Home heating with firewood versus natural gas and heat pump
Scope
Electricity and natural gas supplied to house
Consider emissions from coal and natural gas combustion
Firewood
Me cutting downed trees that father in law is going to push into a burn pile
Ignore trip to Berea, I am going to help on other projects or wife visit family
Impacts
PM – particulate matter
SOx
NOx
CO2
Costs
LCI
My utility bills
COP at 47F is 3.6 and 17F is 2.5, assume 3 overall
Gas furnace that is 80% efficient
think we used about 4600 kWh for heating (15.7 million Btu)
also used 31.4 MCF of natural gas (31.4 million Btu)
Based energy loads on min gas and electric bill over 3 years (assume that was other
loads)
Existing system
Emission factors from Nat gas furnace
http://www1.eere.energy.gov/buildings/appliance_standards/residential/pdfs/furnaces_boilers
/fb_tsd_appendixw_0906.pdf
Co2 kg/GJ
Nox g/GJ
SO2 g/GJ
Natural gas
50.6
40
0
Emission factors based on energy input.
Electricity
http://www.eia.gov/cneaf/electricity/st_profiles/kentucky.html
PM from coal http://www.nrel.gov/docs/fy99osti/25119.pdf
Effect of Wood
Five pickup loads at 65 ft3 each (325 ft3 or 2.5 cords)
Mostly hackberry – http://extension.missouri.edu/explorepdf/agguides/forestry/g05450.pdf
Cord is 3,080 air-dried, 4,000 lb green (7,700 lb or 3,490 kg)
21.6 million btu/cord
Gasoline is 114,000 btu/gal, assume engines 33% efficienct
Chainsaw 1 gallon for all wood + 3.2 ounces oil (33 cc or 1.5 hp or 1.2 kW)
Ignore oil and bar lube, used 114,000 btu, ran for 8 hr then, or 9.6 kWh
Log splitter 3 gallon for all wood (7.5 hp or 5.6 kW)
Ignore oil and hydraulic oil, used 342,000 btu, ran for 4.5 hr or 24.9 kWh
EPA standards (handheld SI engines Federal register 65 FR 24268 in effect in 2000)
200 g/kWh or less of HC+NOx
CO 800 g/kWh
http://www.epa.gov/oms/models/nonrdmdl/nr-003.pdf (older, easier to read
emissions) 340 ppm sulfur – all goes to SO2 (assume)
This is a BIG assumption, but in gasoline car (http://www.epa.gov/otaq/consumer/f00013.htm)
2/3 of HC and NOx was due to HC that is PM
Assume all of the CO goes to CO2, 800 g approx 1200 g CO2???
340 ppm sulfur would be 2.78 g SO2/gal of gasoline
Wood stove specs from EPA
epa.gov/compliance/resources/publications/monitoring/caa/woodstoves/certifiedwood.pdf
36,000 btu/hr max heat output
63% efficient
4.42 g/hr emissions (particulate)
Average 28,000 btu/hr,
These are old emissions 1999 (best I could find for NOx and SOx from burning wood)
http://www.epa.gov/ttnchie1/ap42/ch01/bgdocs/b01s10.pdf
Nox 1 g/kg
Sox 0.2 g/kg
Considering upstream effects
Upstream factors for natural gas and coal – these based on power plant delivery, assume same for each
Line losses appear to be only 1.5% in KY, seems odd, but we will ignore
http://www1.eere.energy.gov/buildings/appliance_standards/residential/pdfs/k-3.pdf
Table K-3.1 Estimated Upstream Emission Factors and Relative Percentages To Direct
Power Plant Combustion Emissions
Coal Emission factor (g/GJ)
Nat Gas Emission factor (g/GJ)
Carbon
2222
5456
SO2
29.2
0
NOx
41.7
153
http://www.nrel.gov/docs/fy07osti/38617.pdf
PM is about 20% higher when coal supply considered
Transportation of firewood (fueleconomy.gov)
2006 Toyota camry versus a 98 GMC pickup
Traveling to Berea to help Father in law on farm, so difference in two vehicles
31 mi/gal versus 18 mi/gal, differential of 13 mi/gal
555 g CO2/mi truck, 355 g CO2/mi car, differential of 200 g/mi
10 trips (I don’t like to store wood at the house in warm weather)
Analysis
Assume energy supplied to house needs to be the same, split evenly in electric and gas
45% reduction in natural gas and electric energy consumption with firewood
45% reduction in CO2 produced
6% reduction in NOx – half of NOx production due to chain saw/splitter
30% reduction in NOx if small engines have half emissions
44% reduction in SOx
45% reduction in PM
LCC
Stove was 4,000, but 1,000 tax credit
Mantle not up to spec, so I spent 2 weeks redoing (-10 marital bliss units)
Log splitter 1,000 (made me very mad trying to split hackberry by hand)
Wood more expensive, takes 40% increase in electric and gas to make equal
But I have a happy cat!