WREC 1996

USE OF A HYBRID ENERGY ANALYSIS METHOD FOR EVALUATING THE EMBODIED ENERGY OF BUILDING MATERIALS

J.A. ALCORN and G. BAIRD

Centre for Building Performance Research, Victoria University of Wellington, PO Box 600, Wellington, New Zealand.

ABSTRACT

The three main methods of energy analysis are outlined and a brief description given of a hybrid analysis method that makes optimum use of all three. The procedures involved in carrying out a hybrid analysis using the case of steel produced from recycled scrap are described and the embodied energy coefficients of a range of building materials are tabulated.

KEYWORDS

embod~denergy;buildingmaterials; ~bridenergyanalysis;environmemalimpact;recycledsteel .

INTRODUCTION

Energy analysis is used to determine the amount of energy used to perform activities and provide specific goods or services. Such an analysis may use a variety of methods to reveal the embodied energy of an activity or service. The three main methods of analysis are as follows:

Statistical Analysis. Uses published statistics to determine the energy used by particular industries. It is a useful and speedy method if the statistics kept are consistent, thorough, pertinent and sufficiently detailed.

Input-Output Analysis. Employs the economic input-output tables of a nation's economy. By examining the dollar flows to and from the energy producing sectors it is possible to trace the energy flows within the national economy, and to equate the dollar output of each sector with its energy usage. The advantage of input-output analysis is that every energy transaction, across the entire national economy, is captured. The principal disadvantages are the aggregation of dissimilar products in individual sectors, and the approximation of physical units by dollar values.

Process Analysis. Involves the systematic examination of the direct and indirect energy inputs to a process. It produces results that are accurate and specific. The main disadvantage of this method is the time and effort required to reach a complete analysis.

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WREC 1996

HYBRID ANALYSIS

Hybrid analysis attempts to incorporate the most useful features of the three analysis methods outlined above, especially input-output and process analyses. A hybrid analysis begins with the readily available data for a process analysis. These are usually the direct energy inputs of the final production stage and the materials acquisition stage immediately upstream of that final stage. Where the acquisition of data for continuing the process analysis any further upstream presents a rapidly escalating effort which outweighs any improvement in accuracy, the process analysis may be truncated and a figure from an input-output analysis substituted.

Because the energy sectors of the inpnt-outpnt analysis do not suffer aggregation errors but are representative, the energy costs of producing each form of energy can be assessed reliably. The direct energy to the process need only be multiplied by the energy coefficient for the appropriate energy source to take this part of the calculation to IFIAS Level 4 (IFIAS, 1974).

EXAMPLE HYBRID ENERGY ANALYSIS

The example of the manufacture of reinforcing bar and wire rod from scrap steel will now be used to illustrate the hybrid analysis method. In New Zealand, scrap steel collected nationally and from the manufacturer's own steel mills is the main material input to the steel plant. Some of the scrap is shredded while larger items are gas cut to a suitable size. Balers compress the scrap ready for transporting from collection points. Other material inputs are silico-manganese, lime, carbon, ferro-silicon, ferro-manganese, burnt lime and oxygen. Energy inputs are electricity and gas. Most of the water used at the steel plant is recycled.

In the example, data derived from published statistics and input-output tables are identified, the latter being due to Baines and Peet (1995). All other data are from process analyses.

Energy Inouts to Scrap. Shredding of Scrap Baling of Scrap Gas Cutting of Scrap Scrap transport to collection points Scrap rail transport Scrap sea transport Total Energy Inputs to Scrap Total scrap Energy intensity of scrap to steel plant

25,239,859MJ 7,911,390MJ no figures available. 45,000,000MJ. 32,760,000MJ 15,876,000MJ 126,787,249MJ 180,000t 704MJ/t

Other Ingredients. (SiMn 4,200t + FeSi 1,4000 x 42,700 MJ/t (AIA, 1993) Lime 2,170t x 1,280MJ/t (AIA, 1993) Burnt Lime 750t x 7,430MJ/t (AIA, 1993) Carbon 1,800t x 29,700MJ/t (calorific content) (Baines, 1993)

x 1.04MJ/MJ (I-O tables, coal mining) Oxygen 1,900,000m 3 x $0.90/m 3 x 43.71MJ/$ (I-O tables) Water $1,700 x 6.27MJ/$ (I-O tables) Total Other Ingredients

239,120,000MJ 2,777,600MJ 5,572,500MJ

53,460,000MJ 74,744,100MJ 10,659MJ 375,684,859MJ

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WREC 1996

Steel Plant. Scrap Inputs to Steel Plant- 704MJ/t x 157,500t scrap Other ingredients Electricity to Steel Plant - 520kWh/t x 3.6 MJ/kWh

x 175,530t steel output x 1.53MJ/MJ (I-O tables) Capital Equipment Energy - $180 million current replacement value

x 0.865(producers price index change since inpnt-output survey) x 3.92MJ/$ (I-O tables) = 610,344,000MJ/20 years (assumed capital equipment life)

