Embodied and operational energy of urban residential buildings in India

Embodied and operational energy of urban residential buildings in India

Accepted Manuscript Title: Embodied and operational energy of urban residential buildings in India Author: K.I. Praseeda B. V. Venkatarama Reddy M. Ma...

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Accepted Manuscript Title: Embodied and operational energy of urban residential buildings in India Author: K.I. Praseeda B. V. Venkatarama Reddy M. Mani PII: DOI: Reference:

S0378-7788(15)30312-1 http://dx.doi.org/doi:10.1016/j.enbuild.2015.09.072 ENB 6192

To appear in:

ENB

Received date: Revised date: Accepted date:

20-3-2015 24-9-2015 30-9-2015

Please cite this article as: K.I. Praseeda, B.V.V. Reddy, M.M. [email protected] Embodied and operational energy of urban residential buildings in India, Energy and Buildings (2015), http://dx.doi.org/10.1016/j.enbuild.2015.09.072 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Embodied and operational energy of urban residential buildings in India K.I. Praseedaa, B. V. Venkatarama Reddyb and M. Manic,* a

Research Scholar, Department of Civil Engineering, Indian Institute of Science, Bangalore, India

b

Professor, Department of Civil Engineering, Indian Institute of Science, Bangalore, India

c

Associate Professor, Center for Sustainable Technologies, Indian Institute of Science, Bangalore,

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India Abstract

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Globally, buildings consume nearly half of the total energy produced, and consequently responsible for a large share of CO2 emissions. A building’s Life cycle energy (LCE) comprises its Embodied

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Energy (EE) and Operational Energy (OE). The building design, prevalent climatic conditions and occupant behavior primarily determines its LCE. Thus, for the identification of appropriate emission-

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reduction strategies, studies into building LCE are crucial. While OE reflects the energy utilized in operating a, EE comprises the initial capital energy involved in its construction (material and burden

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associated with material consumption in buildings. Assessment of EE and OE in buildings is crucial towards identifying appropriate design and operational strategies for reduction of the building’s life

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cycle energy. This paper discusses EE and OE assessment of a few residential buildings in different

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climatic locations in India. The study shows that share of OE and EE in LCE greatly depends upon the types of materials used in construction and extent of space conditioning adopted. In some cases EE can exceed life cycle OE. Buildings with reinforced concrete frame and monolithic reinforced concrete walls have very high EE.

Key words: Embodied energy, building materials, process analysis, input-output method 1.0 Introduction

Buildings are major consumers of energy. Types of energy use during a building’s life cycle comprise embodied energy, operational and maintenance energy, demolition and disposal energy. Embodied energy (EE) represents the total energy consumption for a building construction, i.e., sum of embodied energy of building materials, transportation energy of materials and building construction energy. Embodied energy of building materials represents major contribution to embodied energy in buildings. Appropriate selection of building materials with regard to their embodied energy is crucial

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for limiting embodied energy of buildings. Use of energy intensive materials such as brick, cement, steel, glass etc. results in high embodied energy in buildings. Operational energy (OE) in buildings, resulting mainly from space conditioning and lighting requirements, depends on the climatic conditions of the region and comfort requirements of the occupants. Buildings located in regions experiencing extreme climatic conditions require more

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operational energy to meet the heating and cooling energy demands. The use of electro-mechanical and/or electric systems for space conditioning and artificial lighting in conventional buildings

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contributes to high operational energy. Electro-mechanical space conditioners include compressorchiller based mechanical systems driven by electric motors/pumps. Electric space conditioners

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primarily include heaters and fans driven entirely by electric power.

A comprehensive analysis of energy consumption in buildings requires estimation of embodied and

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operational energy. Such an analysis facilitates study of building’s life cycle energy to identify appropriate energy conservation measures. Also, the study focused on comparison of embodied and

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operational energy of typical urban dwellings in different climate zones, to examine the relative significance of these energy components with respect to the dwelling’s life cycle energy for a life span

any possible inter-relationships.

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2.0 Earlier investigations

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of 50 years. Though there is little logical relationship between OE and EE, the current study examines

There are several investigations pertaining to life cycle energy of buildings. While a few studies partly focus on aspects of embodied energy in buildings, majority of the studies focus on operational energy, its attributes and measures for conservation. Demolition and disposal energy is rarely addressed in various studies since they together form less than 1% of Life Cycle Energy [Sartori and Hestnes 2007, Ramesh et al. 2010]. Tables 1 and 2 summarize the earlier investigations on EE and LCE of buildings.

