Browsing by Subject "Life cycle assessment"

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    Biofuels and sustainable development: Perspectives on the farm and around the globe
    (2014-03) Sheehan, John Joseph
    The idea that biofuels can be sustainable has long been controversial. This research considers three land-related aspects of biofuels sustainability:1. The effect of local farm management practices on the sustainability of land used to produce corn grain as a biorefinery feedstock. 2. The relative sustainability of land used for producing corn and sugarcane as a function of latitude. 3. The land use implications for biofuels of global pasture-based livestock production systems. Local corn farm management choices can make the difference between net negative and net positive carbon footprints for grain delivered to biorefineries. Carbon footprints reported here are based on full life cycle assessments of each farm, including modeled soil emissions of greenhouse gases. For a cohort of farmers surveyed in southwest Minnesota, avoiding excess fertilizer use, adopting no till practices and replacing commercial fertilizer with animal manure leads to negative carbon footprints of up to -117 gCO2eq per ha. Globally, the choice of land managed for corn or sugarcane versus land maintained to support natural ecosystems is highly dependent on latitude. On average sugarcane produces three times more energy per unit area than does maize. Latitudes closer to the equator have higher net primary productivity (NPP), so there is a greater trade-off between biofuel production and ecosystem productivity in the equatorial zones. Sugarcane is still twice as productive on average compared to maize in the amount of biofuel energy produced per unit of NPP. Global pasture systems could reduce their land footprint by several-fold simply by closing the gap between poor performing and high performing pasture systems across climatically-similar parts of the world. Because pasture's global land footprint is so large, closing the performance gap could make vast amounts of land available for biomass feedstocks, with no new land clearing.
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    Life Cycle Assessment of Residential Heating and Cooling Systems in Minnesota: A comprehensive analysis on life cycle greenhouse gas (GHG) emissions and cost-costeffectiveness of ground source heat pump (GSHP) systems compared to the conventional gas furnace and air conditioner system
    (2013-01) Li, Mo
    Ground Source Heat Pump (GSHP) technologies for residential heating and cooling are often suggested as an effective means to curb energy consumption, reduce greenhouse gas (GHG) emissions and lower homeowners' heating and cooling costs. As such, numerous federal, state and utility-based incentives, most often in the forms of financial incentives, installation rebates, and loan programs, have been made available for these technologies. While GSHP technology for space heating and cooling is well understood, with widespread implementation across the U.S., research specific to the environmental and economic performance of these systems in cold climates, such as Minnesota, is limited. In this study, a comparative environmental life cycle assessment (LCA) is conducted of typical residential HVAC (Heating, Ventilation, and Air Conditioning) systems in Minnesota to investigate greenhouse gas (GHG) emissions for delivering 20 years of residential heating and cooling - maintaining indoor temperatures of 68ºF (20ºC) and 75ºF (24ºC) in Minnesota-specific heating and cooling seasons, respectively. Eight residential GSHP design scenarios (i.e. horizontal loop field, vertical loop field, high coefficient of performance, low coefficient of performance, hybrid natural gas heat back-up) and one conventional natural gas furnace and air conditioner system are assessed for GHG and life cycle economic costs. Life cycle GHG emissions were found to range between 1.09 × 105 kg CO2 eq. and 1.86 × 105 kg CO2 eq. Six of the eight GSHP technology scenarios had fewer carbon impacts than the conventional system. Only in cases of horizontal low-efficiency GSHP and hybrid, do results suggest increased GHGs. Life cycle costs and present value analyses suggest GSHP technologies can be cost competitive over their 20-year life, but that policy incentives may be required to reduce the high up-front capital costs of GSHPs and relatively long payback periods of more than 20 years. In addition, results suggest that the regional electricity fuel mix and volatile energy prices significantly influence the benefits of employing GSHP technologies in Minnesota from both environmental and economic perspectives. It is worthy noting that with the historically low natural gas price in 2012, the conventional system's energy bill reduction would be large enough to bring its life-cycle cost below those of the GSHPs. As a result, the environmentally favorable GSHP technologies would become economically unfavorable, unless they are additionally subsidized. Improved understanding these effects, along with design and performance characteristics of GSGP technologies specific to Minnesota's cold climate, allows better decision making among homeowners considering these technologies and policy makers providing incentives for alternative energy solutions.