Research on the Design of Carbon-Neutralized Building in Rural China: A Case Study of “Impression of Yucun”

Abstract

Energy conservation and emission reduction in rural buildings is essential to China’s response to climate change. Within the context of China’s ‘dual carbon’ initiative and the overarching goal of a ‘zero carbon countryside’, the first rural carbon-neutral building in China—‘Impression of Yucun’ was established in Anji County, Zhejiang Province. Accordingly, this study investigates building carbon-neutral design, calculating and analyzing the carbon emissions and offsets facilitated by carbon neutrality technology throughout the buildings’ life cycle. In addition, the comprehensive benefits of the buildings are evaluated from both technical and economic perspectives. The implementation pathway for rural carbon-neutral buildings is also explored. The results demonstrate that through the judicious application of carbon neutrality technology design, the inherent carbon emissions of the buildings amount to 120.91 t and the energy consumption during the operational phase of the building is 64,284.4 kWh/a, correlating to carbon emissions of 33.72 t. The case can theoretically reduce carbon emissions by 65.64 tCO₂ annually by implementing carbon offset measures. Considering photovoltaic cell decay, the building can achieve a carbon-neutral state for the first time in the fifth year of operation, with a net carbon emission of −5.58 tCO₂. Simultaneously, the investment in photovoltaic systems can be recouped between the seventh and ninth years of operation. This study can offer methodological reference and data support for designing and evaluating carbon-neutral buildings.

1. Introduction

The construction industry is one of the three biggest global energy consumers, generating nearly 30% of global carbon emissions [1,2]. Based on the 2020 China Building Energy Consumption Research Report of the National Bureau of Statistics, in 2018, the total carbon emissions from the entire construction industry in China were 4.93 billion tons, accounting for 51.3% of the total carbon dioxide emissions in the country. The production phase, the construction phase, and the operation phase of building materials each accounted for 55.2%, 2.0%, and 42.8% of the total carbon emissions of buildings [3]. With the continuous increase in new buildings and improving people’s living standards in China, energy consumption in the construction industry is gradually increasing, with great potential for energy conservation and carbon reduction [4]. In this context, promoting building energy conservation and emission reduction has become necessary for achieving global carbon neutrality [5].

Since 1986, the Chinese government has encouraged energy conservation and emission reduction in the construction industry by enhancing regulatory constraints and improving standards. A three-level system consisting of “energy-saving buildings”, “green buildings”, and “carbon neutrality buildings” has been established to enhance the requirements for energy conservation and carbon reduction throughout the life cycle of buildings. Carbon neutrality buildings, which apply carbon neutrality technology, can significantly mitigate global warming and contribute to the sustainable development of human society by reducing carbon emissions in construction [6], maintenance [7], operation [8], and even recovery [9].

There are pertinent reports on the carbon-neutral evaluation of various regions and different types of buildings worldwide. For instance, Yamaguchi et al. [10] proposed a novel framework integrating a synthetic population, activity, building stock, and a power distribution network to evaluate the feasibility of net zero energy for dense urban regions in noncold climates. Perwez et al. [11] presented a coupled scheme to integrate an urban building energy model with a physical-based building-integrated photovoltaics potential estimation approach. This coupled scheme is applied to evaluate the feasibility of carbon neutrality of commercial building stock at a multi-scale level. However, localized buildings’ carbon-neutral evaluation in China still requires further study.

China is a prominent agricultural nation worldwide. Based on the Ministry of Housing and Urban-Rural Development’s statistics, the total residential area of the country surpassed 55 billion m² in 2019, and rural buildings accounted for 60% of the national living area [3]. However, over 90% of rural buildings remain high-energy buildings with no unified design planning and energy-saving standards. They also face widespread issues such as an unreasonable energy structure, low energy utilization rates, and substantial carbon emissions [12]. Therefore, constructing carbon-neutral buildings in rural areas has become critical for China to address climate change and achieve the goal of a “zero carbon countryside” [13]. The greenhouse gas emissions from rural energy consumption in 2021 comprised approximately 15% of China’s total greenhouse gas emissions [14]. At present, numerous studies have focused on technological upgrades aimed at reducing carbon emissions in modern buildings, including research and development of green building materials [15], designs for improving the insulation performance of building exterior walls [16], energy-saving optimization of air conditioning systems [17], and efficient utilization of renewable energy [18]. Given the low building density and abundant sunlight, the potential for solar energy utilization is substantial for rural areas. Since the land area of rural residential buildings is roughly equivalent to the projected area of building roofs, the power generation capacity of rural rooftop photovoltaic is considerable in the context of increasingly scarce land for photovoltaic power generation [19]. In 2020, China had 177 million rural households. Based on an average floor area of 120 square meters per household [20], the total floor area of rural dwellings is 21.24 billion square meters. Through high-resolution satellite imagery and artificial intelligence, a statistical analysis was conducted on the status of rural roofs in China. There are a total of 27.3 billion square meters of various types of roof areas in rural regions. Based on the current average installation capacity of 20–40 kilowatts of rooftop photovoltaic per household, the actual available roof installation capacity in rural areas reaches 1.97 billion kilowatts, with a predicted annual power generation close to 3 trillion kilowatt-hours [21]. Compared to China’s total electricity consumption of over 7.5 trillion kilowatt-hours in 2020, 3 trillion kilowatt-hours exceed one-third of the total [22]. Therefore, photovoltaic technology can be critical for achieving carbon neutrality in buildings.

The development trend of decentralized and centralized parallel power grids is gradually emerging. The cost of crucial elements such as photovoltaic and energy storage within the microgrid, which is friendly and interactive with the larger power grid, continues to decrease. The integration of “building photovoltaics and direct flexible buildings with light storage” has emerged. PEDF is a new energy system for buildings equipped with building Photovoltaics and Energy Storage, it adopts a Direct Current distribution system, and the electrical equipment has a power active response function (Flexibility) [23]. PEDF technology has gradually transformed buildings from traditional single-power consumers into new roles of “production, consumption, regulation, and storage” [24]. PEDF technology stabilizes grid fluctuations, absorbs renewable energy, and achieves carbon neutrality in buildings [25]. However, the existing research has primarily focused on independent research on carbon reduction technologies, such as PEDF, green building materials, and energy-saving equipment. There is a lack of integrated evaluation of various technologies and calculation and analysis of carbon emissions throughout the life cycle of carbon neutrality buildings.