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Table 1 – Previous studies on EE of buildings

2

Debnath et al. (1995)

Suzuki et al. (1995)

3

For a 94 m2 house For load bearing house with 1 and 2 storeys and a 4 storey RC frame structure (area ranging from 50 - 200 m2)

Salient observations

2.32 - 5.53

Greater use of wood in building construction reduce EE and CO2 emissions

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1

Buchanan and Honey (1994)

Building characteristics

3-5

Wooden house has lower environmental impact when compared to steel and RC structure

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Reference

Embodied Energy (GJ/m2)

For different types of house constructions in Japan

2.7 - 10.4

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Sl. No.

EE of the studied house is 246% and 240% more than that of a stone masonry house and a rammed house, respectively.

Morel et al. (2001)

Small housing project

5

Thormark (2006)

Initial + recurring EE for 50 years for three different designs of 20 apartments Independent building and multi-dwelling building, using I/O analysis

6.2 and 5.8 respectively

7

Nassen et al. (2007) Huberman and Pearl mutter (2008)

Dormitory complex

3.28 - 4.91

EE accounted for 60% of LCE for 50 years

8

Monahan and Powell (2011)

For three construction types of a low energy house

5.7 - 8.2

Timber with low EE resulted in low EE of building

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239 GJ

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6

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4

6.1 - 7.6

Table 2 – Previous studies on LCE of buildings Sl. No.

1

Reference

Building characteristics

Adalberth (1997)

For three prefabricated single - unit dwellings

3

Mithraratne and Vale (2004)

Housing complex of 20 apartments Three residential buildings with light, concrete and super insulation types

4

Citherlet and Defaux (2007)

Individual house for three different designs

2

Thormark (2002)

LCE for 50 years (GJ/m2)

% share of different energy components

27.4 - 31.7

EE - 11 to 12%, Recurring EE - 4 to 5 %, OE - 84% and Demolition energy 0.3 to 0.5%

15.24

EE - 46%

17.02, 16.24 and 11.83 GJ/m2 for 100 years

OE - 74%, 71% and 57% respectively

200 - 580 MJ/m2/year

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Utama and Gheewala (2009)

8

Ramesh et al. (2010)

Residential and office buildings

Gustavsson et al. (2010)

8 storey wooden framed apartment

10

Gustavsson and Joelsson (2010)

11 residential buildings

33 - 390 kWh/m2

EE - 28% and 16% of LCE, respectively EE - 7 to 107 kWh/m2, OE - 0 to 330 kWh/m2 (80 to 90% of LCE)

8074 kWh/m2

EE - 975 kWh/m2, OE - 8843 kWh/m2, Demolition energy - 10 kWh/m2 and a energy recovery of 1753 kWh/m2

500 - 1020 kWh/m2

EE - 45 to 60% of LCE

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282.6 GJ and 460 GJ

EE - 6.7% and 6.2% respectively

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12.56 and 13.24 GJ/m2 respectively for 40 years

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Utama and Gheewala (2008)

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Sartori and Hestnes (2007)

EE for conventional dwellings 2 to 38% of LCE, EE for low operational energy buildings - 9 to 46%

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5

Residential and non-residential low energy buildings Houses with clay brick and concrete based envelopes High rise residentail apartment of 85 m2 floor area, double wall and single wall envelopes

Literature review reveals a wide range of values for EE (1 – 8.35 GJ/m2) and OE (0.08 –1.19

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GJ/m2/year) for residential buildings. This is attributed to (1) variations in types of materials and

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building envelope and (2) discrepancies associated with the system boundaries adopted to assess EE of materials. A few studies highlight that wood based constructions and the use of soil based low energy materials lead to significant reduction in embodied energy [Buchanan and Honey 1994, Reddy and Jagadish 2003]. Also, some studies advocate optimum use of materials/resources and the use of locally available materials as means of conserving embodied energy [Morel et al. 2001, Kofoworola and Gheewala 2009]. With regard to operational energy assessment, there is no clear consensus regarding different energy components to be included. Some studies include energy consumption for heating, cooling, ventilation and lighting while others include energy consumption for hot water generation, household activities, equipments operation, water supply, waste water treatment etc., in addition to lighting and air conditioning energy. Further, literature provides various classifications for buildings like low energy buildings, zero energy building, net zero energy building etc. based only on operational energy consumption. A few studies discuss the relative significance of embodied energy of buildings in life cycle energy terms. It has been observed that embodied energy in conventional

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buildings could range between 2 and 38% of its life cycle energy. Embodied energy considerably increases while attempting to reduce the operational energy in buildings. Different measures such as building insulation for reducing heat gain, internal or external shading of building, introduction of onsite power generation using solar, wind or hybrid systems etc. increase the material consumption, thereby increasing EE. In such cases EE could be as high as 40 to 60% of life cycle energy of low

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operational energy buildings. Investigations on EE and OE in residential buildings in India are limited. EE assessment to support

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low-energy building design currently lack consensus on the methodology to be adopted. This is further exasperated by the lack of data on the energy involved in the manufacture of building

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materials. Study by K. I. Praseeda et al., 2015 [17] have generated EE data for prominent building materials in India based on first-hand data collection for EE assessment of buildings. The present

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investigation attempts to examine the EE and OE of some urban dwellings spread across different climate zones of India.

