Search

Abstract Life cycle assessment (LCA) was combined with primary data from nine forest harvesting operations in New York, Maine, Massachusetts, and Vermont, from 2013 to 2019 where forest biomass (FB) for bioenergy was one of several products. The objective was to conduct a data‐driven study of greenhouse gas emissions associated with FB feedstock harvesting operations in the Northeast United States. Deterministic and stochastic LCA models were built to simulate the current FB bioenergy feedstock supply chain in the Northeast US with a cradle‐to‐gate scope (forest harvest through roadside loading) and a functional unit of 1.0 Mg of green FB feedstock at a 50% moisture content. Baseline LCA, sensitivity analysis, and uncertainty analyses were conducted for three different FB feedstock types—dirty chips, clean chips, and grindings—enabling an empirically driven investigation of differences between feedstock types, individual harvesting process contributions, and literature comparisons. The baseline LCA average impacts were lower for grindings (4.57 kg CO2eq/Mg) and dirty chips (7.16 kg CO2eq/Mg) than for clean chips (23.99 kg CO2eq/Mg) under economic allocation, but impacts were of similar magnitude under mass allocation, ranging from 24.42 to 27.89 kg CO2eq/Mg. Uncertainty analysis showed a wider range of probable results under mass allocation compared to economic allocation. Sensitivity analysis revealed the impact of variations in the production masses and total economic values of primary products of forest harvests on the LCA results due to allocation of supply chain emissions. The high variability in fuel use between logging contractors also had a distinct influence on LCA results. The results of this study can aid decision‐makers in energy policy and guide emissions reductions efforts while informing future LCAs that expand the system boundary to regional FB energy pathways, including electricity generation, transportation fuels, pellets for heat, and combined heat and power.

The transition to electric vehicles (EVs) will impact the climate, the environment, and society in highly significant ways. This study compares EVs to vehicles with internal combustion engines for three major areas: greenhouse gas emissions (GHGs), fuel costs, and transportation energy burden (i.e. percentage of income spent on vehicle fuels). Excluded in the analysis is the purchase cost of the vehicles themselves. The results reveal that over 90% of vehicle-owning U.S. households would see reductions in both GHGs and transportation energy burden by adopting an EV. For 60% of households these savings would be moderate to high (i.e. >2.3 metric tons of CO _2 e reduction per household annually and >0.6% of energy burden reduction). These reductions are especially pronounced in the American West (e.g. California, Washington) and parts of the Northeast (e.g. New York) primarily due to a varying combination of cleaner electricity grids, lower electricity prices (relative to gas prices), and smaller drive-cycle and temperature-related impacts on fuel efficiency. Moreover, adopting an EV would more than double the percentage of households that enjoy a low transportation energy burden (4% income spent on fuel annually), and if at-home charging is unavailable, this rises to over 75 percent. Addressing this inequity hinges on three major interventions: 1) targeted policies to promote energy justice in lower-income communities, including subsidizing charging infrastructure; 2) strategies to reduce electricity costs; and 3) expanding access to low-carbon transport infrastructure (e.g. public transit, biking, and car sharing).

• A feasibility of nuclear deployment against natural gas for the Canadian oil sands industry. • Nuclear is cost-competitive with natural gas for heat applications such as oil sands extraction but is not cost-competitive for electricity applications such as hydrogen production via electrolysis. • Excess electricity from nuclear cogeneration can supply to the grid to generate revenue and give nuclear energy an advantage. • Nuclear energy enables the Canadian oil sands industry to be part of the transition to a low-carbon energy future. Steam-assisted gravity drainage method is currently the most widely used in Canada for bitumen extraction in the oil sands. The method requires injection of high-temperature steam continuously to allow the bitumen to become more fluid and enable pumping to the surface. Once recovered, the bitumen can be upgraded into synthetic crude oil and sent to refineries. The extraction and upgrading processes require large amounts of energy including steam, hydrogen, and electricity. Typically, natural gas is used as the main fuel source, which causes significant greenhouse gas emissions. Nuclear technology can provide reliable sources of heat and electricity for bitumen extraction and hydrogen production while addressing greenhouse gas emissions and reducing the dependency on natural gas. This study present a conceptual economic analysis of small modular reactors for oil sands extraction and upgrading. Several scenarios were analyzed aiming to achieve deep emission reductions and possibly lower production costs. Further, sensitivity analyses were performed to determine the effects of key parameters on production costs and emissions. The results showed that by replacing natural gas with nuclear energy, the extraction and upgrading facilities can potentially prevent more than 90% of life cycle greenhouse emissions from being released into the atmosphere. Although nuclear technologies are not currently cost competitive with natural gas cogeneration or once through steam generator, increases in natural gas prices and carbon prices would allow nuclear energy to become more competitive. With a carbon price of $170 per tonne, nuclear energy can be a feasible and economical solution in supporting the transition of the Canadian oil sands industry into the new low-carbon economy. [ABSTRACT FROM AUTHOR]

