Retrofit Costs Research Articles

Retrofitting a high-speed marine engine to dual-fuel methanol-diesel operation: A comparison of multiple and single point methanol port injection

As a result of climate change and increasingly stringent emission legislation the shipping industry has started with a transition to sustainable propulsion. Methanol is a viable fuel to reach this goal: it is a great engine fuel (high octane number, high heat of evaporation, and absence of carbon to carbon bonds) and a simple molecule that can be produced in a renewable way. The dual-fuel methanol-diesel technology with methanol injection in the intake has proven to be a promising retrofit solution for vessels. In this concept methanol injectors can be at multiple locations: single point injection (SPI) in the intake duct (assumed to be easier to install) or multiple point injection (MPI) at the intake ports of the cylinders (assumed to give additional in-cylinder cooling to suppress knock). This paper compares MPI and SPI with a focus on maximum methanol energy fraction (MEF), brake thermal efficiency (BTE) and NOx emissions; and compares both injection modes with diesel-only operation. The highest MEF was measured in SPI: 84%. BTE was significantly higher in SPI for high MEFs due to a better combustion phasing resulting from higher intake temperatures. Higher intake temperatures in SPI resulted in higher NOx emissions. Independent of the injection mode, NOx mainly decreased compared to diesel-only operation. It is concluded that SPI is preferred from a cost point of view (maximizing BTE and minimizing retrofit cost) and that MPI is preferred from a sustainability point of view (maximizing MEF and minimizing NOx emissions).

Exploring a Flooding-Sensors-Agnostic Prediction of the Damage Consequences Based on Machine Learning

Recently, progressive flooding simulations have been applied onboard to support decisions during emergencies based on the outcomes of flooding sensors. However, only a small part of the existing fleet of passenger ships is equipped with flooding sensors. In order to ease the installation of emergency decision support systems on older vessels, a flooding-sensor-agnostic solution is advisable to reduce retrofit cost. In this work, the machine learning algorithms trained with databases of progressive flooding simulations are employed to assess the main consequences of a damage scenario (final fate, flooded compartments, time-to-flood). Among the others, several classification techniques are here tested using as predictors only the time evolution of the ship floating position (heel, trim and sinkage). The proposed method has been applied to a box-shaped barge showing promising results. The promising results obtained applying the bagged decision trees and weighted k-nearest neighbours suggests that this new approach can be the base for a new generation of onboard decision support systems.

Unit-level cost-benefit analysis for coal power plants retrofitted with biomass co-firing at a national level by combined GIS and life cycle assessment

To avoid the irreversible impact of global climate change on human society, many countries have recently put forward ambitious goals to accelerate the low-carbon transition of energy systems. Among low-carbon measures, retrofitting existing coal power plants with biomass co-firing is regarded as a promising cost-efficient option to mitigate greenhouse gas and air pollutant emissions. However, the life-cycle economic cost or environmental benefit of this coal-to-biomass retrofit is not identical for various types of power plants in different regions. To facilitate a more efficient biomass utilization strategy in an energy system, it is necessary to carry out a large-scale and high-resolution cost-benefit assessment for the co-firing of biomass and coal in retrofitted plants. Taking China as an example, this study utilized a bottom-up approach and geographic information system, combined with the latest available datasets, to develop a unit-level cost-benefit analysis framework for the coal-to-biomass transition. The results indicate that the coal-to-biomass retrofit costs US$18.3–73.0 for each ton of carbon reduction, and US$21.6–806.5 for each kg of SO2 reduction, at a 25% blending ratio. Installed capacity, operating year, and transportation distance are important influencing factors of cost-benefit heterogeneity. The priority of power unit retrofitting in terms of carbon reductions mainly depends on the cost preference, while that for SO2 reduction is mainly determined by benefit preference. The analytical framework proposed in this study can be used in other countries to formulate an efficient biomass development strategy.