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3.0 Methodology and scope of the study

India is characterized by a variety of geographical and topographical features including mountains,

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rivers, table lands, sea shores etc. and experiences different climatic conditions. According to the Indian National Building Code [NBC, 2005], the country is divided into five major climatic zones as Hot

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and Dry, Warm and Humid, Moderate, Cold and Composite. The urban and peri-urban population lives in conventional modern dwellings, adopting conventional materials like concrete, steel, burnt clay bricks, glass, etc. The present investigation is aimed at examination of dwellings in urban and periurban centres spread across various climatic zones of India. A total of 16 urban dwellings (designated as UD1 - UD16) were examined. Urban dwellings refer to residential buildings using conventional and alternative building materials such as cement, steel, aggregates, burnt clay bricks, stabilized soil blocks, rammed earth etc. These dwellings were identified based on climatic location, age, willingness of the residents and access to data on the building materials used. The selected regions represented four different climatic zones in the country. EE and OE assessment of buildings adopted data from a survey which involved collection of details on (1) building design and geometry, (2) types of building materials and technologies used in the

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construction, and (3) operational energy. Further, the interrelationships between embodied energy and operational energy for various climatic zones of India were examined. For EE estimation, documents such as shop drawings, bills of quantities and specifications were examined for each dwelling to quantify different items of work. EE assessment included two stages. Initially, EE values per unit of different items of work were estimated as the product of EE of materials

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and quantity required for unit amount of the item of work. Further, EE of the dwellings (expressed as GJ/m2 of built-up area) were estimated as the sum of product of the quantity of the items of work and

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the respective EE values derived in the first step. EE of various materials was sourced from the previous study [Praseeda et al., 2014] by the authors on EE assessment of materials based on

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industrial survey.

With regard to OE assessment, for a few houses operational energy was directly derived from their

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energy bills, deducting the energy consumption for appliances such as television, refrigerator, water heater (generally termed as plug loads ) etc., which do not directly contribute to occupant’s thermal

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comfort. In other cases, data regarding the number of electrical fixtures and the duration of operation was collected. While these appliances could contribute to internal heat dissipation (plug load), their

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actual usage was found to be minimal and of not much significance in naturally ventilated buildings. Annual power consumption for each type of fixture was then estimated as the product of power rating

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of the fixture, a power factor, annual hours of operation and the number of fixtures in the dwelling. Operational energy for a few dwellings was not available as these dwellings were unoccupied at the time of survey or the construction of the dwellings had just been completed. Considering a life span of 50 years, the total OE of the buildings was estimated. Life cycle energy in dwellings was estimated as the total of embodied energy and operational energy over its life span. The demolition and disposal energy are generally excluded as they are less than 1% of Life Cycle Energy [Sartori and Hestnes 2007, Ramesh et al. 2010] and difficult to accurately predict. The average life span of buildings is commonly adopted as 50 years in earlier studies on energy consumption in buildings [Adalberth 1997, Cole and Kernan 1996, Ramesh et al. 2010, Praseeda et al. 2014]. The life span of the building could also be its useful life span and need not imply that it is unfit for further use, after 50 years.

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4.0 Types of buildings Urban dwellings include load bearing as well as reinforced concrete (RC) frame structures using conventional materials such as cement, steel, aggregates, burnt clay brick, concrete blocks, etc. Urban dwellings in different climate zones show monotonous/stereotype design features with little consideration to the local climatic conditions. These dwellings include individual houses with single

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and double storey as well as apartment buildings (with 4, 8 and 34 storeys). The age of urban dwellings varied between 2 years and 50 years. Built up area of the dwellings investigated were in the

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range of 28 - 19,500 m2.

Urban dwellings examined have RC floor or roof, with wall materials comprising monolithic RC, stone

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masonry, burnt clay brick masonry, stabilized soil block masonry and rammed earth. Dwellings designated as UD3, UD12 and UD13 have RC frame structure with masonry infill, and UD14 is a RC

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frame structure with monolithic RC walls. All other buildings are load bearing masonry structures (1 and 2 storey height). Among the load bearing buildings designated as UD5, UD6 and UD11 have

have either stone or brick masonry walls.