This study evaluates an actual carbon-neutral building’s carbon emissions, carbon offsetting measures, and economic benefits. It selects “Impression of Yucun”, the first platinum carbon neutrality building in China, as an example. It considers various carbon emissions reduction technologies involved in buildings, uses PKPM-PHEnergy to simulate and calculate the buildings’ energy consumption in operation, conducts carbon accounting for the life cycle of buildings based on the energy consumption simulation results, and analyzes the impact of carbon neutrality measures on the buildings’ carbon footprint. This research elucidates how to achieve the goal of building carbon neutrality through carbon emissions reduction technologies, evaluates the emission reduction potential of multiple carbon-neutral technology combinations, and provides an intuitive reference for designing future carbon neutrality buildings.

2. Materials and Methods

2.1. Case Overview

The case selects “Impression of Yucun”—a public building in Yucun, Tianhuangping Town, Anji County, Huzhou City, Zhejiang Province. The building is located within the middle and low latitudes of the eastern Eurasian continent, under a northern Tropical monsoon climate. The climate is mild, characterized by abundant rainfall and sufficient sunlight. The average temperature is 14 °C, with an extreme maximum of 40 °C and an extreme minimum of −17.4 °C. The annual sunshine duration is 2005 h, with 158 rainy days annually, and the average annual rainfall is 1790 mm.

Figure 1 depicts the appearance of the “Impression of Yucun”. The construction site lies near mountains and fields encircled by mountains and forests with plentiful vegetation. The land area spans 2789 m², the plot ratio is 0.45, the building density is 35%, the green space ratio is 23%, and the total building area is 1622.80 m². “Impression of Yucun” comprises two buildings: a library and an exhibition hall. The library covers a building area of 959.83 m², featuring three floors above ground and one floor underground. The above-ground building area is 600.48 m², and the underground building area is 359.35 m². The exhibition hall is a single-story building with an area of 566.57 m².

2.2. Building Carbon Neutrality Design

2.2.1. Building Envelope

The building sits in a hot summer and cold winter region of China’s climate zone, necessitating the enhancement of the insulation performance of the building envelope [8]. The China Academy of Building Research (CABR) has developed PKPM, a building energy efficiency analysis software (PKPMV3.3), which this study utilizes to conduct building energy efficiency analysis, insulation performance analysis, and external and internal condensation analysis [26].

After simulation optimization, “Impression of Yucun” employs a frame structure and an external wall insulation system. In order to avoid condensation issues within the building, a moisture-proof film, sealant, and insulation materials were installed at the bottom layer during construction. These materials concurrently reduce the indoor temperature, thereby decreasing air conditioning usage. The primary heat transfer coefficient of the optimized envelope for both the library and the exhibition hall is listed in

Table 1. Heat transfer coefficient of the envelope of the library exhibition hall.

Position	National Standard Limit [27]	Library		Exhibition Hall
	Heat Transfer Coefficient W (m2·K)	Heat Transfer Coefficient W (m2·K)	Increase Proportion	Heat Transfer Coefficient W (m2·K)	Increase Proportion
Roof	0.25	0.18	55%	0.18	55%
Exterior wall	0.70	0.18	77.5%	0.17	78.75%
Exterior window	1.8	1.3	40.91%	1.3	40.91%

.

2.2.2. Natural Ventilation

The Tsinghua Swell “Vent2020 Software” (V3 version) was applied to optimize indoor ventilation design to simulate the natural ventilation in the building’s transition season, based on relevant architectural drawings and materials [28]. Vent2020 is an analysis tool that offers wind environment and natural ventilation optimization design for building planning, layout, and spatial division. The software is constructed on the AutoCAD platform and utilizes CFD methods to calculate the regional wind environment.

The building incorporates a north-south transparent window design, installing openable window sashes on each facing facade. The basement hall implements passive measures without power hood measures. Simultaneously, the floor plan layout is rational, with opposite doors set up to generate a robust “ventilation effect”. Figure 2 and Figure 3 illustrate the simulation results of the wind environment in spring and autumn.

Table 2. Summary of simulation results of natural ventilation.

Conditions	The Total Area of the Main Functional Space (m2)	Room Area with Air Changes Greater than 2 Times/h (m2)	Percentage of Compliance
Spring/Autumn	832.37	704.45	84.63%

summarizes the simulation results of the building’s wind environment. It shows that the window and opposite door openings on the building facade effectively enhance natural ventilation. At least 84.63% of the area of the main functional space of the building meets the requirement for a ventilation frequency greater than two times/h during the transition season, complying with the national standard “Technical Standard for Near Zero Energy Consumption Buildings” GB/T 51350-2019 [29] for indoor natural ventilation.

2.2.3. Daylighting

In order to optimize indoor daylighting design, Dali2020 software (SP1 version) was utilized to simulate the lighting conditions of the main functional rooms in the building based on relevant architectural drawings and materials [30]. Dali2020 software uses “Radiance” as the computing core and employs the reverse ray tracing algorithm optimized by the Monte Carlo algorithm. With high computational accuracy, this software can perform dynamic analysis of building lighting throughout the year based on daylight climate data.

The building design adopts a facade window-to-wall ratio and selects daylight glass with high transmittance. The lighting effect can be enhanced by increasing the reflection ratio of the interior materials in the library’s underground floor, increasing the glass transmittance in the courtyard, or using a light guide system in the underground space.

Based on the “Standard for Lighting Design of Buildings” GB 50033-2013 [31] and relevant standards and project data, the simulation parameters were set as follows:

• The all-cloudy day calculation model CIE was adopted.
• Shanghai is in the IV photoclimatic zone, with a photoclimatic coefficient of K = 1.1.
• The outdoor natural light design illuminance value Es = 13,500 lx.
• Based on the construction drawing design instructions, the visible light transmittance of glass is 0.60.
• A plane at 0.75 m above the ground on each floor was selected as the natural lighting analysis surface.
• The reflectance ratio of the ceiling, wall, and ground was set according to the “Calculation Standard for Green Performance of Civil Buildings” JGJ/T 449-2018 [32], as shown in

  Table 3. The reflectance of each internal surface.

