Carbon Emission Accounting and Reduction for Buildings Based on a Life Cycle Assessment: A Case Study in China’s Hot-Summer and Warm-Winter Region

Abstract

At the 75th United Nations General Assembly, China committed to peaking carbon dioxide emissions by 2030 and achieving carbon neutrality by 2060. In response, the national standard “General Specification for Building Energy Conservation and Utilization of Renewable Energy” has been adopted across 20 provinces and cities in seven major regions, including North China, Northeast China, and South China. These regions have implemented stringent energy-saving and emission reduction reviews and quota requirements. Despite this, there is limited research on comprehensive life cycle carbon emission calculations and carbon reduction designs. This study addresses this gap by focusing on economically developed regions with high population density and substantial energy-saving potential, specifically targeting the warm winter and hot summer regions of China. Using a commercial building in Shenzhen as a case study, we established a carbon emission accounting model based on the life cycle assessment (LCA) method. We calculated carbon emissions during the material phase using the project’s bill of quantities and relevant carbon emission factors. Additionally, we used the CEEB 2023 software to design energy-saving and emission reduction solutions for the building. Our comparative analysis reveals that the new design reduces the carbon emissions of the case study building by 13.5%. This reduction not only mitigates the environmental impact of construction but also contributes to the fight against the greenhouse effect, supporting the broader goal of sustainable development.

1. Introduction

In the past few centuries, human activities, especially the Industrial Revolution, have cumulatively impacted our planet, causing drastic changes in our climate. Climate change has increased the intensity and frequency of heatwaves, droughts, hurricanes, and other natural disasters, posing significant threats to human life on Earth. The combustion of fossil fuels as an energy source results in the increased concentration of greenhouse gases such as carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) in the Earth’s atmosphere, leading to a rise in the average surface temperature, known as global warming [1]. Scientists predict that if environmentally harmful practices continue, the Earth’s average surface temperature could increase by 2–6 °C by the end of the 21st century [2,3]. Therefore, it is our responsibility to control greenhouse gas emissions in every possible way. To achieve the goal of reducing CO₂ emissions by 45% by 2030 and reaching net-zero carbon emissions by 2050, many countries have recently made legal commitments to cut CO₂ emissions. However, there is a significant mismatch between global aspirations and current global CO₂ emissions levels.

In September 2020, the Chinese government announced its plan to peak its carbon dioxide emissions before 2030 and aim for carbon neutrality by 2060. Further, the Chinese government proposed accelerating the establishment of a policy system for peak carbon emissions, carbon neutrality, and additional actions, particularly emphasizing energy; construction; critical points for carbon emissions reduction in industries like power, steel, and cement; and corresponding measures, and expediting the formulation of specific work timetables and pathways.

In March 2022, the Chinese Ministry of Housing and Urban-Rural Development issued a notice on the development plan for energy conservation and green building, clearly stating the need to strengthen the statistical and monitoring capabilities in the construction sector, improve the system and indicators for energy consumption statistics in the construction sector, and explore the establishment of a system for energy consumption statistics in urban infrastructure [4]. Standards, systems, and methodologies related to building carbon emissions have attracted significant attention as the foundational technologies for the “dual carbon” work in the construction sector [5]. Therefore, against the backdrop of global carbon peaking and neutrality, it is urgently necessary to clarify the calculation of carbon emissions in the construction sector, delineate the mechanisms for energy conservation and carbon reduction in buildings, enhance the level of energy-saving technologies in buildings, and explore the implementation path for dual carbon goals in buildings.

The existing methods for calculating building carbon emissions mainly include input–output analysis, life cycle assessment (LCA), the measured method, and the intensity estimation method. Input–output analysis combines economic input–output tables and relevant environmental data to convert monetary value into carbon emissions, capturing the entire supply chain’s carbon emissions. However, it faces issues of less accurate macro-level analysis. The measured method achieves accurate data but is challenging and time-consuming, and it is unable to measure processes that have not occurred. The intensity estimation method is simple to operate and calculate but provides coarse results, being more of an approximation than a detailed analysis [6]. This project aims to establish a more operationally robust carbon emissions calculation model based on the LCA method. The project will use CEEB software to design, simulate, and compare carbon emission data from the building operation phase in order to identify an energy-saving and emission-reduction scheme suitable for the building [7,8].

2. Data and Methodology

2.1. Basis of Calculation

2.1.1. Main Standards

Currently, the green and low-carbon standard system in the field of architecture in China is still under development. The mainstream standards related to building carbon emission calculations include the “Building Carbon Emission Calculation Standard” (GBT 51366-2019 [9]), the “Building Carbon Emission Measurement Standard” (CECS 374-2014 [10]), Guangdong Province’s “Guidelines for Building Carbon Emission Calculation “, and Xiamen City’s “Building Carbon Emission Accounting Standard” DB 3502/Z 5053-2019 [11].