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5.0 Results and analysis

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alternative wall materials such as stabilized soil blocks and rammed earth, and remainder of buildings

The present study examined range of EE in dwellings with different structural configuration such as

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load bearing structure, RC frame structure with masonry infill and RC frame with RC monolithic wall. Also, the study enabled a comparison of EE values of urban dwellings with different walling materials. Further, the study also investigated any possible correlation between mass and EE of dwelling, OE and EE of dwellings and EE and LCE of dwellings. The study also examined any correlation between OE and EE of the dwellings with their corresponding climatic location. Following discussion summarizes the results from the study. 5.1 Embodied energy of urban dwellings

Energy in 16 urban dwellings spread across four climate zones of India was analyzed. Table 3 gives EE and OE for urban dwellings including climatic zone, built-up area, brief specifications of major building components and OE for a 50 years life span. The following points emerge from the study. 1. EE is highest for RC frame monolithic walls multi-storeyed apartment building followed by RC frame structure with masonry infill and load bearing masonry dwellings. EE of RC frame with

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masonry infill buildings is in the range 3.79 – 4.25 GJ/m2, whereas EE of load bearing (natural stone) masonry structures is in the lower range of 1.01 – 2.89 GJ/m2. EE significantly increases to a value of 10.51 GJ/m2 for the RC frame and monolithic wall construction for the 34 storey apartment complex. 2. Load bearing (natural stone) masonry buildings have EE in the lower range of 1.01 - 1.24 GJ/m2,

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whereas EE of load bearing burnt clay brick masonry buildings is higher in the range of 2.43 2.89 GJ/m2. The use of alternative walling materials such as stabilized soil blocks and rammed

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earth brings down EE to 1.7 - 2.04 GJ/m2.

Figure 1 illustrates EE values for urban dwellings arranged in ascending order. It is evident that EE of

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RC frame structure with masonry infill is considerably more than that of load bearing masonry buildings. RC frame with RC monolithic walls leads to significantly higher (~250%) EE of the building.

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Comparison of EE of load bearing masonry buildings with different types of walling materials reveals that use of natural materials like stones or low EE materials like stabilized soil blocks or rammed earth

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results in considerable reduction in EE of load bearing buildings.

Fig. 1 – Comparison of EE of dwellings with different structural systems and walling materials

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(A)

Composite climate

1

UD1

78

2

UD2

225

3

UD3

4

UD4

5

UD5

No. of storeys

ce

55

1

1

1

28

1

UD6

42

1

7

UD7

152

1

8

UD8

152

1

(B)

Warm & Humid climate

9

UD9

Ac

65

6

202

Rubble stone masonry foundation, load bearing stone masonry structure, RC roof and cement concrete flooring (A) Rubble stone masonry foundation, load bearing stone masonry structure, RC roof and cement concrete flooring (A) Rubble stone masonry foundation, RC frame structure with burnt clay brick masonry infill, RC roof and mosaic tile flooring Rubble stone masonry foundation, load bearing stone masonry structure, RC roof and cement concrete flooring (A) Rubble stone masonry foundation, load bearing stabilized soil block masonry structure, clay tile roof and cement concrete flooring (B) Rubble stone masonry foundation, load bearing rammed earth walls, RC roof and cement concrete flooring (C) Rubble stone masonry foundation, load bearing burnt clay brick masonry structure, RC roof and cement concrete, mosaic flooring (D) Rubble stone masonry foundation, load bearing burnt clay brick masonry structure, RC roof and cement concrete, mosaic flooring (D)

ed

1

Brief specifications

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Building Designation and climate zone

pt

Builtup area (m2)

Sl. No.

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Table 3 - Embodied and Operational energy for urban dwellings representing four climate zones in India

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Rubble stone masonry foundation, load bearing burnt clay brick masonry structure, RC roof and ceramic tile

EE (GJ/m2)

Yearly OE (GJ/m2) for 50 year life span

LCE (GJ/m2)

Mass of dwelling (t/ m2)

1.24

0.22

12.24

4.68

1.01

NA

NA

4.09

4.12

0.15

11.62

4.04

1.23

0.04

3.23

4.01

1.80

0.05

4.35

4.01

1.80

0.06

4.90

3.17

2.45

0.05

4.95

4.16

2.43

0.05

4.93

4.03

2.89

0.033

4.54

2.72

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11

UD11

256

12

UD12

7932

13

UD13

49250

14

UD14

(D)

Cold climate

15

UD15

2

4

8

19476

34

152

1

82

1

ce

Ac UD16

RC - Reinforced Concrete

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cr Moderate climate

2

Rubble stone masonry foundation, load bearing burnt clay brick masonry structure, RC roof and ceramic tile flooring (E)

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(C)

