1. Introduction
To address the abnormal changes in global climate, the development of sustainable building systems is one of the best strategies [
1,
2]. Due to the broad definition of sustainability, there are differences in understanding sustainable building systems. Building systems under various assessments such as green, ecological, and low carbon can all achieve a certain level of sustainable development [
3,
4,
5,
6]. This paper conducts a quantitative evaluation and exploration of building systems from the perspective of the integration of ecology and low carbon, which is of great significance for designers and government management departments.
This study utilizes two distinct approaches. The emergy analysis, which originates from scholars at the University of Florida in the United States, was initially developed for sustainable assessment and analysis of ecological environments. It has gradually been expanded to a few types, including city areas, wetlands, buildings, economics, and energy [
7,
8,
9,
10,
11,
12,
13,
14,
15,
16]. Building systems are an important application area of emergy analysis, since this method can integrate different types of parameters into a unified platform for comparison. Currently, researchers are conducting design studies on green building systems based on the integration of BIM technology and emergy concepts [
17]. Through quantitative evaluation using emergy analysis, the sustainable design of buildings can be guided [
18]. The whole life cycle emergy framework is also significant for the sustainable design of building systems. Applying such methods enables the comprehensive assessment of various inputs in building systems; effective calculations of energy flow, material flow, and information flow; and optimization of sustainable building designs [
19,
20,
21].
In addition, the establishment of carbon neutrality goals has made research on carbon emissions in building systems urgent. Compared to previous simple calculations, low-carbon and even zero-carbon buildings now have higher requirements for carbon emission calculations. It goes beyond simple carbon accounting and involves areas such as low-carbon building design, low-carbon building operation and maintenance, low-carbon transportation, and simulation in low-carbon software development, significantly broadening the scope of research on low-carbon buildings. In response to this carbon neutrality context, different researchers have conducted analyses and explorations at various levels. For example, researchers have explored the carbon emission effects of different building models [
22]. Researchers have extensively explored low-carbon urban design, focusing on the building level and introducing innovative approaches [
23]. Understanding the evolving nature of carbon emissions, the analysis of emission trends in public buildings has garnered attention [
24]. System dynamics methods are employed by some researchers to predict and analyze carbon emissions in buildings [
25]. Managing carbon emissions in the supply chain is crucial for ensuring the efficient functioning of building systems, leading to increased research interest [
26]. Integrating low-carbon design principles during the renovation of existing buildings is gaining traction in the industry [
27]. Scholars are also investigating the impact of green space design on carbon reduction through the coupling of building and landscape systems [
28]. Government officials are tasked with analyzing the influence of carbon emission quotas on the construction industry [
29]. Zero-carbon buildings are widely recognized as the optimal model for building systems and remain a prominent focus within the industry [
30]. Some researchers have combined the life cycle of building systems with carbon emissions, conducting comparative analyses of the carbon emission intensity and cost [
31]. Researchers are also interested in the relationship between low-carbon and energy efficiency, as well as the impact of carbon emissions on the environment [
32,
33]. Carbon sequestration calculations and analysis have also gained attention to reduce carbon emissions in building systems, especially detailed discussions on carbon sequestration and emission reduction technologies [
34,
35].
The latest developments in the field of ecological emergy and carbon footprint analysis for building systems mainly focus on the following aspects: (1) utilizing ecological emergy methods to assess the resource efficiency and environmental impacts of buildings, including material flow analysis, energy flow analysis, and life cycle assessment. These studies aim to quantify energy consumption, material usage, and waste generation at different stages of the building life cycle; and (2) examining the contribution of buildings to carbon emissions by evaluating the carbon content of building materials, energy consumption during construction, and energy utilization during the operational phase. These studies help guide building design and operations to reduce negative impacts on climate change [
36,
37].
However, the comparative analysis between ecological emergy and low-carbon perspectives, as two different viewpoints, is not well known to the public. The similarities and differences between the two have also not been explored, which is the starting point of this study. The aim of this research is to provide help for building managers in enhancing the sustainability of building systems through the findings and insights presented in this paper.
The specific research objectives of this paper address the following issues: (1) What are the contributions of different stages in building systems from the perspectives of emergy and carbon emissions? (2) How do typical feedback structures affect the sustainability of building systems? (3) How can ecological sustainable measures enhance the evaluation of building systems?