Cryogenic Carbon Capture™ Technoeconomic Analysis

The Cryogenic Carbon Capture™ (CCC) process significantly decreases cost and energy demands for CO2 separation and pressurization to 150 bar compared to alternatives. The process is a post-combustion technology that cools CO2-laden flue gas to desublimation temperatures (−100 to −135 °C), separates solid CO2—that forms from the flue gas—from the light gases, uses the cold products to cool incoming gases in a recuperative heat exchanger, compresses the solid/liquid CO2 to final pressures (100–200 bar), and delivers a compressed CO2 stream separated from an atmospheric pressure light-gas stream. The overall energy and economic costs are about 30-50% lower than most competing processes that involve air separation units (ASUs), solvents, or similar technologies. In addition, the CCC process enjoys several ancillary benefits, including (a) it is a minimally invasive Bolton technology, (b) it provides highly efficient removal of most pollutants (Hg, SOx, NO2, HCl, etc.), and (c) possible energy storage capacity. This report outlines the process details and economic and energy comparisons relative to other well-documented alternatives. This paper presents the results of a detailed techno-economic comparison of CCC with amine-based systems. The comparison uses identical financial and economic assumptions similar process assumptions as the detailed analyses published by US DOE in the greenfield analysis. Specifically, the comparison assumes power plants that produce the same net output, one equipped with and a second without carbon capture. Separately, the paper compares similar analyses for retrofitting existing systems using typical plant characteristics in the US (initial capital costs have been paid, high plant utilization), though there are no DOE estimates available for direct comparison. Financial and technical assumptions for all comparisons are maintained as close to the DOE reference studies as possible. The results demonstrate about 30-50% lower costs and energy demands for capture from greenfield coal plants. Natural gas plants produce substantially lower CO2 concentrations which makes the cost of capturing a ton of CO2 at the same capture rate as the coal plant higher for all processes while the cost of CO2 capture per unit of power generation is lower. However, CCC maintains about the same absolute energy and cost advantages for NG as for coal compared to amine systems. Finally, the costs of retrofitting a station are compared to those of building a new station with and without capture. The retrofit costs are comparable to (slightly lower than) new plant costs without capture. In all cases operating and capital cost comparisons show that the CCC process can be retrofitted to a variety of plants to cost effectively reduce CO2 emissions. Further process integration into the upstream processes and unique process features like water recovery, and integrated energy storage bring the effective cost of carbon capture using the CCC process down further and increase its advantages over alternatives. This technoeconomic analysis shows that the CCC process has the potential to the be lowest cost carbon capture technology under development today.

An engineering‐oriented variable water flow air‐conditioning system terminal flow rate estimation method based on component flow resistance characteristics

AbstractWater flow rate plays an important role in the modeling prediction, fault detection and diagnosis, and performance optimization of the variable water flow air‐conditioning (VWFAC) system. However, flowmeters employed by the system's terminals have not been widely used in engineering applications for the constraints in installation space and high installation and retrofit costs. Therefore, in this study, a terminal flow rate estimation method is proposed for the VWFAC system to reduce the dependency on flowmeters. The water flow rate estimation model is developed based on the flow resistance characteristics inside the air handling unit (AHU) and was trained and verified at the Monitoring and Control Laboratory established in the Dalian University of Technology. The results indicate that the maximum root‐mean‐square error (RMSE) during the training and validation sessions are 0.038 m3/h and 0.028 m3/h, respectively, while the corresponding mean absolute percentage error (MAPE) are below 1.4% and 6.5%, which is acceptable for engineering applications. To improve the flow rate estimation accuracy of the model, water temperature, water flow rate, and pressure difference are suggested to cover a wide varied range during the training session as much as possible. Systematic error is an important index in determining the demands for sensor's accuracy class. According to the results of water flow rate, the systematic errors of the estimates are ranged between 0.51% and 0.76%, only about 1/4 to 1/3 of the measurements systematic errors. Based on the error propagation theory, the water flow rate estimates would be reliable if the systematic error of the pressure measurements does not over twice that of the water flow rate measurements. This flow rate estimation method can be further applied to other thermal engineering systems to bring considerable economic benefits for engineering applications.