2.1.2. Key Accounting Points

(1)

Carbon emissions during the production and transportation stages of building materials [12] include the total carbon emissions from the production and transportation of primary building materials, such as steel bars, cement, and bricks, from the production site to the construction site [13]. By referring to engineering construction-related technical data such as design drawings and procurement lists, the amount of building materials consumed for the construction is determined. When calculating, we select the primary building materials with a weight no less than 90% of the total weight of building materials consumed in construction [14]; building materials with a weight percentage lower than 1% can be excluded from the calculation [15].

(2)

Construction phase carbon emissions include carbon emissions from the completion of sub-projects and implementation processes, as well as carbon emissions generated by construction personnel living and working on-site. The calculation is based on the project’s phase using actual construction energy consumption data and estimated construction energy consumption values.

(3)

During the operational phase of building, carbon emissions primarily stem from energy and resource consumption. Taking residential buildings as an example, energy and resource consumption mainly focus on air conditioning systems, lighting systems, power equipment, and domestic hot water and gas. Carbon emissions arise from the release of energy consumption from various operating systems. Energy consumption monitoring methods and resource accounting methods can be employed for completed projects. For projects yet to be built, energy consumption simulation methods and calculation methods based on design standard parameters are recommended.

(4)

Carbon emissions in the demolition phase include carbon emissions generated from mechanical dismantling, manual dismantling, and the energy consumption associated with the transportation of construction waste. In the absence of actual dismantling data, empirical formulas can be used for calculation.

(5)

Carbon sequestration amount primarily refers to the carbon absorption from greening measures, with vegetation greening being the main approach for building carbon sequestration. The types and areas of construction carbon sequestration can be obtained from architectural blueprints.

2.2. Establishment of Carbon Emission Accounting Model

The carbon emissions accounting boundary for the full life cycle includes the material phase, building operation phase, and demolition phase. The material phase’s carbon emissions originate from the production and processing of building materials, transportation, and the energy consumption of construction machinery. The building operation phase’s emissions stem from cooling systems, hot water boilers, lighting, domestic hot water, elevators, and the carbon reduction effect due to green space carbon sequestration. The demolition phase’s emissions are due to the energy consumed by demolition machinery and the disposal of waste materials.

In accounting for carbon emissions during a building’s life cycle, we employ carbon emission factor calculation during the physical stage, gathering data on materials, machinery, transport distances, and corresponding emission factors. For buildings in operation, carbon emissions calculations fall into two scenarios: one involves collecting annual energy consumption records to determine carbon emissions during operation; the other anticipates emissions for buildings in the design or retrofitting phase via design simulations and software to predict future operational carbon emissions. The case project uses THS’s Building Carbon Emission (CEEB) software for simulation and carbon reduction design, yielding carbon emission data for systems like cooling, heating, air conditioning, lighting, outlets, and elevators during operation. For demolition, we assess emissions based on building floor and area data using empirical formulas, as demonstrated in Figure 1.

2.3. Architectural Carbon Emission Accounting Formula

2.3.1. Carbon Emissions during Building Operations

The calculation scope for carbon emissions during the building operation phase includes HVAC, domestic hot water, lighting and elevators, renewable energy, and the building’s carbon sinks. The carbon emissions here include greenhouse gases such as CO₂, CH₄, N₂O, etc. Using CO₂ as the baseline, the warming effects of a certain greenhouse gas produced over a certain period of time are converted into equivalent CO₂ emissions. This article expresses in terms of CO₂ equivalents. Carbon emissions should be determined based on the energy consumption of different systems and the carbon emission factors of various types of energy. The carbon emissions per unit of built area and the total carbon emissions during the building operation phase are calculated as follows:

$$C_M=\frac{\left[{\sum }_{i=1}^n{(E}_i{EF}_i)-C_p\right]y}{A}$$

(1)

$$E_i={\sum }_{j=1}^n(E_{i,j}-{ER}_{i,j})$$

(2)

• ${\mathbf{C}}_{\mathbf{M}}$—Carbon emissions per unit building area during the operational phase ($\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}/{\mathbf{m}}^2$).
• ${\mathbf{E}}_{\mathbf{i}}$—Annual consumption of the iᵗʰ type of energy for the building (unit/year).
• ${\mathbf{E}\mathbf{F}}_{\mathbf{i}}$—Carbon emission factor for the iᵗʰ type of energy.
• ${\mathbf{E}}_{\mathbf{i},\mathbf{j}}$—Energy consumption of the iᵗʰ type by system j (unit/year).
• ${\mathbf{E}\mathbf{R}}_{\mathbf{i},\mathbf{j}}$—Renewable energy provided to system type j for the iᵗʰ energy type (unit/year).
• i—Types of end-use energy consumed by the building, including electricity, gas, oil, and district heating.
• j—Building energy system types, including heating and air conditioning, lighting, and domestic hot water systems.
• ${\mathbf{C}}_{\mathbf{P}}$—Annual carbon sequestration of the building’s green space ($\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}/$year).
• y—Building’s designed lifespan (years).
• A—Building area (m²).