2. Materials and Methods
2.1. Research Framework
In order to demonstrate the overall idea of this paper, the research framework was designed and organized (
Figure 1) to provide a clearer understanding of the research approach for the primary reader.
The research framework of this study is depicted in
Figure 1. The left side illustrates renewable energy, non-renewable resources, and inputs from artificial services [
38,
39].
The entire system is divided into five modules, namely the five stages of the full life cycle (A/B/C/D/E stages) located at the top; renewable and non-renewable energy inputs located on the left; the impact of improvement strategies and feedback systems located on the right; outputs of the building system located at the bottom, including economic impacts, environmental impacts, and losses; and in the middle are the two types of methods for the building system, LCA–emergy and LCA–carbon emission.
The research framework provides a pathway for implementing the entire study. Various information flows, material flows, and energy flows enter the building system, utilizing quantitative calculation methods for emergy and carbon emissions. The interference of feedback subsystems is considered, and the sustainable status of the building system is analyzed in the end.
2.2. Life Cycle Assessment (LCA) Method
LCA, an established method, systematically evaluates the environmental and resource impacts of a product, process, or service throughout its entire life cycle (
Figure 2). It comprehensively considers stages from raw material extraction to manufacturing, use, maintenance, and final disposal. LCA aims to quantify and assess the environmental, economic, and social impacts associated with a specific product or process. The typical LCA process involves four key steps: goal and scope definition, life cycle inventory, life cycle impact assessment, and interpretation. In the goal and scope phase, the objectives, boundaries, and functional unit of the LCA are determined. The life cycle inventory phase entails data collection on raw material consumption, energy usage, and waste generation. The life cycle impact assessment phase analyzes and interprets the collected data to evaluate environmental and resource-related impacts. Finally, in the interpretation phase, the results are communicated to support decision-making and facilitate improvements. LCA enables the comparison of environmental performance among different products or processes, identification of influential factors, and guidance for sustainable design and decision-making. It finds extensive application in various sectors, such as buildings, energy, transportation, food, and textiles [
40,
41,
42].
The LCA methodology described in this article is defined according to the standard ISO 14040:2006: environmental management, life cycle assessment, and principles and framework. This standard establishes the fundamental principles and framework for conducting LCA, including goal and scope definition, life cycle phase partitioning, functional unit definition, and more.
In
Figure 2, six stages of the building system are included, specifically highlighting the building design phase. In this phase, the calculations for emergy, energy, and carbon emissions are all based on the input of labor costs.
2.3. LCA–Emergy Approach
2.3.1. Emergy Theory
The emergy method is employed to evaluate the sustainability of building systems, utilizing ecological principles. It involves quantitatively measuring and calculating the energy exchanges between the building system and the environment. These measurements are then converted into comparable indicators to assess the impact of the building system on the ecosystem [
43].
The ecological emergy method typically includes the following steps: (1) system boundary determination: identifying the scope of the assessment for the building system, including the interactions between the building and its surrounding environment; (2) data collection: gathering relevant data on energy inputs and outputs, including energy consumption, material usage, waste generation, etc.; (3) energy flow analysis: analyzing the pathways and transformation processes of energy within the building system based on the collected data. This can involve examining energy acquisition, utilization, and emissions, among other factors; (4) energy quantification: converting energy measurements into standard units for comparison and computation purposes; (5) ecological emergy calculation: applying ecological principles to convert energy interactions into ecological emergy. This can encompass considering energy sources, environmental impacts, and the capacity of ecosystems to recover; (6) data analysis and interpretation: analyzing and interpreting the ecological emergy data to evaluate the sustainability performance of the building system. This may involve comparisons with other building systems and analyzing the impacts of different design and operational measures.
The emergy method is more comprehensive compared to ISO/EN standards 14040 and 15978.
ISO 14040 is an international standard that provides guidance on the methodology of the Life Cycle Assessment (LCA). It emphasizes considering the entire product life cycle from the input of materials and energy to waste generation. The standard defines four phases of LCA: goal and scope definition, inventory analysis, impact assessment, and interpretation. By adopting the ISO 14040 standard, a systematic approach can be employed to assess environmental impacts and make the results more comparable and transparent.
EN 15978 is a European standard used to assess the overall sustainability of buildings and infrastructure. It emphasizes the life cycle assessment of buildings, including aspects such as resource consumption, energy use, and environmental impacts. The EN 15978 standard defines methods for calculating the environmental impacts of building materials and energy use and provides a systematic framework for evaluation.