Effect of structural uncertainties on seismic performance of moment frame rehabilitated with steel shear wall

In performance-based engineering, conservatism in acceptance criteria at structural performance levels has increased the cost of retrofitting. When simulating structure response in the presence of uncertainties, seismic demand and structural capacity cannot be expressed certainly, though the possible range of these can be predicted. In the seismic rehabilitation of structures, uncertainties have been studied on existing structures and rehabilitation guidelines have been implemented on these uncertainties by reliability index. Adding a secondary system to rehabilitate existing structure may increase uncertainties and may be effective for results of reliability. Therefore, in this study, reliability of rehabilitated a structure with steel shear wall has been discussed with the aim of quantifying uncertainties. Also, the parametric study of reliability index has been performed on probabilistic variables considered for steel shear wall. The selected structure is a three-storey structure of SAC steel moment frame, which was rehabilitated by steel shear wall. For modeling and analyzing the structure, OpenSees software was used. The structure was subject to incremental dynamic analysis before and after of rehabilitation, with probabilistic variables considered for steel shear wall.

Single and multi-objective optimisation for the retrofit of process water networks

This work develops a generic mathematical model for process engineers and designers to retrofit existing water networks in process plants for water savings. The model is applicable to both direct reuse/recycling and regeneration schemes, with single- and multi-objective optimisation scenarios. The objectives of the model may include minimum water flowrates, minimum extent of retrofits and/or a reasonable payback period. A literature case study involving an existing water network in a pulp and paper mill is solved to elucidate the newly proposed model. The results of single-objective optimisation show maximum annual cost savings of $4,027,919 in the direct reuse/recycling scheme (with a 57.2% freshwater saving) and $4,420,975 in the regeneration scheme (with an 84.5% freshwater saving). For multi-objective optimisation, the use of the constraint method in the direct reuse/recycling scheme generates a range of Pareto optimal solutions for selection by the decision-maker. It was found that 88.1% of the freshwater saving can be achieved with 44.2% of the piping retrofit cost. Although the compromise solution obtained using fuzzy optimisation in the regeneration scheme achieves only 66.6% of the freshwater saving with 86% of the total retrofit cost, the number of new and modified connections is reduced by more than half.

A machine learning-based surrogate model to approximate optimal building retrofit solutions

The building sector has the highest share of operational energy consumption and greenhouse gas emissions among all sectors. Environmental targets set by many countries impose the need to improve the environmental footprint of the existing building stock. Building retrofit is considered one of the most promising solutions towards this direction. In this paper, a surrogate model for evaluating the necessary building envelope and energy system measures for building retrofit is presented. Artificial neural networks are exploited to build up this model in order to provide a good balance between accuracy and computational cost. The proposed model is trained and tested for the case study of the city of Zurich, in Switzerland, and is compared with one of the most advanced models for building retrofit that uses building simulation and optimization tools. The surrogate model operates on a smaller input set and the time required to derive retrofit solutions is reduced from 3.5 min to 16.4 μsec. Results show that the proposed model can provide significantly reduced computational cost without compromising accuracy for most of the retrofit dimensions. For instance, the retrofit costs and the energy system selections are approximated with an average accuracy of R2=0.9408 and f1score=0.9450, respectively. Finally, yet importantly, such surrogate retrofit models may effectively be used for bottom-up retrofit analyses for wide areas and can contribute towards accelerating the adoption of retrofit measures.

