Life Cycle Carbon Research Articles

Carbon emission peaking and emission trading in the building sector

China has established the goal of a carbon emission peak and neutrality schedule. With the life cycle carbon footprint of building in China taking half of the country’s total emission, thus reducing emissions in the building sector is critical to achieving the goal. This paper examines the relevant literature and data, summarizes the focal point and challenging aspects in the process of carbon emission peaking in the building sector and discusses the role of emission trading in this process.

An evaluation of the retrofit net zero building performances: life cycle energy, emissions and cost

ABSTRACT This study aims to assess the comprehensive energy, environmental and economic performance of a retrofit zero energy building (ZEB). Three life cycle assessments were conducted: life cycle energy (LCE), life cycle carbon emissions (LCCE) and life cycle cost (LCC). Actual building construction cost data and energy use data were used in the assessments. The analysis results indicated that during the whole building life span, the operational life stage (B6) was a major contributor to LCE (82%) and LCCE (77%), but not to LCC (18%). Within the life cycle embodied carbon (LCEC), A3 was the life stage with the highest contribution (56%), which is mainly related to the manufacturing of building assemblies. This case study provides new empirical evidence of ZEB performance in the United States. The findings suggest that to achieve the carbon neutrality goal, current ZEB certifications or designations are not adequate to measure actual building performance. A further reduction of operational energy, in addition to reducing the embodied carbon released during manufacturing, should be the focus.

AI-guided auto-discovery of low-carbon cost-effective ultra-high performance concrete (UHPC)

This paper presents an AI-guided approach to automatically discover low-carbon cost-effective ultra-high performance concrete (UHPC). The presented approach automates data augmentation, machine learning model generation, and mixture selection by integrating advanced techniques of generative modeling, automated machine learning, and many-objective optimization. New data are synthesized by generative modeling and semi-supervised learning to enlarge datasets for training machine learning models that are automatically generated to predict the compressive strength, flexural strength, mini-slump spread, and porosity of UHPC. The proposed approach was used to explore new UHPC mixtures in two design scenarios with different objectives. The first scenario maximizes the compressive and flexural strengths and minimizes porosity while retaining self-consolidation. The second scenario minimizes the life-cycle carbon footprint, embodied energy, and material cost, besides the objectives of the first scenario. The life-cycle carbon footprint, embodied energy, and material cost of the UHPC in the second scenario are respectively reduced by 73%, 71%, and 80%, compared with the UHPC in the first scenario. This research advances the capability of developing cementitious composites using AI-guided approaches.

Carbon footprint of New Zealand beef and sheep meat exported to different markets

New Zealand (NZ) is the world's largest exporter of sheep meat and an important exporter of beef. Given the current concern about the impact of food production on climate change, it is important to understand the extent of greenhouse gas (GHG) emissions for NZ exported products. This Life Cycle Assessment study calculated the cradle-to-grave carbon footprint of beef and sheep meat produced in NZ and exported to different markets. Sensitivity analyses were performed to evaluate the effect of different Global Warming Potential (GWP) metrics, carbon sequestration by trees on farms and different allocation methods at the processing stage. The carbon footprint for the cradle-to-farm gate represented 90–95% of the cradle-to-grave for both beef and sheep. At the farm gate (not accounting for the sensitivity analysis studied), the beef results were influenced by the contribution of dairy beef, which showed a 34% lower footprint than traditional beef (8.97 and 6.88 kg CO2e kg−1 LW, respectively). Sheep meat had lower emissions than beef for the on-farm stage (6.01 kg CO2e kg−1 LW). For GWP*, the estimated footprint values were much lower, especially for sheep, where the national flock decreased over the last 20 years. National data on net carbon sequestration by trees within farms was significant and equated to 29% of the total on-farm GHG emissions. The meat processing stage contributed 2–4% of the carbon footprint, while post-processing was 2–6%. Despite the long shipping distances involved, NZ beef and sheep meat supplied to international markets have a full life-cycle carbon footprint at the lower end of other published estimates.

