Selected Articles | Research on Energy-Saving and Carbon Reduction Technical Paths for Near-Zero Energy Consumption Public Buildings

Research on Energy-Saving and Carbon Reduction Technical Paths for Near-Zero Energy Consumption Public Buildings

——Taking the Office Building of a Logistics Support Housing Project as an Example

Zhang Jianhui, Shi Guangchao, Ni Xin,

Liu Da, Zhao Jie, Bi Wenbei

Citation format: Zhang Jianhui, Shi Guangchao, Ni Xin, et al. Research on Energy-Saving and Carbon Reduction Technical Paths for Near-Zero Energy Consumption Public Buildings: Taking the Office Building of a Logistics Support Housing Project as an Example [J]. Green Building, 2024, 16(6): 83-91.

 

Abstract:

Promoting buildings towards near-zero energy consumption has become one of the important paths for the development of the building sector under the "dual carbon" goals. Based on the characteristics of high operating costs and high energy consumption of airport office buildings, taking the office building of a logistics support housing project at Xi'an Airport as an example, starting from the design concept and technical system of near-zero energy consumption buildings, through passive building design, active energy-saving technologies, and renewable energy carbon reduction, the annual operating energy consumption, energy saving rate, and renewable energy utilization rate are simulated and analyzed, thus contributing to the energy-saving and carbon reduction design and technical path research of near-zero energy consumption office buildings at airports in cold regions.

Keywords:

Near-zero energy consumption; Office building; Energy saving and carbon reduction; Technical path

0 Introduction

 

The high emissions and high energy consumption of the building sector have attracted much attention. In 2020, the total energy consumption of the entire building process in China was 2.27 billion tce, accounting for 45.5% of the national total energy consumption; the total carbon emissions were 5.08 billion tCO ₂ ，accounting for 50.9% of the national carbon emissions. The existing stock of public buildings in China has grown rapidly, from approximately 3.8 billion m ² in 2001 to approximately 14 billion m ^{in 2020 [1-4].} Currently, office buildings are the most widely distributed and highest proportion among public buildings, accounting for 34% in 2020. Traditional office buildings are characterized by high energy consumption in artificial lighting and air conditioning, and long usage times ^[5-7] ，and their location, building layout, external envelope insulation, energy efficiency of energy-using equipment, and post-operation management model all directly affect energy consumption and carbon emissions. Therefore, under the premise of meeting different functional needs, near-zero energy consumption buildings have significant energy-saving and carbon reduction effects in the operation stage, can maximize the efficiency of building energy use and reduce building operation carbon emissions, and fully tap the energy-saving and carbon reduction potential of office buildings.

As a large-scale transportation facility, the airport is a cluster of buildings that integrate aviation operations, production support, and life service facilities. Dense personnel flow, large scale of building groups, and high energy demand standards are the significant characteristics of airport buildings. Taking the office building of the logistics support housing project at Xi'an Airport as an example, this paper uses a design method guided by near-zero energy consumption building energy efficiency indicators, based on the climate conditions of the cold region where it is located, combining building energy consumption simulation analysis and carbon emission calculation methods, using passive building design to improve intrinsic energy saving, active energy-saving technologies to reduce energy consumption, and renewable energy utilization to reduce operational carbon emissions ^[8] ，to achieve energy saving and carbon reduction of the project, and propose a technical path suitable for energy saving and carbon reduction of airport office buildings in cold regions.