Total Energy Inputs to Steel Plant Billet production from steel plant Energy intensity for billets from steel plant

110,880,000MJ 375,684,859MJ

502,717,920MJ

30,517,200MJ p.a. 1,019,799,979MJ 170,510t

5,981MJ/t

Bar Mill. Billets to bar mill - 116,270t x 5,981MJ/t Electricity - 31,000,000MJ x 1.53 MJ/MJ (I-O tables) Gas - 134,000,000MJ x 1.13MJ/MJ (I-O tables) Capital Equipment Energy - $130,000,000 rebuilding costs in 1987

x 5.14MJ/$(I-O tables) = 668,200,000MJ/20 years (assumed capital equipment life)

Total Energy Inputs to Bar Mill Output from bar mill Energy intensity for reinforcing bar and structural sections

695,410,870MJ 47,430,000MJ 151,822,000MJ

33,410,000MJ p.a. 928,072,870MJ 104,680t 8.89M.l/kg

Rod Mill. Billets to rod mill - 54,240t billets from steel plant x 5,981MJ/t Electricity - 41,000,000MJ electricity x 1.53MJ/MJ (I-O tables) Gas - 203,000,000MJ x 1.13MJ/MJ (I-O tables) Capital Equipment Energy - assumed same as for Bar Mill at 4% Total Energy inputs to Rod Mill Output from rod mill Energy intensity for wire rod

324,409,440MJ 62,730,000MJ 229,999,000MJ 24,686,000MJ 641,824,440MJ 51,540t 12.45MJ/kg

As can be seen from the above, direct energy to the process (electricity and gas) is multiplied by the I-O energy coefficients, which take account of all the aspects, up to Level 4, of acquiring and delivering electricity and gas to the steel plant. The energy to 'extract' the raw materials is the energy to collect, shred, bale and transport the scrap plus the energy of the other ingredients. Figures for these come from analyses to Level 4, or include input- output energy coefficients to Level 4. The energy of the capital equipment is calculated using input-output coefficients to IFIAS level 4.The energy of the capital equipment to make the capital equipment of the final and all preceding stages is included in the input-output energy coefficients.

Using a hybrid analysis, comprising primarily a process analysis supplemented by an input-output analysis, and with statistical data used where beneficial, the net result was achieved more quickly and accurately than with other analysis methods (see also BuUard et al,, 1976).

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WREC 1996

APPLICATION OF HYBRID ENERGY ANALYSIS

A hybrid analysis method was used in a recent study (Alcorn, 1995) to produce embodied energy coefficients for materials used in the New Zealand building industry. Some of the resulting data is given in Table 1.

Table 1. Embodied energy coefficients of materials used in the New Zealand building industry.

MATERIAL MJ/kg MATERIAL MJ/kg

Aggregate, general 0.10 Insulation, cellulose 4.4 Aluminium, virgin, extruded 166 Insulation, wool 16.1 Aluminium, recycled, extruded 17.3 Lead 35.1 Bitumen 44.1 Paint, solvent based 98.1 Brass 62.0 Paint, water based 88.5 Carpet, wool 106 Paper, building 25.5 Cement 7.8 Paper, kraft 12.6

fibre cement board 13.1 Plaster board 6.1 soil cement pressed brick 0.42 Steel, recycled, sections 8.9

Ceramic brick 2.5 Steel, recycled, wire rod 12.5 Concrete block 0.86 Steel, virgin, general 32.0 Concrete, glass reinforced 3.4 Stone, dimension 0.79 Concrete, 30 MPa 1.4 Timber, kiln dried, dressed 2.5 Concrete, pre-cast 2.0 Timber, glulam 4.6 Copper 70.6 Timber, medium density fibreboard 11.9 Glass, float 14.9 Zinc, galvanising, per kg steel 2.8 Glass, toughened 25.3

ACKNOWLEDGEMENTS

It is a great pleasure to acknowledge the funding assistance of the Building Research Association of New Zealand and the Internal Grants Committee of Victoria University of Wellington, and the support of our colleagues at the Centre for Building Performance Research.

REFERENCES

AIA (1993). Environmental Resource Guide. American Institute of Architects, Washington, DC.

Alcorn, J. (1995) Embodied Energy Coefficients of Building Materials. Centre for Building Performance Research, Victoria University of Wellington.

Baines, J.T. (Ed.) (1993) New Zealand Energy Information Handbook.. Energy Data, Conversion Factors, Definitions. Taylor Baines and Associates, Christchurch.

Baines, J.T., and Peet, N.J. (1995) 1991 Input-Output Energy Analysis Coefficients. Report commissioned by CBPR.

Bullard, W., Penner, S., Pilaff, D.A., (1976). Net Energy Analysis." Handbook for Combining Process and Input-Output Analysis. Energy Research Group, Centre for Advanced Computation, University of Illinois at Urbana-Champaign.

IFIAS (1974). Energy Analysis Workshop on Methodology and Convention. Workshop Report No. 6, International Federation of Institutes for Advanced Study, Stockholm.

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