A Holistic Framework for Determining the Trade-off between Embodied and Operational Carbon Emissions of High-rise Residential Buildings

Buildings’ carbon emissions consist of embodied carbon (EC) associated with the production and transportation of materials and operational carbon (OC) generated from consumed energy during daily use. However, previous studies concentrated on either EC or OC but ignored an integrated analysis of their relationships. Therefore, this paper aims to explore appropriate building envelope design solutions by examining the trade-off between EC and OC of high-rise residential buildings. To achieve this aim, the life cycle assessment method was used to evaluate the EC and OC of the residential buildings using SimaPro and DesignBuilder software. A building information modelling (BIM) model was developed to extract the geometric data and material consumption. A typical 30-story public residential building in Hong Kong was examined. The EC and OC of the case building were calculated as 561 kg CO2e/m2 and 50.18 kg CO2e/m2/yr, respectively. Different low carbon design scenarios were identified from the literature review and the semi-structured interviews with designers and contractors. Results indicate that low carbon concrete is an effective approach for not only reducing the EC by 5%-15%, but saving a mild percentage of OC, and is therefore encouraged. However, changing the thickness of external walls leads to a very limited life cycle carbon reduction (0.99%). Lower U-value of envelopes is recommended as 2.84% and 2.89% life cycle carbon is reduced when adopting insulations for external walls and triple-glazing windows. The findings are valuable for examining the relationships between EC and OC and can support low carbon building decision-making.

Evaluating the impact of building material selection on the life cycle carbon emissions of South African affordable housing

This study evaluated the life cycle carbon emissions of the two most common affordable housing designs primarily used in South Africa. It examined the impact of conventional, alternative and green building materials on life cycle carbon emissions of five main building components: building envelope, internal walls, flooring, windows, and roof systems. The EDGE application modelling software was used to estimate the life cycle carbon emissions of the various building materials and the overall houses. The comparison between the resulting carbon emissions of the three scenarios proved that modifying the building materials from conventional to alternative and green materials is able to reduce ~55% and ~75% of carbon emission of the construction phase, respectively and overall ~10% of life cycle carbon emission of the house. The findings, however, indicated that a change in building material has a more significant impact on the carbon emission in the construction phase than the operational phase. The results, therefore, confirmed the critical role of material selection in affordable housing as the main contributor to the life cycle carbon emissions, given the absence of heating and cooling systems in these housing types. Finally, the finding led to the conclusion that a change in material used for affordable housing alters the method of construction for the proposed materials and consequently lowers the lifecycle carbon emissions produced by the construction industry and improves the sustainability of houses and the housing sector in general.

Internet of Things (IoT)-Integrated Embodied Carbon Assessment and Monitoring of Prefabricated Buildings

Buildings contribute significantly to carbon emissions over their life cycle. Recently, embodied carbon (EC) accounts for an increasing share of life cycle carbon emissions of new buildings as their energy efficiency is improving. However, traditional methods of data collection and communication from diverse carbon sources such as manual recording lead to low-efficient and prone-to-error estimation of embodied carbon emissions. Therefore, this paper aims to propose an Internet of Things (IoT)-integrated embodied carbon assessment and monitoring system (ECAMS) for prefabricated buildings. This system involves three layers, i.e., of data collection, data communication, and data analysis. To provide a theoretical foundation, the EC assessment model is firstly modified to distribute carbon emissions into twelve construction statuses and at five levels of analysis of prefabricated buildings. IoT sensors including radio frequency identification (RFID), acceleration transducer, and global positioning system (GPS) are employed for automated real-time data collection. IoT data will be communicated with building information modelling (BIM) and carbon assessment software through application programming interfaces (APIs). Laboratory tests were conducted to demonstrate the feasibility of sensor-based data collection and communication. The proposed system facilitates more efficient and accurate estimations of prefabricated buildings’ embodied carbon, which should help practitioners to explore effective carbon reduction strategies.

On the tradeoffs between embodied and operational carbon in building envelope design: The impact of local climates and energy grids

The building envelope has a substantial influence on a building’s life cycle operational and embodied carbon emissions. Window-to-wall ratios, wall assemblies, shading and glazing types, have been shown to have a significant impact on total emissions. This paper provides building designers, owners, and policy makers with actionable guidance and a prioritization framework for establishing co-optimized lifecycle carbon performance of facade assembly components in a broad spectrum of climate contexts and energy carbon intensities. A large parametric study of building envelopes is conducted using building performance simulation and cradle-to-gate embodied carbon calculations in 6 US cities. The authors derive the total carbon emissions optimization for commercial office and residential space types using standard code-reference models and open-source lifecycle data. Comparisons between optimal total carbon solutions and (i) optimal operational carbon and (ii) minimum required assemblies, show the impact of under and over investing in envelope-related efficiency measures for each climate. Results show how the relationship between embodied and operational carbon is highly localized, that optimal design variables can vary significantly. In low carbon intensity energy grids, over investment in envelope embodied carbon can exceed as 10 kgCO2e/m2, while under investment in high carbon intensity grids can be higher than 150 kgCO2e/m2.