Life cycle assessment (LCA) was combined with primary data from nine forest harvesting operations in New York, Maine, Massachusetts, and Vermont, from 2013 to 2019 where forest biomass (FB) for bioenergy was one of several products. The objective was to conduct a data‐driven study of greenhouse gas emissions associated with FB feedstock harvesting operations in the Northeast United States. Deterministic and stochastic LCA models were built to simulate the current FB bioenergy feedstock supply chain in the Northeast US with a cradle‐to‐gate scope (forest harvest through roadside loading) and a functional unit of 1.0 Mg of green FB feedstock at a 50% moisture content. Baseline LCA, sensitivity analysis, and uncertainty analyses were conducted for three different FB feedstock types—dirty chips, clean chips, and grindings—enabling an empirically driven investigation of differences between feedstock types, individual harvesting process contributions, and literature comparisons. The baseline LCA average impacts were lower for grindings (4.57 kg CO2eq/Mg) and dirty chips (7.16 kg CO2eq/Mg) than for clean chips (23.99 kg CO2eq/Mg) under economic allocation, but impacts were of similar magnitude under mass allocation, ranging from 24.42 to 27.89 kg CO2eq/Mg. Uncertainty analysis showed a wider range of probable results under mass allocation compared to economic allocation. Sensitivity analysis revealed the impact of variations in the production masses and total economic values of primary products of forest harvests on the LCA results due to allocation of supply chain emissions. The high variability in fuel use between logging contractors also had a distinct influence on LCA results. The results of this study can aid decision‐makers in energy policy and guide emissions reductions efforts while informing future LCAs that expand the system boundary to regional FB energy pathways, including electricity generation, transportation fuels, pellets for heat, and combined heat and power. [ABSTRACT FROM AUTHOR]

Concrete is the second most used material after water and the production of cement is responsible for 5–8% of global carbon dioxide emissions. The development of low-carbon concretes is pursued worldwide to help the construction industry make its contribution to decarbonising the built environment and achieving carbon reduction targets agreed under the Paris Climate Agreement. However, there is uncertainty around the actual amount of greenhouse gas emissions that can be avoided by employing alternative types of concrete. This study quantifies the carbon footprint intensities of Australian cement and concrete production, including ordinary Portland cement, standard ordinary Portland cement concrete, blended cement-based concrete and geopolymer concrete production. For the first time, an input-output based hybrid life-cycle assessment method is used for these products. The main goal of this paper is therefore to make a methodological comparison between process-based and hybrid life cycle assessment using the Australian cement and concrete production as a case study. A comparison with published results from process-based life-cycle inventories as well as a decomposition of results into product categories is provided. The hybrid life cycle assessment resulted in higher greenhouse gas emissions for ordinary Portland cement and all types of concrete due to the methodology incorporating an economy-wide system boundary, which includes the emissions from upstream processes. For geopolymer concrete in particular, the results were also dependent on the method applied for allocating greenhouse gas emissions from fly ash and slag. The findings from this study are likely to inform the development of strategies and policies aimed at greenhouse gas reduction in the cement and concrete industries. [ABSTRACT FROM AUTHOR]

There are numerous strategies available to design and construct a low energy or nearly zero energy building (NZEB). However, the design strategy for a building depends on a high number of factors including location, climate, cost, available resources, etc. For instance, for countries like Ireland, which have a temperate oceanic climate, a key to achieving NZEB is a high thermal and air tightness performance of the building envelope, installing highly efficient space and water heating systems, and utilising renewable technologies for energy and heat generation. The challenge is to find the best combination of design strategies that would tackle the energy performance problems of a particular building. For example, is it better to design a super-insulated building with minimum heating requirements, or provide less insulation but install a large amount of renewable energy sources? This paper presents the outcomes of a number of case study buildings in Ireland, which focus on the life cycle cost and environmental analysis (using energy and global warming potential as indicators) of NZEBs using various heat sources, such as a gas boiler, biomass boiler, a domestic gas fired combined heat and power unit, heat pump and renewable technology. With the de-carbonisation and increased efficiency of the electricity grid, the low global warming potential (GWP) emissions of biomass fuels and the depletion of fossil fuels, future buildings should be (i) designed and constructed to be super-insulated with high air-tightness performance resulting in minimum heating requirements and (ii) operate with heating systems that have low impact on the natural environment, such as a biomass boiler or heat pump. [ABSTRACT FROM AUTHOR]

