Carbon emission reduction in the construction industry and the coordinated development of the building materials industry

The construction industry is one of the world's largest final energy consumers and greenhouse gas emitters.

According to the 2021 Annual Development Research Report on Building Energy Efficiency in China, in 2019, the construction energy consumption and building operation energy consumption of the construction industry were 1.4 billion tons and 1.02 billion tons of standard coal, accounting for about 29% and 21% of the country's total energy consumption, respectively, and the carbon dioxide emissions of the entire construction industry chain were about 5 billion tons, accounting for more than 50% of the national emissions. It can be seen that the low-carbon transformation of the construction sector is crucial for China to achieve the "dual carbon" goal, and it is also very important for the world to achieve net zero emissions.

China has announced the "1+N" policy system for carbon peak and carbon neutrality, but the obstacles and paths for China's construction industry to achieve carbon peak and carbon neutrality have not been fully studied.

Why the construction industry should be zero-carbon

The fundamental goal of the construction industry to achieve zero carbon is to change the energy structure from the current fossil energy to renewable energy, with the actual purpose of not only mitigating climate change, but also achieving sustainable development. By solving the problem of energy security, that is, from relying on imported foreign oil and gas to using domestic space resources such as wind and solar, and by solving the problem of air pollution, that is, from deep purification to eliminating pollution sources, the pollution problem will be completely solved. The ensuing energy revolution is a more profound change, which will comprehensively change the whole process of energy production, conversion, transmission and terminal application.

Construction-related carbon emissions include the production of building materials, the construction, maintenance and demolition of works, and the operation of buildings. A large number of building materials are required for new construction, renovation and maintenance of construction projects, and the carbon emissions in the production process of building materials account for about 25% of the carbon emissions of China's industrial production. Saving the amount of building materials, recycling waste building materials products and developing new low-carbon and zero-carbon building materials are the work that needs to be carried out at present, and the impact of the change of building materials on the building structure system and the impact of the change of the building structure system on the building form also play an important role.

How to reduce carbon emissions in the operation of construction projects

There are direct emissions from the combustion of fossil fuels, indirect emissions from input electricity, and indirect emissions from external heating during the operation of construction projects. The building energy revolution with the goal of zero carbon is to completely eliminate the use of fossil energy in construction projects and fully realize the electrification based on green electricity. The construction project has changed from a simple power consumption end to a trinity of "production, storage and consumption", thereby helping the development of zero-carbon power. Through the energy-saving design of new buildings and the energy-saving renovation of existing buildings, the unity of energy-saving demand and the pursuit of a better life is realized.

The realization of electrification must rely on the development of new energy, including the increase in the proportion of wind power and photovoltaic power generation in future energy, which requires more than 100 million acres of installation space, and also solves the problem of power generation and electricity consumption space and time are not synchronized. Construction works are a bridge between charging piles and power grids, and the charging and consumption of new energy vehicles contribute to energy storage and peak shaving. On the other hand, the terminal energy unit changes from the traditional rigid load to the new flexible load, which also helps the regulation of the power system.

How to provide an energy supply system for a building

The energy supply is aimed at zero carbon, including electricity, heat and charging piles, the performance transformation of existing buildings and the transformation of mechanical and electrical systems, and the requirements of new buildings to achieve zero carbon. The specific contents are: the transformation with the goal of installing and absorbing photovoltaic power, that is, the full implementation of photovoltaic in urban and rural buildings; the construction of community charging pile system to adapt to the development of new energy vehicles, that is, the synchronous construction of new charging systems; the full realization of a new heating system with the goal of zero carbon heat source; the thermal insulation transformation of the existing building envelope to reduce the heat demand for old buildings in the northern region; scientific planning, We will improve the efficiency of urban building electromechanical systems and transform power distribution, optical, storage, direct and flexible buildings, and plan to make 60 billion square meters of existing buildings and 10 billion square meters of new buildings in the future zero-carbon.

Carbon emission accounting methods in the building sector

The calculation and accounting of building carbon emissions is a rigid demand for the construction industry to achieve the goal of carbon peak and carbon neutrality. With the gradual refinement of energy conservation and carbon reduction, discussions on future building energy consumption quota management, energy efficiency labeling, carbon trading and green finance have attracted extensive attention from the government and relevant institutions, and the importance of building carbon emission calculation will become more and more prominent.

The national standard "Calculation of Carbon Emissions from Buildings" GB 51366 proposes three stages of carbon emission calculation for building materials, including the production and transportation stage, the construction and demolition stage and the operation stage, and standardizes the calculation scope and method of carbon emissions from the whole life cycle of buildings.

In addition, the national standard GB 55015 puts forward specific requirements and performance indicators for energy-saving design, energy-saving renovation and renewable energy application.