Hybrid solar energy and waste heat driving absorption subcooling supermarket CO2 refrigeration system: Energetic, carbon emission and economic evaluation in China

A novel hybrid solar energy and waste heat driving absorption subcooled carbon dioxide (CO2/R744) booster refrigeration system (SE + WH) is proposed to improve the energy efficiency of the traditional CO2 refrigeration system used in supermarkets. The thermodynamic and energy conversion model of the system is established. Then, the optimization method of the two-dimensional golden section search algorithm is introduced to optimize the system energy efficiency taking the variation of ambient temperature and solar radiation intensity into account. Moreover, considering the maldistribution of solar energy and the influence of meteorological conditions in China, eight typical cities are selected to assess the annual performance factor and life cycle carbon emissions to achieve energy saving and carbon emission potentials. The performance of hybrid solar energy and waste heat driving absorption subcooled CO2 booster refrigeration system is the best with the COP enhanced by 3.05–42.30 % at the solar radiation intensity of 1200 W/m2 and the temperature of 0–35 °C in contrast to the baseline system. In addition, the discharge pressure of the new proposed hybrid system can be reduced by 7.86 % when the ambient temperature is 34 °C. The annual performance factor of the new proposed hybrid system in Haikou can be increased by 14.47 %, and the life cycle carbon emissions are effectively reduced by 39.54 %. The payback period is also reduced by 4.01 % and 3.37 % for Beijing and Shanghai. Consequently, the novel configuration of the hybrid absorption subcooling subsystem is recommended, particular in hot or warm climate areas with rich solar energy.

Hybrid CO2 air source heat pump system integrating with vapor injection and mechanical subcooling technology for space heating of global application: Life cycle techno-energy-enviro-economics assessment

As a heating method for the sustainability of residential buildings in clean space heating, carbon dioxide (CO2) air source heat pump is an environment-friendly solution to replace fuel-fired boiler. Four hybrid configurations of vapor injection integrated with dedicated mechanical subcooling (VI + DMS) technologies are developed, to deal with the problem of traditional CO2 system energy efficiency deterioration in cold regions, and compared with traditional transcritical CO2 baseline heat pump (BASE), R410A heat pump, coal-fired boiler and four CO2 heat pump systems adopting single technique of VI or DMS. Genetic algorithm is utilized to optimize the operation variables. The comprehensive techno-energy-enviro-economics performances of the nine systems among the whole lifetime are assessed. The influences of heating terminal selection and climate condition are discussed for 40 typical cities in 8 climate zones around the world. The results demonstrate a maximum coefficient of performance (COP) is obtained for transcritical CO2 vapor injection heat pump with flash tank and dedicated mechanical subcooling (VI-FT-DMS), and the COP of VI-FT-DMS system using traditional designed radiator as heating terminal is as high as 1.94 at the ambient temperature of −30 °C. The hybrid VI + DMS CO2 heat pump achieves a significant enhancement in heating season performance factor of 10.61 ∼ 30.37 % and the throttling irreversibility can be remarkably reduced with the exergy efficiency promoted by 12.76 ∼ 64.34 %. The life cycle cost is declined by 14.71 ∼ 22.38 % in contrast to BASE, and life cycle carbon emission reduces by 4.77 ∼ 22.12 %, indicating apparent advantage in environmental performance. The hybrid VI + DMS CO2 heat pump system is a promising solution to apply for clean space heating in the cold, very cold and subarctic zones.

