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Analysis of air distribution and building energy saving in air-conditioned rooms?

Discusses the importance of indoor thermal comfort and the influence of air conditioning airflow organization on indoor thermal comfort and building energy saving. Unreasonable air distribution in air-conditioned rooms will not only reduce people's thermal comfort, affect work efficiency and physical and mental health, but also increase the initial investment and operating expenses of equipment. The optimization of indoor air conditioning airflow organization should not only consider the thermal comfort of indoor personnel environment, but also consider reducing the energy consumption of air conditioning operation to realize building energy saving.

People spend most of their life indoors, and the thermal comfort of indoor environment will have a great impact on study, work and life. A good indoor thermal environment can not only improve people's mood, but also improve the efficiency of study and work. Due to the restriction of architectural design itself and the influence of economic conditions such as project cost, unreasonable air conditioning design often leads to unreasonable indoor air conditioning airflow organization in some new buildings.

In addition, due to the development of society and the improvement of people's living standards, a large number of existing buildings need to be equipped with air conditioning systems, and the existing buildings will be limited by the conditions of the buildings themselves when they are rebuilt, resulting in unreasonable air conditioning airflow organization after the renovation. With global warming and the rapid increase in the number of buildings, the use of air conditioners in buildings has become very common. Therefore, the importance of air distribution in air-conditioned rooms is increasingly prominent. Unreasonable air distribution in air-conditioned rooms will not only reduce people's thermal comfort, affect work efficiency and physical and mental health, but also increase the initial investment and operating expenses of equipment. This paper mainly discusses the air distribution and building energy saving in air-conditioned rooms.

1 Thermal comfort of indoor environment

Air-conditioned buildings are usually closed buildings. If there is no reasonable indoor air distribution, the thermal comfort of indoor environment will become worse, leading to symptoms such as cold, stuffy nose, headache, dizziness and fatigue, and the effect may not be as good as that of well-ventilated ordinary buildings. The research on indoor thermal comfort (the idea of expressing satisfaction with thermal environment) in foreign countries started earlier than in China, and Bedford put forward seven evaluation indexes of thermal comfort as early as 1936. At present, the most widely used is the expected average evaluation index PMV, which is put forward by Professor Danish Square to objectively measure thermal sensation. The PMV index represents the feelings of most people in the same environment, but it may not represent the feelings of all people because of the physiological and psychological differences between people.

Among them, there are six main factors affecting PMV index: air temperature, relative humidity, wind speed, average ambient radiation temperature, thermal resistance of human clothes and metabolic rate. PMV is divided into seven grades. Research shows that even if PMV=0, 5% people are still dissatisfied with the environment. Therefore, Professor Fang Ge put forward PPD index to predict the percentage of dissatisfaction, and used PMV-PPD * * to evaluate the thermal comfort of air-conditioned rooms. The farther away from the thermal neutral environment, the greater the percentage of dissatisfaction. In the case that the human body normally dresses according to the seasons, the range in which the human body feels more comfortable is shown in Table 2. The air distribution is closely related to the thermal comfort of air-conditioned rooms.

The study of air distribution began in the 1920s, and the poor comfort caused by cold air blowing in air conditioning attracted the attention of researchers in the field of air conditioning. In the following decades, the airflow state was simulated by theory, experiment and computer fluid dynamics software, and the movement of indoor airflow organization was studied in detail The research shows that there are many factors that affect the indoor air distribution in air-conditioned rooms, including the position and form of air supply outlet, air supply parameters, the position of air return outlet, the geometric shape of the room and the position of heat source.

2 indoor air conditioning airflow organization

The air distribution in air-conditioned rooms mainly includes upper delivery, lower delivery, upper delivery, lower delivery, side delivery and middle delivery. This paper studies the comfort of air-conditioned rooms under three air supply modes: side air supply, up air supply and down air supply, and finally draws the conclusion that the comfort of side air supply is the best. Through the research and analysis of the PMV-PPD index of the test results, Huang Feng concluded that the test points near the air supply outlet in the side air supply mode were more comfortable, which provided a reference for the layout of indoor workstations. The indoor comfort is the most uniform in the downward air supply mode, but the air outlet is close to people, which is easy to produce a blowing feeling and affect people's comfort. The upper air supply mode is easy to form a dead zone in the back wall of the room.