  Location	Material	The Reflectance of the Internal Surface
  Ceiling	Recommended values in JGI/T 449 “Calculation Standard for Green Performance of Civil Buildings”	0.75
  Wall		0.60
  Floor		0.30

  .

The simulation results are shown in Figure 4 and Figure 5.

Table 4. Statistical of indoor lighting coefficient conforming area in buildings.

Building	The Total Area of the Main Functional Space (m2)	Conforming Area (m2)	Percentage of Compliance
Library	372.92	254.52	68.25%
Exhibition hall	425.82	425.82	100%
Total	798.74	680.34	85.17%

lists the statistics regarding areas where the indoor lighting coefficient aligns with the standard. These data illustrate that a reasonable exterior window wall ratio and using high-transmittance glass significantly enhance indoor natural lighting. In the main functional space of the building, at least 85% meet the lighting requirements of the current national standard, “Building Lighting Design Standard” GB 50033-2013 [28].

2.2.4. High-Efficiency Air Conditioning Equipment

The library implemented a modular air-cooled heat pump system (COP 3.5), thereby improving energy efficiency by 25% compared to the 2.8 value specified in the “Energy Efficiency Design Standard for Public Buildings” GB 50189-2005 [33]. The exhibition hall integrated a multi-connected system (IPLV of 7.5), thus enhancing energy efficiency by 31.58% compared to the standard requirement of 5.7. Simultaneously, the energy efficiency of selected fans and water pumps aligned with the energy-saving requirements stipulated in the standard.

The library’s air conditioning terminal employed a fan coil unit with a centralized fresh air system, and the exhibition hall’s air conditioning terminal employed a direct expansion centralized fresh air system. Both systems have intelligent regulation functions. The library’s air conditioning system operates with a control device, and the exhibition hall’s air conditioning equipment is primarily regulated by localized and decentralized controls, enabling automatic regulation and control, automatic conversion of operating conditions, equipment interlocking, and automatic protection. These mechanisms effectively ensure optimized unit operation at low-energy consumption throughout the year.

In locations such as the staircase reading area and the landscape lounge in the exhibition hall, measures such as ceiling fans were adopted to reduce the air conditioning’s operating time.

2.2.5. Volume Ratio of Green Plants

Based on relevant studies, the average 40-year lifespan of urban trees can absorb between 11–18 kgCO₂ annually [34]. Consequently, this project increased the area dedicated to greenery and logically combined trees, shrubs, and lawns. A total of 190.44 m² of trees, 333 m² of shrubs, and 1294.2 m² of lawns were planted, resulting in a complementary and overlapping effect with trees as the primary component, shrubs filling the understory, and flowers and grasses populating the ground. The green plants’ volume ratio reached 1.10 [35], creating an effective green carbon sequestration impact.

$$GPR=\frac{\sum (L{A}_i\times P{A}_i\times N_i)+S_f\times 3+S_g}{S}$$

(1)

where $GPR$ is the volume ratio of green plants (%); $L{A}_i$ is the leaf area index of Class i trees; $P{A}_i$ is the projected area of Class i trees (m²); $N_i$ is the number of Class i trees; $S_f$ is the area occupied by shrubs in the site (m²); $S_g$ is the area occupied by grass in the site (m²); $S$ is the area of the site (m²).

2.2.6. Green Building Materials

In this case, green building materials were judiciously employed to effectively protect the environment and human health. The structures were renovated from the office buildings of the wire drawing factory and cement factory, thereby preserving the original form and structure during construction and significantly reducing the use of primary building materials such as steel, concrete, and cement. In addition, 100% of the selected premixed concrete and mortar and 75% of indoor decoration materials such as sanitary ware, waterproof materials, sealants, inorganic coatings, paper gypsum boards, ceramic floor tiles, doors, windows, and glass were green building materials. These methods substantially curtailed the carbon emissions from high-energy and high-emission building materials.

2.2.7. PEDF System

The building utilizes a direct, flexible optical storage system to supply power to direct current (DC) loads, including air conditioning and equipment in the exhibition hall. Simultaneously, various energy storage systems, including 256 kWh lithium-ion and lithium iron phosphate batteries, are configured, storing excess electricity produced by the photovoltaic cells in the energy storage batteries. This setup leads to a flexible DC system incorporating “rooftop photovoltaic + energy storage + DC distribution + flexible electricity consumption”. Consequently, it enables the complete electrification of the building and offers the potential for achieving carbon-neutral buildings.

The roofs of the library and exhibition hall are entirely covered with photovoltaic power generation modules spanning a total of 605 m², as depicted in Figure 6. The conversion efficiency of these monocrystalline silicon photovoltaic panels stands at 20.23%. The basic operating strategy of the system is as follows: from 22:00 to 8:00, the energy storage system charges, ensuring that the power of the energy storage system exceeds the load power during the charging process. The energy storage system discharges between 8:00 and 11:00. Subsequently, from 11:00 to 13:00, the system resumes charging the energy storage system. Between 13:00 and 18:00, the energy storage system remains on standby, and finally, from 18:00 to 22:00, the system discharges the energy storage system.

2.2.8. Smart Management Platform

The smart management platform was established for this project. The main control equipment is located in the zero-carbon equipment room on the B1 level of the library, and a large visual screen is situated in the exhibition hall on the F1 level. The platform performs the following vital functions:

• Intelligent control of major energy-consuming devices, monitoring of energy consumption behavior, identification of energy consumption loopholes, and provision of abnormal alarms.
• Assurance of stable operation of the photovoltaic power generation system, continuous monitoring, and abnormal alarm of photovoltaic power generation capacity, actual electricity consumption, and operation status.
• Optimization and adjustment of the electricity consumption of the PEDF system to effectively achieve demand-side management, eliminate the daily peak and valley price difference, balance user electricity load, and reduce user costs.
• Capability to monitor and display the operating status of building energy consumption, statistical parameters such as energy consumption and energy-saving rate, and automated generation of energy consumption reports and related reports. All energy-consuming equipment adopted itemized and graded measurement, and water-saving appliances were equipped with ultrasonic remote water meters to facilitate the itemized and graded measurement of water consumption.