Few studies have simultaneously evaluated the impact of alternate wetting and drying (AWD) on profit and life cycle greenhouse gas (LC-GHG) emissions based on a farm survey for all rice (Oryza sativa L.)-cropping seasons in a year. This study explores whether AWD allows farmers to increase profits and reduce LC-GHG emissions compared with conventional water management. To achieve this objective, survey data were collected by a structured interview from two groups of farmers in An Giang Province in Vietnam: one group was defined as AWD farmers who attended a training course and answered that they conducted AWD, and the other was defined as non-AWD farmers who did not attend the course and answered that they did not conduct AWD. The survey data were analysed by a regression approach and cradle-to-farm gate life cycle assessment. The results showed that the impact of AWD on profit varied depending on the season. The impact of AWD on profit was significant and positive for the early wet season (p < 0.05) and throughout the year (p < 0.1), but the impact was not significant for the dry and late wet seasons. In contrast, LC-GHG emissions by AWD farmers were significantly lower for all seasons when compared to non-AWD farmers. Although few studies have analysed the impacts of AWD on profits in the early wet season, AWD farmers may obtain higher profits than non-AWD farmers due to water from precipitation, which may reduce severe water stress and alleviate some of the adoption constraints. Based on these results, this study recommends implementing AWD throughout the year in An Giang Province if irrigation and drainage systems are available. The results on seasonal variations in impacts and the overall annual impact of AWD on profits and LC-GHG emissions will help farmers make decisions and help to achieve mitigation targets in the nationally determined contribution under the Paris Agreement. [Display omitted] [ABSTRACT FROM AUTHOR]

• CLT building showed 30% less LGHGE compared with a RC building in Melbourne. • A reduction of 1.3% of LCC was observed for CLT compared with a RC building in Melbourne. • CLT building has an advantage in terms of LCC and LCGHGE in the construction/EOL phases, but not in the operation phase. • Energy efficient methods and reuse/recycling at EOL can enhance LC performance of CLT buildings. Engineering wood products have significant potential as a sustainable alternative for concrete and steel in construction. Cross Laminated Timber (CLT) can add value to conventional timber products due to its high strength-to-weight ratio, simple installation, aesthetic features and environmental benefits. Recent changes in the national construction code permit structural timber buildings with a height of up to 25m, which demonstrates the strong commitment of the construction industry to adopt more sustainable practices. This paper aims to compare life cycle greenhouse gas emissions (LCGHGE) and life cycle cost (LCC) of CLT and reinforced concrete (RC) in identical midrise residential buildings in three most populated cities in Australia. It has shown that the CLT building has 30 % less LCGHGE compared with the RC building over a life span of 50 years in Melbourne, and 34% and 29% reduction in LCGHCE in Sydney and Brisbane, respectively. The results from LCC analysis showed that CLT building is 1.3% lower than conventional RC in Melbourne, and 0.9% lower in Sydney and Brisbane. The initial and end of life phases reflected reductions in LCGHGE and LCC for the CLT building whilst the operation phase incurred higher values. The extended service life of buildings has a major impact on the operational phase while changes in the discount rate have strong effects on the lifecycle operational and maintenance costs. Overall the CLT building outperformed the RC building in terms of LCGHGE and LCC across three cities. However, further savings in the operational phase with energy efficient methodologies and reuse or recycling of timber products at the end of life of the building can reinforce CLT as a sustainable alternative to RC construction. [ABSTRACT FROM AUTHOR]

• Proposed a modeling framework to optimize bike sharing system's fleet size and rebalancing. • Less frequent rebalancing can reduce dock-less BSS life cycle GHG emission rate. • The current dock-less BSS in Xiamen, China is significantly oversupplied with bikes. • Rebalancing vehicle fleet can be optimized to reduce rebalancing GHG emissions. • Having multiple rebalancing depots can help reduce system's GHG emissions. Bike sharing systems (BSSs), being viewed as providing green transportation modes, are growing rapidly in recent years. While BSS operators try to improve the system performance through bike rebalancing and launching more bikes, the current BSSs are facing several sustainability challenges. Bike oversupply could bring intensive greenhouse gas (GHG) emissions due to manufacturing excessive bikes, while frequent bike rebalancing could significantly increase fuel consumption of rebalancing vehicles. Existing studies only optimized given BSS from the system operational perspective (i.e. rebalancing), with predetermined bike fleet size and rebalancing frequencies. However, the bike fleet size and rebalancing should also be optimized from the life cycle's perspective. This study proposes a framework to obtain the optimal bike fleet size and rebalancing strategy to minimize the system's life cycle GHG emissions, integrating a simulation model for fleet size estimation, an optimization model for bike rebalancing, and a life cycle assessment (LCA) model to quantify the system's GHG emission rate. The framework is applied to a dock-less BSS in Xiamen, China as a case study to evaluate the tradeoff between having more bikes (requiring less rebalancing) and more frequent rebalancing (requiring fewer bikes). Our results show that (1) the current BSS in Xiamen is significantly oversupplied, with only 15% of current bikes needed to serve the same demands; (2) decreasing bike fleet size through more frequent rebalancing will increase the system's life cycle GHG emissions; and (3) choosing appropriate rebalancing fleet size, loading capacity, and setting multiple depots can reduce a BSS' rebalancing GHG emissions. [ABSTRACT FROM AUTHOR]