Engineering Sustainable Systems


Research projects are an integral component of the ESS program.  Below are some examples of the research conducted by previous ESS students.

The role of pickup truck electrification in the decarbonization of light-duty vehicles

Electrification can reduce the greenhouse gas (GHG) emissions of light-duty vehicles. Previous studies have focused on comparing battery electric vehicle (BEV) sedans to their conventional internal combustion engine vehicle (ICEV) or hybrid electric vehicle (HEV) counterparts.

Former ESS student Maxwell Woody extends the analysis to different vehicle classes by conducting a cradle-to-grave life cycle GHG assessment of model year 2020 ICEV, HEV, and BEV sedans, sports utility vehicles (SUVs), and pickup trucks in the United States. This study shows that the proportional emissions benefit of electrification is approximately independent of vehicle class. For sedans, SUVs, and pickup truck we find HEVs and BEVs have approximately 43% and 60% lower cradle-to-grave life cycle emissions, respectively, than ICEVs in our base case model. This results in a lifetime BEV over ICEV GHG emissions benefit of approximately 40 tonnes CO2e for sedans, 48 tonnes CO2e for SUVs, and 62 tonnes CO2e for pickup trucks. The benefits of electrification remain significant with increased battery size, reduced BEV lifetime, and across a variety of drive cycles and decarbonization scenarios. However, there is substantial variation in emissions based on where and when a vehicle is charged and operated, due to the impact of ambient temperature on fuel economy and the spatiotemporal variability in grid carbon intensity across the United States. Regionally, BEV pickup GHG emissions are 13%–118% of their ICEV counterparts and 13%–138% of their HEV counterparts across U.S. counties. BEVs have lower GHG emissions than HEVs in 91%–94% of counties and lower GHG emissions than ICEVs in 95%–98% of counties. As consumers migrate from ICEVs and HEVs to BEVs, accounting for these spatiotemporal factors and the wide range of available vehicle classes is an important consideration for electric vehicle deployment, operation, policymaking, and planning.

View the journal article associated with this research in Environmental Research Letters:

Life Cycle Greenhouse Gas Emissions of the USPS Next-Generation Delivery Vehicle Fleet

The United States Postal Service (USPS) plans to purchase 165,000 next-generation delivery vehicles (NGDVs) between 2023 and 2032. The USPS submitted an environmental impact statement (EIS) for two NGDV procurement scenarios: (1) 90% internal combustion engine vehicles (ICEVs) and 10% battery electric vehicles (BEVs) (“ICEV scenario”) and (2) 100% BEVs (“BEV scenario”).

To correct several significant deficiencies in the EIS, former ESS student Maxwell Woody conducted a cradle-to-grave life cycle greenhouse gas (GHG) assessment of these two scenarios. Our analysis improves upon the USPS’s EIS by including vehicle production and end-of-life emissions, future grid decarbonization, and more accurate vehicle operating emissions. In the base case, researchers find that the ICEV and BEV scenarios would result in 15% greater and 8% fewer GHG emissions, respectively, than the USPS estimate. Favorable vehicle and grid development would result in 63% lower BEV scenario emissions than the USPS estimate. Consequently, the study calculates a cumulative lifetime emission reduction of 57–82% (14.7–21.4 Mt CO2e) from procuring 100% BEVs instead of 10% BEVs, compared to the USPS’s estimate of 10.3 Mt. Given the long NGDV lifetimes, committing to the ICEV scenario squanders an ideal use case for BEVs, jeopardizes meeting our climate goals, and forgoes potential climate and environmental justice co-benefits.

View the journal article associated with this research in Environmental Science and Technology:

Life Cycle Assessment of Urine Diversion and Conversion to Fertilizer Products at the City Scale

Urine diversion has been proposed as an approach for producing renewable fertilizers and reducing nutrient loads to wastewater treatment plants.

