## [answered] Bren School of Environmental Science &amp;amp; Manageme

Bren School of Environmental

Science &amp; Management

1st Assignment ? Industrial Ecology ? ESM282 ? W08

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m This exercise has been developed at the

Centre for Environmental Strategy, University of Surrey, UK

for its ENVIRONMENTAL LIFE CYCLE PROGRAMME Exercise 1: Calculation of energy in an LCA

b) Getting to work The deadline for this assignment is 23 January 2008, 10:00am. Please hand in a hardcopy of

groups of up to 3 students.

Only maths required are addition, multiplication and division. Pay special attention to the necessary conversion of physical units. All the information you need to solve the problems are given in

Geyer via email (geyer@bren.ucsb.edu). Th When you have done the exercises you should ? Feel confident in dealing with different units in quantitative analysis, and be able to convert

between them.

? Understand the distinction between feedstock, process and primary energy. ? Appreciate the role of different assumptions, and the need for transparency, in undertaking this

type of analysis. I hope you enjoy this exercise and look forward to discussing the results with you!

Copyright Centre for Environmental Strategy 2002

https://www.aceyourstudies.com/file/219747/1st-assignment-08/ This exercise has been developed at the

Centre for Environmental Strategy, University of Surrey, UK

For its ENVIRONMENTAL LIFE CYCLE PROGRAMME Exercise 1a: Drying your hands wall-mounted electric hot air blower sh is

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m 1. 2. washable and re-usable cotton towel 3. disposable paper towels made from

100% recycled fibre Exercise: Th 1) Identify a suitable functional unit based on service provision. Define the three reference flows

and draw flow diagrams of the three product systems.

2) Calculate estimates of energy consumption when you dry your hands in each of the three ways

shown above. Consider only those processes for which information is given on the next page.

Aggregate and express energy use as total primary energy requirements.

3) Where, do you think, are the largest sources of error in this first order analysis? Copyright Centre for Environmental Strategy 2002

https://www.aceyourstudies.com/file/219747/1st-assignment-08/ Data:

Electric hand dryers:

? Electric hand dryers are rated at 2 kW

? It takes approx. 30 s to dry your hands. sh is

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m Cotton roller towels:

? Distance to laundry where cotton towels are washed and dried: 30 km.

? Capacity of van: 200 rolls on forward and return journey.

? Diesel consumption of van: 16 litres / 100km

? Delivery of clean towels and removal of dirty towels is undertaken by the same van

? Length of towel: 40m

? Length of each pull of the towel: 20cm

? Dry weight of towel: 4.5kg

? Required electricity for washing: 0.33 kWh per kg of cotton

? Drying requires the evaporation of 1kg of water per kg of dry cotton

? The latent heat of evaporation of water1 : 2500 kJ/kg

? The dryers at the laundry are electrically powered.

Disposable paper towels:

? Made from 100% by mass of post-consumer recycled paper fibre (pulp)

? Energy consumption of recycling plant: 0.28 tonnes of oil + 400 kWh of electricity per

tonne of recycled paper towels

? Transport distance from the paper towel production plant to point-of-use: 200km

? Diesel consumption of truck: 45 litres per 100 km

? Capacity: 30 tonnes of paper on the outward journey, empty on the return journey

? Weight of one dry paper towel: 20 g. Th See Appendix for further data. 1 Latent Heat is defined as the heat which flows to or from a material without a change to temperature. The heat will

only change the structure or phase of the material. e.g. transferring water from the fluid phase to vapour phase.

Copyright Centre for Environmental Strategy 2002 https://www.aceyourstudies.com/file/219747/1st-assignment-08/ This exercise has been developed at the

Centre for Environmental Strategy, University of Surrey, UK

For its ENVIRONMENTAL LIFE CYCLE PROGRAMME

Exercise 1b: Getting to work sh is

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m a.) car b.) bus c.) bicycle Exercise: 1) Identify a suitable functional unit based on service provision. Define the three reference flows

and draw flow diagrams of the three product systems. Th 2) Calculate estimates of energy consumption for getting to work by car, bus and bicycle. Aggregate and express energy use in primary energy.

3) Are there any factors that should be explored using sensitivity analysis? Data: ?

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?

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? Distance to work is 18 km.

Diesel consumption of the car: 35 miles per gallon

Diesel consumption of the bus: 35 l / 100 km

Calorie consumption for 15 min cycling at 15 km/h: 98 kilocalories.

1 kg bread loaf contains 2,470 kilocalories.

The primary energy requirements to produce and deliver 1 kg bread are 17 MJ. See Appendix for further data.