1 Project Overview

 

The project is located within the land of Xi'an Xianyang International Airport, approximately 1.2 km from T3 terminal. The project covers an area of 15,811 m ² . The office building is a reinforced concrete frame structure with a total construction area of 13,746 m ² ，7 stories above ground, and a building height of 41.35 m. The building has a 2-story outdoor terrace near the main entrance on the first floor, creating an entrance gray space. This design not only provides passengers with additional leisure and communication space, but also enhances the functionality and visual appeal of the building through its combination with the company showroom and atrium. In addition, the northwest side of the building is equipped with a staff kitchen to meet the daily needs of employees. On the 2nd and 3rd floors of the building, open-plan office spaces are designed to promote communication and collaboration among employees. Floors 4 to 7 have open-plan and independent offices to meet different office needs and adapt to the needs of employees with different job natures. To further improve the indoor environment and office quality of the building, two-story-high gardens are designed in the corners of every two floors. These gardens not only help to improve the microclimate of the building, but also provide employees with visual comfort and psychological relaxation, thus improving the overall office experience. The project team comprehensively considers functionality, comfort and aesthetics, aiming to create an efficient, healthy and attractive office space. The exterior and interior design renderings are shown in Figure 1.

The design team first used the energy efficiency indicators for near-zero energy consumption public buildings in cold regions from the national standard GB/T 51350—2019 "Technical Standard for Near-Zero Energy Consumption Buildings" ^[9] as a basis, and effectively controlled the building's heat exchange by optimizing the building's shape factor and window-wall ratio; second, high-performance envelope materials were used, combined with cold and hot bridge elimination design in key parts, to further improve the building's insulation and heat insulation performance; in addition, the application of external shading and passive windows helps to reduce the impact of solar radiation on the indoor thermal environment, while reducing the building's energy consumption while ensuring indoor comfort; to further reduce the energy consumption of air conditioning and heating systems, the design team designed a regional energy station, using medium and deep geothermal resources, combined with variable frequency centrifugal refrigeration air conditioning units and full heat recovery fresh air units, to achieve efficient energy utilization and a significant reduction in energy consumption; the use of rooftop solar photovoltaic power generation systems improves the building's renewable energy utilization rate, ultimately achieving the design goal of near-zero energy consumption office buildings. The technical measures adopted in this project are shown in Figure 2.

2 Passive Building Design

 

2.1 Layout and Shape Design

The project site is triangular, with a height difference of about 5 m between the north side and the airport's west entrance road, and is level with the existing airport's west cargo area on the south side. The project uses a building design that adapts to the local climate. The overall layout uses the terrain to form a height difference space between the north and south squares, as shown in Figure 3. A double-first-floor office is designed according to the height difference of the surrounding roads, taking into account the harmony and unity of the layout and the overall form of the building.

In terms of building shape and facade design, the shape coefficient is minimized as much as possible, the building's external enclosure area is reduced, and unnecessary concavities and convexities are avoided. The building shape coefficient of the office building is 0.14, which is less than the s ≤ 0.40 stipulated for the shape coefficient in cold regions, as shown in Table 1.

While ensuring sufficient natural daylighting in the building's interior, the window-wall ratio is strictly controlled. Increasing the area of the south-facing transparent enclosure structure is beneficial for winter solar heat gain. The window-wall ratios of the east, south, west, and north sides of the office building are 0.29, 0.45, 0.27, and 0.29, respectively. After multiple load and energy consumption analyses, the window-wall ratios of each orientation do not exceed 0.5, ensuring that excessive external window glass area does not increase energy consumption. The window-wall area of the building is shown in Table 2.

2.2 Indoor and outdoor wind environment optimization and natural daylighting utilization

This project maximizes the use of natural ventilation to improve the indoor and outdoor environmental comfort of the building. Therefore, in areas with high pedestrian traffic, the wind pressure on the outer window surface during the transitional seasons is utilized, and the openable area of external windows is increased to enhance natural ventilation in the main office areas, improving indoor air quality and comfort. To achieve a good indoor wind environment and window ventilation effect, sufficient wind pressure difference is needed on the outer window surface, i.e., the absolute value of the wind pressure on the outer surface of the external window must be greater than 0.5 Pa in the closed window state. In addition, the location of the building must effectively avoid the dominant wind direction in winter to reduce heat penetration losses in the building enclosure structure. ^[10] The outdoor wind environment simulation of the project site is based on the following several working conditions, and the outdoor wind environment of the building is optimized, as shown in Table 3 and Figure 4.