ESS Student Stephen Hilton used life cycle assessment to compare environmental impacts of the operations phase of urine diversion and fertilizer processing systems [via (1) a urine concentration alternative and (2) a struvite precipitation and ion exchange alternative] at a city scale to conventional systems. Scenarios in Vermont, Michigan, and Virginia were modeled, along with additional sensitivity analyses to understand the importance of key parameters, such as the electricity grid and wastewater treatment method. Both urine diversion technologies had better environmental performance than the conventional system and led to reductions of 29–47% in greenhouse gas emissions, 26–41% in energy consumption, approximately half the freshwater use, and 25–64% in eutrophication potential, while acidification potential ranged between a 24% decrease to a 90% increase. In some situations, wastewater treatment chemical requirements were eliminated. The environmental performance improvement was usually dependent on offsetting the production of synthetic fertilizers. This study suggests that urine diversion could be applied broadly as a strategy for both improving wastewater management and decarbonization.

View the journal article associated with this research in Environmental Science and Technology: https://pubs.

Wireless Charging and Shared Autonomous Battery Electric Vehicles (W+SABEV): Synergies that Accelerate Sustainable Mobility and Greenhouse Gas Emission Reduction

Emerging technologies play important roles in shaping future mobility systems and impacting sustainability performance of the transportation sector in major economies, such as the United States of America (USA) and China.

ESS student Kevin (Zicheng) Bi applies a life cycle framework in this study to demonstrate and evaluate the synergies of the following four emerging transportation system technologies both qualitatively and quantitatively: (1) wireless charging; (2) shared mobility services; (3) autonomous driving; and (4) battery electric vehicles (BEV). The new concept of a wireless charging and shared autonomous battery electric vehicle (W+SABEV) system is introduced and modeled. First, an analytical framework is presented to assess the pros and cons of the W+SABEV system vs. a conventional plug-in charging BEV system, adhering to the principles of sustainable mobility and highlighting the impacts and dynamics of the disruptive technologies on the key parameters that define sustainable mobility. Second, a quantitative analysis presents the synergies of the four technologies by modeling a W+SABEV system and demonstrates that the combination of the four technologies can shorten the payback time of greenhouse gas (GHG) emission burdens for infrastructure and vehicles. Compared to a plug-in charging BEV system, a W+SABEV system pays back the additional GHG emission burdens of wireless charging infrastructure deployment within 5 years if the wireless charging utility factor (ratio of en route charging time vs. trip time) is above 19%.

View the journal article associated with this research in Mitigation and Adaptation Strategies for Global Change:

Life Cycle Comparison of Manual and Machine Dishwashing in Households

Machine dishwashers are a unique consumer appliance since they are often substituted with manual dishwashing. Although some studies indicate machine dishwashers use less energy and water than manual dishwashing, their scopes are limited to the use phase.

ESS student Gabriela Porras evaluates the full life cycle burdens for both manual and machine dishwashing following typical and recommended behaviors. Use phase behaviors are observed through a laboratory study and survey, while burdens are calculated using a life cycle assessment framework. The study finds that typical manual dishwashing behaviors result in the greatest greenhouse gas emissions (GHG). Even when recommended behaviors for machine dishwashers are not followed, they outperform typical manual dishwashing. Although manufacturers do not include typical behaviors like pre-rinsing when estimating their value-chain emissions profile, these activities can increase lifetime GHG emissions by 17%. The sustainability of the average American household can be significantly enhanced by following recommended machine dishwashing instead of typical manual dishwashing, thereby reducing GHG emissions by 72%.

Read more about the research here:

Green Principles for Vehicle Lightweighting

A large portion of life cycle transportation impacts occur during vehicle operation, and key improvement strategies include increasing powertrain efficiency, vehicle electrification, and lightweighting vehicles by reducing their mass. The potential energy benefits of vehicle lightweighting are large, given that 29.5 EJ was used in all modes of U.S. transportation in 2016, and roughly half of the energy spent in wheeled transportation and the majority of energy spent in aircraft is used to move vehicle mass.

