table 3 shows the

quantities of petroleum products (mostly industrial oils imported from Thailand and China),

electricity and liquefied natural gas sales to construction industry (for construction of buildings and

not for civil infrastructure). The direct GHG emissions are calculated using the following formula:

(1)

where the total GHG emission from construction is expressed as carbon equivalent. isfloor area

ratio of the the building to the total floor area of building constructed in 2005. This allows us to

estimate the fraction of the total construction-related emissions and energy consumption that can

be attributed to the the building. Since the total floor area of the building is 52,094m2

and the total

floor area built in the whole of Singapore in 2005 is 10.419km2

[24] the ratio is 0.005. is the

quantity of the commodity c consumed. is the average tariff of the commodity c. is the

emission factor for the GHG type g for every commodity c, expressed as (kgCO2 per kWh) or (kgCO2 per

kg of commodity). The three types of emissions with the highest Global Warming Potential (GWP)

were considered - that is, CO2, methane and nitrous oxide.

Unlike the method employed by Kofoworola and Gheewala [19], the primary energy factor was

not considered explicitly in eq.(1); this is because in calculating the emission factors for eachcommodity, the EE and EEm from all major life cycle stages (that is, material acquisition, production,

infrastructure and transportation) were already included. In fact, this method is expected to be more

accurate. The values of the variables in eq. (1) are shown in table 3.

2.3 Building operation

As shown in table 1, the energy consumptions and emissions due to electricity and water

consumptions were considered. The common areas of the building hosts a range of services and

facilities such as common corridors, staircases, ramped-up driveways, bin centres, car parking lots,

lifts (passenger and cargo), loading/unloading bays, smoke control systems, and fire protection


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systems. Energy is required in these areas for different functions, including provision of lightings to

all common areas, the powering of lift motors for lift operations, pumps for distribution of water

supplies, and fans for smoke control systems. The power supply to common areas are tracked by a

master electricity sub-meter, which is separated from the leased and sold units in the buildings

(these units have their own electricity sub-meters for individual accounting and billing). This model

enables building owner to monitor and manage power consumption for areas under their operations

control effectively. The monthly electricity consumptions are closely monitored by facilities

executives. The total amount of purchased energy for the period between 1 Jan 2010 to 31 Dec 2010

was used for this study, and it was found to be 1,946,430 kWh. The GHG emissions from the use of

electricity were then computed using the tier 2 (country-specific) approach recommended by the

Inter-governmental Panel on Climate Change (IPCC) [25]. That is,

(2)

where means a fuel mix of 80% natural gas and 20% fuel oil, and the emission factorof

0.5863kgCO2/kWh was taken from Tan et al. [26].

Singapore gets 60-70% of its water supply from imported water (from Malaysia) and the local

water catchment areas. Our LCA of water considered the main stages of the water treatment

process screening and grit removal, primary sedimentation, coagulation and flocculation,

secondary settling, filtration, sludge processing, disinfection and distribution. The system boundary

is shown in Fig.1. Similar to the electricity case, the emission from water consumption can be

computed as follows:

(3)

Wong [27] found that the emission factor of water in Singapore is approximately 0.150 kg CO2-e / m3

of

water. The total water consumption for the assessment year was 40,188.9m3

(obtained from the

facilities managers of the building).

Since the design lifespan of the building is 30 years, we estimate its lifetime emissions and energy

consumption during the operation phase by multiplying the values derived above by 30 years.

2.4 Building maintenance and renovation, EEr

For this life cycle stage, the EEr associated with the renovation of the different areas within the

building was considered. Due to possible changes in the tenants, individual units in the building may

undertake their own renovation works. These may include the changing of carpets, wall tiles and

installations of new computers. However, for the past few years, it has been observed that several

types of materials namely, concrete, cement, sand screed, and mild steel represent about 80% of

the renovation materials; only these were considered. The formula used is


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(4)

where is the average lifespan of the material and is the design lifespan of the building,

which was taken to be 30 years. is the quantity of the material and is the embodied energy of

material per unit mass. Eris the energy required for the renovation to be performed on material i.

