Study on natural ventilation strategy and technology of high-rise office buildings?

The definition of intelligent building given by the American Institute of Intelligent Building is: "Intelligent building is a building with high efficiency, high function and high comfort, which integrates structure, system, service, operation and their interrelationships and achieves the best combination." In the current national standard "Green Building Evaluation Standard", it is required that architectural design and structural design should have measures to promote natural ventilation. However, after the development of air conditioning technology, the value of natural ventilation was once ignored by people. The energy crisis, indoor air quality, residents' health problems caused by closed air conditioning and the demand of global sustainable development have made natural ventilation highly valued by scientists and their related personnel again. Rational use of natural ventilation can not only reduce energy consumption, but also provide fresh and clean natural air, improve indoor air quality and meet people's requirements for a comfortable and healthy indoor environment.

With the development of modern cities and buildings, the utilization of natural ventilation is more complicated than that of traditional buildings. On the one hand, this complexity is manifested in the more complex functions and diverse forms of buildings, on the other hand, people have higher requirements for indoor thermal environment. At the same time, whether different climatic conditions and architectural forms can make use of natural wind needs more theoretical research and technical support. The concept of humanized design has been deeply rooted in people's hearts, which requires designers to study every new material and technology that can benefit buildings and users, and put it into design practice after integration. This paper will focus on the feasibility scheme of "introducing natural ventilation technology into high-rise office buildings" with engineering examples, so as to promote the application of natural ventilation technology and the sustainable development of buildings.

2 About natural ventilation

Natural ventilation is a relatively economical way of ventilation. It does not consume electricity, but also can obtain large ventilation. It is simple, easy to operate, saves energy and is beneficial to environmental protection. Widely used in industrial and civil buildings. The concept or description of natural ventilation is different at home and abroad, but in general, the so-called natural ventilation has the same feature: relying on the wind pressure generated by outdoor wind and the hot pressure generated by the temperature difference between indoor and outdoor air to make the air flow, thus providing fresh indoor air, diluting indoor odor and pollutants, and removing residual heat and moisture.

The natural ventilation of the standard floor of an office building in Shanghai is simulated, and the indoor temperature with and without windows is compared in typical transitional seasons. The results show that natural ventilation with windows can better meet the requirements of indoor temperature and air exchange times in transition season, reducing the running time of air conditioning by 200 1h/a and energy consumption by 30.61kwh/(a m2).

Office buildings are mostly high-rise buildings. Because outdoor air quality, temperature, humidity, wind environment and sound environment can not always meet the needs of natural ventilation, the main strategies of natural ventilation in office buildings are: mixed use of natural ventilation and mechanical ventilation, intermittent natural ventilation and utilization of natural ventilation.

The mixed use strategy of natural ventilation and mechanical ventilation mainly refers to the use of natural ventilation as far as possible when conditions permit, and mechanical ventilation is only used as an auxiliary means when necessary. In high-rise buildings, with the change of vertical height, the wind pressure difference between inner and outer floors is different, so mixed ventilation is usually considered in actual operation. According to the actual situation and different needs of various parts of the building, different ventilation methods are adopted, or natural ventilation and mechanical ventilation are adopted at the same time, or mechanical ventilation is adopted during the day and natural ventilation is adopted at night.

Intermittent natural ventilation refers to opening windows or vents when outdoor conditions are suitable, closing windows or vents when they are not suitable, and using natural ventilation. Spring and autumn with suitable temperature are the most suitable seasons for natural ventilation. In summer, according to the study of human thermal comfort, when the ambient temperature exceeds 34℃, most people will still feel hot even if there is wind blowing, so when the outdoor temperature is higher than 34℃, it is not suitable to open the window for ventilation. In most cases, the office does not need 24-hour ventilation, as long as enough air changes are ensured. This intermittent natural ventilation strategy can also be used when the noise is loud, and making full use of natural ventilation at night is also an effective means to obtain comfortable and energy-saving effect. As long as natural ventilation is used reasonably, the office can use air conditioning for 20% of the year, which will greatly reduce the energy consumption of air conditioning.