BIM-based approach for the integrated assessment of life cycle carbon emission intensity and life cycle costs

The construction industry is well known for generating a large amount of carbon emissions and this, together with huge costs of buildings during their life cycle, seriously affects its environmental and economic sustainability. That reducing the former tends to increase the latter is a highly significant problem exacerbating the situation. Finding a solution with the lowest carbon emission at a certain cost is an urgent problem to be solved. Research to date aimed at remedying the situation, however, has been largely focused on either treating the two issues independently or partially conjoined, with little progress in their integrated assessment. In response, this study presents a method for integrating the life cycle carbon emissions (LCCE) and life cycle costs (LCC) of buildings to assess their life cycle carbon emission intensity (CEI) based on BIM technology. Through a public building in China as a case study, the feasibility of the method is verified, the key stages of building carbon emissions are analyzed using CEI, and the conversion of high carbon emission materials to low carbon emission materials is explored. The proposed methodology and framework provide solutions and ideas for achieving optimal costs commensurate with low carbon emissions throughout the building life cycle, facilitating the assessment of carbon emissions at the decision-making and design stages, achieving the optimization of building carbon emissions and costs, and enhancing building life cycle sustainability.

Development of a life cycle net zero carbon compact house concept

The paper presents the development process of an innovative, prefabricated compact house, which aims at creating a net zero greenhouse gas emission building design over the whole life cycle. Building Information Modelling helped to quantify the required building materials. Dynamic building simulations were performed in DesignBuilder to calculate the energy demand of the building for the operational period. To evaluate the financial feasibility and the carbon balance of the building, life cycle assessment and life cycle costing were used. A heat and moisture transfer simulation was carried out to provide a more accurate analysis and to identify possible moisture problems.The assessment showed that the ratio of embodied impacts and operational impacts is typically 1:2 for wooden buildings and 1:1.5 for brick buildings. Life cycle carbon neutrality could be achieved in both cases with additional photovoltaic panels installed on the roof. However, a major difference between timber and brick buildings is the time factor: while the initial emissions from the production of brick buildings are gradually offset with excess solar energy, timber buildings act as carbon storage with negative emissions over the study period and the carbon is only released at the eventual end-of-life stage. The necessary size of photovoltaics is largely influenced by the avoided grid impact: if dynamic decarbonization of the electricity mix is considered, the size of photovoltaics required is about 1.5 times larger to offset the environmental load of the construction due to the diminishing benefits.

Prospective Sustainability Screening of Sodium‐Ion Battery Cathode Materials

AbstractSodium‐ion batteries (SIB) are considered as a promising alternative to overcome existing sustainability challenges related to Lithium‐ion batteries (LIB), such as the use of critical and expensive materials with high environmental impacts. In contrast to established LIBs, SIBs are an emerging technology in an early stage of development where a challenge is to identify the most promising and sustainable cathode active materials (CAM) for further research and potential commercialization. Thus, a comprehensive and flexible CAM screening method is developed, providing a fast and comprehensive overview of potential sustainability hotspots for supporting cathode material selection. 42 different SIB cathodes are screened and benchmarked against eight state‐of‐the‐art LIB‐cathodes. Potential impacts are quantified for the following categories: i) Cost as ten‐year average; ii) Criticality, based on existing raw material criticality indicators, and iii) the life cycle carbon footprint. The results reveal that energy density is one of the most important factors in all three categories, determining the overall material demand. Most SIB CAM shows a very promising performance, obtaining better results than the LIB benchmark. Especially the Prussian Blue derivatives and the manganese‐based layered oxides seem to be interesting candidates under the given prospective screening framework.

Life Cycle Carbon Emission Assessment of Building Refurbishment: A Case Study of Zero-Carbon Pavilion in Shanghai Yangpu Riverside

Life cycle building carbon assessment can promote the development of carbon emission reduction. The main difficulties in the process of assessment are the boundary selection and inventory collection, especially when carbon emission assessment is needed in the early stage of design and construction, or when the calculation relates to disposal and refurbishment. It is significant to make full and rational use of design documents, standard documents, and related software. This paper focuses on the life cycle carbon emission assessment of building refurbishment. It explores the carbon emission assessment methodologies and procedures in every phase of the building life cycle, taking a zero-carbon pavilion refurbishment project as a case study. This case study is located in the Shanghai Yangpu Riverside Park, refurbished from an existing hydrologic monitoring building. The carbon emission reduction potential of renovation and the solar photovoltaic system applied in the building are analyzed. The data was collected referring to architectural design documents and related standards. The energy consumption during the operational phase is simulated using DesignBuilder. The life-cycle carbon emission per floor area of the existing building renovation scenario is 2.39 t, and the new building scenario is 2.69 t, which are both at a low level among other cases. The refurbished existing building saves nearly one-third of the carbon dioxide emissions during the construction phase compared to new construction. The application of a photovoltaic system also saves one-third of energy consumption and carbon emissions during the operational phase.

