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Example of Small LCA Project
Steps of an LCA
Life Cycle Assessment Framework
Goal
definition and
scope
Inventory
analysis
Impact
assessment
Interpretation
Goal Definition and Scope
• Evaluate burning firewood in residential
application as a supplement to fossil
• House is in Kentucky and current heating is
with an air source heat pump and natural gas
furnace
• Determine impact of current fossil fuel
consumption with supplemental wood heat
Scope Continued
• Consider impact of power plant and
combustion of nat gas in house
• Harvest and transport of firewood from Berea
• Impacts considered
– CO2
– NOx
– SOx
– Particulate matter (PM)
– Costs
Inventory Analysis - Procedure
• Obtained previous years utility bills
• Picked lowest month and used that bill as
baseload electrical/gas consumption
• Estimated fuel consumption for chainsaw and
log splitter
• Estimated quantity and energy value of
firewood
Existing Appliance Performance
• Air source heat pump
– COP at 47F is 3.6, COP at 17F is 2.5
– Assume average of 3.0
– Actually two heat pumps in house, assume both are
same (similar performance)
• Gas furnace is 80% AFUE
• Use on a seasonal heating basis
– 4600 kWh of electricity (15.7 million Btu)
– 31.4 MCF (31.4 million Btu)
• We need 76.2 GJ/heating season in the house
Emissions from Fossil
• Natural gas appliances in residential
applications – DOE EERE (2008 standards)
• Emissions from power plants DOE – EIA KY
electric profile (2009)
• PM from coal combustion NREL (1999)
Wood Burning Characteristics
• Energy content from University of MO for
hackberry (21.6 million btu/cord)
• Estimated 2.5 cords of firewood (5 pickup
loads)
• Emissions from fireplace – EPA certified stoves
– 36,000 btu/hr output at 63% efficient
– 4.42 g PM/hr
• Other emissions (NOx and SOX) from 1999 EPA
document (g/kg basis)
Wood Harvest
• EPA standards for SI gasoline engines under 18
hp (Federal Register for 2000)
• Assume engines are 33% efficient – no
reference
• Emissions listed for
– CO (assume all goes to CO2)
– HC+NOx (from EPA, 2/3 of this category would go
to PM, assume this is true, based on cars)
– Gasoline 340 ppm sulfur – assume goes to 2.78 g
SO2/gallon
Results – Impact Assessment
• Emission factors (fossil and wood burning)
• Total emissions for house (fossil and wood
burning)
Results – Emission Factors
Emission Factor (g/GJ or kg/GJ)
3500
3000
2500
CO2 (kg/GJ)
NOx (g/GJ)
SOx (g/GJ)
PM (g/GJ)
2000
1500
1000
500
0
Natural gas
Considers upstream emissions
Electricity
Wood
Results – Emissions from Original
Emissions in a Heating Season (kg or g)
60000
50000
CO2 (kg)
NOx (g)
SOx (g)
PM (g)
40000
30000
20000
10000
0
Natural gas
Electricity
Total
Results – Emissions with Stove
Emissions in Heating Season (kg or g)
60000
50000
40000
CO2 (kg)
NOx (g)
SOx (g)
PM (g)
30000
20000
10000
0
Natural gas
Electricity
Wood
Total
Results Net Changes
Reduction Using Wood Stove (%)
40
20
0
-20
CO2
NOx
SOx
PM
-40
-60
Reduction
Interpretation - Existing
• Air source heat pump reduces impact due to
COP
– Use half the energy of natural gas
– Get over 2/3 of useful heat from electricity
• Natural gas high NOx emissions
• Coal has high CO2, SOx, and PM
Interpretation - Wood
• 45% reduction in fossil energy
• Assumed evenly split between gas/electric
• Significant reduction in CO2 and SOx relative
to base case
• PM slightly lower than base
• NOx increased relative to base case
– Small SI engines big part of NOx emissions
Impact of Various Stages
CO2 kg
NOx g
SOx g
PM g
Gas comb.
926
732
-
-
Gas upstream
100
2,800
-
-
Gas subtotal
1,026
3,532
-
-
Coal comb.
2,391
2,053
6,506
22,812
381
266
4,562
Coal upstream
61
Coal subtotal
2,452
2,434
6,772
27,375
Wood comb.
0
3,490
698
7,956
Wood upstream
193
4,421
56
5,922
Wood subtotal
193
7,911
754
13,878
13,877
7,527
41,253
System total
3,670
Summary of Impacts
Life Cycle Costing
• $661/yr in heating for fossil case
• With wood stove increases to $759/yr
– Due to cap cost of stove (~400/yr)
• Would take a 40% increase in electric and nat.
gas cost to be equal
• No value on time handling firewood
Potential Problems
• Uncertainty in electricity used for heating –
based on lowest electric bill
• Assumed a SI engine efficiency
• Assumed conversion of HC to PM
– Other conversions from g C to g CO2 and g S to g
SO2
• Splitting of energy reduction – assumed equal
gas and electric
Other Potential Problems
• Wife not happy
with me gutting the
fireplace and
redoing it according
to manufacturer’s
specs
• Estimates on fuel
consumption during
wood cutting
• Happy cat though