Through the ecological emergy method, the comprehensive performance of a building system in terms of energy utilization, environmental impacts, and ecosystem restoration can be assessed. This helps guide architectural design and operational decisions, promoting the development of the building industry towards greater sustainability.
2.3.2. Emergy Calculation Model
Emergy calculation model can be found in
Table 1.
2.3.3. Emergy Indicators
This paper utilizes three core indicators of emergy to assess the ecological sustainability of building systems. The specific parameter types and details can be found in
Table 2.
The Whole Life Energy Analysis of the building stages is based on energy consumption as an indicator, collecting and calculating the energy in each stage of the building’s life cycle. Unlike emergy analysis, energy calculations do not include calculations for material flow or information flow. However, the advantage of an energy analysis is its ability to accurately measure the energy values at each stage, providing architects and managers with tangible impacts and meaningful references. The energy calculation for the operational stage of the building in this study is predicted and analyzed according to national standards.
2.4. LCA–Carbon Emission Model of Five Processes
Figure 3 visually represents the carbon emission trajectories of the building system using a comprehensive life cycle approach. It integrates carbon emissions throughout five key stages: namely, building material production, building material transportation, building construction, building operation, and building demolition. The corresponding calculation formulas for each stage are provided in
Figure 3 [
44].
2.5. Feedback Subsystem Analysis
The building system, functioning as a complex operational entity, is subject to diverse feedback information throughout its operation. This feedback can be classified into three categories based on their types: information flow, material flow, and energy flow. Moreover, considering the feedback structure, these systems can be categorized into three distinct types: open-loop feedback systems, closed-loop feedback systems, and cross-feedback systems. This article explores the influence of these three feedback systems to enhance the precision of overall system operations and elevate the effectiveness of sustainable building systems.
Figure 4 illustrates the specific structures of these three categories. Compared to the open-loop feedback system, the closed-loop feedback system and cross-feedback system have the greatest corrective effect on the entire building system but also impose an increased burden on its operation. It is important to emphasize that the impact of the cross-feedback system exhibits nonlinear effects, which increases the uncertainty of changes in emergy and carbon emissions.
3. Case Study
3.1. Case Introduction
This building case is a newly constructed ecological building complex with a primary focus on commercial activities, planned to operate for 50 years. The total building area is approximately 60,000 square meters and is divided into three building modules interconnected by corridors. The key feature of the entire building is its response to climate change, incorporating sustainability design from both ecological and low-carbon perspectives, as shown in
Figure 5. The sustainable design strategies include seven categories: ecological grass ditch, ecological vegetation buffer zone, artificial ecological wetland, ecological infiltration basin, ecological rainwater garden, permeable paving surface, and ecological tree box filter.
Here are the specific spatial parameters for a commercial complex building with an area of 60,000 square meters:
Total building area: 60,000 square meters. Commercial space ratio: 40% (24,000 square meters), including retail stores, shopping malls, and other commercial spaces. Office space ratio: 30% (18,000 square meters), including offices, meeting rooms, and shared workspaces. Restaurant space ratio: 20% (12,000 square meters), including restaurants, cafes, and fast-food outlets. Public area facilities: including leisure areas, children’s playgrounds, green landscapes, outdoor terraces, etc., occupying the remaining 10% of the area (6000 square meters). Number of parking spaces: determined based on requirements. Typically, ample parking spaces are provided in a commercial complex. Assuming 1 parking space is provided per every 100 square meters of commercial space, the approximate total number of parking spaces would be around 240.
The sustainable design strategies in this case include: (1) energy efficiency: utilizing efficient insulation materials, energy-saving equipment, and smart control systems to reduce energy consumption, as well as incorporating renewable energy sources such as solar and wind power; (2) material selection: choosing renewable, environmentally friendly, and low-carbon emission building materials to reduce reliance on finite resources and lower the carbon footprint of the construction; (3) water resource management: implementing low-flow faucets, water-saving appliances, and rainwater harvesting systems to minimize the use of freshwater resources and establish effective wastewater treatment; (4) building layout and design: optimizing building orientation and layout to maximize natural lighting and ventilation, reducing the need for artificial lighting and air conditioning systems; (5) waste management: implementing effective waste sorting, recycling, and disposal systems to minimize waste and pollutants generated during construction activities; (6) green spaces: increasing green coverage and incorporating landscape design around the building to provide a comfortable outdoor environment and promote biodiversity conservation; (7) sustainable operation and maintenance: establishing an efficient energy management system and conducting regular inspections and maintenance of equipment to ensure the long-term high performance of the building. These diverse sustainable design strategies aim to decrease the carbon footprint, resource consumption, and negative environmental impacts of the building, ultimately achieving a more sustainable approach to design and operation.