16

150

Rubble stone masonry foundation, load bearing stabilized soil block masonry structure, RC roof and ceramic tile flooring (F) Rubble stone masonry foundation, RC frame structure with burnt brick masonry infill, RC roof and ceramic, mosaic tile flooring Rubble stone masonry foundation, RC frame structure with burnt brick masonry infill, RC roof and flooring using vitrified tiles, ceramic tiles, granite, cement concrete and clay tiles RC raft foundation, RC frame structure with RC walls, RC roof and granite, ceramic tile flooring

ed

UD10

pt

10

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flooring (E)

Rubble stone masonry foundation, load bearing burnt clay brick masonry structure, RC roof and Kota stone flooring (G) Rubble stone masonry foundation, load bearing stone and burnt clay brick masonry structure, RC roof and cement concrete flooring

2.76

0.04

4.76

2.23

2.04

0.01

2.54

3.03

3.79

NA

NA

2.93

4.25

NA

NA

2.29

10.51

NA

NA

11.40

2.69

0.056

5.49

4.38

1.71

NA

NA

4.59

NA - Not

Available

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5.2 Correlation between mass and embodied energy of the dwellings The mass or weight of a building reflects its material configuration. There has been no discussion in literature on any correlation between mass of the building and it’s EE. Mass of the building was assessed while assessing the volumes of usable space in the building. The mass of the dwellings expressed in tonne/m2 of built-up area is given in Table 3. Fig. 2 provides a plot of building mass

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versus EE for the 16 case studies. The plot reveals that there is no definite correlation between building mass and EE of buildings, except that excessive use of reinforced concrete in frames as well

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as walls could result in higher mass and EE.

Since EE of a building is a product of EE and quantity of materials, there could be a correlation

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between overall mass and EE of the building. But the study showed no correlation between mass and EE of the dwelling which could prove that EE of the material has the major impact on EE of the

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buildings and not the mass.

Fig. 2 – Embodied energy versus mass of building Figs. 3 and 4 show pie charts for distribution of mass and EE among various components of typical load bearing and RC frame with masonry infill buildings. The following observations are made from the results given in Table 3 and Figures 2 – 4.

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The mass of the low rise load bearing masonry buildings range between 2.23 – 4.68 t/m2 with a mean mass of 3.76 t/m2 (standard deviation = 0.78 t/m2). RC frame with masonry infill walls possess mass in the range 2.29 – 4.04 t/m2 with a mean value of 3.09 t/m2 (Standard Deviation = 0.89 t/m2). The mass of RC frame with RC monolithic walls is significantly high at 11.4 t/m2. RC frame with masonry infill walls have lower mass per unit area as compared to the load bearing masonry buildings. This

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can be attributed to the thicker walls traditionally adopted in load – bearing constructions.

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building

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Fig. 3 – Share of EE and mass among different building components for load bearing masonry

Fig. 4 – Share of EE and mass among different building components for RC frame structure with infill masonry walls

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Distribution of mass among different components of load bearing masonry building illustrated for a typical case shows that foundation and walls constitute a dominant share (87%) of the total mass. Foundation and walls constitute 38% and 39% of mass respectively, whereas roof and floor system constitutes 21%. In contrast, bulk of EE (63%) is embedded in walls and supporting structure followed by roof/floors having 28% of the EE. Though foundation comprises 38% of the mass, its contribution

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to EE is only 6%. This is mainly due to use of natural stone masonry in the foundation. In case of RC frame masonry infill walls, bulk of the mass (43%) is in walls and supporting structure,

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followed by floors/roof (28%) and foundation (27%). In contrast to distribution of mass, EE distribution shows 50% energy in walls and supporting structure followed by floors/roof (34%) and foundation

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(12%).

The average mass of load bearing masonry buildings is 3.76 t/m2 and of RC frame structure with

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masonry infill is 3.09 t/m2. Though the average mass of load bearing masonry buildings is higher than that of RC frame with masonry infill building, the average EE is 50% lower at 2 GJ/m2, when

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compared to average EE of RC frame with masonry infill (4.05 GJ/m2). For the extreme case of RC frames with RC monolithic walls building both mass (11.4 t/m2) as well as EE (10.51 GJ/m2) are very

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high when compared to RC frame masonry infill buildings. 5.3 Operational Energy (OE) in urban dwellings

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OE mainly comprises energy consumption for lighting and space conditioning. Space conditioning implies regulating indoor thermal comfort for occupant’s productivity, using passive methods or mechanical means such as room heaters/coolers or fans. OE has been assessed based on energy consumption data collected for each case study (see Table 4). In the present study, a few dwellings in cold and composite climate zones have electro - mechanical air-conditioning by means of portable air conditioners or window AC units. Other dwellings in these climate zones use electric ceiling fans in conjunction with passive methods of space conditioning such as regulating natural ventilation, clothing level etc. for thermal comfort. Dwellings in warm – humid climate zone adopt extensive use of ceiling fans during summer and no electro - mechanical space conditioning during winter. Dwelling in moderate climate zone did not adopt any mechanical space conditioning system.