2.3.2. Construction Phase Carbon Emissions

We calculate the total energy consumption during the construction phase using the construction procedure energy consumption estimation method. We compute the building construction phase’s carbon emissions as:

$$C_{JZ}=\frac{{\sum }_{i=1}^n{E}_{jz,i}{EF}_i}{A}$$

(3)

• ${\mathbf{C}}_{\mathbf{J}\mathbf{Z}}$—Carbon emissions per unit of the built-up area during construction ($\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}/{\mathbf{m}}^2$).
• ${\mathbf{E}}_{\mathbf{j}\mathbf{z},\mathbf{i}}$—Total energy consumption of the i^th type during the construction phase (kWh or kg).
• ${\mathbf{E}\mathbf{F}}_{\mathbf{i}}$—Carbon emission factor for the i^th energy type ($\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}/\mathbf{k}\mathbf{W}\mathbf{h} \mathbf{o}\mathbf{r} \mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}/\mathbf{k}\mathbf{g}$).
• A—Constructed area (m²).

2.3.3. Material Production Phase Carbon Emissions

We account for carbon emissions during the material production phase as:

$${\mathit{C}}_{\mathit{S}\mathit{C}}={\sum }_{\mathit{i}=1}^{\mathit{n}}{\mathit{M}}_{\mathit{i}}{\mathit{F}}_{\mathit{i}}$$

(4)

• ${\mathbf{C}}_{\mathbf{S}\mathbf{C}}$—Carbon emissions during the material production phase ($\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}$).
• ${\mathbf{M}}_{\mathbf{i}}$—Energy consumption for the i^th main construction material.
• ${\mathbf{F}}_{\mathbf{i}}$—Carbon emission factor for the i^th main construction material ($\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}/\mathrm{u}\mathrm{n}\mathrm{i}\mathrm{t}\mathrm{o}\mathrm{f}\mathrm{m}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{a}\mathrm{l}$).

2.3.4. Material Transportation Phase Carbon Emissions

We ascertain carbon emissions during the material transportation phase as:

$${\mathit{C}}_{\mathit{y}\mathit{s}}={\sum }_{\mathit{i}=1}^{\mathit{n}}{\mathit{M}}_{\mathit{i}}{\mathit{D}}_{\mathit{i}}{\mathit{T}}_{\mathit{i}}$$

(5)

• ${\mathbf{C}}_{\mathbf{y}\mathbf{s}}$—Carbon emissions during the material transportation process ($\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}$).
• ${\mathbf{M}}_{\mathbf{i}}$—Energy consumption for the i^th main construction material (t).
• ${\mathbf{D}}_{\mathbf{i}}$—Average transportation distance for the i^th main construction material (km).
• ${\mathbf{T}}_{\mathbf{i}}$—Carbon emission factor per unit weight per transportation distance for the transportation mode of the i^th material.

2.3.5. Demolition Phase Carbon Emissions Calculation

According to the “Guidelines for Building Carbon Emission Calculation” of Guangdong Province of China, the energy consumption of building construction, the emissions during the construction process, and the simplified relationship with the number of building stories are:

$$\mathrm{Y}=\mathrm{X}+1.99$$

(6)

where X represents the number of above-ground stories of the building and Y denotes the carbon emissions per unit area, measured in $\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}/{\mathbf{m}}^2$.

3. Results

3.1. Project Overview

The project is a shopping mall building in Shenzhen, Guangdong, located at 23.30° N and 113.83° E. The design life span is 50 years, with seven above-ground stories reaching a height of 33.6 m, a total floor area of 27,783 square meters, and an orientation angle of 90° north. The solar radiation absorption coefficients for the external walls and the roof are both 0.75. Figure 2 is an observational image of the building model.