3.2. Date Collection
This study entails extensive computation and necessitates the collection and processing of data. The dataset can be broadly classified into two types: basic data and corresponding emergy conversion rates and carbon emission factors. The basic data are further categorized into three groups: namely, information flow data, energy flow data, and material flow data. The emergy conversion rate data encompass information flow emergy conversion rates, energy flow emergy conversion rates, and material flow emergy conversion rates [
38]. The carbon emission factors are obtained from reputable institutions like the Intergovernmental Panel on Climate Change (IPCC) [
39]. It is crucial to highlight that the feedback subsystems of the entire building system have been considered to rectify the basic dataset.
Figure 6 visually presents the process of data collection and processing in this study.
5. A Comprehensive Discussion
5.1. The Research Findings and Discussion
In this article, the sustainability of the building system is examined through a comprehensive analysis that considers emergy, energy consumption, and carbon emissions across its entire life cycle. By conducting calculations and organizing data from these three perspectives, a holistic understanding of the building’s sustainability performance is obtained.
Similar conclusions: Irrespective of whether the emergy or carbon emissions perspective is considered, the operational phase of the building consistently emerges as the primary influencing stage, with its impact proportion progressively growing over time. However, the study acknowledges that the operational phase of commercial buildings introduces complexities due to the diverse inputs and outputs involved, including foot traffic, operating hours, and maintenance. These factors contribute to the multifaceted nature of the analysis conducted in this study.
Differences: While the operational phase’s significance in terms of emergy, energy consumption, and carbon emissions is recognized across different perspectives, the specific proportions may differ. This variability in proportions offers valuable insights for architects and building managers to consider when making decisions regarding sustainable practices in building design and management. Consequently, a nuanced understanding of the differing impacts within the operational phase can inform more targeted and effective strategies to optimize sustainability throughout the building’s life cycle.
With regards to the emergy method, it is important to critically evaluate its strengths and limitations in comparison to ISO/EN standards 14040 and 15978. While the emergy method offers a broader scope and a holistic assessment of energy consumption throughout the life cycle of a building system, its application in scientific research and its comparisons with the existing standards have been relatively limited. Therefore, further empirical studies and validation are necessary to fully understand its effectiveness and potential contributions.
In terms of its strengths, the emergy method provides a comprehensive understanding of environmental implications by considering not only the environmental impacts but also emphasizing the quantification of energy inputs, outputs, and transformations. This approach allows for a more integrated analysis of the sustainability aspects, enabling a deeper understanding of the resource utilization efficiency, energy conservation, and overall environmental protection.
However, it is essential to critically assess the limitations and potential drawbacks of the emergy method. While ISO/EN standards provide standardized guidance and frameworks that ensure comparability and transparency of the results, the emergy method may lack the same level of acceptance and widespread adoption in scientific research and practice. The absence of comprehensive evaluations and comparisons with previous studies in the literature highlights the need for a critical analysis of its limitations and gaps.
The highlight of this article is the integration of two research methods to assess the sustainability of a building system from both ecological and carbon footprint perspectives. This approach has not been extensively explored by researchers thus far [
49,
50,
51,
52,
53,
54].
To address these shortcomings, future research should aim to conduct in-depth comparative studies of the emergy method and carbon footprint based on ISO/EN standards, examining their effectiveness in different contexts, industries, and product types. Such studies would contribute to the knowledge base by providing empirical evidence and insights into the relative advantages and disadvantages of each approach.
5.2. Limitations and Shortcomings in the Research
From an emergy perspective, the overall sustainability of the building system is inadequate, with the most critical sustainability indicator (ESI) continuously decreasing. Sustainable improvements are needed to enhance sustainability. The ESI indicator experiences substantial variations, ranging from 2.7 to 1.2/0.6/0.2 (transiting from a sustainable state to an unsustainable state).
Building carbon sinks refers to the process of absorbing and storing carbon dioxide in the air through building and land use practices. They play an important role in sustainable architecture and urban planning. Building carbon sinks can help reduce greenhouse gas concentrations in the atmosphere, especially carbon dioxide. They are a crucial component of sustainable building and urban planning. By maximizing the utilization of natural resources, reducing energy consumption, and mitigating greenhouse gas emissions, building carbon sinks contribute to establishing a more sustainable society and environment.
