Example of Small LCA Project
Mar 31, 2015
Example of Small LCA Project
Steps of an LCALife 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
Considers upstream emissions
Natural gas Electricity Wood
Em
issi
on F
acto
r (g
/GJ
or k
g/G
J)
0
500
1000
1500
2000
2500
3000
3500
CO2 (kg/GJ) NOx (g/GJ) SOx (g/GJ) PM (g/GJ)
Results – Emissions from Original
Natural gas Electricity Total
Em
issi
ons
in a
Hea
ting
Sea
son
(kg
or g
)
0
10000
20000
30000
40000
50000
60000
CO2 (kg) NOx (g) SOx (g) PM (g)
Results – Emissions with Stove
Natural gas Electricity Wood Total
Em
issi
ons
in H
eatin
g S
easo
n (k
g or
g)
0
10000
20000
30000
40000
50000
60000
CO2 (kg) NOx (g) SOx (g) PM (g)
Results Net Changes
Reduction
Red
uctio
n U
sing
Woo
d S
tove
(%
)
-60
-40
-20
0
20
40
CO2 NOx SOx PM
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 StagesCO2 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 Coal upstream 61 381 266 4,562 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 System total 3,670 13,877 7,527 41,253
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