ESS students Cailin Buchanan and Krutarth Jhaveri collected and reviewed previous work on lightweighting, identified key parameters affecting vehicle environmental performance (e.g., vehicle mode, fuel type, material type, and recyclability), and proposed a set of 10 principles, with examples, to guide environmental improvement of vehicle systems through lightweighting. These principles, based on a life cycle perspective and taken as a set, allow a wide range of stakeholders (designers, policy-makers, and vehicle manufacturers and their material and component suppliers) to evaluate the trade-offs inherent in these complex systems. This set of principles can be used to evaluate trade-offs between impact categories and to help avoid shifting of burdens to other life cycle phases in the process of improving use-phase environmental performance.

View the journal article associated with this research in Environmental Science and Technology::

Decision Support Algorithm for Evaluating Carbon Dioxide Emissions from Electricity Generation in the United States

Currently, there is no consensus on appropriate methods for calculating greenhouse gas emissions resulting from specific electricity loads. Previous research revealed significant differences in emissions when different methods were used, a situation that could result in divergent sustainability or policy recommendations.

ESS student Nicole Ryan illustrates the distribution of emissions estimates based on method characteristics such as region size, temporal resolution, average or marginal approaches, and time scales. Informed by these findings, a decision support algorithm is presented that uses a load’s key features and an analyst’s research question to provide recommendations on appropriate method types. the article defines four different cases to demonstrate the utility of the algorithm and to illustrate the variability of methods used in previous studies. Prior research often employed simplifying assumptions, which, in some cases, can result in electricity being allocated to the incorrect generating resources and improper calculation of emissions. This algorithm could reduce inappropriate allocation, variability in assumptions, and increase appropriateness of electricity emissions estimates.

View the journal article associated with this research in the Journal of Industrial Ecology:

Investment cost and view damage cost of siting an offshore wind farm: A spatial analysis of Lake Michigan

Investment and view damage costs are important determinants in siting locations for offshore wind farms (OWF) in the Lake Michigan region. This study is limited to the Michigan state boundary for the OWF sites and viewshed impacts. Investment cost depends on the depth and distance to shore of the farm. View damage cost depends on household density and consumer willingness to pay to avoid the visual disamenity of wind turbines. Both these costs are dependent on the geographic location and are summed to create an aggregate cost.

Using ArcGIS, ESS student Amy Chiang mapped the OWF siting locations, with spatial analysis revealing the northern region of the lake at the minimum aggregate cost. The view damage cost contributes at most 68%, but on average 7%, to the aggregate cost. The aggregate levelized cost of energy (LCOE) ranges from 183 to 368 $/MWh (average of 256 $/MWh). The view damage LCOE contribution to the aggregate LCOE is 3% on average and 46% at most. View damage impact is the dominating factor only around a small shoreline region (due to large impacted populations). A series of maps are presented that highlight the investment and view damage tradeoffs which can inform OWF siting in Lake Michigan.

View the journal article associated with this research in Renewable Energy:

Labeling Electric Vehicles

In the United States, information concerning energy and greenhouse gas (GHG) emissions for light-duty cars and trucks has traditionally been presented in terms of fuel economy i.e. miles per gallon. Since gasoline and diesel vehicles have historically dominated the new vehicle fleets, this was an appropriate basis on which to evaluate and compare the energy consumption and emissions characteristics of new vehicles. However, fuel economy is not as accurate of an indicator for electric vehicles (including both plug-in hybrids and battery electrics) since the associated emissions from these vehicles depends on the fuel mix used to generate the electricity.

In his work as part of the U.S.-China Clean Energy Research Center – Clean Vehicles Consortium, ESS student, Nathan MacPherson, evaluated the U.S. EPA vehicle label by modeling a plug-in hybrid (PHEV) and a pure battery electric vehicle (BEV) from a vehicle life cycle perspective. Regional variations in greenhouse gas emissions from electricity use and variations in the utility factor (fraction of PHEV driving on electricity) were explored. The life-cycle model results showed that only 25% of the representative PHEVs life-cycle GHG emissions were reflected on the EPA label. Furthermore, a 100 gCO2eq/mi difference was found between the PHEV operating in the highest and lowest carbon intensive electric grid regions.