Life cycle carbon, energy, water, and landuse footprints of agricultural residue-based biojet fuel in Bangladesh

Biojet fuel is a low carbon alternative to fossil jet fuel. There is limited literature on life cycle environmental performance of biojet fuel from 2nd generation biomass feedstocks. This work (i) assesses biojet fuel potential from rice, wheat, jute and potato residues in Bangladesh, and (ii) conducts farm to factory gate attributional Life Cycle Assessment of biojet fuel. Different scenarios suggest Bangladesh can produce 1074 to 2548 million liters of biojet fuel annually, with 1810 million liters per annum being the most optimistic potential. This is 4.5 times higher than the current jet fuel demand of the country. Carbon, energy, and landuse footprints of biojet fuel are lower than fossil jet fuel, however, water footprint is higher. Energy Return on Investment (EROI) of biojet fuel ranges from 1.60 to 1.78. The results will contribute to UN SDGs 7 & 13 and biojet fuel development in Bangladesh.

4E analysis of an integrated solar-biomass heating system: A case study in rural housing of northern China

Primary energy shortage and serious environmental pollution have aroused considerable interest in the investigation of renewable energy heating systems. The integrated solar-biomass heating system has been a proven solution for this. This present work focuses on demonstrating the sustainable potential of integrated solar-biomass heating system into a rural housing to stabilize its performance and assessing its economic and environmental benefits. Accordingly, a 4E (energy, exergy, economic, and environmental) analysis was conducted to analyze and evaluate the performance of the system based on the in-situ testing. The results demonstrate that the presented system can provide an improved thermal environment with an average indoor temperature of 16.49 °C. During the testing period, solar energy and biomass contributed 49.19 % and 50.81 % of the total energy demand of 6972.23 MJ, respectively. Subsequently, the average exergy efficiency of the integrated system, the solar heaters, the biomass boiler, and the radiators were 3.35 %, 2.65 %, 12.42 %, and 89.16 %, respectively. Besides, the presented system can save 1749.29 kg of standard coal every year, and the life-cycle carbon footprint was 78.65 % less than that of the traditional coal-fired boiler-based heating system. These results indicate that the integrated system can significantly reduce primary energy consumption and provide remarkable economic and environmental benefits.

An integrated life-cycle greenhouse gas protocol accounting on oil palm trunk and empty fruit bunch biofuel production

Improper discard of oil palm trunk and empty fruit bunch renders massive greenhouse gases. Turning these palm wastes into solid biofuels could aid in carbon reduction. The embodied environmental impacts of the solid biofuel densification process are neglected in carbon emission quantification studies applying Greenhouse Gas Protocol while the significance of classifying the system's direct and indirect carbon emissions were overlooked in those utilising life cycle assessment. Despite the prospect of both methodologies to complement their limitations for carbon emissions quantification, no study integrates both methodologies to investigate direct and indirect emissions systematically from a life cycle perspective. An integrated framework of life cycle assessment and Greenhouse Gas Protocol is developed to quantify the direct and indirect carbon emissions of oil palm trunk and empty fruit bunch densification from cradle-to-gate for three pellet plants in Indonesia and Malaysia. The emissions are categorised into three emission scopes: Scope 1, Scope 2, and Scope 3 according to the Greenhouse Gas Protocol, integrated with avoided emissions which are quantified via life cycle assessment. The pellet plants generate 534.7–732.3 kg CO2-eq/tonnepellet per hour, in which Scope 1 (i.e., direct emissions) is the major emission scope due to high emissions from wastewater production and drying fuel combustion. Washing equipment (169.2–439.0 kg CO2-eq/tonnepellet per hour) and burners (87.1–214.5 kg CO2-eq/tonnepellet per hour) are the hotspots found in the pellet plants. Producing empty fruit bunch pellets could reduce 62.0–74.1 % of emissions than landfilling the empty fruit bunch. Empty fruit bunch pellet and oil palm trunk pellet are recommended to co-fire with coal to phase down coal usage in achieving COP26 pledge. This study provides data-driven insights for quantifying carbon emissions through the integrated framework and could be a reference in future life cycle carbon footprint studies of the biomass densification process.