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Table 4 - Annual operational energy in urban dwellings

Climate zone

Operational Energy (GJ/m2/year)

Composite climate Warm-Humid climate Moderate climate Cold climate

0.04 - 0.22 0.03 - 0.04 0.01 0.06

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Sl. No. 1 2 3 4

The dwellings in cold and composite climate zone have higher OE, followed by dwellings in the warm–

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humid and moderate climate zones. Higher OE in cold and composite climate zones is attributed to extensive use of electric room conditioners. Dwellings designated as UD1 and UD3 in composite

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climate zone have relatively higher OE due to the higher occupancy and corresponding comfort requirements. The urban dwellings examined in the present study lack the passive building thermal

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performance exhibited in vernacular dwellings and also adaptive resilience by occupants [Shasthry et

5.4 Life Cycle Energy (LCE) of dwellings

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al. 2012].

Life Cycle Energy (LCE) in buildings includes EE, OE, recurring embodied energy and

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demolition/disposal energy [Cole and Kernan 1996, Adalberth 1997a, Oka and Suzuki 1998, Sartori

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and Hestnes 2007]. Recurring embodied energy is attributed to any repair or refurbishment works during the building’s life span. Contribution of recurring embodied energy to life cycle energy of buildings has been observed to be insignificant. For residential buildings, recurring embodied energy represents less than 5% of life cycle energy [Adalberth1997b]. Demolition and disposal energy represents less than 1% of life cycle energy in dwellings [Adalberth 1997b, Scheuer et al. 2003]. In the current study, LCE of the dwellings was estimated as the sum of embodied and operational energy over 50 years of the building’s life. The recurring embodied energy and demolition energy have not been accounted for as their contribution is low, and these estimates are difficult to predict. Also, gathering information on recurring embodied energy and demolition energy is difficult for the existing buildings. Table 5 gives EE and OE in the dwellings for a 50 year building’s life span for the 11 cases. For other cases OE data was not available. Figure 5 provides LCE of the dwelling as total of respective EE and OE. The energy analysis shows that LCE of urban dwellings examined falls in the range of 2.54 - 12.54 GJ/m2. EE represents 10 – 80% of LCE. For dwellings UD1 and UD3 in

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composite climate zone, higher OE has resulted in higher LCE. EE and cumulative OE for 50 years are comparable for most of the case studies. This reveals the significance of EE in limiting the LCE in these dwellings. Comparison of EE and OE of a dwelling aids in identifying potential areas for energy conservation. A higher EE as compared to OE for dwellings demands proper material selection keeping in mind

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structural performance, durability and cost. A higher OE requires measures for conservation of energy used for lighting and space-conditioning. Literature indicates that the share of EE in LCE does not

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exceed 20% [Adalberth 1997, Ramesh et al. 2010]. The present study shows that the share of EE in LCE of conventional dwellings is in the range of 35 - 80%. Figures 6 and 7 show plots of EE versus

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between EE and OE and EE and LCE for the dwellings.

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OE and EE versus LCE for the buildings examined. These Figures reveal no definite correlation

Fig. 5 – LCE for the dwellings as cumulative of EE and OE

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Fig. 6 – EE versus OE for the dwellings

Fig. 7 – EE versus LCE for the dwellings

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With reference to share of OE (during 50 years life cycle) and EE in buildings, three types of building categories can be identified. (1) Dwellings with EE greater than OE (Fig. 8) (2) Dwellings with OE greater than EE (Fig. 9)

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(3) Dwellings with equal OE and EE share (Fig. 10) In Figures 8, 9 and 10, EE is represented as a horizontal straight line since it is generally assumed

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constant through the building’s life span in the absence of any recurring embodied energy data. OE is represented by an inclined straight line since OE at the end of a year is a cumulative value based on

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the assumption that the annual OE remains constant throughout its life cycle. Annual OE may generally not remain constant through buildings life cycle. It is important to note that since change in

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occupant preference/lifestyle and vocation changes are difficult to predict, OE has been kept constant. Use of energy efficient appliances could also lower OE, but this also has not been factored

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in. The building itself will be aging, and minor modifications and occupant behaviour with regards to operation of doors and windows, operation and installation of new plug loads, life style changes, and

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an increase or decrease in the number of occupants will all influence annual OE. However, since these variations are difficult to estimate, for purposes of a base-line estimate, assuming a constant

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OE through a building’s life span is justified.