2.2.9. Energy Consumption Simulation

To compute the carbon emissions of the building’s operational phase, it is first necessary to determine the building’s energy consumption. Following the building’s design completion, this study utilized the passive low-energy building simulation analysis software PKPM-PHEnergy (PKPMV3.3) [36] for energy consumption simulation. The model for this case is depicted in Figure 7.

The method of calculation and basic parameters of energy consumption indicators adhere to the following requirements:

• Meteorological parameters are selected in accordance with the existing standard, “Building Energy Efficiency Meteorological Parameter Standard” JGJ/T 346-2014 [37].
• The range for calculating annual heating and cooling consumption should encompass heat loss from the enclosure and heat (or cold) demand for processing fresh air. Heat (or cold) demanded for processing fresh air should be deducted from heat (or cold) recovered from exhaust air.
• For calculating domestic hot water energy consumption, its hot water consumption index must meet the requirements of the current national standard, “Water Saving Design Standard for Civil Buildings” GB50555-2010 [38].
• The primary energy consumption index range includes heating, air conditioning, lighting, domestic hot water, and elevator energy consumption, which can incorporate the renewable energy supply. The conversion coefficient of various energy types and primary energy should align with the “Technical Standards for Buildings with Near Zero Energy Consumption” GB/T 51350-2019 [29].
• The energy consumption calculation for the heating, ventilation, and air conditioning system should account for the effects of partial load and intermittent use.
• The calculation of lighting energy consumption can account for the influence of daylight and automatic control.
• The use of renewable energy should be calculated.

2.3. Calculation Method for Building Carbon Emissions

Currently, the international consensus on carbon emissions calculations for the entire life cycle of buildings is as follows: carbon emissions include explicit and implicit carbon emissions, with building operation carbon emissions composed of direct and indirect emissions. The definitions of each segment are detailed below:

• Direct carbon emissions from buildings refer to carbon emissions resulting from direct fossil fuel consumption during the operational phase, primarily generated by cooking, hot water use, and decentralized heating within the building.
• Indirect carbon emissions from buildings refer to carbon emissions from two secondary energy sources, electricity and heat, consumed during the operational phase, which constitute the main sources of carbon emissions from building operations.
• Implicit carbon emissions from buildings refer to carbon emissions generated by building construction and building material production, also known as built-up carbon emissions.

2.3.1. Accounting System Boundary and Data Selection

Calculating implicit carbon emissions from buildings includes the carbon emissions from building materials and components throughout their life cycle. Referencing ISO21930:2017 “Sustainability of Building and Civil Engineering—Core Rules for Environmental Product Declaration of Building Products and Services” [39], this study divided implicit carbon emissions into four phases: the production phase of building materials, the construction phase, the use phase, and the scrapping phase.

During calculating, the carbon emission factor of electricity is taken as 0.5246 kgCO₂/kWh, specified in the “2020 Zhejiang Province Greenhouse Gas Inventory Compilation Guidelines” for the provincial power grid. The carbon emission factor data for other energy sources are sourced from Appendixes A–E of the «Building Carbon Emission Calculation Standard» GB/T51366-2019 [40]. The data of building materials usage is sourced from the bill of quantities. The annual energy consumption data of energy consuming units such as air conditioning, lighting, and domestic hot water during the construction operation phase were simulated and calculated using PKPM-PHEergy software.

2.3.2. Calculation Method for Life Cycle Carbon Emissions

The carbon emissions calculation formulas for each phase are derived from the «Building Carbon Emission Calculation Standard» GB/T51366-2019 [40] (except for formulas with references). Due to the wide variety of materials used in the buildings with different characteristics, and the small amount of secondary building materials, the calculation results took a relatively small proportion in the life cycle of the building, so the main building materials were selected to calculate implicit carbon.

• Implicit carbon in the production phase of building materials

The carbon emissions generated during the building materials’ production phase should incorporate the carbon dioxide released from the upstream production of these materials and the transportation of raw materials to the processing site. The carbon emissions during the production of building materials should be determined based on Equations (2) and (3).

$$C_{JC}={\sum }_i{C}_{jc,i}$$

(2)

$$C_{jc,i}={\sum }_j{C}_{rm,j}+{\sum }_j{M}_{jc,j}{D}_j{T}_j +{\sum }_j{E}_{jc,j}E{F}_j$$

(3)

where $C_{JC}$ is the carbon emissions during the production phase of building materials (tCO₂); $C_{jc,i}$ is the product carbon emissions of the i-type building materials (tCO₂); $C_{rm,j}$ is the product carbon emissions of the i-type building materials and the j-type raw materials (tCO₂); $M_{jc,j}$ is the weight of the j-type raw materials used in the production of the i-type building materials (t); $D_j$ is the average transportation distance of the j-type raw material used in the production of the i-type building materials (km); $T_j$ is the carbon emission factor of the j-type raw material transportation mode utilized in the production of the i-type building materials (kgCO₂/(t·km)); $E_{jc,j}$ is the j-type energy consumption employed in the production process of the i-type building materials (kWh or kg); $E{F}_j$ is the carbon emission factor of the j energy used in the manufacturing process of i building materials (kgCO₂/kWh or kgCO₂/kg).

2.

Implicit carbon during the construction phase

Carbon emissions from the construction phase should include carbon emissions from the transportation of building materials to the project site, as well as construction and installation activities, and the carbon dioxide released during the use of building materials. Given the lack of comprehensive data on the current use process of building materials and the minor environmental impact of such a process allocated to the building construction phase, this aspect is ignored. Only carbon emissions from the transportation of building materials to the project site and carbon emissions generated from construction and installation activities are considered. Carbon emissions from the transportation of building materials to the project site are calculated by Equation (4).

$$C_{ys}=\sum _{i=1}^n{M}_i\times D_i\times T_i$$

(4)

where $C_{ys}$ is the carbon emission of building materials during transportation (kgCO₂); $M_i$ is the consumption of i-type primary building materials (t); $A_i$ is the average transportation distance of i-type building materials (km); $T_i$ is the carbon emission factor per unit weight of transportation distance of i-type building materials under transportation mode (kgCO₂/(t·km)).

