Eco-audits and Tools
Eco-audit
Fast initial assessment
Look for “hot spots” with greatest impact
material, manufacture, transport, use, disposal
Often one phase contains 80% of impact
Eco-audit
Main purpose is COMPARISON
This allows alternate designs to be investigated
Inputs to an Eco-Audit
Bill of materials
Process Choice
Transport Requirements
Duty Cycle
Disposal Route
Additional inputs
Data for embodied energies, process energies,
recycle energies, carbon intensities
Use this data to match with first set of user inputs
Outputs
energy and/or carbon footprint of each phase of life
bar chart or table, as desired.
USER INTERFACE
•Bill of materials
•Shaping processes
•Transport Needs
•Duty Cycle
•Disposal Route
LOOKUP TABLES
•Embodied energy/CO2
•Process energy /CO2
•Transport energy /CO2
•Conversion efficiencies
ECO-AUDIT TOOL
TABULAR DATA
•Life-phase energy
•Data used
•Calculation steps
•Component breakdown
•...
Bottled Water example
1 liter PET bottle with PP cap
bottle weighs 40 grams
cap weighs 1 gram
Both are molded and filled with water in France.
Filled bottles transported to London (550 km in 14 ton truck)
Bottles refrigerated for 2 days (average) before being served at restaurant
“Green” restaurant - 100% recycling.
•
Let’s use 100 bottles for our basis of study. This uses 1 cubic meter of
refrigeration.
Bottled water BOM &
Mfg.
Component
Material
Process
Mass
(kg)
Matl Energy
(MJ/kg)
Matl CO2
(kg/kg)
Proc Energy
(MJ/kg)
Proc CO2
(kg/kg)
Bottle (100)
PET
Molded
4
84
2.35
6.8
0.79
Cap (100)
PP
Molded
0.1
95
2.7
8.6
0.27
Dead weight
(water)
Water
--
100
--
--
--
--
104.1
345.5
9.67
28.06
3.19
TOTALS
Bottled water transport
Traveling 550 km; and 100 bottles weight 104.1 kg
14 ton truck uses 0.9 MJ/ton-km
0.9 * 550* 104.1/1000 = 51.5 MJ
Bottled water - use
Bottles are refrigerated for an average of 2 days.
We can find that energy efficient refrigerators use
10.5 MJ/m3/day (and 13.5 MJ/m3/day for freezing)
100 bottles use up 1 cubic meter of space, so
21 MJ for 2 days of refrigeration
Electrical refrigerator, so must divide by efficiency
(36%) -> 21/0.36 = 58.33 MJ
Bottled water - disposal
In general, we have 5 options:
Landfill
Incineration
Recycling
Re-engineer
Re-use
Bottled water - disposal
Our restaurant has excellent recycling. Recycling
actually contributes negative energy/carbon to the
calculations.
We get 35 MJ/kg back from PET recycling, and save
0.98 kg/kg CO2.
We get 40 MJ/kg from PP and 1.15 kg/kg CO2.
4 kg of PET and 0.1 kg of PP -> 4*35+0.1*40
-144 MJ from recycling.
Summary
Step
Energy (MJ)
CO2 (kg)
Materials
345.5
9.67
Manufacturing
28.06
3.19
Transportation
51.5
6.66
Usage
58.33
3.8
Disposal
-144
-4.03
Totals
339.39
17.59
Bottle - Energy
Bottle - Carbon
Energy breakdown
Carbon Breakdown
Case Study:
Electric tea kettle
2 kW kettle
Made in SE Asia,
transport to Europe (12,000 km)
boils 1 liter in 2 minutes,
used 2x per day, 300 days/year
lasts for 3 years
sent to landfill at end
Bill of Materials
Component
Material
Process
Mass (kg)
Material
Energy
(MJ/kg)
Total
Material
Energy (MJ)
Process
Energy
(MJ/kg)
Total Process
Energy (MJ)
Kettle body
PP
Molding
0.86
94
80.84
8.6
7.396
Heating element
Ni-Cr
Deformation
0.026
130
3.38
2.6
0.0676
Casing/heater
Stainless
Deformation
0.09
81
7.29
3.4
0.306
Thermostat
Ni alloy
Deformation
0.02
72
1.44
2.1
0.042
Internal insulation
Alumina
Powder
0.03
52
1.56
27
0.81
Cable sheath (1m)
Nat. Rubber
Molding
0.06
66
3.96
7.6
0.456
Cable core (1m)
Cu
Deformation
0.015
71
1.065
2
0.03
Plug body
Phenolic
Molding
0.037
90
3.33
13
0.481
Plug pins
Brass
Deformation
0.03
72
2.16
2.3
0.069
Packaging,
padding
Foam
Molding
0.015
110
1.65
11
0.165
Packaging (box)
Cardboard
Construction
0.13
28
3.64
0.5
0.065
Other small
Proxy: PC
Proxy:
molding
0.04
110
4.4
11
0.44
Other phases
Transport: Air freight (8.3 MJ/ton-km)
8.3 * 12,000 * 1.35/1000 = 134.5 MJ
Usage: 3 years, 300 days/year, 3 minutes per day, twice per day
90 hours * 2kW = 180 kWhr = 648 MJ
Electric, so divide by efficiency to get actual usage (UK has 40%
efficiency)
648/0.40 = 1,620 MJ
Land fill - 0.2 MJ
Overall
Tea Kettle
What is best choice of action?