The indoor floor plan of the office building fully considers natural ventilation. During the transitional seasons, combined with the wind pressure distribution diagram of the external window surface corresponding to the windward and leeward sides of the building, the positions of doors and windows are reasonably arranged to achieve comfortable indoor environmental conditions. The prevailing wind direction in summer is selected for densely populated areas, which have good natural ventilation in summer, reducing summer air conditioning energy consumption. The office building design includes an atrium, which forms a "chimney" effect with the main entrance, improving the indoor microclimate, as shown in Table 4 and Figure 5.

The project, through the design and utilization of buffer layers, reduces building energy consumption while creating a comfortable and pleasant internal working environment. In the office area, by increasing the window area, the utilization rate of natural light is improved, effectively reducing the energy consumption generated by office lighting, and simultaneously improving the visual comfort of the indoor environment. In the atrium area, a large-volume green vertical space is designed. This space not only provides abundant green landscape for the interior of the building, but also introduces sufficient natural light through skylights on the upper part, improving the skylight illuminance and evenness of the central area of the core tube. The percentage of all-natural daylighting time (DA) simulation analysis diagram for each floor of the building is shown in Figure 6 (DA values of the main lighting rooms of the office building, i.e., the proportion of time during which the calculated points on the work surface throughout the year exceed the minimum illuminance requirement of 450 lx).

2.3 Near-zero energy consumption enclosure structure energy-saving design

2.3.1 Energy saving of opaque enclosure structure

The thermal performance of the opaque enclosure structure is an important component of the building's performance, accounting for approximately 40% of the total building's heat transfer. The design team improves the building enclosure structure's insulation and heat insulation performance, reducing the building's heating and cooling loads, and effectively improving the building's climate adaptability. At the same time, using high-efficiency heating and cooling equipment indoors reduces the building's operating costs and creates a comfortable and efficient work and living environment for users. The thermal performance of the main enclosure structures meets the requirements of GB/T 51350-2019 for near-zero energy consumption public buildings in cold climates. Specific parameters are shown in Table 5.

2.3.2 Energy saving of transparent enclosure structure

The project's transparent enclosure structure uses a passive exterior window design. The outside of the window is equipped with an electric active exterior shading system to adapt to different lighting conditions. The curtain wall structure uses tempered double-glazed laminated glass on the outside and a three-pane, two-cavity aluminum-clad wood composite passive window on the inside. Specifically, 6 mm double silver Low-E glass is combined with a 12 mm air layer, and another layer of 6 mm glass is added to form a high-efficiency heat insulation system. Both the upper and lower ends of the external window glass have 100 mm wide local ventilation openings to ensure indoor and outdoor air exchange. An electric shading device is also designed in the middle of the double-layer window, which can be adjusted according to the actual needs of the room.

In terms of thermal performance, the heat transfer coefficient of the external window is 1.22 W/ (m ² ·K), and the solar heat gain coefficient (SHGC) is 0.26, which indicates that the window can effectively introduce outdoor radiant heat in winter, reducing indoor heating loads. Considering the shading needs in summer, through the adjustment of the electric shading system, the shading coefficient can reach more than 0.8, effectively providing heat insulation. In addition, the airtightness level of the external window is higher than grade 8, ensuring good airtight performance. The skylight uses a broken bridge aluminum alloy structure and is equipped with 6 mm double silver Low-E glass and a 9 mm air layer multilayer glass. Its solar heat gain coefficient is 0.29, and the overall heat transfer coefficient is 1.82. By adding external shading facilities, the shading coefficient of the skylight can also reach more than 0.8 to meet the shading needs in summer.

