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With the continuous advancement of air conditioning technology, people are able to control the indoor environment more effectively, creating unprecedented demands for a comfortable indoor climate, which has led to a gradual reduction in the use of natural ventilation as a means of achieving such a favorable climate. However, in today’s world faced with global energy shortages, increasing pressure to save energy, deteriorating air quality (IAQ), and issues such as building syndrome (SBS), it has become necessary to reexamine natural ventilation, this traditional climate-adaptation technique. This ancient yet effective method is receiving unprecedented attention these days. The invention of air conditioning allows people to actively control their living environment, rather than passively adapting to nature as before ； The widespread use of air conditioning has led people to gradually neglect the use of natural ventilation. Today, with the widespread use of air conditioning technology, and under the dual pressures of energy conservation and maintaining good indoor air quality, scientists around the world are forced to reexamine natural ventilation as a traditional technique. Against this backdrop, reintroducing natural ventilation, a traditional building ecological technique, into modern architecture holds even greater significance than before. I. Principles of natural ventilation technology: Natural ventilation, in its usual sense, refers to the creation of air flow through purposefully created openings. This flow is directly influenced by the pressure distribution on the building’s exterior surface and the characteristics of the various openings. The pressure distribution is the driving force, while the characteristics of each opening determine the flow resistance. Regarding natural ventilation, there are mainly two reasons for air movement within a building: wind pressure and the density difference between indoor and outdoor air. These two factors can act alone or together. 1. Natural ventilation under wind pressure is caused by pressure differences in the atmosphere. If the wind encounters obstacles in its path, such as trees and buildings, energy conversion occurs. Dynamic pressure is converted into static pressure; as a result, positive pressure is generated on the windward side (about 0.5–0.8 times the dynamic pressure of the wind), while negative pressure is generated on the leeward side (about 0.3–0.4 times the dynamic pressure of the wind). Due to the pressure difference created by passing over the building, air flows into the interior through gaps in the windows on the windward side and other openings, while the indoor air exits through openings on the leeward side, thereby creating natural ventilation driven by wind pressure for overall air exchange. The wind pressure around a building is related to the building’s geometric shape, its orientation relative to the wind direction, the wind speed, and the natural terrain surrounding the building. 2. Natural ventilation under thermal pressure is caused by the temperature difference between indoor and outdoor air, which is what is known as the “chimney effect”. Due to the temperature difference, a density difference between the interior and exterior arises, resulting in a pressure gradient along the vertical direction of the building walls. If the indoor temperature is higher than the outdoor temperature, there will be higher pressure at the upper part of the building, while lower pressure exists at the lower part. When there are openings at these positions, air enters through the lower openings and exits from the top. If the indoor temperature is lower than the outdoor temperature, the direction of air flow is reversed. The magnitude of the hot pressure depends on the height difference between the two openings and the air density difference between the inside and outside. In practice, architects often use structures such as chimneys, ventilation towers, and atriums to create favorable conditions for natural ventilation, thereby ensuring that buildings have good ventilation. 3. Natural ventilation under the combined effect of wind pressure and thermal pressure: In actual buildings, natural ventilation is the result of the combined action of wind pressure and thermal pressure, with each having a varying degree of influence. Since wind pressure is influenced by factors such as weather, outdoor wind direction, building shape, and the surrounding environment, the combined effect of wind pressure and thermal pressure is not a simple linear addition. Therefore, architects must take various factors into full consideration to enable wind pressure and thermal pressure to complement each other and work in close coordination, thereby achieving effective natural ventilation for the building. 4. Mechanically assisted natural ventilation: In some large buildings, due to the long ventilation paths and high flow resistance, relying solely on natural wind pressure and thermal pressure is often insufficient to achieve natural ventilation. In cities where air pollution and noise pollution are severe, natural ventilation can also bring in polluted outdoor air and noise, which is detrimental to human health. In such cases, a mechanically assisted natural ventilation system is often used. The system features a complete air circulation pathway, supplemented by eco-friendly air treatment methods (such as soil pre-cooling, pre-heating, and heat exchange using deep well water), and utilizes certain mechanical means to accelerate indoor ventilation. II. Advantages of natural ventilation technology Natural ventilation is a technique widely used in modern buildings to improve the thermal environment within them and reduce air conditioning energy consumption. The fundamental purpose of using natural ventilation is to replace (or partially replace) air conditioning systems. This replacement process has two crucial advantages: first, it enables effective passive cooling – when the outdoor air temperature and humidity are low, natural ventilation can lower the indoor temperature and remove humid air, thereby ensuring thermal comfort for people. Even when the outdoor conditions are beyond the comfortable range and energy is needed to cool and dehumidify the space, natural ventilation can be used to introduce treated fresh air, eliminating the need for fans and avoiding noise. This helps to reduce energy consumption and pollution, in line with the principles of sustainable development. Secondly, it can provide fresh and clean natural air (fresh air), which is beneficial to people’s physical and mental health. Poor indoor air quality is largely due to a lack of sufficient fresh air. The constant temperature environment created by air conditioners also weakens the body’s resistance, leading to various \"air conditioning diseases\". Natural ventilation can remove polluted air from indoors, and it also helps to meet the psychological need for interaction between humans and nature. III. Limiting factors in the design of natural ventilation systems As a free technology, the application of natural ventilation is inevitably constrained by environmental factors. In regions with relatively mild outdoor temperatures and humidity levels (such as the UK), the application of this technology is highly developed. Based on their experience in using it, the following outlines the limitations associated with the use of natural ventilation technology. (1) The limitation of heat gain indoors is a prerequisite for natural ventilation; this is possible only