Car Bumpers
Bumpers provide energy absorption for
passengers. Early bumpers were steel with
chrome plating -- they have changed over the
years, now typically plastic coatings.
Let’s compare a steel bumper to an aluminum one
(underlying structure - not exterior skin).
Bumpers
Steel - 35 MJ/kg
Aluminum - 210 MJ/kg
BUT - we use less weight of aluminum for the
same performance
Steel - 14 kg
Aluminum - 10 kg
Bumpers
The car has to move the bumper around when it
moves. (F=ma). Gasoline powered cars use
about 2.06 MJ/ton-km to move things.
If the car drives 25,000 km per year and lasts 10
years then we have 250,000 km. Multiply by the
weight of the bumper and we get the energy of
usage.
Bumpers
Material
Mass
(kg)
Material
Energy
(MJ/kg)
Total
Material
Energy
(MJ)
Total
Use
Processing
Total Use
Processing Energy
Energy
Energy
Energy
(MJ/ton(MJ/kg)
(MJ)
(MJ)
km)
Low alloy
steel
14
35
490
2.6
36.4
2.06
7,210
Aluminum
10
210
2100
2.6
26
2.06
5,150
Bumpers
Bumpers
The benefit to Al bumpers came primarily from the
usage - the miles driven.
What if we assumed a different number of miles
per year?
Or a different number of years that the car is kept?
The embodied energy is a combination of a fixed
amount (material + manufacture) and a variable
amount (usage - based on miles).
Family Car use vs materials
Argonne National Labs has a model (GREET) to
evaluate energy and emissions for automobiles.
They looked at many cars, but let’s look at a typical
conventional ICE car compared to a lightweight
ICE car.
The light weight car weighs 39% less than the
traditional.
Material
Carbon steel
Stainless
Cast iron
Wrought Al (10% recycled)
Cast Al (35% recycled)
Cu/Brass
Mg
Glass
TP Plastics
TS plastics
Rubber
CFRP
GFRP
Pt (catalyst)
Electronics
Convention Lightweight
al (kg)
(kg)
839
0.0
151
30
64
26
0.3
39
94
55
33
0
0
0.007
0.27
254
5.8
31
53
118
45
3.3
33
65
41
17
134
20
0.003
0.167
Material
Energy
(MJ/kg)
32
81
17
200
149
72
380
15
80
88
110
273
110
11,700
3,000
Convention Lightweight
al energy
Energy
(MJ)
(MJ)
26,848 8,128
470
2,567
527
6,000 10,600
9,536 17,582
1,872 3,240
114
1,254
585
495
7,520 5,200
4,840 3,608
3,630 1,870
- 36,582
- 2,200
82
35
810
501
Lightweight
So it is worse for the environment to make a
lightweight car.
But, as we know transportation energy is
significant. We should use less energy driving a
lighter weight car.
Conventional gasoline cars use 2.06 MJ/ton/km
So the transportation energy will be:
2.06 * mass * km driven
Usage
If we assume 15,000 mi/year and the car is kept for
5 years, then we can compare use energy:
Conventional
Lightweight
336 GJ
207 GJ
It’s not even close for 5 years - these are reported
in GJ (1,000 MJ)!
Payback
Let’s consider a 2 kW wind turbine.
We can do the calculations of materials,
manufacturing, transportation and usage based on
a detailed description of the product.
Usage energy will be maintenance for one year.
Wind Turbine
Phase
Energy (MJ)
CO2 (kg)
Material
18,000,000
1,300,000
Manufacture
1,200,000
97,000
Transport
280,000
20,000
Use (maint.)
190,000
14,000
TOTALS
19,670,000
1,431,000
Wind Turbine
The turbine is rated at 2MW.
That means at optimum performance it generates
2MW (wind blowing at speed). Let’s say it only
gets 1/4 of that as a realistic estimate.
So we have 0.5 MW * 365.24 days * 24 hrs/day =
4,383 MW-hrs = 15,779,000 MJ in one year
ROI
We invested 19.7 TJ in making and installing and maintaining the
turbine.
We get back 15.8 TJ each year.
19.7/15.8 = 1.25
So it takes 1.25 years (15 months) to get back the invested energy.
It is rated for 25 years, so we get back 20 times the invested energy.
But, it takes about 2,000 of these to replace a single coal plant
Exercise
1,700 W steam iron.
Weighs 1.3 kg
Heats up on full power for 4 minutes then used for
20 minutes on half power.
5 year life, after which it hits the landfill.
Component
Mass
Material
Process
Body
0.15
PP
Molded
Heater
0.03
Nichrome
Drawn
Base
0.80
Stainless
Cast
Cable sheath
0.18
PU
Molded
Cable core
0.05
Copper
Drawn
Plug body
0.037
Phenolic
Molded
Plug pins
0.03
Brass
Rolled
Bill of Materials