3.

Implicit carbon during the operation phase of buildings

Implicit carbon during the operation of buildings includes the carbon dioxide released from the use, maintenance, repair, renovation, and replacement transportation of decoration materials or their auxiliary products. Due to the small environmental impact of using and maintaining decoration materials or their auxiliary products during the construction phase, this aspect is ignored.

4.

Operating carbon during the operation phase of buildings

The operational phase of a building is the longest consuming phase of its life cycle, with energy consumption and corresponding carbon emissions accounting for a significant proportion of the building’s life cycle. Energy consumption and carbon emissions in the operational phase primarily refer to those generated by the regular use of the building’s functional space, mainly including energy consumption and carbon emissions generated by conventional needs such as air conditioning, lighting, and domestic hot water. The carbon emissions during the building operational phase are determined by Equation (5).

$$C_M=\sum _{i=1}^n{(E}_i\times {EF}_i)+E\times EF$$

(5)

where $C_M$ is the carbon emission during the building operation phase (tCO₂); $E_i$ is the amount of non-renewable energy, except electricity used in building operation (kWh); ${EF}_i$ is the carbon emission factor of i energy; $E$ is the amount of purchased power utilized in building operation (kWh); $EF$ is the carbon emission factor of electricity in the region where the building is located (tCO₂/kWh).

During the operation, the annual energy consumption of energy-consuming units such as air conditioning, lighting, and domestic hot water is calculated using PKPM-PHEergy software. The carbon emission factor of electricity, valued at 0.5246 kg CO₂/kWh, as specified in the 2020 Zhejiang Province Greenhouse Gas Inventory Compilation Guidelines, is utilized as the emission factor.

5.

Implicit carbon during the scrapping phase of buildings

The implicit carbon emissions during the building scrapping phase encompass carbon dioxide emissions generated by building demolition, waste transportation, and waste disposal.

(1)

Carbon emissions during the demolition phase of buildings

Yousheng [41] conducted detailed research on energy consumption during the demolition phase of buildings, obtaining the correlational relationship between carbon emissions and the number of building floors during the demolition. The empirical formula is displayed in Equation (6).

$$C_{CC}=0.06x+2.01$$

(6)

where $C_{CC}$ is the carbon emission per unit building area during the process of building demolition (kgCO₂/m²), and $x$ is the number of building floors above the building.

(2)

Carbon emissions from waste disposal

Construction waste is categorized into reusable, recyclable, and worthless waste materials. Once the building is demolished, recyclable materials such as steel and glass can be repurposed. Based on the “Guidelines for the Evaluation of Carbon Neutral Buildings” [42], China’s first industry standard focusing on carbon-neutral buildings, 50% of the carbon emissions of the primary raw materials replaced can be calculated after recycling.

6.

Net carbon emissions, including carbon offsetting measures

PEDF technology is a novel building distribution technology that furthers electric energy substitution and grid-friendly interaction based on improving building energy efficiency. It serves as a crucial technical pathway to support carbon neutrality in the construction field.

The calculation method for photovoltaic power generation on the roof of the library and exhibition hall is based on the “Building Carbon Emission Calculation Standard” GB/T 51366-2019 [40], as shown in Equation (7).

$$E_{pv}={IK}_E(1-K_s){ \times A}_p$$

(7)

where $E_{pv}$ is the annual power generation of the photovoltaic system (kWh); $I$ is the annual solar irradiance on the surface of the photovoltaic cell (kWh/m²), taking 1293.72 kWh/ m²; $K_E$ is the conversion efficiency of the photovoltaic cell (%), taking 20.23%; $K_s$ is the loss efficiency of the photovoltaic system (%), taking 25%; $A_p$ is the net area of photovoltaic panels of the photovoltaic system (m²).

Based on research from the China Academy of Building Materials Industry Planning and Research Institute, the carbon reduction per unit building area of green enclosure materials in hot summer and cold winter areas is 2.06 kg.CO₂/(m²·a) [43].

The calculation method provided in the “Carbon Neutral Building Evaluation Guidelines” [42] is adopted for declaring carbon neutrality in the life cycle, as illustrated in Equation (8).

$$C_N=\frac{C_E}{n}+C_o-C_{AE}$$

(8)

where $C_N$ is the net carbon emission of the building and should be ≤0 (tCO₂); $C_E$ is the implicit carbon emission of the building (tCO₂); $C_o$ is the carbon emission of the building operation (tCO₂); $C_{AE}$ is the carbon emission offset measure (tCO₂); $n$ is the duration of the carbon neutrality plan of the building.

3. Results and Discussion

3.1. Analysis of Carbon Emissions in the Life Cycle of Buildings

3.1.1. Analysis of Implicit Carbon Emissions in Buildings

Implicit carbon emissions from buildings primarily occur in the building materials production phase, the building materials transportation phase, the building construction phase, and the building demolition phase. The construction phase includes the transportation of building materials and construction. Recyclable materials are recovered during the building demolition phase to achieve carbon neutrality to reduce carbon emissions. The carbon emissions in each phase of this study are listed in

Table 5. Calculation of carbon emission during the production phase of building materials.

Types of Building Materials		Weight of Building Materials	Carbon Emission Factor	Carbon Emission (tCO2)
Non-recyclable materials	Concrete	127.75 m3	295 kgCO2/m3	37.69
	Building mortar	290.43 t	2.51 kgCO2/t	0.73
	Cement	9.28 t	735 kgCO2/t	6.82
	Brick	30.32 m3	336 kgCO2/m3	10.19
	Gravel	143.07 t	2.18 kgCO2/t	0.31
	Bamboo	14.04 t	−1.43 tCO2/t	−20.08
	Subtotal			35.66
Recyclable material	Steels	43.735 t	2365 kgCO2/t	103.43
	Glass curtain wall	8.65 t	1130 kgCO2/t	9.77
	Subtotal			113.2
Total				148.86

,

Table 6. Carbon emission calculation during the transportation phase of building materials.