View the journal article associated with this research in the Journal of Industrial Ecology:

Lightweight Material Production and Use in Vehicles

As vehicle manufacturers continue to increase vehicle efficiency in response to more stringent regulation, advanced powertrains and vehicle lightweighting have become major technologies of interest. Manufacturers are likely to rely on a combination of both technologies to meet new fuel economy standards, combining lightweight and energy intensive materials like aluminum with the electrified powertrains such as those in plug-in hybrid electric vehicles (PHEVs). When considering the overall environmental impact of these designs, life cycle assessment should be used to ensure that decreases in vehicle energy consumption are not offset by increases in energy use from material production.

ESS student Joseph Colett, part of the U.S. – China Clean Energy Research Center – Clean Vehicles Consortium, is modeling U.S. primary aluminum production and light-weight PHEV energy use in an effort to quantify life cycle greenhouse gas emissions. Preliminary results indicate that large variations in life cycle greenhouse gas emissions exist between aluminum production regions and that these variations in material production can influence the overall environmental performance of aluminum light-weighted PHEVs.

Optimal Replacement Policy for Household Air Conditioners

Air conditioning is responsible for 13% of all energy demanded by the residential sector the United States.  The average efficiency of new central air conditioning equipment has risen overtime.  Replacing existing air conditioning equipment with new, more efficient equipment can save energy, but additional energy is required to manufacture the new equipment and dispose of the old equipment.  A life cycle approach is needed to evaluate this tradeoff.

During his ESS program, Robb De Kleine examined how the timing of replacement of central air conditioning equipment impacted the energy consumption, greenhouse gas emissions, and cost to the consumer.  The project entailed disassembling a central air conditioning unit to understand and measure its material composition in addition to modeling the estimated energy consumption of the equipment based on the different climates in the US.  In addition, other factors such as refrigerant leakage, duct leakage, and equipment maintenance were explored in different scenarios.  The results showed that in order to minimize energy consumption equipment should be replaced on average every 3.2-8.2 years, while minimizing greenhouse gas required replacement an average every 6.8-14 years, and finally minimizing consumer cost required replacement on average every 10-21 years.

View the research report here: CSS10-02 LCO_Residential_AC

Environmental Assessment of Plug-in Hybrid Electrics Vehicles in Michigan

Plug‐in hybrid electric vehicles (PHEVs) have been recognized for their potential to reduce petroleum consumption by using electric energy to power the vehicle during some or all driving times.  The Michigan Public Service Commission wanted to understand how sales of PHEVs would impact the electrical grid and the impact on total State emissions from both the transportation and electricity sectors.

ESS students Jason McDonald and Allison Schafer as part of a team of SNRE students created computer models to represent the energy (petroleum or electricity) consumption of PHEVs based on driving behavior and to predict the mix of fuels (coal, natural gas, nuclear, hydro) used for electricity generation in the State at any given time over the next 20 years.  They also considered several different charging scenarios to represent how and when consumers would be able to charge their vehicles.  Across all scenarios, they found that PHEVs have the potential to decrease statewide GHG emissions 0.4% to 10.7% in 2030, and displace from 0.5 to 9 billion gallons of gasoline from 2010‐2030.

View the research report here: CSS10-08 PHEV

Indoor Shrimp Aquaculture

Rising global demand for seafood and declining catches have created a new impetus to expand seafood production through aquaculture.  Shrimp aquaculture has the potential to reduce pressure on overexploited wild stocks.

An ESS student, Wenting Sun, studied the environmental impacts of indoor recirculating shrimp aquaculture systems using life cycle assessment.  Having local indoor shrimp aquaculture systems can reduce transportation energy and emissions compared to shipping the shrimp from conventional outdoor aquaculture systems in China and southeast Asia. However, for shrimp consumers in Michigan, the research suggested that buying shrimp farmed on the US coast is environmentally preferable, because inland farms have a higher environmental impact resulting from the production of artificial saltwater, which outweighs the transportation benefit.  Compared to buying Michigan-produced shrimp, purchasing shrimp from the Southern coast saved 70% of total life cycle energy.

View the research report here:CSS09-15 Shrimp LCA

Photos: free-stockepadilla, Argonne National Laboratory, and via Flickr

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