Seismic retrofit solutions using base isolation for existing RC buildings: economic feasibilty and pay-back time

The existing reinforced concrete buildings typical of the Mediterranean area commonly have poor seismic performance and high vulnerability to the seismic events. As demonstrated by recent post-earthquake reconstruction processes, they commonly exhibited significant damage to structural components and to infills and partitions resulting in very high repair costs. This suggests that effective seismic strengthening interventions should aim at both improving the safety and reducing the expected annual losses. Nowadays, the seismic retrofitting of existing RC buildings by using base isolation is becoming popular because of the high effectiveness as seismic protection strategy. However, the high costs of installation are limiting the widespread in the common design practice. In this context, a unique design parameter capable of combining the increasing seismic safety, the cost of installation and the reduction of the expected losses can be useful to draw simple cost-benefits considerations. This research work proposes a PBEE-based methodology to quantify the Pay-Back Time (PBT) of seismic retrofit solutions for existing RC buildings. The non-linear response of base isolated building is assessed and a comparison with different strengthening solutions is proposed to show the applicability of the PBT as a unique design parameter to select the most effective retrofit solution. A database of 59 RC buildings retrofitted by using base isolation during the L’Aquila reconstruction process, where actual retrofit costs are available, is used for the validation. Finally, these data are used to calibrate a simple formulation of the PBT to be used in the design practice.

A cost-effective building retrofit decision-making model – Example of China’s temperate and mixed climate zones

Sustainable building retrofitting has attracted serious research attention in recent years as it can significantly reduce energy consumption and thus help achieve energy reduction targets set by governments around the world. In this paper, a sustainable retrofit decision-making model is developed to uncover the optimal set of retrofit solutions according to local climatic conditions, building features, and retrofit costs. Net present value (NPV), a common method for analyzing the feasibility of a building retrofit solution, is used to determine the optimal retrofit solution of existing high-rise residential buildings in a temperate zone and hot summer-cold winter zone, involving prototypical 1990s apartments of 116 and 53 m2 floor areas respectively. This reveals that the lighting system, wall insulation, and upgraded window glazing are essential optimal retrofit measures for the temperate zone, whereas the heating system and shading devices are also essential for the hot summer-cold winter zone. The results indicate that the optimal NPV can be obtained by pursuing a 40% energy saving, as it can result in energy saving of up to 50 kWh/m2/year and 95 kWh/m2/year at an average retrofit cost of approximately USD 1.30 and 3.20 m2/year in the temperate and hot summer-cold winter zones respectively. The sensitivities associated with the most influential optimal NPV and energy savings input parameters are critically analyzed; these can be used by decision-makers to determine the risks and uncertainties related to various cost-effective retrofit measures. The model can help in devising the most suitable sustainable retrofit measures for existing buildings commensurate with the energy reduction targets of policy and decision-makers in the two climate zones. It is also amenable to being adapted for other climatic zones to identify the most appropriate sustainable building retrofit for particular local climatic conditions and building characteristics.

Performance evaluation and sustainable, cost-effective and energy-efficient process enhancement measures for Pagla sewage treatment plant, Bangladesh

At present, Pagla Sewage Treatment Plant (STP) is the only sewage treatment plant in Dhaka, the capital city of Bangladesh, with a capacity to treat 120 million litres per day (MLD) of sewage. Evidence suggests that the plant is overburdened and cannot by itself handle the wastewater generated in Dhaka. Furthermore, the treatment plant is hampered by a number of functional problems which limit both its capacity to treat wastewater, and the efficiency of the treatment process. Rectifying the functional problems of the plant and implementing enhancement measures would greatly improve the functionality of Pagla STP. A thorough evaluation was carried out on the performance of the plant and a detailed process flow diagram developed. Several functional problems were identified, mostly pertaining to the primary sedimentation tanks and the unused sludge lagoons. The influent and effluent characteristics of Pagla STP were also assessed using BOD5 values as the primary criteria. It was found that the influent BOD5 value was 832 mg/L and effluent BOD5 was 497.5 mg/L, against design values of 120 mg/L and 50 mg/L respectively. Based on the evaluation, theoretical analysis was done, and a sustainable, cost and energy efficient retrofit was proposed whereby the sludge lagoons would be converted to anaerobic lagoons to facilitate biological pretreatment. It is estimated that implementing such an enhancement would increase the treatment capacity of the plant beyond its original design. Furthermore, theoretical calculations show up to 5,000 m3 of methane gas can be generated daily from the plant, which is enough to power 6,000 homes with renewable energy.