3.2. Sources of Basic Data

To calculate and analyze building carbon emissions, it is necessary to collect relevant basic data. Following the analysis of carbon emission sources described earlier and using the established accounting model, one must acquire the required data in the following ways:

(1)

The carbon emissions from the material phase encompass the total emissions from material production, transportation, and the construction stage. The types and quantities of materials, types and quantities of machinery, and the types and amounts of energy required for carbon emission calculations all come from the bill of quantities of the case project’s labor and machinery [20].

(2)

Operational phase carbon emissions calculations must ascertain the annual energy consumption of air conditioning, lighting, elevators, and household appliances. To measure emissions in this phase, the relevant standards and literature should be combined with THS’s carbon emission professional software, CEEB, to set the parameters for the enclosure structure, lighting system, elevator, and air conditioning energy consumption.

(3)

The case building is currently in operation and has not yet entered the demolition and scrapping phase [21]. Empirical estimation methods are used for carbon emissions in this stage [22].

(4)

The sources of carbon emission factors are from Chinese standards and research data of other scholars, detailed in

Table 1. Sources of basic data.

Life Cycle Phase	Data Type	Data Sources
Material phase	Building material consumption	List of project materials
	Building material transportation distance	List of project materials
	Model of transport machinery	List of project materials
	Type of construction machinery	List of project materials
	consumption of machine operating hours	List of project materials
Operational phase	Cold supply	The authors’ design
	Air conditioning fan	The authors’ design
	Lighting	The authors’ design
	Lift	The authors’ design
	Domestic hot water	The authors’ design
Demolition phase	Building area, number of building floors	Design document
Carbon emission factors	Energy and carbon emission factor	Building Carbon Emission Computing Standard (GBT-51366-2019), Guangdong Province’s “Guidelines for Building Carbon Emission Calculation”; Refs. [23,24,25,26,27,28,29,30]
	Building material carbon emission factor
	Power grid carbon emission factor
	Building material transport carbon emission factor

.

3.3. Calculation of Carbon Emissions in the Material Phase

3.3.1. Carbon Emissions in the Production Stage of Building Materials

Here, the total emissions without the material recycling coefficient from the production of building materials stood at 13,870.63 tons, which was derived from Equation (3), as shown in

Table 2. Summary of carbon emissions in the building material production phase.

Material		Unit	Dosage	Carbon Emission Factors $(\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}/\mathbf{u}\mathbf{n}\mathbf{i}\mathbf{t})$	Carbon Emission $\left(\mathbf{t}{\mathbf{C}\mathbf{O}}_2\mathbf{e}\right)$
Electricity		kW·h	86,380.6	0.53	45.78
Low-carbon steel welding rod synthesis		kg	30.06	20.5	0.62
Water		t	9244.48	0.17	1.57
Geotechnical cloth		m2	12,430.85	0.77	9.57
Steel protective tube		kg	4368	2.2	9.61
Round nail L50-75		kg	2211.69	2.31	5.11
The bolt		kg	3064.37		7.08
Wire mesh: Φ 0.8 mm		m2	149,143.5	6.42	957.50
Iron parts, comprehensive		kg	166.15	2.19	0.36
Galvanized iron wire: Φ 4.0		kg	74.26	2.35	0.18
Other iron parts		kg	534,382.04	2.19	1170.30
Adapting piece		kg	255.53		0.56
Engineering clay		m3	19.58	6.99	0.14
Commercial concrete C30		m3	17,164.65	295	5063.57
Commercial concrete C40		m3	6967.42	360.6	2512.45
Commercial concrete C20		m3	282.92	230	65.07
Dry-mixed masonry mortar	M15.0	t	36.83	182.28	6.71
	M10.0	t	72.64	172.92	12.56
Fir wood, sawed material		m3	544.4	73.9	40.23
Wood formwork: 2440 × 1220 × 15		m2	46,406.09	1.11	51.51
Plastic adhesive tape: 20 mm × 50 m		roll up	6541.65	0.29	1.90

.

3.3.2. Carbon Emissions in the Building Material Transportation Stage

We evaluated the carbon emissions from the transportation of construction materials. Concrete, sourced locally and transported by road at an average distance of 40 km, contrasts with other materials, which are transported over an average distance of 500 km, as summarized in

Table 3. Summary of carbon emissions in the building material transportation stage.

