Nowadays, everyone inevitably touches or uses paper. The thesis is a rational article that studies various academic fields and describes the achievements of academic research. Then the question comes, how to write an excellent paper? The following is my carefully organized thesis on dialectics of nature of Beihang University, hoping to help everyone.
[Abstract]
This paper first introduces the principle of natural ventilation technology in buildings, points out the economic and environmental benefits of natural ventilation, then demonstrates how to realize natural ventilation in architectural design, puts forward that traditional natural ventilation technology should adapt to the natural geography and climate characteristics of the building area, and analyzes the perfect combination of natural ventilation and regional climate with examples. The purpose of this paper is to arouse people's attention to the traditional suitable technology of natural ventilation in regional architectural design.
[Keywords:]
Natural ventilation; Principle; Advantages; Regional architecture; design
With the continuous development of air-conditioning technology, people can more and more actively control the indoor environment, creating unprecedented indoor comfortable climate requirements, thus making people gradually dilute the application of natural ventilation as a climate suitability technology. However, in today's global energy shortage, increasing pressure on energy conservation, air quality deterioration (IAO) and building syndrome (SBS), people have to re-examine the traditional climate suitability technology. Today, natural ventilation, an ancient and effective technology, has received unprecedented attention. The appearance of air conditioning enables people to actively control their living environment instead of passively adapting to nature as before; The extensive use of air conditioners makes people gradually dilute the application of natural ventilation. With the popularization of air conditioning technology today, scientists all over the world have to re-examine the traditional technology of natural ventilation under the dual pressure of saving energy and maintaining good indoor air quality. In this context, it is more important than ever to reintroduce natural ventilation, a traditional architectural ecological technology, into modern architecture.
First, the principle of natural ventilation technology
Generally speaking, natural ventilation refers to the flow of air through purposeful openings. This flow is directly affected by the pressure distribution on the external surface of the building and the characteristics of different openings. Pressure distribution is the driving force and the characteristics of each opening determine the flow resistance. As far as natural ventilation is concerned, there are two main reasons for air flow in buildings: wind pressure and indoor and outdoor air density difference. These two factors can work independently or together.
1, natural ventilation under wind pressure
Wind is formed by atmospheric pressure difference. If the wind meets obstacles, such as trees and buildings, it will produce energy conversion. Dynamic pressure changes to static pressure, so the windward side generates positive pressure (about 0.5-0.8 times of wind speed dynamic pressure) and the leeward side generates negative pressure (about 0.3-0.4 times of wind speed dynamic pressure). The pressure difference across the building urges the air to flow into the room from the windows and other gaps on the windward side, while the indoor air is discharged from the leeward side, forming a comprehensive ventilation with wind pressure and natural ventilation. The wind pressure around the building is related to the geometric shape of the building, the orientation of the building relative to the wind direction, the wind speed and the natural terrain around the building.
2. Natural ventilation under the action of hot pressing
Hot pressing is caused by the temperature difference between indoor and outdoor air, which is called "stack effect". Because of the temperature difference, there is a density difference between indoor and outdoor, and a pressure gradient appears along the vertical direction of the building wall. If the indoor temperature is higher than the outdoor temperature, the pressure in the upper part of the building will be higher and the pressure in the lower part will be lower. When there are holes in these positions, air enters from the lower opening and flows out from the upper part. If the indoor temperature is lower than the outdoor temperature, the air flow direction is opposite. The size of hot pressing depends on the height difference between the two openings and the air density difference between indoor and outdoor. In practice, architects often use chimneys, ventilation towers, patios, atriums, etc. to provide favorable conditions for the use of natural ventilation, so that buildings have good ventilation effects.
3. Natural ventilation under the action of wind pressure and hot pressing.
Natural ventilation in practical buildings is the result of the combined action of wind pressure and hot pressure, but their respective functions are strong and weak. Because wind pressure is influenced by weather, outdoor wind direction, building shape, surrounding environment and other factors, wind pressure and hot pressing are not simply linear superposition. Therefore, architects should fully consider various factors, make wind pressure and hot pressing complement each other and cooperate closely to realize effective natural ventilation of buildings.
4, mechanical auxiliary natural ventilation
In some large buildings, because of the long ventilation path and large flow resistance, it is often not enough to rely solely on natural wind pressure and hot pressing to achieve natural ventilation. For cities with serious air pollution and noise pollution, direct natural ventilation will also bring outdoor air pollution and indoor noise, which is not conducive to human health. In this case, a mechanically assisted natural ventilation system is usually used. The system has a complete air circulation channel, supplemented by ecological air treatment means (such as soil pre-cooling, pre-heating, deep well water heat exchange, etc.). ), and through certain mechanical means to accelerate indoor ventilation.
Second, the advantages of natural ventilation technology
Natural ventilation is a widely used technology to improve the thermal environment of buildings and save energy consumption of air conditioning. The fundamental purpose of adopting natural ventilation is to replace (or partially replace) air conditioning and refrigeration systems. This substitution process has two important meanings: First, effective passive refrigeration is realized. When the outdoor air temperature and humidity are low, natural ventilation can reduce the indoor temperature without consuming non-renewable energy, take away humid gases and realize human thermal comfort. Even if the outdoor air temperature and humidity exceed the comfort zone, it needs to consume energy to reduce temperature and humidity, and the treated fresh air can be transported by natural ventilation without fan energy consumption and noise. This is conducive to reducing energy consumption and pollution, in line with the idea of sustainable development. Second, it can provide fresh and clean natural air (fresh air), which is beneficial to people's physical and mental health. The poor indoor air quality is largely due to the lack of enough fresh air. The constant temperature environment caused by air conditioning also reduces the human body's resistance and causes various "air conditioning diseases". Natural ventilation can eliminate indoor dirty air and meet people's psychological needs of communicating with nature.