Copyright Centre for Environmental Strategy 2002

https://www.aceyourstudies.com/file/219747/1st-assignment-08/ Appendix: Background Information

The energy used in a system under analysis is measured in ?joules? (J); larger values are expressed in multiples of 10 and prefixes are used to denote the multiplication factor (see Table A1).

For example, 1,000,000 J is written as 1 MJ. Use of a common unit for different energy carriers

allows the calculation of one value for total energy use in a system despite the fact that the energy

comes from different sources. sh is

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m Other units that are sometimes used in assessing energy use are:

? Kilowatt (kW): one kilowatt refers to delivery of energy at a rate of ?one kilojoule/second?

(or ?1,000 joules/second?). There is no conversion factor to MJ because kW measures a rate

of use rather than absolute use.

? Kilowatt hour (kWh): one kWh is delivery of energy at a rate of ?one kilojoule/second? for

one hour, i.e. 1 kJ x 60 seconds x 60 minutes = 1 kJ x 3600. The conversion factor is therefore 1 kWh = 3.6 MJ.

Calorie (cal): this is defined as the energy needed to raise the temperature of one gramme of water

by one degree Celsius (1 ?C). The conversion factor is 1 cal = 4.19 J.

Energy use in a system under analysis can be categorised in different ways:

? Feedstock energy: heat of combustion of raw material inputs, which are not used as an energy

source, to a product system.

? Process energy: energy input required to operate processes (or equipment within processes)

excluding energy inputs for production and delivery of this energy.

? Production and delivery energy: the energy input required to extract, process, refine and deliver energy or material inputs to processes.

? Total primary energy: the sum of the feedstock energy, process energy, and production and

delivery energy. Th In LCA the total primary energy is conventionally assessed because it represents the aggregated

total use of energy resources. It is important to include both the process energy and the production and delivery energy in the analysis as the difference between the process energy and the total

primary energy can be large due to the efficiencies of conversion for different energy carriers. For

example, in Europe electricity is produced at an average efficiency of 31%. In other words, an

input of 100 MJ of primary energy results in an output of just 31 MJ electricity. Table A2 gives

some production and delivery energies from different energy carriers. Feedstock energy may or

may not be important in the analysis depending upon what materials are used in the system; it is

generally advisable to indicate clearly what proportion of the total primary energy is feedstock

energy.

The heat transferred to the surroundings on combustion of an energy carrier is measured as either

the Net Calorific Value (NCV) or the Gross Calorific Value (GCV). The difference between these

two arises according to whether the water in the combustion products remains in the vapour phase

or whether it condenses; in the former case, the value is the NCV and in the latter case the value is

the GCV. The differences between gross and net values are approximately 5% for solid and liquid

fuels and 10% for gases. In LCA, either the NCV or the GCV can be used provided that the

Copyright Centre for Environmental Strategy 2002

https://www.aceyourstudies.com/file/219747/1st-assignment-08/ Table A1: Units for Energy Analysis

Multiplication Factor

103

106

109

1012

1015

1018 Prefix

kilo

mega

giga

tera

peta

exa SI Symbol

kJ

MJ

GJ

TJ

PJ

EJ sh is

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m Table A2: Data for Energy Analysis

Energy Carrier Net Calorific Value Production and Deliv(MJ/kg)

ery Energy (MJ/kg)

Hard coal

27.1

2.3

Fuel oil

42.7

4.1

Diesel

42.8

4.1

Natural gas

46.1

4.2

Electricity

1 MJ delivered

2.23 MJ/MJ delivered

Source: Audsley et al., 1997; electricity from SAEFL 1998 Total Primary Energy

(MJ/kg)

29.4

46.8

46.9

50.3

3.23 MJ/MJ delivered Density of Some Fuels Density of heating oil EL = 840 kg/m3

Density of diesel = 840 kg/m3

Some Conversion Factors Th 1 mile = 1.609 km

1 calorie = 4.184 joules

1 Ws = 1 joule

1 gallon = 3.7854 litres

1 m3 = 1000 litres

References Audsley, A., S. Alber, R. Clift, S. Cowell, P. Crettaz, G. Gaillard, J. Hausheer, O. Jolliet, R.

Kleijn, B. Mortensen, D. Pearce, E. Roger, H. Teulon, B. Weidema and H. van Zeijts.

1997. Harmonisation of Environmental Life Cycle Assessment for Agriculture. Final Report for Concerted Action AIR3-CT94-2028. Silsoe Research Institute, Silsoe, Bedford.

SAEFL 1998: Life Cycle Inventories for Packagings. Environmental Series No. 250/1. Swiss

Agency for the Environment, Forests and Landscape (SAEFL), Berne. Copyright Centre for Environmental Strategy 2002

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