Material		Weight (t)	Transportation Range	Carbon Emission Factors	Carbon Emission
			(km)	$(\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}/\mathbf{t}·\mathbf{k}\mathbf{m})$	$\left(\mathbf{t}{\mathbf{C}\mathbf{O}}_2\mathbf{e}\right)$
Low-carbon steel welding rod synthesis		0.03	500	0.115	0.002
Geotechnical cloth		37.29	500	0.115	2.144
Steel protective tube		4.37	500	0.115	0.251
Round nail L50-75		2.21	500	0.115	0.127
The bolt		3.06	500	0.115	0.176
Wire mesh: Φ 0.8 mm		417.6	500	0.115	24.012
Iron parts, comprehensive		0.17	500	0.115	0.01
Galvanized iron wire: Φ 4.0		0.07	500	0.115	0.004
Other iron parts		534.38	500	0.115	30.727
Adapting piece		0.26	500	0.115	0.015
Engineering clay		50.93	500	0.115	2.928
Commercial concrete C30		40,508.6	40	0.115	186.34
Commercial concrete C40		16,930.8	40	0.115	77.882
Commercial concreteC20		679.01	40	0.115	3.123
Dry-mixed masonry mortar	M15.0	36.83	500	0.115	2.118
	M10.0	72.64	500	0.115	4.177
Fir wood, sawed material		313.03	500	0.115	17.999
Wood formwork: 2440 × 1220 × 15		417.65	500	0.115	24.015
Plastic adhesive tape: 20 mm × 50 m		0.26	500	0.115	0.015
Hard plastic pipe DN20		5.37	500	0.115	0.309
Single-layer maintenance film		10.99	500	0.115	0.632
Parting agent		17.78	500	0.115	1.022
Total					378.03

based on Equation (5).

3.3.3. Carbon Emissions during the Construction Phase

The construction phase emissions were deduced from the machinery and energy consumption listed in the project inventory. By consulting building carbon emission metrics and applying carbon emission factors, we obtained a total of 8,070,586.72 kg, as detailed in

Table 4. Summary table of carbon emissions during the construction phase.

Name of Material Machine	Unit	Quantity	Energy Used by the Working Machine			$\mathbf{Carbon} \mathbf{Emissions} \left(\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}\right)$
Concrete			Energy Type	Energy Consumption per Unit	Energy Units	Build Carbon Emissions
Crawler single bucket hydraulic excavator (1 m3)	Crawler	2.94	diesel oil	63	kg	574.76
Steel wheel vibrating road roller; quality of work (15 t)	machine team	15,066.77	diesel oil	86.3	kg	4,030,755.5
Crawler hydraulic excavator BY-VH 350	machine team	102.98	diesel oil	83.12	kg	26,535.72
Crawler single-bucket hydraulic excavator; bucket capacity (0.6 m3)	machine team	2.06	diesel oil	33.68	kg	215.29
Crawler rotary digging drill; pore size (1500 mm)	machine team	16.88	diesel oil	164.32	kg	8600.45
Truck-mounted crane; Lifting capacity (8 t)	machine team	70.81	diesel oil	28.43	kg	6240.79
Lorry; load mass (6 t)	machine team	466.48	diesel oil	33.24	kg	48,067.7
AC; arc welder capacity (32 kV·A)	machine team	8.77	electricity	96.53	kW·h	483.02
Mortar mixer; drum capacity (400 L)	machine team	3.57	electricity	15.17	kW·h	30.85
Mud pump; exit diameter (100 mm)	machine team	25.97	electricity	234.6	kW·h	3474.86
Woodworking circular sawing machine; diameter (500 mm)	machine team	2839.26	electricity	24	kW·h	38,861.51
Concrete leveling machine; power (5.5 kW)	machine team	95.08	electricity	23.14	kW·h	1254.75
Diesel oil	kg	1,329,370.54	/	/	/	3,859,960.31
Electricity	kW·h	86,380.6	/	/	/	45,531.21
Total						8,070,586.72

.

3.3.4. Summary of Carbon Emissions in the Material Phase

The material phase includes the production phase of building materials, the transportation phase, and the construction phase. The summarized results of the material phase for this case are shown in

Table 5. Summary table of carbon emissions during the material phase.

Building Stage	Production Phase	Transportation Phase	Construction Phase	Material Phase
Carbon emission $\left(\mathrm{t}{\mathrm{C}\mathrm{O}}_2\mathrm{e}\right)$	13,870.63	378.03	8070.59	22,319.25
Percentage	62.15%	1.69%	36.16%	100%

, and the analysis diagram is shown in Figure 3.

3.4. Carbon Emission in the Operation Phase

3.4.1. Carbon Sinks

Our research targets an independent shopping mall with a construction area of 27,782 square meters. Besides this structure, the complex includes office buildings and high-rise residential areas. Details on the park’s vegetation types and areas appear in

Table 6. Summary table of carbon sequestration in the carbon sink.