In summary, eq. (4) calculates the number of times a certain material will be replaced throughout

the design lifespan of the building, and multiply the result by the embodied energy of a unit mass of

that material during renovation; this is then added to the energy required for working on that

material to yield the total EEr.

Since these materials were replaced once per year, we take the value ofLi as one. The value ofEr

was taken from Yap [28]. Inventories for transportation of the salvaged concrete and steel to

recycling centres were computed based on an average distance of around 30km using the same

model used in reference [29].

2.5 Building end-of-life

As mentioned earlier, traditionally, the literature covered only the demolition or recycling of

demolition wastes during this life cycle stage. Besides considering these, we also adopted the

extended system boundary perspective to explore the energy consumption and emissions due to

management of wastes produced during the operation phase.

2.5.1 Demolition of buildings

Energy consumption in this phase was calculated from the use of demolition machinery and

tools. Phua [30] conducted a series of case studies on demolition projects of similar scale, each of

which requires an average of 4 months to complete. Energy consumption is estimated from the use

of onsite generators and from electricity bills. Diesel consumptions are found for tractors, crushers,

breakers, backhoes and electro-magnetic separator/sorter. The total amount of electricity and fuels

recorded for each of the demolition projects was then divided by the total mass of wastes collected

in each project to give the average energy consumption and emission intensity of demolition. This

intensity was applied to estimate the buildings energy requirements and emission during demolition

in the future.

After demolition, the wastes are transported to the sorting centre in the north-western part of

Singapore. The distance between the building and this centre is about 35km. Assuming that the rates

of recovery of different types of building materials in the building are similar to the cases covered in

Phuas study, and that the trucks used for transporting these wastes always travel with full loads, the

total fuel demand of transportation can be estimated. The total emissions and energy consumption

of this stage included the EE and EEm of the fuels (mostly diesel) used in the demolition process.


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2.5.2 Extended system boundary perspective: management of wastes generated during operation

General Industrial Waste (GIW) accounts for at least 80% of the total 2.613 Mtons of waste

generated from the building in the year of this study. Majority of the waste are wet food wastesgenerated from the processing of food products. As part of performance monitoring, it is a

requirement for the waste collection contractor to submit daily waste disposal records reflecting the

volume of waste sent to incineration plants. Such requirement had allowed for monthly waste

volume output to be recorded and these records were used for this research. Recyclable wastes

accounted for only about 1% of the wastes generated, whereas the remaining 19% was divided

between sewage and sludge wastes; since consistent data for these wastes was absent, they were

left out from the study.

GHG emissions from the incineration plant and transportation of wastes were accounted for; this

included transportation of wastes from the building to incineration plant (Senoko Power Plant,situated in the north part of Singapore), transportation of ash from incineration plant to Tuas Marine

Transfer Station, subsequent shipping of the ash offshore to Pulau Semakau landfill site and the final

landfilling of the ash. Fig.2 summarizes the system boundary of this stage. CO2 emissions factor from

incineration in Singapore was adopted from Tan et al. [26] namely, 1.6kgCO2 per kg of waste

incinerated.

Methane (CH4) emissions are generated as a result of incomplete combustion during the

incineration. Hence, such emissions are more significant for incinerators which are poorly

maintained or having low oxygen level. In large and well-functioning incinerators, such emissions are

usually small in volume. Nevertheless, we considered this type of emissions as well, using the IPCCtier 1 method:

(5)

where, the factor 21 is the GWP of CH4, IWiis the total amount of solid waste of type i(wet weight)

incinerated (measured in thousand tons per year), EFCH4 is the aggregate CH4 emission factor in kg CH4

per thousand tons of waste, and the factor 10-6

is for converting the unit kilogram to thousand tons.

Since the Senoko incinerator belongs to the continuous incineration, stoker type, the typical EFCH4 is

taken to be 0.2 [25].

During the combustion process, Nitrous Oxide (N2O) is emitted at relatively low combustion

temperature of between 500C and 950C. The amount of N 2O emissions from waste combustion

depends on the type of technology, combustion conditions, technology applied for NOx removal as

well as the contents of the waste stream. Similar to the case of methane emissions, N2O emissions

can be calculated using the IPCC tier 1 method:


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(6)

where 310 is the GWP of N2O, IWi is the total amount of solid waste of type i (wet weight)

incinerated (measured in thousand tons per year), and EFN2O is the aggregate N2O emission factor in

kg N2O per thousand tons of waste. The typical EFN2O for the incinerator that Senoko Power Plant

typifies is 47 [25].