Hierarchical optimization of policy and design for standalone hybrid power systems considering lifecycle carbon reduction subsidy

To achieve the target of carbon neutrality, the present work proposes a lifecycle carbon reduction subsidy policy to promote the exploitation of renewable energy technologies in remote areas. The hierarchical optimization of policy and design for a standalone hybrid renewable energy system is further conducted based on the proposed subsidy policy. The upper-level policy optimization model aims to maximize the renewable energy fraction and minimize the subsidy expenses borne by the government simultaneously, and the lower-level design optimization model aims to minimize the net present cost borne by the system operator. Four meta-heuristic algorithms coupled with a standard iterative method are employed to solve the hierarchical optimization problem, and their performances are comprehensively assessed in terms of convergence, robustness, and computational efficiency. Besides, an improved K-means clustering algorithm along with a tailored optimal K-value selection strategy is employed for scenario reduction. The results of the case study show that: (ⅰ) teaching-learning-based optimization performs the best convergence and robustness as it achieves the balance of exploration and exploitation. (ⅱ) the nexus between policy and system design presents a piecewise pattern, implying that the system configuration will change significantly only when the subsidy policy exceeds a certain threshold. (ⅲ) the proposed subsidy policy is expected to increase the renewable energy fraction to 99.23% and reduce the lifecycle carbon emissions by 80.7%. Overall, the proposed subsidy policy and its impact mechanism on system design can provide theoretical support for the government to formulate tailored policies for different preferences, and the proposed optimization framework and methodology can be directly extended to practical applications.

A multi-objective optimization strategy for building carbon emission from the whole life cycle perspective

This research proposed an integrated strategy for building performance optimization from the whole life cycle perspective to explore the optimal building scheme. After the feature elimination, the ensemble learning model (ELM) was trained to obtain a high-precision model for predicting life cycle carbon emissions (LCCE), life cycle costs (LCC), and indoor discomfort hours (IDH). Then, the optimal optimization algorithm was selected among three different optimization algorithms. Finally, the best building scheme was chosen according to the newly proposed solution. The results showed that the ELM could achieve high prediction efficiency by combining input feature evaluation and screening, multi-sampling methods, and hyperparameter optimization. The R2 value of ELM can reach 0.980, while the Two-Archive Evolutionary Algorithm for Constrained multi-objective optimization (C-TAEA) was the optimal optimization algorithm. The best equilibrium solution proposed in this study solved the problem of different optimization ranges of different objectives and maximized the optimization value. Finally, the best equilibrium scheme reduced the LCCE by 34.7%, the LCC by 13.9%, and the IDH by 26.6%. Therefore, this strategy can efficiently optimize building objectives and produce a more balanced and optimal building scheme, thus making it widely applicable in building performance optimization.

Life cycle performance evaluation of cascade-heating high temperature heat pump system for waste heat utilization: Energy consumption, emissions and financial analyses

Inspired by the principle of cascade energy utilization, the concept of cascade-heating is introduced, and five layouts of cascade-heating high temperature heat pump (HTHP) systems are proposed and optimized to utilize the waste heat. The energy consumption, carbon and pollutant emissions, life cycle cost (LCC) and payback period (PBP) models are established. Meanwhile, detailed comparisons are made with conventional HTHPs and boilers. The results indicate it is more positive for cascade-heating HTHPs in terms of energy consumption, carbon and pollutant emissions, LCC and PBP. The primary energy consumption of cascade-heating water cooled saturated suction system (CWSAS) is declined by 1.8–22.8% and 3.4–19.2% in contrast to conventional HTHPs and traditional boilers, respectively. The life cycle carbon emissions of CWSAS are reduced by 1.7–6.1% and 76.5% compared to conventional HTHPs and electric boiler. The pollutant emissions can also be prominently declined by adopting cascade-heating HTHPs. For life cycle economic performance, LCC of cascade-heating flash tank superheated suction system (CFSUS) can be reduced by 4.5–18.3% compared with traditional HTHPs. Furthermore, PBP of CFSUS is the lowest of 3.1 years, and 15.4–65.9% shorter than traditional HTHPs. CWSAS is the most recommended configuration on account of its remarkable overall energy, environment and economic performances.