Green Plants	Period of Growth Modifying Factor	${\mathbf{C}\mathbf{O}}_2$ Fixation Rate for the Year $(\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}/{\mathbf{m}}^2·\mathbf{a})$	Area (m2)	Number of Years	Carbon Fixation
					$\left(\mathbf{t}{\mathbf{C}\mathbf{O}}_2\mathbf{e}\right)$
Mixed area of trees, shrubs, and plants (average planting spacing of trees < 3.0 m, soil depth > 1.0 m)	1	30	880	50	1320
Broad-leaved tree	1	22.5	1260		1417.5
Small broad-leaved trees, coniferous trees, sparse leaf trees	1	15	800		600
Palms	1	10	2100		1050
Densely planted bushes (about 0.9 m high, soil depth > 0.5 m)	1	7.5	400		150
Perennial vines (soil depth > 0.5 m)	1	2.5	360		45
Grass and flower beds, natural weeds, lawns, and aquatic plants	1	0.5	6600		165
The proportion of the building area to the total building area of the park					0.19
Total					917.66

. We allocate carbon sequestration to the building based on its proportional construction area, applying the standard carbon fixation parameter per square meter. Over 50 years, the total carbon sequestration for saplings amounts to 917.66 tons, as summarized in Table 6.

3.4.2. Analysis of Carbon Emission in the Operation Phase

Equations (1) and (2) were utilized to calculate carbon emissions during the operation phase, as detailed in

Table 7. Analysis table of carbon emissions in the operation phase.

Categories	$\mathbf{Design} \mathbf{Building} \mathbf{Carbon} \mathbf{Emissions} \mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}/\left({\mathbf{m}}^2·\mathbf{a}\right)$	Proportion
Cold supply	59.24	61.84%
Air conditioning	11.64	12.15%
Lighting	19.72	20.58%
Other	5.2	5.43%
Carbon sequestration capacity	0.66	/
Total carbon emissions	95.80	100.00%

, with the analytical diagram presented in Figure 4.

3.5. Demolition Phase Carbon Emissions

By applying Equation (5) to calculate the carbon emissions during the demolition phase, ${\mathbf{C}}_{\mathbf{C}\mathbf{C}}=\mathbf{Y}\times \mathbf{A}$ can estimate these emissions, with ‘A’ representing the area. This project’s demolition carbon emissions calculations are shown in

Table 8. Emissions inventory for building demolition phase.

$\mathbf{Area} \mathbf{of} \mathbf{Structure} ({\mathbf{m}}^2)$	Number of Stories	$\mathbf{Carbon} \mathbf{Emissions} \mathbf{per} \mathbf{Unit} \mathbf{Area} (\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}/{\mathbf{m}}^2)$	$\mathbf{Demolition} \mathbf{Carbon} \mathbf{Emissions} \left(\mathbf{t}{\mathbf{C}\mathbf{O}}_2\mathbf{e}\right)$
27,782.53	7	8.99	248.76

.

3.6. Summary of Carbon Emissions throughout the Entire Life Cycle of a Building

Carbon emissions throughout a building’s entire life cycle encompass the material phase, operational phase, and demolition phase, with the operational phase being the most significant in terms of emissions. Thus, it is the most critical stage for carbon reduction efforts. The detailed data and analysis results are shown in

Table 9. Summary of carbon emissions throughout the whole life cycle of a building.

	Material Phase	Demolition Phase	Operational Phase
Carbon emissions (${\mathbf{t}\mathbf{C}\mathbf{O}}_2\mathbf{e}$)	22,319.25	248.76	133,080.57
Carbon emissions per square meter ($\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}/{\mathbf{m}}^2$)	803.34	8.95	4790.00
Percent of emissions (%)	14.34%	0.16%	85.50%

and Figure 5.

4. Discussion of Carbon Reduction Strategies

4.1. Purpose of Carbon Reduction Design

China’s GB 55015-2021 [31] “General Code for Energy Conservation and Renewable Energy Utilization in Buildings” stipulates that an average of 40% should reduce the carbon emission intensity of new residential and public buildings based upon the energy-saving design standards implemented in 2016. The GB/T 50378-2019 [32] “Assessment Standard for Green Building” specifies that construction projects should analyze carbon emissions and adopt measures to lower carbon intensity per unit area, with a rating value of 12 points. These regulations underpin the purpose of carbon reduction design and serve as essential references for achieving the “dual carbon” goals.

4.2. The Project’s Carbon Reduction Strategies at Various Stages

Data analysis reveals that emissions from the operational phase are predominant; thus, targeted carbon mitigation analyses and designs are crucial. Reducing emissions during operations focuses on the carbon outputs caused by air conditioning, heating, and lighting [33]. Deductions from solar photovoltaic and wind turbine energy savings are also relevant. Priority should be given to the building’s intrinsic design—shading, maintenance structure, HVAC systems, and the impact of the carbon sequestration system during operation. Currently, the optimization of domestic hot water, elevators, and renewable energy sources is not under consideration [34].