SenokoPower Plant consumes around 0.05TWhe annually for its internal operations (including

the various operations related to electricity generation) 3% of which is derived from the

combustion of about 1.3Mtons of wastes. By direct proportion, the 2,613 tons of wastes produced

by the building that is combusted at Senoko accounts for about 10,916MJ of electricity generated for

its operations. The remaining 97% of Senokos energy supplies are derived from natural gas; the EE

and EEm of natural gas were also considered in this life cycle stage. Data for the entire

transportation sequence and final landfilling of the incinerator ash was taken from an earlier study

by Kua [29]. The energy consumptions and emissions results derived for one year were multiplied by

30 years to represent the lifetime energy consumptions and emissions of the building.

3. ResultsThe raw materials acquisition and processing of building materials of the building required a total

of 27.9TJ of energy and emitted about 10.94 Mtons of CO 2 equivalence. A comparison of the

embodied and operation energy over its lifespan of 30 years indicated that the embodied energy

was about 13.2% of the operation energy (regardless of whether the embodied energy of the water

consumed is also considered). This value agrees well with a similar building operating in similar

tropical climatic conditions in Thailand [19]. However, the 30-year operation energy of the the

building was found to be 5.96GJ/m2; this implies an annual energy consumption of 55.2kWh/m

2,

which is within the 15th

percentile of commercial buildings in Singapore.

Comparisons of the energy consumption and GHG emissions of the various life cycle stages were

made with and without considering waste management.

3.1 Waste management not considered

The building is expected to consume 245.45 TJ of energy and emit 42.88 ktons of GHG

throughout its 30-year lifespan. The contributions of the various life cycle stages to the life cycle

GHG emissions and energy consumption were shown in Figs. 3 and 4. Materials production

accounted for 13.71% of the GHG emissions and 11.37% of the energy consumption. This agrees

with the results of Ramesh et al. [6] and Koforowola et al. [19]. The construction process accounted

for only 0.96% of the emissions and 0.91% of the energy consumption, which also agree well with

previous studies ([6], [19], [31], [32], [33] and [34]). Lifespan operation of the building is expected to

consume 86.10% of the total energy and emit 80.27% of the GHG emissions. Demolition accounted

for about 0.37% of the energy consumption and 0.40% of the GHG emissions, which agree well with

the study by Koforowola et al. [19].


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3.2 Waste management considered

If the waste management stage is considered within the system boundary, it was found that the

life cycle energy consumption and GHG emissions were increased to 246.46 TJ and 169.26 ktons

respectively. This means that waste management increases the total life cycle GHG emissions by

3.95 times.

As shown in Figs. 5 and 6, waste management contributed 74.67% of the total emissions, and the

operation and material production phases contributing 20.33% and 3.47% of the emissions

respectively. The share of emissions of all other life cycle stages also decreased. Since the energy

demand of waste management is typically low, it contributed 0.47% of the energy consumption and

did not significantly change the distributions of energy observed in the previous section.

3.3 Sensitivity analysis

An important part of a LCA is examining how results can change in the presence of uncertainties

and variability in data. The comparisons involving waste management were based on the

assumption that the annual waste generation rate of the building is maintained throughout its

lifespan. However, the relative emission contributions of waste management and operation will

change with the amount of waste generated. As shown in Fig. 7, waste management contributes

more emission than operation unless the lifetime emission from waste management is only 35

ktons. For this to happen, an average annual fractional change in emission, r, is required and it can

be found by solving the following equation:

(7)

where 4.213 ktons is the GHG emission from the 2.613 Mtons of wastes produced during the year of

study. r was found to be about 0.88; that is, for waste management and operation to contribute

equal percentage of emissions, there has to be a reduction of 12% of waste production every year.