Figure 8 provides a comparison of EE and OE in dwellings in warm–humid and moderate climate zone, for two case studies: UD9 and UD10. It is interesting to note that EE of these dwellings is more than the cumulative OE at the end of a 50 years life span. This is because hardly any energy intensive space conditioning measures were used in these dwellings. These cases show dominant EE over OE.

Plots of EE and OE over a 50 year period are shown in Figure 9 for two case studies: UD3 and UD6. Here, EE and OE lines intersect at different periods over the life span. For example, EE and cumulative OE lines intersect at 28 years period for UD3, indicating that initial EE of the building is nearly equal to its cumulative OE for 28 years.

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Fig. 8 – Dwellings with EE greater than OE over 50 year life cycle

Fig. 9 – Dwellings with OE greater than EE over the building life cycle

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Similarly, for UD6, the EE and OE lines intersect at 29 years of life span. These case studies belong to the composite climate zone which demands intense space conditioning almost throughout the year because of the extreme climatic conditions. Therefore, OE is high and the cumulative OE at the end of the 50 year life cycle is more than EE. Figure 10 shows a comparison of EE and OE for another two case studies: UD7 and UD15 in composite and cold climate. Here, the cumulative OE of the dwellings

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at the end of a 50 years life cycle corresponds with their EE. These dwellings have relatively higher EE attributed to greater built-up area and a higher mass of load bearing burnt clay brick masonry

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walls. Also, OE in these dwellings is comparatively lower for the prevalent climatic condition which can

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be attributed to the occupancy characteristics and their indoor comfort requirements.

Fig. 10 – Dwellings with equal OE and EE at the end of the life span Table 5 provides a comparison of the results from the present study and literature on EE and OE for urban residential buildings. The comparison reveals that the EE values estimated from the present study are comparable with that from literature. This can be attributed to the similarities in the building materials used. However, results on OE values from the current study reveals noticeably lower values in comparison with those from literature. This can be attributed to the fact that most studies from

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literature belong to space – conditioning (heating and cooling) systems that carry a much higher OE footprint.

Table 5 – Comparison of results from present study and literature on EE and OE of buildings

1 2

Embodied Energy Operational Energy (for 50 years)

Energy value (GJ/m2) From present study 1.23 - 10.5 0.50 - 11.00

From literature 1.01 - 8.35 4.32 - 59.40

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Energy

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Sl. No.

6.0 Conclusions

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Embodied and operational energy of typical conventional urban dwellings located in four different climatic zones of India were examined. Embodied energy of the dwellings ranged from 1.01 - 10.50

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GJ/m2. Urban dwellings using alternative materials like stabilized soil blocks, rammed earth etc. for walls have embodied energy below 2.0 GJ/m2 and those with burnt clay brick masonry walls have embodied energy in the range of 2.40 - 2.90 GJ/m2. The dwellings with RC frame structure and

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masonry infill walls have higher embodied energy in the range of 3.8 - 4.25 GJ/m2. This can be attributed to increased use of energy intensive materials like cement, steel, glass, aluminum, etc. The

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EE steeply rises to 10.5 GJ/m2 with RC frame and monolithic RC walls. No definite correlation has

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been found between EE of the buildings and the climatic zone for the cases examined. The average mass of load bearing masonry structures (3.84 t/m2) is more than that of RC frame structures (3.09 t/m2). No definite correlation exists between embodied energy and mass of the building. In some of the load bearing masonry dwellings, walls and floors/roof have been found to contribute 91% to the EE of the building and 60% to the total mass of the building. In case of dwellings with RC frame structure with masonry infill, the contribution of walls and supporting structure to building’s EE and total mass is 50% and 43% respectively. Floors and roof contribute 34% and 28% of building’s embodied energy and total mass respectively. Annual OE in urban dwellings falls within a range of 0.01 - 0.22 GJ/m2. Life cycle energy for urban dwellings is in the range of 2.54 - 12.54 GJ/m2. Urban dwellings in the composite climate zone revealed the highest life cycle energy followed by dwellings in the cold climate zone, the warm–humid climate zone and the moderate climate zone, in decreasing order. Also, the analysis revealed no definite correlation between EE and OE, and EE and LCE in these dwellings. EE for a few urban

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dwellings is comparable to their 50 year OE. This can be mainly attributed to the use of load bearing masonry (reducing the use of steel and concrete) and the absence of active space conditioning. For LCE in urban dwellings, literature values (range from 13.97 - 80.06 GJ/m2) are significantly higher when compared to the range obtained (2.54 - 12.24 GJ/m2) in the present study. This can be attributed to the fact that most studies from literature belong to case of space – conditioning (heating

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and cooling) systems that carry a much higher OE footprint. In the current study, variations in occupancy characteristics and lighting energy demand have resulted in significant variation in the

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range of OE values.