4.2.1. Shading Analysis

In hot-summer and warm-winter regions, solar radiation through windows significantly impacts air-conditioning loads and indoor thermal environments. Architectural shading is a key measure used to address this. External shading can dramatically decrease annual per-area carbon emissions [35]. Shading improves internal environmental comfort, light control, ventilation, and blocks excessive heat from entering, culminating in reduced indoor temperatures and HVAC energy needs, thus lowering energy consumption and carbon emissions [36]. This project implemented 0.5 m of external shade.

4.2.2. Maintenance Structure

Enhancing the thermal performance of a building’s maintenance structure can markedly reduce heating and cooling loads, leading to energy savings and lowered carbon emissions. Improving insulation reduces heat loss through the structure, thus diminishing carbon emissions in the operational phase [37].

In the maintenance structure design, the heat transfer coefficient of the roof and the exterior wall is changed. As shown in

Table 10. Structural parameters of building maintenance.

Maintain the Structure	Reference Building	Designed Building
		1	2	3	4
Roof heat transfer coefficient /[w/(m2·K)]	0.4	0.4	0.3	0.2	0.12
External wall heat transfer coefficient /[w/(m2·K)]	1	0.7	0.6	0.5	0.48

, the annual cumulative cooling consumption demonstrates that the smaller the heat transfer coefficient, the lower the annual cumulative cooling consumption, and the carbon emission is also low, as shown in Figure 6.

From the perspective of maintaining building structures, opting for low-carbon materials is an effective way to cut emissions throughout a building’s life cycle. Concrete, cement, steel, and aluminum in buildings are major sources of carbon emissions [38,39]. Research indicates that using low-carbon construction products can reduce the total life cycle carbon emissions by around 10%. Materials certified for environmental performance or other low-carbon certifications can result in lower emissions under identical design conditions. Renewable materials, hemp concrete, shell concrete, and straw are emerging trends in the field of low-carbon building materials.

4.2.3. Carbon Reduction Strategies during the Material Phase

Malls have extended operational hours and strict indoor climate control, resulting in high energy consumption by air conditioning systems [40]. These form the primary application of carbon reduction technologies in commercial buildings. The case study project implemented an efficient air conditioning system, replaced with magnetic levitation chillers, variable frequency pumps, and high-efficiency LED lighting [41]. Figure 7 and Figure 8 illustrate a before-and-after design comparison of carbon emission intensities for the cooling system and lighting system, respectively.

This case study focuses on an existing project. The starting point of this research is to execute a carbon reduction design during the usage phase using CEEB software simulation. A comparison of before and after the design implementation pinpoints carbon reduction breakthroughs, but carbon reduction design during the material phase is beyond the empirical scope of this study. That being said, energy conservation and emission reduction in the material phase typically follow the measures outlined below [42].

(1)

Employment of systemized standardized temporary facilities during construction.

To achieve carbon reduction goals, all temporary structures during project construction should use systemized standardized temporary facilities [43]. Office areas should use standardized container houses and detachable prefabricated rooms; construction sites should adopt standardized temporary hole edge protection, standardized processing sheds, standardized fences, prefabricated modular roadway plates and steel roadway solutions, and standardized safety passages. All auxiliary facilities like lifting cages, concrete hoppers, and construction elevator safety doors should have standardized production.

(2)

Increase in green material usage proportion and the formulation of rational material transport plans.

In terms of material production and transportation, choosing energy-saving and eco-friendly materials is one of the key actions in executing energy-saving design standards. Considering material lifespan and recyclability, opting for high-strength, high-temperature resistant, corrosion-resistant, high-performance, and recyclable building materials can decrease carbon emissions related to building maintenance during operation phases as well as reduce carbon emissions from constructing new materials by recycling used materials. Moreover, “local sourcing” can directly decrease building material transportation distance, while selecting appropriate transportation tools according to different material needs enhances transport efficiency, both contributing to lowered total carbon emissions during transportation.

Utilize high-strength steel or waste materials to reduce raw material production and to lower carbon emissions. Substituting ordinary building materials with waste materials enhances the material utilization rate, reducing production volume.

4.2.4. Optimizing the Energy Structure and Enhancing the Utilization Rate of Clean Energy

Vigorously developing clean energy is a crucial lever for achieving carbon peak and carbon neutrality goals. Establishing an efficient and rational renewable energy system for buildings, such as photovoltaic power generation, solar water heating, water-source heat pumps, and distributed wind energy generation, contributes to the green and sustainable development of buildings.

