Design for Sustainability

Jerome J ConnorDepartment of Civil and

Environmental EngineeringMIT

Design for sustainability

• Sustainability - state• The needs of the present generation are

met without compromising the ability of the future generation to meet their own needs

• (1987 Brundtland report)Two Aspects:

Social – meet human needsEcological - preserve environment

Design for sustainability

• Sustainable - the ability to maintain into perpetuity ; capable of being maintained

• Sustainable design - goal is to produce objects using only renewable resources and which , in operation , deplete only renewable resources

California Study• California – Sustainable Building Task

Force , a group of 40 state agencies formed to integrate green building designprinciples into state projects LEEDReport – “The costs and financial benefitsof green buildings”

2% investment initially yields paybackof 20% (10 fold increase ) over building life – assumed to be about 20 years

Design for sustainability• Sustainability objectives:

1. Eliminate contributions to systematic increases in concentrations of substances from the earth’s crust (carbon dioxide, nitrous oxides)

Dematerialization – reduction of material flows --increased resource productivity ( eg more efficient engines)-- less waste - recycling

Substitution – exchange of products and processes ( combustion engines vs fuel cells , biomass vs fossil fuels)

Design for sustainability

2. Eliminate contribution to systematic increases in concentrations of substances produced by society-- efficent use of substances produced by

society-- substitute more abundant compounds

Design for sustainability

3.Eliminate contribution to systematic physical degradation of nature through overharvesting,…-- efficent use of natural resources and land-- caution in modification of nature

4. Meet human needs in society worldwide-- health – ecological pollution--availability and distribution of resources

Engineering for sustainability

• Use life cycle assessment• LCA – the process of evaluating the

effects that a product has on the environment over the entire period of it’s life cycle- covers all processes required: extraction , processing , manufacture , distribution , use , reuse , maintenance , disposal “Cradle to Grave” approach

LCA

• Why use LCA?• Product orientated – industrial activity

evolves around products• Integrative – integrates all the problems ;

avoids problem shifting ( pass on problems)

• Quantitative tool – based on scientific data• Provides useful information for decision

making with environmental consequences

LCA• Types of problem shifting

-one stage of the life cycle to another-one sort of problem to another-one location to another

examples:-electric car vs diesel or gas powered car-aluminuum vs plastic window frames-chemical waste exported from one country to another-contaminated materials are recycled into another product

(ash byproducts of coal fired plants recycled as additives for cement used for concrete products)

LCA

• Goal definition and scope – product , functional basis , level of detail ( problem boundary )

• Inventory analysis –establish process flow chart , quantify environmental input and output

• Impact assessment – group and quantify into a limited number of impact categories

• Improvement assessment – evaluate opportunities for improvement

Inventory analysis• Specify processes required in manufacture , use

, and eventual disposal of a product• Each process has inputs and outputs – called

flows• Economic flows – goods , services , products

that are used to produce something• Environmental flows – interventions extracted

from or placed into the environment – resources used and emissions , wastes

• Construct process flow table (matrix)

LCA – Example 1• Illustrative Example-- process 1 produces electric energy

2 liters fuel generates 10 kwh energyemits 1.0 kg of CO2 and 0.1 kg of SO2

-- process 2 produces fuel100 liters crude oil produces 50 litersof fuel oilemits 10 kg of CO2 and 2 kg of SO2

Economic flows are fuel oil and electrical energy

Environmental flows are crude oil (extraction of natural resource) and emissions (CO2 and SO2 ) to the environment

2 processes and 2 economical flows unique solution

Process flow matrix• 2 d representation – table or spreadsheet form

Rows relate to flow variableslist economic flows first – Nec variablesthen environmental flows–Nev variables

Columns relate to processes - one column per process – Np processes

Can interpret process as a vector with Nec + Nev entries = Nf entriesTotal process is defined by matrix of size Nf rows and Np columns

P = P1 + P2 + …..Pnp

LCAProcess represented as a column vectorFirst rows – economic flowsNext rows – environmental flowsFor process i

⎭⎬⎫

⎩⎨⎧

=i

ii B

AP

ecN

evN

LCA• Represent total process

vector as a set of column vectors

• Specify the desired final economic flows as a vector , f *

[ ]npPPPP ....21=

⎥⎦⎤

⎢⎣⎡=

⎥⎥⎦

⎤

⎢⎢⎣

⎡=

BAP

np

np

BBBAAA

....