Considering the design of the external windows and skylights comprehensively, it is ensured that the comprehensive solar heat gain coefficient is not less than 0.45 in winter and not more than 0.30 in summer. This design not only effectively utilizes solar radiant heat gain in winter to reduce heating demand in office areas, but also avoids a significant increase in summer cooling loads through shading measures. Specific node structures of passive exterior windows and skylights are shown in Figure 7.

2.3.3 Key parts thermal bridge

In the design of near-zero energy consumption buildings, the thermal bridge problem at key parts of the enclosure structure is a key consideration factor, directly affecting building energy efficiency and indoor environmental comfort. This project draws on the experience of thermal bridge treatment in passive houses and adopts a series of measures to eliminate or weaken the thermal bridge effect, optimizing the building's insulation performance and energy-saving effect. The main insulation material of the exterior wall uses double-layer self-insulating masonry blocks, with a 60 mm thick rock wool strip sandwiched in the middle, effectively reducing the heat transfer coefficient and improving insulation performance. Thermal bridge anchors are used to avoid components that may cause thermal bridges, such as exterior wall fixing rails, keel, and brackets, ensuring the continuity and integrity of the insulation layer. In the parts where pipes pass through the exterior wall, sleeves are reserved, and sufficient insulation gaps are ensured to prevent heat transfer through the pipes, forming a thermal bridge. At the same time, indoor switches, sockets, and junction boxes and other electrical equipment are placed on the inner wall to avoid adverse effects on the exterior wall insulation performance. Some thermal bridge prevention node designs are shown in Figure 8.

2.3.4 Airtightness zoning design

This project's building air tightness follows the requirements of GB/T 51350-2019 regarding air tightness design and construction. It uses reasonable airtight partitioning based on different functional units and energy consumption of the building, and conducts specialized airtightness design; it adopts simple modeling and node design to reduce nodes that are difficult to handle in terms of airtightness; the location of the airtight layer is clearly marked in the building's design and construction drawings to ensure the airtight layer is continuous and encloses the entire external enclosure structure, as shown in Figure 9.

2.4 Building Sound Insulation Design

This project is adjacent to the airport flight area, and the building itself has high requirements for sound insulation and vibration reduction. To address this issue, the project's sound insulation and vibration reduction design meets or exceeds current sound insulation standards. Calculations are performed for each frequency band using relevant methods, and the final materials selected must ensure that each frequency band meets the sound insulation requirements while appropriately improving the sound insulation standards: Noise and vibration factors from electromechanical equipment indoors and underground are considered; sound insulation and noise reduction measures are adopted for the interior walls and ceilings of rooms containing vibrating and noise-generating electromechanical equipment; sound insulation and vibration reduction measures are implemented at the points where electromechanical equipment and pipelines connect to the main building structure (walls, beams, slabs, and columns); sound insulation measures are implemented for the floors adjacent to the main functional rooms, with sound insulation and vibration reduction pads laid on the floor slabs; sound insulation and noise reduction measures are adopted for the interior walls and ceilings of other rooms with noise requirements, such as meeting rooms and multi-functional halls.

3 Active Energy Saving and Emission Reduction

 

3.1 Energy-Saving Technologies for High-Efficiency Heating and Air Conditioning Systems

This project conducts optimal energy-saving design in terms of system efficiency and equipment efficiency for the heating, air conditioning, and fresh air systems. Summer cooling load 550 kW, cooling index 44.6 W/m ² ; winter heating load 404 kW, heating index 32.8 W/m ² . Air conditioning chilled (hot) water is centrally supplied by the energy station. The air conditioning system's hot and cold water is uniformly supplied by the energy station. The energy station uses a high-efficiency variable-frequency centrifugal chiller unit. A large temperature difference system is used in summer; in winter, the main heat source is utilizing medium-deep geothermal energy for winter air conditioning heating. The coefficient of performance (COP) of the selected chiller is 5.746, and the integrated partial load performance coefficient (IPLV) is 7.839, both meeting the relevant energy-saving standards.