Thus, the present study provides typical range of EE and OE of conventional dwellings in different

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climate zones. The study highlights the shift in range of EE values for change in material use from low EE materials to conventional materials with high EE. The study observes that use of alternative

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walling materials such as stabilized soil blocks, rammed earth results in low EE of buildings. References

Environment 32 4 (1997) 321 – 329.

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1. Adalberth K., Energy use during the life cycle of single unit dwellings: Examples, Building and

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2. Bloom D. E., Population dynamics in India and implications for economic growth, PGDA working paper no. 65, Program on the global demography of aging, Harvard School of Public Health,

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Boston (2012), Retrieved on May 2012 from

www.hsph.harvard.edu/pgda/WorkingPapers/2011/PGDA_WP_65.pdf 3. Buchanan A. H., Honey B. G., Energy and carbon dioxide implications of building construction, Energy and Buildings 20 3 (1994) 205 – 217. 4. Citherlet C., Defaux T., Energy and environmental comparison of three variants of a family housing during its whole life span, Building and Environment 42 (2007) 591 – 598. 5. Cole R.J., Kernan P.C, Life cycle energy use in office buildings, Building and Environment 31 4 (1996) 307 – 317.

6. Debnath A., Singh S V., Singh Y. P., Comparative assessment of energy requirements for different types of residential buildings in India, Energy and Buildings 23 (1995) 141 – 146. 7. Gustavsson L., Joelsson A., Sathre R., Life cycle primary energy use and carbon emission of an eight storey wood framed apartment building, Energy and Buildings 42 (2010) 230 – 242.

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8. Gustavsson L., Joelsson A., Life cycle primary energy analysis of residential buildings, Energy and Buildings 42 (2010) 210 – 220. 9. Huberman N., Pearlmutter D., A life cycle energy analysis of building materials in the Negev desert, Energy and Buildings 40 (2008) 837 - 848. 10. Kofoworola O. F., Gheewala S. H., Life cycle energy assessment of a typical office building in

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Thailand, Energy and Buildings 41 (2009) 1076 – 1083. 11. Mithraratne N., Vale B., Life cycle analysis model for New Zealand houses, Building and

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Environment 39 (2004) 483 – 492.

12. Monahan J., Powell J. C., An embodied carbon and energy analysis of modern methods of

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construction in housing: A case study using life cycle assessment framework, Energy and Buildings 43 (2011) 179 – 188.

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emissions in the production phase of buildings: An input-output analysis, Energy 32 (2007) 1593 –

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15. NBC, National Building Code of India (SP – 7), 2005, Bureau of Indian Standards, New Delhi, India.

16. Praseeda K. I., M. Mani., Reddy B. V. V., Assessing impact of material transition and thermal comfort models on embodied and operational energy in vernacular dwellings (India), Energy Procedia 54 (2014) 342 – 351.

17. Praseeda K. I., Reddy B. V. V., M. Mani., Embodied energy assessment of building materials in India using process and input – output analysis, Energy and Buildings 86 (2015) 677 – 686. 18. Ramesh T., Ravi Prakash., and Shukla K.K., Life cycle energy analysis of buildings: An overview, Energy and Buildings 42 (2010) 1592 – 1600. 19. Reddy B. V. V., Jagadish K.S., Embodied energy of common and alternative building materials and technologies, Energy and Buildings 35 (2003) 129-137.

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20. Sartori I., and Hestnes A.G., Energy use in the life cycle of conventional and low energy buildings: a review article, Energy and Building 39 (2007) 249–257. 21. Shasthry V., Mani M., Tenorio R., Impacts of modern transitions on thermal comfort in vernacular dwellings in warm – humid climate of Sugganahalli (India), Indoor Built Environment (2012) 1 – 20.

house construction in Japan, Energy and Buildings 22 (1995) 165 – 169.

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22. Suzuki M., Oka T., Okada K., The estimation of energy consumption and CO2 emission due to

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23. Thormark C., A low energy building in a life cycle – its embodied energy, energy need for operation and recycling potential, Building and Environment 37 (2002) 429 – 435.

building, Building and Environment 41 (2006) 1019 – 1026.

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24. Thormark C., The effect of material choice on the total energy need and recycling potential of a

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25. Utama A., and Gheewala S H., Life cycle energy of single landed houses in Indonesia, Energy and Buildings 40 (2008) 1911-1916.

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26. Utama A., and Gheewala S. H., Indonesian residential high rise buildings: A life cycle energy

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assessment, Energy and Buildings 41 (2009) 1263 – 1268.

Highlights:

- Operational and Embodied Energy examined for urban dwelling in four climatic zones - Share of Operation and Embodied Energy depends on material and space conditioning - No correlation exists between embodied energy and building mass - Urban dwellings in composite climate reveal highest life cycle energy

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