....

21

21

LCA

• = goal value for the i’th economic flow variable

• define f as the economic flow vector (size is )

if

1Nec ×

LCA

• f* =goal=

⎪⎪⎪⎪

⎭

⎪⎪⎪⎪

⎬

⎫

⎪⎪⎪⎪

⎩

⎪⎪⎪⎪

⎨

⎧

)(....

)2()1(

ecNecf

ecfecf

LCA

• Scale the processes• is the scale factor

for process i• Resultant economic

flow vector is

• Write as

is

fAs

fAsAsAs

PsPsPs

npnp

npnp

=

=+++

+++

....

....

2211

2211

LCA

•Determine the corresponding environmental flows

• If ,there is a unique solution for

gBs =

fAs =

npec NN =

s

fggfBA

fAs1

1

∆==

=−

−

)(

LCA – Example 1• Illustrative Example-- process 1 produces electric energy

2 liters fuel generates 10 kwh energyemits 1.0 kg of CO2 and 0.1 kg of SO2

-- process 2 produces fuel100 liters crude oil produces 50 litersof fuel oilemits 10 kg of CO2 and 2 kg of SO2

Economic flows are fuel oil and electrical energy

Environmental flows are crude oil (extraction of natural resource) and emissions (CO2 and SO2 ) to the environment

2 processes and 2 economical flows unique solution

Matrix representation of Example 1

ProduceElectric energy

ProduceFuel oil

Economic goals andEnv. flows

Fuel(l) -2 +50 f1 (0)

Electric energy(kwh)

+10 0 f2 (1000)

C O2 +1 +10 g1

SO2+0.1 +2 g2

Crude oil (l) 0 -100 g3

Results for example 1

• For 1000 kwh and zero fuel oil left

• f*={0 , 1000 }

• s={ 100 , 4 }• g = { 140 kg of , 18 kg of

and 400 liters of crude oil used }2CO 2SO

Multi-functionality and allocation• Co-production- 2 or more economic flow

outputs such as co-generation• 2 or more waste outputs such as

combined waste treatment • 1 waste output used as an economic flow input

in recycling processexamples are paper, ground asphalt , fly

ash residue , grey water for toilet flushing • Single process with multiple functions ,ie ,

multiple economic flowstimber growing produces multiple wood

products

Multifunctionality and allocation• Causally coupled functions

--Oil refining-refined oil products + bitumen-- Timber harvesting - timbers ,laminated

beams ,plywoods, chips, fuel• Deliberately coupled functions

-transport people and cargoIn general, more economic flows than processes.

Results in an over-determined system of algebraic equations

Multifunctionality – example 2• Cogeneration for example 1• 2 liters of fuel produce 18 MJ of heat as

well as 10 kwh of electric energy. All other data the same.

• Have a new economic flow, heat• The problem now has 3 economic flows

and only 2 processes –over-determined• One strategy is to add another process

associated with heat

Multifunctionality – example 2Elec + heat

Fuel oil Heat flows

Fuel oil (l) -2 50 -5 (0)

Elec (kwh) 10 0 0 (1000)

Heat (MJ) 18 0 90 (0)

CO2

(kg) 1.0 10 3 (60)SO

2(kg) .1 2 0 (14)

Crude oil (l) 0 -100 0 (-200)

Comparison –with and withoutco-generation

• For 1000 kwh of electrical energy produced• No co-generation

140 kg of CO2

18 kg of SO2

400 liters of crude oil used• With co-generation

60 kg of CO2

14 kg of SO2

200 liters of crude oil used

Closed loop recycling• Unit process transforms a negative valued

product (a waste) into a positive valued product ( an economic flow )