Ventilation and air conditioning design is conducted based on building layout and functional characteristics. The office building uses air handling units with heat recovery, and the indoor fresh air flow organization is top-supply and top-return; high-efficiency, low-noise fans are selected, and the power consumption per unit air volume Ws value is less than 0.24; the winter and summer full-heat exchange efficiency of the heat recovery fresh air unit is 73%, and the PM of the fresh air unit _2.5 filtration efficiency is >95%, effectively reducing the energy consumption of the fresh air system.

3.2 Energy Saving in Lighting, Elevators, and Electrical Equipment

This project uses an intelligent lighting system. All selected lighting fixtures are high-efficiency, energy-saving LED lighting fixtures, using energy-saving controls. Rocker switches are used for zoned control in equipment rooms, and infrared time-delay sensors are used for control in public corridors, etc., to meet lighting energy-saving control requirements. The intelligent lighting system sets lighting for all areas to peak mode and normal mode, etc., through loop matching mode to achieve optimal control effects and save electricity. The lighting power density of the main rooms is below 70% of the target value of the current lighting energy-saving standards, as shown in Table 6.

The office building elevators are all machine-room-less elevators with programmed centralized control and group control functions. They automatically switch to energy-saving operation mode when there are no external calls and no preset instructions in the cabin for a period of time. All selected electrical products are low-energy-consumption products, with high efficiency and high power factor equipment selected. The substation uses low-loss, low-noise SCB13 energy-saving power transformers. Non-fire-protection equipment uses variable-frequency speed control motors to reduce the energy consumption of electromechanical equipment.

3.3 Intelligent System and Energy Consumption Monitoring Platform

This project develops and sets up a near-zero energy consumption building energy consumption monitoring and management platform to achieve comprehensive monitoring of the actual operating energy consumption of the office building. By collecting and recording various sub-item energy consumption data, electricity data, and floor-by-floor electricity data, the system can statistically analyze this data and store the analysis results in a central database. This data management strategy not only facilitates retrieval and viewing at any time but also provides a reference for subsequent equipment management and energy operation allocation.

The platform has the ability to operate continuously and stably for a long time and ensures that the collected data is saved for no less than 3 years. The system is designed with comprehensive metering functions, capable of classified metering of electricity, water, and heat energy consumption, and detailed metering of electricity consumption by item and floor. In addition, the application of this platform helps to optimize the allocation of internal building resources and improve energy efficiency through refined management. Overall, the implementation of the energy consumption monitoring and management platform significantly promotes the improvement of the intelligent level of building energy management and the achievement of energy conservation and emission reduction goals.

4 Renewable Energy Carbon Reduction

 

4.1 Rooftop Solar Photovoltaic Power Generation System

Combining the annual average daily solar radiation, building solar shading, rooftop equipment, etc., of the site where the office building is located, the office building and the building adjacent to the restaurant comprehensively consider the selection of photovoltaic components, the operation mode of the photovoltaic array, the fixed bracket, the flat layout, and the minimum distance between the components and the roof. High-efficiency single-sided monocrystalline silicon photovoltaic components are laid out flat along the roof vertically on the roof of the office building and the building adjacent to the restaurant, with a total installed capacity of 133.1 kWp, a total of 253 units, and a coverage area of approximately 641.3 m ² . According to calculations from professional photovoltaic system software, the annual theoretical power generation is approximately 141,600 kW·h. Compared with the building using traditional coal-fired power generation, the annual savings in standard coal and the total amount over 25 years are shown in Table 7.