Di Yu Hui combined with low-frequency air supply, analyzed and compared the comfortableness of three air supply modes, namely, 0.3Hz, 0.4Hz and 0.5Hz, and concluded that the human thermal comfortableness was better when the air supply mode was 0.3Hz up and 0.5Hz down. Side air supply can keep indoor air flowing, which is closer to the form of indoor natural wind. At present, in general civil buildings, the commonly used air distribution forms of air conditioning are upward circulation and side air supply; There are few air distribution forms of downdraft air conditioning; Central air supply is mainly used for air conditioning systems in large spaces.

The air distribution forms of indoor air conditioning with good thermal comfort are the air supply mode of air conditioning side in hotel rooms and the air supply mode of diffuser in office buildings. At present, most hotel rooms choose the mode of fan coil plus fresh air, because the hotel room area is small and the indoor floor height is relatively low. The adoption of side air supply mode will not make air-conditioned air blow directly to the personnel activity area, which will make people feel cold. The advantage of fan coil unit is that guests can adjust the room temperature by changing the air volume at will through a three-speed switch. In office buildings, flat square diffusers are often used for air supply. This diffuser has a plurality of concentric and parallel guide vanes, so that the air can flow on the ceiling after flowing out and fully diffuse before reaching the working area of the staff.

The air distribution forms of indoor air conditioning that easily lead to poor thermal comfort are slit air supply outlet, lamp tray air supply outlet, louver air supply outlet, split air conditioning and cabinet air conditioning. The air distribution of this kind of air conditioner belongs to "direct blowing" type, which often causes the air supply flow of indoor air conditioner to be too concentrated, making the temperature and air supply speed of indoor air conditioner unevenly distributed. People close to the air outlet of the air conditioner usually have to endure a strong sense of blowing, but those far away from the air conditioner and the air conditioner are not easy to reach, and the local temperature is high, which will form a vortex dead zone in the corner. In order to ensure the thermal comfort of air-conditioned indoor environment, it is necessary to analyze and design the air distribution of indoor air conditioning in detail to ensure the uniformity of indoor air conditioning temperature and air supply speed, especially for the analysis of air distribution in air-conditioned offices with high personnel density.

At present, in the design of central air-conditioning system, designers often pay more attention to the capacity selection of air-conditioning equipment and the analysis of air distribution in large space, while ignoring the analysis and calculation of air distribution in offices with high personnel density, which leads to improper selection or too few air outlets in such offices, resulting in too concentrated air supply, uneven indoor temperature and strong local blowing sensation, and even some staff can not work normally in summer, and idle and abandoned stations sometimes occur.

3 air conditioning air distribution on the impact of building energy consumption

Unreasonable air distribution in air-conditioned rooms will not only affect the thermal comfort of indoor environment and the work efficiency of personnel, but also lead to excessive selection of air-conditioning system equipment, increase the operating energy consumption and operating cost of air conditioners, and directly affect building energy conservation. Because the indoor air conditioning temperature is uneven, designers and equipment purchasers have to make up for the unreasonable indoor air distribution by increasing the equipment capacity, thus forming the equipment selection and procurement pattern of "big horse-drawn cart". In addition, unreasonable air distribution in air-conditioned rooms will also lead to prolonged air-conditioning operation time, increased operating conditions of high wind speed and large air volume, and increased air-conditioning operation cost and building energy consumption.

The study of air distribution optimization in air-conditioned rooms can not emphasize the thermal comfort of indoor environment unilaterally, and can not ignore the close combination with engineering practice, so as to conduct a single and isolated study. The optimization of air distribution in air-conditioned rooms needs comprehensive analysis from all directions and angles through field investigation and engineering practice. It is necessary to meet the demand of indoor thermal comfort, but also to reduce the energy consumption of air conditioning operation and realize the goal of building energy saving.

This paper discusses the importance of indoor thermal comfort and the influence of air conditioning airflow organization on indoor thermal comfort and building energy saving. Unreasonable air distribution in air-conditioned rooms will not only reduce people's thermal comfort, affect work efficiency and physical and mental health, but also increase the initial investment and operating costs of equipment. The optimization of indoor air conditioning airflow organization can not be a single and isolated analysis and research, but should be comprehensively analyzed from all directions and angles in combination with the environmental thermal comfort requirements of each station in the area, so as to reduce the energy consumption of air conditioning operation and achieve the purpose of building energy saving.

The above analysis of air distribution and building energy saving in air-conditioned rooms was collected by Zhong Da Consulting Company.

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