Types of Building Materials		Weight of Building Materials	Transport Distance (km)	Transport Vehicles	Carbon Emission Factor (kgCO2/(t.km))	Carbon Emission (tCO2)
Non-recyclable materials	Concrete	127.75 m3	250	30 t heavy truck	0.078	6.23
	Building mortar	290.43 t	250		0.078	5.66
	Cement	9.28 t	250		0.078	0.18
	Brick	30.32 m3	250		0.078	1.18
	Gravel	143.07 t	250		0.078	2.79
	Subtotal					16.04
Recyclable material	Steels	43.735 t	250	30 t heavy truck	0.078	0.85
	Glass curtain wall	8.65 t	250		0.078	0.17
	Subtotal					1.02
Total						17.06

,

Table 7. Carbon emission calculation during the construction phase.

Energy Category	Library- Exhibition Hall	Calorific Value (TJ)	Carbon Emission Factor (tCO2/TJ) or (tCO2/kWh)	Carbon Emission (tCO2)
Gasoline (kg)	156.34	7.19 × 103	67.91	0.49
Diesel (kg)	24.36	1.11 × 103	72.59	0.08
Electricity (kWh)	14,844.08	--	5.24 × 10−4	7.78
Total				8.34

and

Table 8. Calculation of carbon emissions during the demolition phase.

Building	Number of Floors of above Ground	Building Area (m2)	Carbon Emissions per Unit Area kgCO2/m2	Carbon Emissions (tCO2)
Library	3	959.83	2.19	2.10
Exhibition hall	1	566.57	2.07	1.17
Total				3.27

, which are 148.86, 17.06, 8.34, and 3.27 t, respectively. Part of the materials after demolition can be recycled, and the recoverable carbon emissions are 56.62 t, as shown in

Table 9. Recyclable materials recycling to save carbon emissions.

Types of Building Materials		Weight of Building Materials	Carbon Emissions Factor	Carbon Emissions (tCO2)	Recovery Ratio	Energy Saving Carbon Emission (tCO2)
Recyclable material	Steels	43.735 t	2365 (kgCO2/t)	103.43	50%	51.73
	Glass curtain wall Steels	8.65 t	1130 (kgCO2/t)	9.77	50%	4.89
	Total					16.04

. Therefore, the total implicit carbon emissions of the building are 120.91 t, summarized in

Table 10. Summary of implicit carbon emissions of buildings.

System Category	Production of Building Materials	Construction	Usage	Scrap	Total
Carbon emissions (tCO2)	148.86	25.4	/	−53.35	120.91

.

The scrapping phase includes building demolition and recycling of recyclable materials.

Figure 8 shows the distribution of carbon footprint in five different phases of implicit carbon emissions in buildings. The production phase of building materials has the highest proportion of carbon emissions, accounting for 63.57%, followed by the transportation phase of building materials with 7.29%. Notably, the recycling phase of recyclable materials has negative carbon emissions, accounting for −24.18%. In addition, using biomass building materials is an effective strategy to reduce carbon emissions; a portion of bamboo used in the buildings in this study is reduced by 20.08 t CO₂.

3.1.2. Analysis of Carbon Emissions of Building Operation

In order to achieve carbon neutrality, energy consumption is reduced through thermal insulation enclosure structures, natural ventilation, natural lighting, and energy-saving air conditioning in the operation phase of the building, thus decreasing carbon emissions. After 8760 h of energy consumption calculation, the annual energy consumption for heating, air conditioning, lighting, and elevator operation of “Impression of Yucun” is obtained, as shown in

Table 11. Annual energy consumption of library and exhibition hall.

Building	Air Conditioning (kWh)	Lighting (kWh)	Domestic Hot Water (kWh)	Total (kWh)
Library	26,965.38	13,025.64	660.36	40,651.38
Exhibition hall	7230.37	16,402.65	0	23,633.02

. The total energy consumption of the library and exhibition hall are 40,651.38 kWh and 23,633.02 kWh, respectively. The energy consumption of air conditioning in the library is relatively high, followed by lighting energy consumption. The lighting energy consumption of the exhibition hall accounts for a relatively large proportion, followed by air conditioning energy consumption, which relates to the building’s function and the number of hours personnel use.

The annual carbon emissions during the operation of the library exhibition hall are shown in

Table 12. Annual carbon emissions from the operation of library and exhibition hall.

Building	Air Conditioning Carbon Emissions (tCO2)	Lighting Carbon Emissions (tCO2)	Domestic Hot Water Carbon Emissions (tCO2)	Total Carbon Emissions (tCO2)
Library	14.15	6.83	0.35	21.32
Exhibition hall	3.79	8.60	0	12.40

. The total carbon emissions of the library and exhibition hall are 21.32 t and 12.40 t, respectively. Figure 9 shows the annual carbon emission distribution ratio of the operation library and exhibition hall. The total carbon emissions of the library are higher than those of the exhibition hall, with 63.26% and 36.74%, respectively. The highest carbon emissions come from library air conditioning, exhibition hall lighting, and library lighting, accounting for 41.96%, 25.50%, and 20.26%, respectively.

The annual energy consumption and carbon emission of the building operation are summarized in

Table 13. Summary of annual operating energy consumption and carbon emissions of the library and exhibition hall.

Building	Total Energy Consumption (kWh)	Energy Consumption per Unit Area (kWh/m2)	Total Carbon Emissions (tCO2)	Carbon Emissions per Unit Area (kgCO2/m2)	Proportion (%)
Library	40,651.38	42.35	21.32	22.21	63.23
Exhibition hall	23,633.02	41.71	12.40	21.89	36.77
Total	64,284.4	84.06	33.72	44.10	/

, with a total energy consumption of 64,284.4 kWh and total carbon emissions of 33.72 t. Energy consumption was effectively reduced by improving the energy efficiency of the building envelope and air conditioning equipment. Simultaneously, intelligent control energy-saving measures were implemented for the main energy-consuming equipment, such as intelligently controlling the operating parameters of the air conditioning without manual intervention, scientifically and accurately controlling the air conditioning operation, and significantly reducing air conditioning energy consumption.