Based on the identified deficiencies at both levels, optimization strategies and their effectiveness validation are carried out in
Section 5.3.
5.3. Improvement and Optimization Measures
5.3.1. Measures for Improving Ecological Emergy Perspective
To enhance the sustainability, this architectural design integrates a range of sustainable features depicted in
Figure 5. These include eco-pavement, eco-garden, small-scale ecological wetlands, and ecological landscapes. Apart from improving the overall sustainability of the building system, these ecological designs also play a role in carbon reduction efforts by contributing to carbon sequestration to some extent. With the incorporation of these features, the building design not only promotes environmental conservation but also supports the goal of reducing carbon emissions.
The results obtained from the calculations for EYR, ELR, and ESI are presented in
Figure 17. These indicators help mitigate the environmental pressure on the overall building system and enhance sustainability. However, due to the limited design area, the improvement effect is not significant. The sustainability improvement is approximately 4.1% (ESI indicator).
5.3.2. Measures from the Perspective of Carbon Sinks
Vegetation also contributes to regional carbon reduction, and the carbon reduction types involved in this case include vegetation carbon reduction and material carbon reduction. The calculation formulas can be found in
Table 3.
Considering a calculation period of 50 years, the total carbon reduction calculated using the formulas in
Table 3 can reach 24.6 tCO
2. Although the overall carbon reduction effect may not be significant, this is due to limitations in land area and the volume of building materials.
Therefore, for architects and engineers, increasing the proportion of ecological design in land use and the share of carbon sequestration building materials is an essential path to carbon reduction.
6. Conclusions
In the face of worsening climate conditions, this study has explored sustainable architecture, particularly through the utilization of ecological emergy and carbon emissions calculation models. It has conducted calculations and assessments throughout the entire life cycle of buildings, providing new insights for relevant practitioners. Additionally, this paper has also considered the impact of feedback subsystems in the building system and validated the effectiveness of open-loop feedback systems, closed-loop feedback systems, and cross-feedback systems. This further enhances the accuracy of the entire sustainable building process.
When considering the emergy and carbon emissions perspectives, the operational stage of a building demonstrates the highest emergy consumption and carbon emissions throughout its life cycle. However, the proportions of these two factors are not equivalent. As the building system remains in operation, the emergy consumption and carbon emissions in the other four stages progressively decrease, while those in the operational stage gradually increase. It is important to note that this change is not linear but varies over time, reflecting the complex dynamics involved in the building’s life cycle.
However, there are contents in this study that require further investigation. The building system is a complex and dynamically evolving system, requiring research on the dynamic emergy and carbon footprint of the entire building system. The next step in research is to explore the sustainable dynamic characteristics from the perspectives of emergy and carbon footprint, with a particular focus on incorporating artificial intelligence and neural network prediction models into the study of sustainable building systems.
This study provides a new perspective for architects and building managers by coupling ecological and low-carbon technologies to achieve sustainable improvement in building systems. For example: (1) Design optimization: By evaluating the ecological emergy and carbon footprint of different design options, architects can make informed decisions to optimize the sustainability performance of buildings. They can identify areas of high energy consumption or carbon emissions and implement design strategies to minimize them. (2) Performance evaluation: These methods enable architects and building managers to assess the ecological and carbon performance of existing buildings. By quantifying the energy consumption and carbon emissions of a building throughout its life cycle, they can identify areas of inefficiency and prioritize improvements, leading to energy savings, cost reductions, and reduced environmental impact. (3) Decision-making support: Evaluating ecological emergy and carbon footprint provide data-driven information that supports decision-making processes. Architects and building managers can compare different design alternatives, material choices, or operational strategies based on their ecological and carbon impact. This helps in making more sustainable choices that align with environmental goals and regulatory requirements. (4) Communication and marketing: Highlighting the ecological emergy and low carbon footprint of a building can enhance its market value and reputation. Clients and stakeholders increasingly value sustainable design and construction practices. By quantifying and communicating the environmental benefits, architects and building managers can attract environmentally conscious clients, differentiate themselves in the market, and establish a positive brand image. Overall, the methods of ecological emergy and carbon footprint provide architects and building managers with essential tools to integrate sustainability considerations into their decision-making processes, helping them create more environmentally friendly and efficient buildings.