4.2 Medium-Deep Geothermal Utilization System

This project uses a cascade utilization method with a high-efficiency and energy-saving heat pump unit for the medium-deep geothermal energy system of the regional energy station to provide heat sources for the office building's air conditioning and domestic hot water systems, as shown in Figure 10. Two medium-deep geothermal wells are drilled, one for extraction and one for injection, with a water extraction temperature of 75 ℃. The primary plate exchanger outlet water passes through the secondary plate exchanger to provide 60 ℃ hot water for the air conditioning system; if heat is insufficient, the secondary plate exchanger outlet water passes through the heat pump system to supplement heat for the air conditioning system; high-temperature geothermal water passes through the primary plate exchanger to provide heat for the domestic hot water system. This achieves cascade and full utilization of the heat of medium-deep geothermal water, greatly reducing the consumption of fossil fuels and ₂ CO2 emissions.

5 Energy Efficiency Indicators and Operational Carbon Reduction

 

Based on the above near-zero energy consumption technical measures, the project uses energy consumption simulation analysis software with a DOE kernel. By simulating the building's annual heating and cooling needs, lighting electricity consumption, and total primary energy consumption, it can be calculated that the energy consumption (electricity consumption) of the office building itself is 23.64 kW·h/(m ² ²), with a comprehensive energy saving rate of 65.95% and a renewable energy utilization rate of 43%. Unlike the proportion of energy consumption in conventional office buildings, the lighting system energy consumption accounts for the largest proportion of building energy consumption in near-zero energy consumption office buildings, followed by HVAC system energy consumption. Specific data is shown in Table 8.

Based on the near-zero energy consumption energy efficiency simulation results of the office building, and in accordance with the national standards GB/T 51366—2019 "Building Carbon Emission Calculation Standard" and GB 55015—2021 "Building Energy Efficiency and Renewable Energy Utilization Code" regarding the calculation of building operational carbon emissions, the carbon emission CEEB calculation is performed using CAD as a platform, and the building's operational carbon emission indicators are output: According to the electricity carbon emission factor of 0.581 kgCO ₂ ₂/(kW·h), the annual operating carbon emission intensity of the building is 9.19 kgCO ₂ ₂/(m ² ²), which is a 55.84% reduction based on the public building energy-saving design standards implemented in 2016, and a decrease of 11.62 kgCO ₂ ₂/(m ² ₂/(m²) in carbon emission intensity. Specific data is shown in Table 9.

6 Conclusion

 

This paper studies energy-saving and carbon-reduction technologies for near-zero energy consumption office buildings in cold regions. Compared with conventional office buildings, it comprehensively considers the regional climate characteristics and the unique environmental impact of the location. It makes the best use of low aspect ratios, reasonable window-wall ratios, building shading, and other passive design methods combined with near-zero energy consumption enclosure energy-saving technologies to significantly reduce the building's energy consumption; through active energy-saving and consumption-reducing measures, it improves the operating efficiency of HVAC, electrical lighting, and other equipment, reducing the building's comprehensive energy consumption; it fully explores the usable renewable resources in and around the building to reduce the use of traditional energy and achieve the goal of reducing building operational carbon emissions.

In addition, this paper optimizes the indoor and outdoor wind environment, natural lighting, and building sound insulation and noise reduction measures of the building. Combined with passive building design, active energy saving and consumption reduction, and near-zero energy consumption building technologies using renewable energy, it significantly improves the indoor environmental quality of the office and achieves energy saving and carbon reduction in office buildings. It provides technical support and reference cases in response to the "dual carbon" goals, aiming to promote the energy-saving and low-carbon development of office buildings in the cold regions of Northwest China.

 

References:

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Funding Project:

Shaanxi Provincial Construction Science and Technology Planning Project "Research on Building Carbon Measurement and Carbon Emission Reduction Technology in Representative Cities of Shaanxi Province" (2022-K56)

Author Introduction:

First Author:

Zhang Jianhui, Master's student, engineer, research direction is ultra-low energy consumption buildings and intelligent construction technology for airports, currently employed by Western Airport Group Co., Ltd.

Corresponding Author:

Shi Guangchao, Master's student, senior engineer, research direction is green building and near-zero energy consumption building, currently employed by China United Northwest Engineering Design and Research Institute Co., Ltd.