“If we had a little more flexibility.” perceptions of programmatic challenges and opportunities implementing government-funded low-income energy efficiency programs

Since 1976, the U.S. Department of Energy's Weatherization Assistance Program (WAP) has provided state block grants for no-to low-cost energy efficiency retrofits for more than 7 million low-income households. Yet, more than 35 million households meet income-qualifications for the program. While numerous program evaluations demonstrate the energy- and non-energy-related benefits of WAP, some argue low uptake, and a low rate of return on retrofit costs to energy savings. To further our understanding of government-funded low-income energy efficiency program implementation, we examined local agency-level perceptions of challenges and opportunities. Findings from semi-structured interviews with program managers, representing one-third of Michigan's WAP funding and retrofit production, suggest three funding-related challenges: funding instability; funding allocation formula; and limited advertising and marketing funding, and two regulatory-related challenges: cumbersome paperwork and restrictive guidelines. Program managers also identified three workaround opportunities: collaboration with utilities and other organizations; intra-agency innovation and integration; and strategic productivity and per unit spending. Lastly, one recommendation for further exploration would be testing the efficacy of granting local agencies greater flexibility to work around funding and regulatory challenges to increase the number of households weatherized, reduce long waitlists and deferral rates, and use staff time more efficiently.

Sustainable building retrofit model for high-rise, high-density city: a case in Hong Kong

Considering the significant consumption of energy in existing building stocks, effective retrofitting has great potential for reducing such consumption and promoting sustainability in existing buildings. This study aims to develop a sustainable retrofit decision-making mechanism for high-rise buildings in Hong Kong, China, by uncovering the optimum set of retrofit solutions based on the local climatic conditions, building features and cost. Based on a prototype building in Hong Kong, the study employed the net present value (NPV) to unveil the most suitable solutions to maximise the energy efficiency of existing buildings and minimise their retrofit costs, integrating the energy simulation. This study revealed that it is desirable to adopt an optimal set of measures for achieving a 40% energy improvement since the energy conservation can be as much as 82 (kWh/m2)/year with the optimal NPV of more than US$3300 over a 20 year life span. However, the cooling system, building energy management system and thickness of wall insulation are the most influential factors to the optimum NPV and energy conservation in Hong Kong. The identified optimal set of cost-effective retrofit measures can be effectively implemented for sustainable retrofit projects in the existing building, and the developed methodological framework can be suitably adapted for sustainable building retrofit projects in different climatic zones. The decision-making model is validated by the process of calculating energy consumption, selecting practical retrofit measures and analysing retrofit benefits when taking the local building standards into account.

Experimental and numerical study on the seismic behavior of high-strength steel framed-tube structures with end-plate-connected replaceable shear links

With the aim of improving the seismic performance and resiliency of steel framed-tube structures (SFTSs), high-strength SFTSs with end-plate-connected replaceable shear links (HSS-FTS-RSLs) were developed in this work. The deep beams and columns used high-strength steel (HSS), while the replaceable links used conventional or low yield point steel. The replaceable shear links acted as ductile fuses at the mid length of the deep beams to dissipate energy by shear yielding. A series of quasi-static cyclic tests were performed to investigate the seismic behavior and replaceability of HSS-FTS-RSLs through three two-thirds-scale sub-assemblage specimens. The test results indicated that all specimens produced a stable and full hysteretic response, resulting in an excellent inelastic deformation and energy dissipation capacity under cyclic loading. The shear links exhibited a large inelastic shear deformation capacity in excess of 0.12 rad. The residual interstory drift and residual link shear deformations of the specimens, which allowed for the easy installation of the new links, exceeded 0.36% and 0.0084 rad, respectively. The replacement of the links had a limited effect on the initial stiffness. The inelastic deformation and damage to the sub-assemblage specimens were concentrated only within the shear links, while the other structural components maintained elasticity under cyclic loading. This indicated that the HSS-FTS-RSLs could achieve a quick rehabilitation after a major earthquake and reduce the retrofit cost. In addition, nonlinear finite element (FE) models of test specimens were implemented in ABAQUS. The analysis results showed that the load-carrying capacity, initial stiffness, development of the plasticity, and failure models obtained by the FE models were in good agreement with the experimental responses.