The energy consumption values per unit area of the library and exhibition halls were similar, and the carbon emissions per unit area were identical. Scholars analyzed the data from China’s building sample database, obtaining the carbon emission intensity of different building types in the operation and maintenance phase [44]. Carbon emissions per unit area during the operation of ordinary buildings, green buildings, and “Impression of Yucun” were 40.2 kg.CO₂/(m²·a), 23.9 kg.CO₂/(m²·a), and 22.05 kg.CO₂/(m²·a), respectively. It shows that green buildings save 40.5% more energy than ordinary buildings, and carbon-neutral buildings save 45.15% and 7.74% more energy than ordinary buildings and green buildings, respectively.

As the energy efficiency level of buildings increases, the carbon emission intensity during the operation phase of buildings progressively decreases. This is primarily attributed to the utilization of high-performance enclosures such as thermal insulation materials, thermal insulation doors and windows, and recyclable materials such as green building materials in the design of green and carbon-neutral buildings. These provisions and using renewable energy and ecological carbon sinks significantly reduce carbon emissions during the building operation phase.

3.2. Analysis of Carbon Offsetting Measures of the Life Cycle for Buildings

3.2.1. Analysis of Emission Reductions Using Carbon Offsetting Measures

The photovoltaic system in this study is estimated to generate 118,755.25 kWh annually, with 42,638 kWh generated by the library and 23,685.18 kWh generated by the exhibition hall, offsetting 62.30 tCO₂ per year. Through DC power supply and distribution, the study’s solar photovoltaic power generation system provides electricity for a load of DC air conditioners and other equipment in the exhibition hall. The energy-saving system intelligently controls the air conditioning, and excess electricity is locally stored and connected to the grid. This design’s photovoltaic power generation capacity can fully meet the internal electricity consumption of the library and exhibition hall, thereby achieving 100% green electricity and zero carbon emissions in total.

Using green building materials to replace corresponding traditional materials can reduce carbon emissions by 3.34 tCO₂ per year during building operation and maintenance.

3.2.2. Carbon Neutrality Analysis of Buildings

The design life of the public buildings in this study is 50 years, during which the carbon neutrality plan of the buildings will be continuously implemented. Based on the calculations in Section 3.1, the operational carbon emissions are 33.72 tCO₂ per year, and the implicit carbon emissions throughout the life cycle of the building amount to 120.91 tCO₂. According to the calculations in Section 3.2.1, this case can reduce carbon emissions by 65.64 tCO₂ per year through photovoltaic power generation and utilizing green building materials. However, considering the attenuation of photovoltaic cells, with a rate of 2% in the first year and not more than 0.5% annually after that, the annual net carbon emissions data can be obtained by substituting the above equation. Figure 10 shows the carbon footprint of the building’s carbon neutrality plan for the first five years. In the building’s fifth year of operation, the project can reach carbon neutrality for the first time, with net carbon emissions of −5.58 tCO₂. Until the end of the building’s use, buildings will continue to operate with zero or negative carbon emissions, maintaining carbon neutrality.

This study’s buildings reduced energy consumption during construction and operation using recyclable materials. They improve the energy-saving efficiency of enclosures and air conditioning units, thereby decreasing implicit and operational carbon emissions. The buildings’ carbon reduction capacity is enhanced using renewable energy photovoltaic power generation and energy storage systems. These buildings can offset their carbon emissions, maintaining zero or even negative carbon emissions after reaching the carbon-neutral state. Hence, there is no need for these buildings to purchase carbon emission offsets from outside sources, as they can directly meet the requirements of building carbon neutrality.

3.3. Analysis of Building Economic Benefits

The total investment for the “Impression of Yucun” project is 14.3029 million yuan. Compared to conventional buildings that meet the requirements of current relevant standards, including local standards, the additional cost of using carbon reduction technology is 2.0488 million yuan, and the incremental cost is 1262.51 yuan/m².

Table 14. The incremental cost of three-star technical measures for carbon neutrality buildings.

Category		Carbon Neutrality Technical Measures	Unit-Price	General Building Technology	Unit-Price	Usage	Incremental Cost (Million)
1	Passive technology	Roof energy-saving improvement	1300 yuan/m3	Ordinary roof	400 yuan/m3	56.22 m3	5.06
2		Energy-saving improvement of exterior walls	1300 yuan/m3	Ordinary exterior wall	400 yuan/m3	79.27 m3	7.13
3		Energy-saving improvement of external windows	285 yuan/m2	Ordinary exterior window	260 yuan/m3	745.6 m2	1.86
4		Active sunshade	400 yuan/m2	--	0	352.79 m2	14.11
5		Light guide tube	yuan/piece	--	0	4 piece	4.00
6		Unpowered hood	160 yuan/piece	--	0	4 piece	0.06
7		Ceiling fan	400 yuan/piece	--	0	4 piece	0.16
8	Equipment energy efficiency improvement	High energy efficiency air-cooled heat pump unit	100 yuan/kW	Level 3 energy-efficient air conditioning	50 yuan/kW	188.4 KW	0.94
9		Energy-efficient multi-line system	100 yuan/kW		50 yuan/kW	121.8 KW	0.61
10	Photovoltaic equipment	Roof monocrystalline silicon photovoltaic power generation system	40.94	--	0	1 set	40.94
11		Optimize energy storage and flexible distribution	70	--	0	1 set	70
12	Intelligent control	Unmanned intelligent control platform	--			--	60
Total incremental cost (million)							204.88
Total building area (m2)							1622.80
Incremental cost per unit area (yuan/m2)							1262.51

lists the incremental measures and cost details.

After an energy consumption simulation analysis, the annual power consumption of the building is 64,284.4 kWh, and the annual power generation of the solar photovoltaic system is 118,755.25 kWh. The photovoltaic power generation system can fully offset the building’s electricity consumption. The renewable energy replacement rate reached 184.73%, enabling the buildings to achieve zero carbon operation. The total investment cost of the PEDF system is approximately 1 million yuan.

Energy storage systems such as batteries can store excess electricity generated by the photovoltaics on-site, becoming a flexible and adjustable node that interacts with the utility and helps realize peak filling. Through an intelligent platform system to optimize power regulation, when the peak electricity price is 1.2064 yuan/kWh, the photovoltaic power generation investment payback period is approximately seven years, saving an annual operating cost of 143,266.33 yuan, and the cost-efficiency ratio is 14.33%. When the peak electricity price is 0.9014 yuan/kWh, the payback period for photovoltaic power generation is nine years, saving an annual operating cost of 107,045.98 yuan, and the cost-efficiency ratio reaches 10.70%. Although the one-time investment is relatively large, considering the system’s expected life of 25 years, the system has good economic benefits and considerable promotion potential.