This is equivalent to every one of the 204 units in the building reducing his/her daily waste

production by 4.2kg for the first year. It was assumed that reducing the waste generation will

neither affect nor be affected by the use of electricity and/or water during the buildings operation

stage.

4. Integrated multi-level policy and technology strategies to reduce the impact of wastemanagement

Conventional LCEA and LCGA for buildings point to the operation stage of buildings as the stage

where most attention is needed to reduce the overall environmental impact of buildings. This has

given rise to technology, design and policy strategies focusing on energy conservation and

renewable energy utilization. However, if the system boundary is extended to include the impacts

due to the management of the wastes, this study showed that incineration of wastes produces much

more emissions than the operation of buildings. Hence, the extended system boundary perspective


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provided a hint that attention should be put on reducing the generation of all types of wastes (and

not just on C&D wastes) during the operation phase of the building and increasing the recycling of

those wastes that have to be inevitably produced.

It is important to note that total life cycle emissions of a building cannot be reduced merely

through building-level strategies. For example, if local power stations rely on incineration of wastes

as a cheap method of generating electricity, then there may be a certain degree of resistance from

municipalities to fully support waste recycling. To be successful in increasing total recycling rate and

hence reducing incineration, what is needed is a confluence of policies operating coherently at

different scales to increase waste sorting, collection and recycling. This can be seen as a form of

integrated sustainability policy, which was defined by Kua [35] as a policy that tackle multiple

objectives or indicators at the same time in a coherent manner. Fig.8 showed a multiple time- and

spatial-scale model that defined the operational scales and material flow relations among different

downstream life cycle stages of buildings and the physical environments in which they are

embedded. To reduce the reliance on waste incineration for energy production, differentapproaches at the building, precinct and national levels are required. A near term strategy is to shift

toward a higher utilization of natural gas as fuel for power plants. A long term solution is to increase

the share of renewable energy at the national or municipal/precinct levels; a detailed discussion of

renewable energy policies is beyond the scope of this study.

Concurrently, more efforts should be made to increase waste sorting and collection at the

building and precinct levels (readers are referred to [36] and [37] for more discussions on this

matter). As material flows across different geographical levels (Fig.8), energy is consumed for

transportation and GHG is emitted. Therefore, strategies taken at the building and precinct levels are

preferred (shaded blocks in Fig.8). In the building, the majority of the 80% of the GIW generated are

food wastes, so building and precinct level strategies such as decentralized food waste digesters and

micro-generators could be considered. Energy generated can be directly fed back to the building or

the national grid. Asian Square Tower One in Singapore has recently installed a biodiesel generator

that runs on waste cooking oil collected from the towers own and neighbouring food centres. This

system can be improved by installing an onsite modular bio-digester and connecting it to the biofuel

generator.

Residential buildings can be redesigned to encourage waste sorting at the building level. For

example, more than 80% of Singapores population live in high-rise flats where wastes are disposed

in common refuse chutes. Recently, the Singapore government has initiated changes to the design of

new flats in a new housing estate known as Punggol New Town. The new design provides separate

chutes for different types of wastes, and it is hoped that this will encourage more residents to sort

their wastes into recyclables and non-recyclables at source. Nationwide and within precincts, efforts

were made to re-design the immediate physical surrounding of a building to encourage waste

sorting; an example is the town councils installing more recycling bins within close proximity of a

building. However, these measures may not result in substantial increase in waste recycling; this is

because local waste recyclers find it difficult to clean collected recyclables that are contaminated

with food wastes and hence a considerable portion of these recyclables are incinerated instead.


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Therefore, in addition to providing separate chutes, the government should consider providing a

special chute outlet for food wastes and encourage residents to clear food wastes from recyclables

before discarding recyclables in appropriate chutes. The food wastes can then be collated at the

precinct-level facility, where a bio-digester can be employed to produce biogas from the wastes; the

biogas can then be used to run a biofuel generator. Possible feedstock sources include food centres,

supermarkets and restaurants near the precinct. These food wastes can be collected through a

system comprising manual collection by commercial vendors and automated technologies (such as

waste suction system). Incentives should also be provided to encourage households sort out food

waste at home. For example, if separate metering is possible, each household will pay a lower

electricity tariff for electricity generated from food wastes. This system, however, requires a

separate micro-grid to be constructed and keeping the electricity cost down will require substantial

subsidies from the government. Incentives should also be provided for firms to undertake the

collection of wastes and operating the decentralized technologies (such as the biofuel generator).