Thirdly, the restrictive conditions in the design of natural ventilation system.
As a free technology, natural ventilation technology is bound to be limited by the environment. For areas with mild outdoor temperature and humidity (such as Britain), the application of this technology has been very mature. According to their application experience, the restrictive conditions of natural ventilation technology application are introduced.
(a) indoor thermal limit
The premise of applying natural ventilation is that the outdoor air temperature is lower than the indoor air temperature. Through indoor air ventilation, outdoor air is introduced into the room to reduce the indoor air temperature. Obviously, the greater the temperature difference between indoor and outdoor air, the better the effect of ventilation and cooling. For buildings that generally rely on air conditioning system to cool down, the application of natural ventilation system can reduce the operating load of air conditioning at an appropriate time, such as fresh air operation of air conditioning system in transitional seasons. For buildings that completely rely on natural ventilation system to cool down, its use effect depends on many factors, and the heat gain of buildings is one of the important factors. The greater the heat gain, the less likely it is to meet the indoor comfort requirements by cooling down. At present, the research results show that the indoor heat gain of buildings that rely entirely on natural ventilation should not exceed 40W/m2.
(B) the requirements of the building environment
After the application of natural ventilation and cooling measures, the indoor environment of buildings depends on the outdoor environment to a great extent. In addition to the temperature and humidity parameters of the air, indoor air quality and noise control will also be destroyed by the outdoor environment. According to some current standards, the outdoor noise of naturally ventilated buildings should not exceed 70dB；; Especially when opening windows, ensure that the noise in the area around the room does not exceed 55dB. At the same time, the outdoor air quality of natural ventilation air inlet should meet the relevant hygiene requirements.
(3) Limitation of building conditions
For buildings with natural ventilation, we should refer to the above two requirements in architectural design and give full play to the advantages of natural ventilation.
1, building location
Whether there are trunk roads, railways, etc. It is generally believed that the building facade should be 20 meters away from the main traffic road to avoid air pollution or noise interference; Or, when designing the ventilation system, the place near the main traffic road is taken as the exhaust side of ventilation. The regional dominant wind direction and wind speed determine the design of natural ventilation system according to the local dominant wind direction and wind speed, and pay special attention to whether the building is downstream of the surrounding polluted air. Because the urban environment is different from the rural environment, the surrounding environment has different effects on the building ventilation system, especially other buildings or obstacles around the building will affect the wind direction, wind speed, lighting and noise around the building.
2. Architectural modeling
The width of building shape directly affects the form and effect of natural ventilation. One-sided ventilation can be used for buildings with a building width of less than 10 m; Bilateral ventilation can be used for buildings with a width not exceeding15m; Otherwise, other auxiliary measures will be needed, such as chimney structure or mixed mode of mechanical ventilation and natural ventilation. Building Orientation In order to make full use of wind pressure, the air inlet of the system should face the dominant wind direction around the building. At the same time, the orientation of the building also involves the choice of measures to reduce heat gain. The window-to-wall ratio of the external wall on the air inlet side of the window system should consider controlling natural lighting and solar heat gain, which is generally 30%-50%. Building structures can be divided into light, medium and heavy. For medium or heavy buildings, due to their large thermal inertia, technical measures such as night ventilation can be combined to improve the operation effect of natural ventilation system.
3. Interior design of buildings
The higher the story height, the better the natural ventilation. The form of indoor partition directly affects the organization of ventilation airflow and ventilation volume. Vertical passages or air ducts in buildings can effectively organize natural ventilation by using stack effect generated by vertical passages.
4. Indoor personnel
Influence of indoor personnel density, equipment and lighting heat gain For buildings with building heat gain exceeding 40W/m2, natural ventilation system and mechanical refrigeration system can be set up in appropriate areas according to the types and distribution of heat sources in the building. Working hours Working hours will affect the choice of other auxiliary technologies (such as night ventilation system).
(D) the impact of outdoor air humidity
The application of natural ventilation can obviously reduce the indoor air temperature, but it has little effect on adjusting or controlling the indoor air humidity. Therefore, in very humid areas, natural ventilation measures are generally not available.
Iv. Precautions for Natural Ventilation in Buildings
In the process of using natural ventilation technology, appropriate technical measures should be taken to ensure that natural ventilation can achieve good ecological benefits in full combination with local climate and environmental conditions. Natural ventilation not only considers the influence of common factors such as climate, building orientation, outdoor greening and ventilation structure details, but also considers the following two factors more and more:
① Solar energy strengthens natural ventilation. The building components of solar enhanced natural ventilation mainly include roof solar chimney, Trombe wall and solar air collector installed integrally with the building. In order to achieve better cooling effect in summer, these practices are usually combined with other building components to form an organized natural ventilation system;
② Computer simulation of natural ventilation. Computer simulation technology, especially computational solid mechanics (CFD) plays a very important role in the design of self-ventilation. It uses the control equations such as continuity equation, momentum equation and energy equation to analyze the aerodynamic force, and then uses computer software to carry out computer simulation, and obtains intuitive and intuitive results, which provides an important reference for architects to design a reasonable building wind environment. Therefore, with the continuous development of computer simulation technology, computer simulation will undoubtedly play a great role in promoting the design of natural ventilation.
In a word, natural ventilation technology, as an ecological technology to adapt to the climate, should be combined with solar energy, building materials, natural lighting, underground cold storage and heat storage, automatic control and other technologies, and use computer simulation technology to analyze practical cases and conduct quantitative and in-depth research on it. It is believed that with the continuous development of the concept of ecology and sustainable development, natural ventilation, a cheap and healthy way, will be used more and more.
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