4.2.5. Employing Smart Technologies to Create an Informational Operation System

Digital technologies propel the “increase in sources and reduction of consumption” for building energy. They help construct a smart operations platform for buildings, reducing energy use in ventilation, air conditioning, and lighting. Integrating a full life cycle energy management system enables the visualization of energy consumption indicators and a high-energy consumption response. This enables energy scheduling and management to lower energy costs and reduces carbon emissions during operations [44].

4.2.6. Carbon Sequestration and Reduction

This project’s greening carbon sequestration approach involves horizontal greening in the park area, aiming to achieve a carbon reduction of 0.66 kg per square meter of building area annually. To enhance the carbon reduction effect, a combination of vertical greening and park greening or integrating greening with photovoltaic roofing could be implemented. The literature has demonstrated that combining photovoltaic rooftops with vertical greening can reduce up to 52% of neighborhood carbon emissions [45].

4.3. Comparison of Carbon Reduction after Design

After design and computation, the reduction in carbon emission intensity post-design is 14.9$\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}/{(\mathbf{m}}^2·\mathbf{a})$, surpassing the threshold of 7$\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}/{(\mathbf{m}}^2·\mathbf{a})$, confirming the efficacy of the carbon reduction design.

Table 11. Comparison of the carbon reduction effects before and after the design’s implementation.

Carbon emissions of the original buildings, $\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}/{(\mathbf{m}}^2·\mathbf{a})$	110.7
Building carbon emissions post-carbon reduction design, $\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}/{(\mathbf{m}}^2·\mathbf{a})$	95.80
Reduction in carbon emission intensity, $\mathbf{k}\mathbf{g}{\mathbf{C}\mathbf{O}}_2\mathbf{e}/{(\mathbf{m}}^2·\mathbf{a})$	14.90
Carbon reduction percentage post-design (%)	13.46%

illustrates the change in building carbon emission intensity before and after the implementation of the carbon reduction design. Figure 9 compares the carbon emission intensity before and after implementing carbon reduction designs.

5. Conclusions

In conclusion, our research focused on calculating building carbon emissions and implementing carbon reduction strategies. The comparative analysis demonstrated that buildings designed with carbon reduction measures showed a 13.46% decrease in carbon emission intensity from pre-design levels. This highlights the crucial role of carbon accounting and reduction design in promoting energy saving and emission reduction in buildings.

We developed a life cycle assessment (LCA)-based carbon accounting framework that integrates the entire life cycle of a building into its energy consumption phases. These phases include material, operation, and demolition. We identified various carbon emission sources for each phase, proposed data collection methodologies, and matched appropriate accounting methods to these emissions. For the material phase, we considered emissions from production, transportation, and construction by extracting summary tables for materials, labor, and machinery for the case study buildings, followed by calculating the carbon emissions using emission factors. During the operational phase, we collected data on energy usage, renewable energy consumption, carbon sequestration, and maintenance materials, as well as applied carbon emission factors. The demolition phase used actual energy consumption for its carbon emission calculations, in contrast with the formula-based methods used for other phases.

Our case study of a commercial building in China’s hot-summer and cold-winter region revealed that the operational phase contributes the most to total life cycle carbon emissions, followed by the material and demolition phases. Therefore, energy conservation and emission reduction measures should prioritize the operational and material phases, although the demolition phase should also be adequately addressed in energy-efficient designs.

In terms of carbon reduction design, our study targeted the operational phase and found that a lower heat transfer coefficient for the building envelope significantly reduced carbon emissions. Additional strategies included modifying shading types, implementing high-efficiency air conditioning systems, and using energy-efficient lighting. Using THS’s CEEB software simulation, we observed significant energy-saving and emission-reduction effects through enhanced building shading, efficient air conditioning systems, and LED lighting. We proposed seven strategies for achieving energy conservation and emission reductions during the operational and material phases. Energy conservation and emission reduction are critical issues for society and humanity, forming part of the sustainable development path we must steadfastly pursue.

The limitations of this study lie primarily in two areas: identifying the most effective combination of emission reduction measures and understanding the cost implications of using heat-insulating materials for energy saving and emission reduction. These issues will be the focus of future research for our group, involving in-depth analysis and investigation.

Our research findings are applicable to the construction and usage stages of buildings, including design, procurement, construction, and operation phases. By applying our results before finalizing the design scheme, it is possible to assess in advance the environmental conditions, energy consumption, and carbon emissions during building operation. The real-time assessments of design modifications can help designers choose energy-efficient, low-carbon, environmentally friendly, and sustainable solutions, thereby reducing greenhouse gas emissions in the construction industry and contributing to environmental sustainability.