when the outdoor air temperature is lower than that inside. By ventilating the indoor air, outdoor air is brought in, thereby reducing the temperature of the indoor air. Obviously, the greater the temperature difference between indoor and outdoor air, the better the effect of ventilation for cooling. For buildings that typically rely on air conditioning systems to cool down, the use of natural ventilation systems can reduce the load on the air conditioning units at appropriate times; a typical example is the operation of the air conditioning system with fresh air only during the transitional seasons. For buildings that rely entirely on natural ventilation systems for cooling, their performance depends on many factors, among which the heat gain of the building is a key one. The greater the heat gain, the lower the likelihood of achieving indoor comfort levels through cooling. Current research findings indicate that in buildings cooled solely by natural ventilation, the heat gain inside should not exceed 40 W/m2. (II) Requirements of the building environment: After natural ventilation measures are applied for cooling, the indoor environment of a building relies to a large extent on the outdoor environment for regulation. In addition to air temperature and humidity parameters, indoor air quality and noise control are also affected by the outdoor environment. According to some current standard requirements, in buildings with natural ventilation, the noise level outside the building should not exceed 70 dB ； Especially when the windows are open, it is necessary to ensure that the noise level in the areas around the indoor space does not exceed 55 dB. At the same time, the outdoor air quality at the natural ventilation inlets should meet relevant health requirements. (III) Limitations due to building conditions: For buildings that rely on natural ventilation, architectural design should take into account the above two requirements in order to make full use of the advantages of natural ventilation. 1. Are there any major roads, railways, etc., in the area surrounding the building’s location? It is generally recommended that the building’s facade be at a distance of 20 meters from such traffic routes, in order to avoid contamination by polluted air or noise interference ； Alternatively, when designing the ventilation system, the area near traffic arteries can be used as the exhaust side for ventilation. The dominant wind direction and speed in the area are used to determine the design of the natural ventilation system, with special attention paid to whether the building is located downstream of areas where polluted air exists. Due to the differences between urban and rural environments, the surrounding environment has varying effects on building ventilation systems; in particular, other buildings or obstacles around a structure affect factors such as wind direction and speed, natural lighting, and noise levels in that area. 2. Building shape: The width of a building directly affects the pattern and effectiveness of natural ventilation. Buildings with a width of no more than 10 meters can use single-sided ventilation ； Buildings with a width of no more than 15 meters can use bilateral ventilation ； Otherwise, other auxiliary measures will be required, such as chimney structures or a combination of mechanical ventilation and natural ventilation. To make full use of wind pressure, the air intake of the system should face the prevailing wind direction surrounding the building. At the same time, the orientation of the building also relates to the choice of heat reduction measures. For the window area system, the window-to-wall ratio on the exterior wall on the air intake side should take into account both natural lighting and the control of heat generated by solar radiation, typically ranging from 30% to 50%. Building structure types: Building structures can be light, medium, or heavy structures. For medium or heavy structures, due to their high thermal inertia, technical measures such as evening ventilation can be employed to improve the performance of the natural ventilation system. 3. In interior architectural design, larger ceiling heights help to utilize the thermal pressure generated by the indoor heat load, thereby enhancing natural ventilation. The form of interior partitions directly affects the organization of ventilation airflow and the volume of ventilation. Vertical passages or ducts within a building can be utilized to take advantage of the chimney effect generated by these passages in order to effectively organize natural ventilation. 4. The density of people inside the building, as well as the heat generated by equipment and lighting, play a role in determining the heat gain of the building; for buildings with a heat gain of over 40 W/m2, natural ventilation systems and mechanical cooling systems can be installed in appropriate areas, depending on the types and distribution of heat sources within the building. Working hours will influence the choice of other auxiliary technologies (such as evening ventilation systems). (IV) Impact of outdoor air humidity: Natural ventilation is effective in reducing indoor air temperature, but it has little effect on regulating or controlling indoor air humidity. Therefore, natural ventilation measures generally cannot be used in very humid areas. IV. Considerations for natural ventilation in buildings: When applying natural ventilation techniques, it is necessary to take full account of the local climate and environmental conditions, and adopt appropriate technical measures to ensure that natural ventilation achieves good ecological benefits. In addition to taking into account ordinary factors such as climate, building orientation, outdoor landscaping, and details of ventilation systems, natural ventilation is increasingly considering the following two factors: ① Solar energy to enhance natural ventilation. Building components that utilize solar energy to enhance natural ventilation mainly include roof solar chimneys, Trombe walls, and solar air collectors integrated into the building. To achieve better cooling effects in summer, these methods are usually combined with other building elements to form an organized natural ventilation system ； ②Computer simulation of natural ventilation. Computer simulation techniques, particularly Computational Fluid Dynamics (CFD), play a very important role in the design of natural ventilation systems. These techniques use control equations such as the continuity equation, momentum equation, and energy equation to analyze aerodynamic phenomena, and then computer software is employed to carry out simulations that produce visual results. Such results provide valuable insights for architects to create reasonable wind environments within buildings. Therefore, with the continuous development of computer simulation technology, computer simulation will undoubtedly play a significant role in advancing the design of natural ventilation. In summary, as an ecological technology suitable for different climates, natural ventilation technology should, in its practical application, be combined with technologies such as solar energy, building materials, natural lighting, underground heat storage and cooling, and automatic control. Computer simulation techniques should also be utilized to analyze actual cases and conduct in-depth quantitative research on them. It is believed that as the concepts of ecology and sustainable development continue to evolve, natural ventilation – a cheap and healthy method of ventilation – will be utilized more and more often.