Perceived attributes of hurricane-related retrofits and their effect on household adoption

Understanding how homeowners make protective action decisions is important for designing policies and programs to encourage those actions and community resilience as a whole. This paper focuses on the role of homeowner perceptions of attributes of the protective actions themselves in influencing household protective action decisions. Specifically, using a combination of revealed and stated preference data from a mailed survey of homeowners in North Carolina (n = 234), we fitted mixed logit models to predict the probability a homeowner has or intends to structurally retrofit (strengthen) her home to mitigate hurricane wind and flood damage. We found evidence supporting the hypotheses that a higher probability of undertaking a retrofit is associated with homeowner beliefs that: (1) The retrofit cost is not too high, (2) the installation does not require too much effort, (3) they understand how it works, (4) it would add to home value, (5) it would protect lives, (6) it would protect property, and (7) it would not make the home less attractive. This work shows that homeowners make retrofit decisions based on a portfolio of perceived attributes that depend on the type of retrofit under consideration. Although cost is important, other factors carry considerable weight in the decision as well. Further, findings suggest that study of one type of protective action (e.g., having an emergency kit) may not be generalizable to other actions (adding hurricane shutters) without considering these attributes.

Retrofitting High-Rise Residential Building in Cold and Severe Cold Zones of China—A Deterministic Decision-Making Mechanism

This study aimed to develop a deterministic decision-making mechanism for finding the optimum set of retrofit solutions of existing high-rise residential buildings in two different climatic zones of China. The retrofit solutions were critically examined with different energy saving targets based on the local climatic conditions, building features, and retrofit costs in cold and severe cold zones comparatively. By making the extensive review and analyzing considerable statistics data and cost information, net present value (NPV) method was employed in the prototype building apartments to develop this deterministic model. The results demonstrated that the heating system is the most important factor in saving energy and obtaining the optimum revenue in these two regions. The highest optimal NPV can be obtained by achieving 60% energy saving in the cold zone, as energy saving is around 319 kWh/m2/year with the total retrofit costs of USD $3560, while it is 281 kWh/m2/year with the total retrofit costs of USD $3480 to achieve the 50% energy-saving target in the severe cold zone. Based on the analysis of energy savings and retrofit costs, the results can be effectively implemented for the purpose of creating sustainable retrofits in existing buildings, and the model can be adapted for selecting appropriate retrofit choices in other climatic zones.

Multi-scale cost-benefit analysis of the Los Angeles Soft-Story Ordinance

A multi-scale (building-specific and portfolio) cost-benefit analysis of the Los Angeles soft-story Ordinance for woodframe residential buildings is presented. Building-specific loss functions (shaking intensity versus loss ratio) are computed by implementing the FEMA P-58 seismic loss assessment methodology on a set of archetype buildings that reflect the variations in key structural characteristics (e.g. 1st story wall layout, number of stories) of the approximately 12,000 buildings affected by the Ordinance. The cost-benefit ratio is assessed as the retrofit cost divided by the reduction in earthquake-induced losses that result from the retrofit. At the individual building level, both intensity and time-based cost-benefit assessments are performed. The latter uses the expected annual losses to determine the break-even time, which is the duration needed to recoup the upfront cost of the retrofit. The average break-even time when considering all archetypes is four to five years. At the portfolio-scale, an average cost-benefit ratio of 0.32 is obtained for a hypothetical Mw 7.1 Puente Hills scenario earthquake. A first-of-its kind stochastic event-set cost-benefit assessment is also performed, where all events (approximately 8000) that are significant to the region are considered. From this assessment, it was determined that the probability of achieving a desirable cost-benefit ratio (value between 0.0 and 1.0) within a 50-year period is approximately 0.9.