The strategy of using natural ventilation refers to making full use of natural ventilation through reasonable architectural design according to the architectural characteristics of office buildings. At present, there are many problems in the application of natural ventilation in most architectural designs, and the indoor air quality of office buildings is not ideal. Most of the working elders feel dizzy and unhappy when they work in a closed air-conditioned office environment for a long time. Even in the transitional season (that is, the season when the air conditioner is not turned on), many office workers still feel depressed. This feeling of office environment is related to the design mode of office building shell (namely, all-glass curtain wall or curtain wall with large glass area ratio), energy utilization mode (namely, fully enclosed ventilation and air conditioning system) and space design mode (namely, "layered" design mode). Through analysis, the causes of the above-mentioned status and problems come from the restrictions of outdoor air quality and noise on the use of natural ventilation, the influence of operation mode of air conditioning system in office buildings, the restrictions of natural ventilation technology, the restrictions of outdoor wind speed on the use of natural ventilation, the security risks of window opening on the facade, the restrictions of office building heat and architectural modeling on natural ventilation, and the consideration of natural ventilation design in most office buildings.

Natural ventilation form of high-rise building

In practical engineering applications, the common natural ventilation forms of high-rise buildings are curtain wall window opening and double-layer ventilation curtain wall. The common opening methods of curtain wall windows are fixed window, sliding window, casement window, hanging window and casement window. Double-deck ventilation curtain wall is divided into internal circulation, external circulation (whole, corridor, channel, box) and open double-deck curtain wall according to air circulation mode.

In the double curtain wall structure, a relatively closed space is formed between the inner curtain wall and the outer curtain wall. Air enters the space through the lower air inlet and leaves the space through the upper air outlet. This space is called a hot aisle. The air in the hot aisle is always in a flowing state and constantly exchanges heat with the outer surface of the inner curtain wall, so the double curtain wall is also called the hot aisle curtain wall. It changed the structural form of the traditional curtain wall, saving energy by 50% compared with the traditional curtain wall, and the thermal insulation performance reached the international second class. Adopt uncoated glass to realize natural lighting and save electricity; It has dual functions of heat preservation in winter and heat insulation in summer, effectively reducing the use of air conditioners and achieving energy-saving effects. The dust-proof and ventilation function of double-layer curtain wall makes it not affect the ventilation of windows in bad weather (especially in sandstorm areas), and improves the indoor air quality. At the same time, the double-layer curtain wall structure makes it possible to naturally ventilate the curtain wall of super high-rise buildings, thus meeting the physiological and psychological needs of users for natural ventilation to the greatest extent.

Study on Natural Ventilation Design of Sinosteel Tianjin Xiangluowan Project

Project overview

Sinosteel Tianjin Xiangluowan Project is located in Xiangluowan 1 business circle, surrounded by Haihe River in the north and east, adjacent to the main road in the business circle in the west, and connected to the other side of Haihe River in the east by landscape bridge (Figure 1). The design concept of this project is to unify the architectural form, structural stress and cultural symbols into a "honeycomb" hexagonal prototype. The facade of the whole building consists of five hexagonal windows of different sizes, which is a brand-new development and innovation of the classic "hexagonal windows" in China classical architecture (Figures 2, 3, 4 and 5). The whole project consists of two towers and a podium. The first tower is a five-star hotel with a total height of102m; Tower 2 is an office hotel complex with a total height of 358 m; The podium is the hotel lobby and supporting commercial and catering facilities.

Technical exploration of natural ventilation strategy

Monographic research on electromechanical design

In the electromechanical design of this project, we strive to build an intelligent office and an information expressway with advanced communication and computer network technology, including structured integrated wiring and optical cable transmission, integrated service digital network, 10 Gigabit Ethernet, digital program-controlled exchange communication, etc. In terms of air conditioning system design, hotel air conditioners provide cooling and heating all year round, and office buildings adopt variable air volume air conditioning (AVA) system. While ensuring excellent indoor air quality, it can realize energy-saving operation and provide convenient 24-hour refrigeration system for office tenants. The fresh air of the air conditioning system is equipped with a heat recovery device to recover the hot and cold air in the exhaust air, and the waste heat recovery of boiler flue gas is used to preheat domestic hot water. The refrigeration unit with high energy efficiency ratio is equipped with computer room group inspection and BMS system, and all equipment will be optimally controlled according to the change of total cooling load. The air conditioning and ventilation system of the whole building adopts direct digital control (DDC) system for automatic control, which realizes digitalization of operation management and computer operation.