• Secondary material fed back into the unit process of the product system

• Example - crude oil produces fuel oil and waste- waste combined with fuel oil to produce electricity

RecyclingProduce fuel oil

ProduceElec/oil

ProduceElec/waste

goal

Fuel (l) 50 -1 0 0

Elecenergy(kwh

0 5 a1000

Waste (kg) 50 0 -1 0

CO2 (kg) 10 .5 x

SO2 (kg) 2 .05 y

Crude oil(l) -100 0 0

Waste water recycling

Effluent

Grey H2O

Stored grey H2O

Clean H2O

SourceGround H2O

Flush H2O

byproducts

Grey waterdischarge

Waste water recyclingTreat

(1.0)

StoreGrey H2O(.95)

ExtractCleanH2O(.525)

Store clean H2O as flush

goal

Flush H2O(l) +.5 +1 +1Effluent (l) -1 -1Grey H2O (l) +.95 -1.0 0Clean H2O (l) +1 -1 0ResourceExtractions and env flows

x +.5 -1

Impact AssessmentConcerned with environmental flowsDefine “Impact Categories” Reference ISO 14042 (2000)

climate change – global warmingacidificationhuman toxicityresource depletion

Category Indicators• Each category has an indicator ( or

possibly indicators ) which is a measure ofthe state of the category

Examples• Global warming – infrared absorption

kg of CO2 equivalent• Acidification – release of H+

kg of SO2

• Resource depletion – measured by resource depletion units (RDU)

RDU

• A unit for aggregating resourcesmeasure of reduced availability

hi = numerical value for the indicatorof category i

Characterization Model

Category indicators are related to the environmental flow variables resulting from a particular process

hi=function of g1,g2 , …, gnev = hi( ) hi is generally a nonlinear function of the environmental flowswork with first order expansion about a steadystate background intervention ,

g

0g

Incremental indicators

hibackground = hi ( g0)

g = incremental environmental interventionExpand hi in Taylor series about g0

hi = qi gqi is a row vector which characterizes the impact of the incremental environmental interventions on category i

∆

∆ ∆

Category vectorsDefine category vector h as a column

vector

Define Q as a matrix of size Nc by Nev

⎪⎪⎭

⎪⎪⎬

⎫

⎪⎪⎩

⎪⎪⎨

⎧

∆

∆∆

=∆

nch

hh

.2

1

h

∆

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡

=

ncq

qq

Q 2

1

.

Characterization vectors

Thenh= Q g

zero entries in Q represent no impactof the corresponding environmentalintervention

∆ ∆

Example of the Matrix Qh1 – acidification kg SO2

h2 – global warming kg CO2

h3 – resource depletion –RDUg1 – CO2

g2 – SO2

g3 – lite crude oilReference ISO source

Q matrix

⎥⎥⎥

⎦

⎤

⎢⎢⎢

⎣

⎡

−150001.1010

Q=

Impact assessment

• No cogenerationh= { 18 , 141.8 ,600 }

• With cogenerationh = { 14 , 61.4 , 3000 }

• apply weighting factors – normalize h indices

Normalization

Define a reference value for category ihri = equivalent quantity for areference time , eg , tons/year

Express category impact measure as adimensionless ratio of the actual value to the reference value

ri

ii h

hh ∆=∆

Weighting factors and weighted impact assessment

• Define wi as the weighting factor for category i

• Form weighted sum

ii

i hwI ∆×=∑

Strategies• Embodied energy – energy required to

extract and process the raw materials , manufacture the product , and transport the product from source to end use

High : concrete ,metals , asphalt , glass petroleum based thermoplasticsLow : wood , fibers , re-used , re-cycled, by-products of other processes

• Durability – materials with high embodied energy are generally more long lasting

concrete , stone

Embodied energy and CO2materials embodied

energy (GJ/ton)

embodiedCO2 (kg/ton)

In – situ concrete

0.84 119

common bricks 5.8 490

timber 13 1644

structural steel 25.5 2030

plasterboard 27 180

aluminium 200 29200