A multi-criteria approach to affordable energy-efficient retrofit of primary school buildings

The majority of the buildings was built before the energy efficiency prospering in the construction sector. Hence, they are consuming an enormous energy amount that can be preserved considerably by applying some not even advanced retrofit measures. Schools' low budget is a problem that managers are encountered. Thus the high retrofit cost can prevent taking proper actions. However, considering the measures leading to higher energy efficiency with appropriate cost and payback period, together with taking the lifespan of buildings and the economic benefits during this extended period, would make the actions attractive. This research aims at defining a multi-parameter approach to distinguish energy efficient measures with proper cost, payback period and CO2 emission for primary school buildings’ retrofit. It is following the concept of cost-optimal building retrofit introduced by the EPBD-recast. To assess the proposed approach, two typical school buildings were considered as case studies, the model was created and validated by real consumptions, and then some measures were applied to the envelope, mechanical and lighting system. After driven cost-optimal measures, the comfort analyses were conducted and some of the measures were excluded due to worsening the comfort conditions. The results indicate that, in the suitable cost-optimal scenarios, the potential of primary energy savings and CO2 emission reductions are approximately 60%, and savings for global cost would amount to more than 42%, while the payback periods are less than seven years.

Postcombustion Capture or Direct Air Capture in Decarbonizing US Natural Gas Power?

This analysis investigates the cost of carbon capture from the US natural gas-fired electricity generating fleet comparing two technologies: postcombustion capture and direct air capture (DAC). Many of the existing natural gas combined cycle (NGCC) units are suitable for postcombustion capture. We estimated the cost of postcombustion retrofits and investigated the most important unit characteristics contributing to this cost. Units larger than 400 MW, younger than 14 years, more efficient than 45%, and with a utilization (capacity factor) higher than 0.5 were found to be the most promising for retrofit. Counterintuitively, DAC (which is usually not considered for point-source capture) may be cheaper in addressing emissions from nonretrofittable NGCC units. DAC can also address the residual emissions from retrofitted units. Moreover, the economic challenges of postcombustion capture for small natural gas-fired units with low utilization, such as gas turbines, make DAC look favorable for these units. After considering the cost of postcombustion capture for the entire natural gas-related emissions and incorporating the impact of learning-by-doing for both carbon capture technologies, our results show that DAC is the cheaper capture solution for at least 1/3 of all emissions.

Optimal seismic retrofit method for reinforced concrete columns with wing walls

Seismic retrofit of reinforced concrete (RC) columns using wing walls can be used to improve the shear and flexural strength of the column through a relatively simple process. However, the feasibility and efficiency of the seismic retrofitting of RC frames with wing walls heavily depends on the selection of number of columns to be retrofitted, the cross-sectional dimensions of wing walls, and the quantity of re-bars of the wing wall. In this study, an optimal seismic retrofit design method is proposed to minimize not only the initial retrofit cost but also the earthquake-induced damage expected during the life cycle of the building. The seismic performance of structures before and after the application of the retrofit has been verified with the comparison of four response parameters: pushover curves, the inter-storey drift ratios, the energy dissipation capacities, and failure modes. The proposed retrofit method is applied to seismic retrofit of a six-storey RC building example and an actual RC building structure in use. For the retrofit of actual building structure, with an initial retrofit weight of 70.85 kN, which corresponds to 1.85% of the weight of the non-retrofitted building, the energy dissipation capacity was increase by 3.02 times and the life cycle cost (LCC) of the retrofit was reduced to 69.47% of the required LCC for the non-retrofitted building. In addition, it has been confirmed that no storey collapse occurred in collapse prevention level, which indicates the most severe failure mechanism of a structure due to an earthquake.