As can be seen from the above general situation of electromechanical design, the electromechanical air conditioning system designed in this project belongs to the all-air system, and the fresh air is sent indoors after being treated by the outdoor fresh air unit. Usually, the fresh air unit is used to meet the indoor hygiene requirements rather than bear the indoor load. The supply air temperature, relative humidity and carbon dioxide (CO2) concentration are all controlled by the fresh air unit. Variable air volume air conditioning (AVA) system installs a frequency converter on the fan, analyzes the temperature through the indoor induction probe, changes the frequency of the frequency converter through the central controller, and controls the indoor temperature by changing the speed of the fan. Constant air volume air conditioning system has improved in energy saving and indoor air comfort, but there are still many shortcomings in central air conditioning system.

Possibility of opening the front window

This project is located in Luo Xiang Bay, Tianjin, surrounded by Haihe River, with good air quality and beautiful surrounding environment. From the point of view of outdoor air quality and noise, it is possible to open windows on the facade. From the point of view of electromechanical energy-saving design, this project adopts variable air volume air conditioning (AVA) system. The increase of fresh air volume will change the system load, and the effect of environmental protection and energy saving can be achieved through the control of the controller.

The influence of outdoor wind speed on natural ventilation is studied through field data collection. The extreme pressure given in the wind tunnel pressure test report of Tianjin Sinosteel International Plaza (hereinafter referred to as the report) has considered the internal pressure value of the closed structure, so the results given can be directly used as the standard value of wind load for the design of the envelope structure. According to the statistical results, the wind pressure value of the tower facade is basically consistent with the standard value; The negative pressure at the corner of T2 tower is very high (Figure 8). Therefore, curtain wall windows should be avoided at the corner of T2. It can be found from the report that the standard value of the maximum wind pressure (above 100m) after angle removal is mostly between-4 and 2.5. According to "Classification and Testing Methods of Air-tightness, Water-tightness and Wind-pressure Resistance of Exterior Doors and Windows of Buildings", the wind-pressure resistance rating is Grade 6, and the window opening on the facade can meet the requirements.

Study on the Safety of Opening Windows in High-rise Buildings

By increasing the height of indoor floor under the window, the design of high window is adopted to meet the safety requirements of internal personnel, and at the same time, the problem that the workstation near the window is greatly affected by natural ventilation can be solved. On the premise of meeting various structural indexes, opening the window sash can increase the application of safety technology, such as intelligent electric window opener, which can be linked with air conditioning system and fire fighting system to strengthen the safety and reliability of window opening on the facade of high-rise buildings.

Study on facade design, curtain wall system and facade window opening

The facade design is a classic "hexagonal window" in China classical architecture, with a 300-wide outer window sill (Figure 9). When the hanging window is used, the outer aluminum curtain wall will not protrude after opening, so as not to damage the overall shape of the hexagonal window (Figure 10). The facade of this project adopts unit curtain wall, which reduces outdoor work and high-altitude field construction, ensures the processing quality of the factory and provides good conditions for window opening. (Numbers 1 1, 12)

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According to the design conditions of this project, as well as the analysis of the geographical position, natural conditions, plane function, facade characteristics and curtain wall structure of this project, the improved indoor ventilation strategy measures are put forward to the owner in the construction drawing stage, that is, by opening the window, the mixed mode of natural ventilation and mechanical ventilation is adopted to improve the comfort of the office and reduce the energy consumption of air conditioning.

At present, the occupancy rate of office buildings in Beijing is about 65%, and the occupancy rate of individual office buildings has increased because of their beautiful design, reasonable space and comfortable environment. It is everyone's social responsibility to design and build a more comfortable and energy-saving office building. Skills and environmental protection design concepts will continue to promote the innovation of materials and technologies, and the transfer of new materials and technologies will promote the development of buildings in a more energy-saving and healthy direction.

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