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
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