Local businesses trading products and goods made from recycled paper and plastic (such as indoor

panels made from recycled plastic fibres) should also be given monetary incentives (such as, lowerstore rental rates) to operate in the precinct.

5. ConclusionsWhile traditional way of demarcating system boundary for whole-building LCA has been helpful

in highlighting the importance of energy conservation and emission reduction in the operation

phase of buildings, extending the traditional boundary to include waste management reinforced the

need to reduce waste production and increase waste recycling in building operation. This study

showed that unless drastic waste reductions occur within the building, lifetime emissions from

waste management will exceed lifetime emissions from operation of the building. This led one to

think about how building technology and design can be changed so that waste recycling can be

improved. A few examples were described in this work. Most important, we argued that technology

innovations and design modifications will only result in net waste reduction if they happen in

coherence with other policies within an integrated framework.

References

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[5] International Standard Organization, ISO14040:2006, Environmental management -- Life cycle

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Fig.1 System boundary for water supply to GEK

Fig.2 System boundary for management of industrial wastes produced by GEK.

System Boundary

Screenin and Grit Removal

Primar Sedimentation

Coa ulation & Flocculation

Secondar Settlin

Filtration

Slud e rocessin

Disinfection

Distribution Process

Channelling of water from

Malaysia (import)

Inputs Outputs

Electricity and fuel

Channelling of water from

reservoirs

ChemicalsGHG emissions

GHG Emissions

Fuel

System Boundary

Industrial Waste Collected

Tipped off and incinerated at Waste

Incineration plant

InputsOutputs

Incineration Process

Electricity

Ash transported to landfill site at Semakau

via marine transfer at Tuas and then

processed in Semakau.

gure(s)


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Fig.3. Contributions of life cycle stages toward life cycle GHG emissions (when waste

management was notconsidered).

ProductionConstruction

Operation

Renovation

Demolition80.27%

13.71%4.67%

0.40%

0.96%


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Fig.4. Contributions of life cycle stages toward life cycle energy consumption (when waste

management was notconsidered).

Production

Construction

Operation

Renovation

Demolition86.10%

11.37%1.25%

0.37%

0.91%


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Fig.5. Contributions of life cycle stages toward life cycle GHG emissions (when waste

management was considered as well).

Production

Construction

Operation

Renovation

Incineration

74.67%

20.33%

3.47%

1.18%


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Fig.6. Contributions of life cycle stages toward life cycle energy consumption (when waste

management was considered as well).

Production

Construction

Operation

Renovation

Demolition

Incineration85.74%

11.32%

0.91%

0.47%0.37%

1.25%


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0

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100 120 140 160 180

PercentagecontributionoftotalGHGemissions

Total GHG emissions from life cycle stage (ktons)

Waste management

Operation

126.4

74.7

44.5

35

Fig.7. Comparison between the GHG emission contributions of the operation stage and waste management stage.


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OPERATION/USE OF

BUILDINGS

BUILDING LEVEL

PRECINCT/

MUNICIPAL LEVEL

NATIONAL LEVEL

INTERNATIONAL

LEVEL

WASTE

PRODUCTION

WASTESORTING

WASTE

SORTING

USE OF BUILDINGS

INCINERATION

INCINERATION

ENERGY

PRODUCTION

NATURAL GAS

RENEWABLES

TIME

ENERGY

PRODUCTION

RENEWABLES

WASTE

SORTING

WASTE

RECYCLING

WASTE

RECYCLING

WASTERECYCLING

GEOGRAPHICAL

SCALES

Fig. 8 Multiple time- and spatial-scale framework, describing the operational scales and possible material flow relations among

different downstream life cycle stages of buildings and the physical environments in which they are embedded.


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Traditional LCA boundary for buildings is extended to include waste management. Greenhouse gas emissions from waste management are higher than the use phase. We proposed an integrated framework in which building level strategies are used to

promote waste sorting, collection and recycling.

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