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Evaluating Wood Burning as Residential Heat Source in Kentucky: An LCA Study

This project assesses the impact of burning firewood alongside fossil fuels for heating in a Kentucky home, considering CO2, NOx, SOx, PM emissions, and costs. It evaluates existing appliance performance, emissions from fossil fuels and wood burning, wood harvesting and combustion characteristics, and the net changes in emissions and costs. The study also highlights potential problems and uncertainties encountered during the assessment.

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Evaluating Wood Burning as Residential Heat Source in Kentucky: An LCA Study

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Presentation Transcript

  1. Example of Small LCA Project

  2. Steps of an LCA

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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)

  8. 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)

  9. 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

  10. Results – Impact Assessment • Emission factors (fossil and wood burning) • Total emissions for house (fossil and wood burning)

  11. Results – Emission Factors Considers upstream emissions

  12. Results – Emissions from Original

  13. Results – Emissions with Stove

  14. Results Net Changes

  15. 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

  16. 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

  17. Impact of Various Stages

  18. Summary of Impacts

  19. 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

  20. 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

  21. 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

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