However, the dynamic changes in China's emission reduction process and population and economic development will bring challenges to the carbon budget calculation of the construction industry, and the complex changes in the connotative carbon of buildings will also bring technical challenges to the carbon budget calculation.

At present, the calculation and accounting of building carbon emissions are divided into narrow and broad senses. In the narrow sense, the carbon emissions of building operations refer to the carbon emissions of building operations. In a broad sense, carbon emissions from building operations usually refer to carbon emissions throughout the life cycle, involving the production and construction process of building materials, as well as building operation, maintenance, demolition, recycling and other links.

Some experts believe that there are generally two goals for calculating carbon emissions, one is to calculate whether a single project, park project or new technology has really reduced emissions, which requires the calculation of carbon emissions throughout the life cycle of buildings. Another goal is to determine how much carbon emissions are per year to meet the needs of carbon trading and carbon management, which only needs to calculate the carbon emissions caused by the actual operation of the building. In addition, the existing carbon emission accounting system cannot reflect the differences of carbon emission factors at different times of the year and within the day, and in the context of the application of a large proportion of renewable energy, the key issue is to give hourly carbon emission factors, dynamically calculate the annual hourly carbon emissions and carbon emission responsibilities, and evaluate the positive role of building energy storage and regulation in matching supply and demand in the power system.

It should be pointed out that although GB 51366 puts forward the general provisions for the calculation of carbon emissions from building materials production, it is not accurate and perfect, and the suggested standard can refer to the carbon dioxide emission calculation standards of various building materials products formulated by the building materials industry in order to calculate the carbon emissions of the construction sector and solve the basic problems of low-carbon development of the construction industry.

Building scale and carbon emissions

The total amount of urban housing construction and per capita occupancy in China continue to increase with social and economic development. According to the statistics of 12 large cities, the per capita construction area is between 45~70 square meters / person, and the average is 56 square meters / person, which is still at a low level compared with developed countries. According to the calculation of the development volume ratio of urban construction land, the per capita construction area can reach 70~100 square meters per person in the future.

Investment in housing and infrastructure as a high percentage of GDP has been an important driver of GDP growth for many years. On the one hand, it is necessary to prevent the blind growth of housing supply, and avoid the urban development mode of "large-scale demolition and large-scale construction", which causes existing buildings to be underutilized, short building lifespans, and a large amount of resource consumption and carbon emissions caused by demolition and construction; on the other hand, it is necessary to improve the residential attributes of housing, reduce the investment attributes of housing value preservation, and make the total supply and holding of housing basically equal to the actual demand. With the transformation of urban economic structure and the deepening of economic system reform, the urban growth model will inevitably shift from infrastructure investment-oriented to residential consumption-oriented, and the total amount of urban buildings and per capita ownership level will inevitably remain at a relatively reasonable level.

In the "second half" of urbanization, there has been an increasing number of inter-city migrations, especially the migration of middle-income groups, well-educated talents and families from small and medium-sized cities to central cities, creating new housing demand in large cities, and then making housing in small and medium-sized cities partially idle. Urbanization population flow is a multiple, multi-directional and multi-directional flow process, which will continue to affect the relationship between housing demand and supply.

The process of urbanization has brought three major challenges to the peak of carbon dioxide emissions in buildings: one is the urbanization process and the risk of carbon lock-in in buildings, the second is the unbalanced development of urbanization and the cascade peak of carbon emissions in provincial buildings, and the third is the spatio-temporal mismatch of housing supply and demand and the waste of carbon emissions. Considering the stage of urbanization, we should promote the peak of carbon emissions of provincial buildings in an orderly manner. There are huge differences in the urbanization development of different provinces and cities in China, with the lowest urbanization rate of less than 40% and the highest urbanization rate exceeding 80%. Therefore, when formulating the provincial building carbon peak target, we should fully consider the stage of urbanization, avoid "one size fits all", achieve upper and lower linkage, and orderly promote the peak of carbon emissions in various regions under the premise of ensuring the peak time and peak target of carbon emissions in the national construction sector.

Green construction and low-carbon building materials

Green construction is a construction concept proposed by China's construction engineering industry in the context of "sustainable development", "circular economy" and "low-carbon economy". Green construction refers to the construction activities that focus on the whole life cycle of the building in accordance with the requirements of green development, through scientific management and technological innovation, and adopt construction methods that are conducive to saving resources, protecting the environment, reducing emissions, improving efficiency and ensuring quality, so as to realize the harmonious coexistence of man and nature.

From the perspective of the whole process of engineering construction, the construction stage includes planning, design, procurement, production and construction, and has the right to decide the choice of building materials supply chain. From the perspective of the whole life cycle, the concept of green and low-carbon development runs through the whole process of engineering construction and the upstream and downstream industrial chain, a large number of new green construction methods are adopted, green building materials are fully adopted, and near-zero energy buildings are vigorously promoted, and the on-site emissions of construction waste are greatly reduced, and the final emissions are greatly reduced, so as to realize the green and low-carbon development of the whole industrial chain of engineering construction.