The PEDF system can realize the regulation function of the microgrid: (1) the excess electricity generated by the photovoltaic system is locally stored, becoming a flexible and adjustable node; (2) when the photovoltaic power is insufficient due to weather, sunlight, and other reasons, compensation electricity is provided for the buildings through the discharge of energy storage batteries; (3) the system interacts with the municipal power grid. Surplus photovoltaic power generation is transmitted to the grid through a grid connection and used for peak filling to save electricity costs. At the same time, energy storage systems can be used for demand response, transformer expansion, and emergency power supply. Energy storage systems can effectively achieve demand-side management, fully utilize peak-valley electricity prices during the day and night and in different seasons, reasonably allocate them, eliminate the difference between peak-valley prices during the day and night, balance customer load, and reduce customer costs.

3.4. Realization Path of Rural Carbon Neutrality Buildings

Rural buildings possess inherent advantages when utilizing solar photovoltaic systems and PEDF systems. These advantages can mitigate power quality issues that arise from large-scale grid connections, alleviate the pressure of grid expansion, reduce line losses, and enhance the reliability of power supply, while also improving energy utilization efficiency.

In addition, potential carbon-neutral technological pathways can be considered in phases throughout the life cycle of a building.

Table 15. Implementation path of building carbon neutrality.

Phase	Classification	Specific Path
Production phase	Decarbonization of traditional building materials	Optimize process flow, raw material substitution, CCUS technology
	Application of low-carbon building materials	Natural wood, low-carbon concrete, new carbon fixing materials
	Decarbonization of building materials transportation	Transportation electrification and new energy substitution
Construction phase	Intelligent construction	Comprehensive application of BIM, technology, robot replacement
	Prefabricated technology	Steel structure, PC structure, and wooden structure
	“Four Sections and One Environmental Protection”	Energy saving, land saving, material saving, water saving, and environmental protection
Operation phase	Low carbon design of buildings	Passive design
	Renewable energy utilization	Building photovoltaic integration, geothermal energy, wind energy
	Building energy efficiency improvement	Energy efficiency improvement of lighting and air conditioning equipment, energy system management
Demolition phase	Building recycling	Research on recycled materials, industrialization of construction waste
	Optimization of the demolition plan	Disassembly method and technology

indicates that traditional building materials are decarbonized in the production phase while green building materials are introduced. During the construction phase, the promotion of prefabricated construction and the application of digital technology are encouraged. In the operational phase, striving for energy substitution, electrification, and improving energy efficiency is essential. Finally, it is crucial to enhance the demolition plan and optimize the recycling and use of building materials in the demolition phase.

Taking the first rural carbon-neutral building in China, “Impression of Yucun”, as an example, the following pathways can be identified to enhance rural buildings’ green and low-carbon development.

(1) Improving the level of building energy-saving design

With respect to energy-saving design, full consideration should be considered to the natural ventilation of buildings, reinforced air convection, reduced usage of air conditioning and other equipment, and maximized use of renewable energies such as solar, wind, geothermal, hydro, and bio energies. Likewise, selecting renewable materials with low energy consumption and minimal pollution should be prioritized.

The vigorous promotion of photovoltaic power generation in buildings, combined with the adoption of a distributed photovoltaic power grid connection system in conjunction with building electricity, can help to avoid energy loss caused by the transmission process. This can also reduce building electricity consumption, foster self-production and self-use, and hasten the achievement of zero carbonization in buildings.

(2) Realizing low-carbon construction of buildings

The Rural single buildings, which are relatively dispersed and involve less construction work, are not conducive to management. In order to ensure energy saving and emission reduction, the construction phase must adhere to methods characterized by low energy consumption, low emissions, and low pollution. Low carbon design of rural buildings should emphasize resource conservation, building material conservation, selection of local materials, and using green building materials to reduce resource consumption during production and transportation.

(3) Improve ecological carbon sequestration and sequestration capacity

By fully considering the carbon sequestration capacity of plants and selecting native plants with short growth cycles, harmful environmental substances such as carbon dioxide and sulfur dioxide can be reduced in the region. This can purify the air, soil, and water and maximize the carbon sequestration capacity of green plants.

4. Conclusions

To evaluate the emission reduction potential of various carbon neutrality technology combinations in rural buildings, this study analyzes China’s first rural carbon-neutral building in terms of its life cycle carbon emissions and carbon offset measures. It also evaluates the economic benefits of carbon neutrality technology. The following conclusions can be drawn:

(1)

The implicit carbon emissions of buildings were 120.91 t, with the carbon emissions of the building materials production phase accounting for the highest proportion at 63.57%. The energy consumption during the operational phase of the building was 64,284.4 kWh/year, corresponding to 33.72 tCO₂. The carbon emissions from library air conditioning accounted for the highest percentage, at 41.96%.

(2)

By applying carbon offset measures, including light storage, PEDF, and green building materials, the building can achieve carbon neutrality by the fifth year of operation, with a net total of −5.58 tCO₂ by the end of its use.

(3)

When the peak electricity price of buildings was 1.2064 yuan/kWh, the payback period for photovoltaic power generation was about seven years. When the peak electricity price was 0.9014 yuan/kWh, the payback period for photovoltaic power generation investment was nine years. The cost-effectiveness ratios of the two scenarios reached 14.33% and 10.70%, respectively, and the annual operating costs saved were 143,266.33 yuan and 10,704,598 yuan, respectively, indicating significant economic benefits.

(4)

This study assesses the carbon reduction potential of combining multiple carbon-neutral technologies by calculating the carbon emissions of buildings throughout their life cycle. It provides a valuable reference for the design of rural carbon-neutral buildings. The potential for promoting carbon-neutral buildings in rural areas of China is demonstrated through the analysis of the economic benefits of carbon-neutral buildings. However, since this research only considered specific carbon offset measures, further evaluation will be needed in the future. This should include examining the carbon emission characteristics of carbon-neutral buildings over a longer life cycle.