Building materials products mainly include cement and concrete. The cement industry is a major emitter of carbon dioxide, which is determined by the characteristics of cement production and application. Cement production and preparation processes have electricity consumption, the indirect carbon dioxide emissions produced are about 60 kg/ton of cement; cement clinker calcination is usually burned with coal, and the direct carbon dioxide emissions produced are about 170 kg/ton of clinker; the main raw material for cement clinker production is limestone, which will decompose and release a large amount of carbon dioxide after high temperature calcination, that is, the carbon dioxide emissions in the production process are about 300 kg/ton of cement.

Carbon emission reduction in the construction process and building application is directly related to cement production and varieties, and the implementation path of "zero-carbon buildings" should be analyzed from the whole life cycle, and the carbon adsorption function of cement-based materials in construction projects should also be analyzed, and the carbonization and transformation trend of cement-based materials should be predicted.

The analysis shows that the carbon emissions of China's construction industry exceed half of the country's total emissions, and the carbon emissions of cement and concrete structure construction alone account for as much as 20%. Therefore, promoting the low-carbon development of cement and concrete materials, tapping the low-carbon potential of concrete, and vigorously developing recycled concrete have become the key tasks to achieve the goal of carbon neutrality in buildings.

Zero-carbon operation of the building

On the basis of the whole life cycle of buildings, zero-carbon buildings with zero comprehensive carbon emissions have gradually become an important means for the construction industry to achieve green and sustainable development. This requires the reduction of carbon emissions to be taken into account at the engineering design stage, and the construction of new zero-carbon buildings to reduce carbon emissions at the source. For new buildings, it is necessary to control the use of materials during the construction stage, and high-quality and long-life building materials should be selected to promote the recycling and utilization of building materials and reduce resource waste.

In terms of structure selection, a light structure that can be assembled and modularized should be selected, redundant decoration should be removed, and standardized production should be promoted to reduce construction pollution, improve labor efficiency, and reduce energy consumption. During the construction phase, it is also necessary to control the energy demand of the building itself. In the interior of the building, an efficient, low-carbon, and intelligent operation and maintenance management model should be created, and the green and low-carbon management of the whole life cycle of the building should be realized by intelligent means.

While controlling the use of materials and energy, we should also control the carbon emissions of buildings. It is necessary to promote the construction of urban forests and urban agriculture, and increase the amount of green construction land.

In the process of realizing the zero-carbon operation of buildings, the innovative application of digital technology should be fully carried out. Artificial intelligence and big data technologies are important measures to implement building carbon reduction plans, from real-time optimization of design, development and construction plans by combining digital means in the design stage, to adopting smart management platforms in the building construction process, and planning carbon reduction strategies through real-time collection of carbon emission data during operation.

Zero-carbon energy supply system

The zero-carbon path of buildings is centered on energy conservation, through the full realization of green electrification, no longer using fossil fuels, and at the same time to achieve zero-carbon electricity supply and heating system, which is also the goal of the future urban energy supply system. It is estimated that by 2060, China's power generation capacity will reach 13 trillion kWh, and new energy power generation can reach 11.5 trillion kWh, while coal-fired power generation will only reach 0.5 trillion kWh, about 3.85% of the total power generation, which is only used for peak shaving of the power system.

The energy consumption of urban buildings should first consider the installation space of wind power and photovoltaics. It is preliminarily estimated that 870 million kW photovoltaic power generation systems can be installed on the roofs of urban buildings in China, with an annual power generation of 1 trillion kWh, which can provide a quarter of the electricity consumption of buildings. The zero-carbon power system of the future is a building that integrates the functions of power generation, consumption, storage and regulation.

In addition, China's rural areas have ample roof area that can be converted into huge photovoltaic power generation potential. According to preliminary estimates, 2 billion kW of rooftop PV can be installed in rural areas, with an annual power generation capacity of 2.5 trillion kWh. Through a large number of rural surveys, it is found that the annual electricity consumption of rural households generally does not exceed 3000kWh, and some even less than 500kWh. Therefore, the potential of photovoltaic power generation in rural areas is far greater than its own electricity demand, and it is possible to achieve real self-consumption and surplus electricity grid through reasonable allocation, so that the whole village can become a green power plant.

The building materials industry is not only an important industrial category of the country's social economy, but also an indispensable foundation for the construction industry. While achieving the "double carbon" goal, the building materials industry needs to support the carbon emission reduction of the construction industry, which requires research and development of more new low-carbon building materials based on the low-carbon development needs of the construction industry, so as to promote the green, low-carbon and sustainable development of the building materials industry.