Air quality and related research in the hottest ch

2022-08-15
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Indoor air quality and related research

Abstract: This paper introduces the relevant research results of indoor air quality at home and abroad. The content includes the causes of IAQ problems, the influencing factors of IAQ, evaluation methods and relevant measures to improve IAQ

key words: indoor air quality sick building syndrome evaluation methods influencing factors

1 indoor air quality

the research on indoor air quality can be traced back to the early 20th century, when people began to adopt ventilation methods to improve the indoor air environment. The emergence of refrigeration and air conditioning system has created a comfortable air conditioning environment for people. The global energy crisis in the 1970s made the refrigeration and air conditioning system, a major energy consumer, face a serious test. Energy saving and consumption reduction became the key link in the design of air conditioning system. One of the energy-saving measures is to reduce the amount of fresh air entering the house, but this measure has led to the deterioration of the indoor air environment and the emergence of "sick building syndrome". Since the 1980s, refrigeration air conditioning has entered a new stage of development. One of the symbols of the new stage is the transformation from comfortable air conditioning to healthy air conditioning

indoor air quality has become a cutting-edge research topic in modern architectural science. It involves medical hygiene, building environmental engineering, architectural design and other aspects. The purpose of the research is to create a hygienic, healthy and comfortable indoor air environment

2 the reason why IAQ problem has attracted increasing attention

2.1 IAQ is an important factor affecting labor productivity [1]

research shows that indoor air pollutants mainly include carbon dioxide, carbon monoxide, formaldehyde, volatile organic compounds, radon, asbestos, inhalable dust, smoke, bacteria, etc. Some pollutants, such as bacteria, carbon monoxide, radon, asbestos, etc., directly affect the health of personnel. Formaldehyde, dust, smoke, etc. will cause extreme discomfort or even disgust to the human body, and these feelings will lead to a decline in productivity. A survey shows that [2], the longer the building is used, the higher the dissatisfaction rate of people with indoor air quality, and the more the productivity will decline. Although the concentration of some indoor pollutants does not exceed the upper limit set by the authority, indoor personnel can still feel this low concentration pollution, which determines the freshness of the air and affects the acceptability of indoor air quality

2.2 the emergence of sick building syndrome (SBS)

in order to reduce the energy consumption of air conditioning, people on the one hand improve the air tightness and thermal insulation of buildings, and at the same time reduce the standard of indoor minimum fresh air volume, which leads to the increase in the concentration of indoor harmful substances due to the lack of fresh air dilution, resulting in eye and throat irritation, nasal congestion, headache, dizziness, nausea, chest tightness, fatigue, dry skin, sleepiness Irritability and other symptoms are collectively referred to as "sick building syndrome". The World Health Organization (who) estimates that at present, nearly 30% of new and renovated buildings in the world are affected by SBS, and about% of office workers are often troubled by SBS symptoms. Due to the decline of indoor air quality, work efficiency has decreased and employees' absenteeism has increased, resulting in a large number of economic losses such as product losses, employees' sick leave and direct medical expenses

2.3 changes in living and working patterns of modern people

according to statistics, people usually spend 80% of their time indoors, and the concentration of some indoor pollutants is higher than outdoor, so people pay more and more attention to IAQ. The average number of breaths of an adult is 10 ~ 15min-1, and each time it requires 0.5 liters of air. Based on the average life span of 70 years, each person needs 270000 m3 of air in his life. This air enters the human body and enters the body for exchange through physical diffusion in the alveoli with a total surface area of 60 ~ 80m2. It is conceivable that under such a long exposure time and such a large contact area, the indoor air quality has a great impact on people's health [4]. People unconsciously and helplessly inhale these pollutants, and under their long-term interference, they are adversely affected psychologically and spiritually, resulting in the disorder of the autonomic nervous system, decreased immunity, changes in behavior and organ function, and the potential harm they suffer is immeasurable [5]

with the improvement of people's living standards, the requirements for quality of life are higher and higher, and the awareness of self-protection is enhanced. People begin to realize that high-quality air is the guarantee of indoor personnel's health. The concern and vigilance about indoor air quality are increasingly strengthened

3 factors affecting indoor air quality

3.1 a large number of new materials and agents

the design basis of fresh air volume in civil buildings is to take people as the main source of pollution. Nowadays, a large number of new building materials, decoration materials, new coatings and adhesives are constantly used, new office appliances are constantly emerging, and efficient and simple cleaners, pesticides and deodorants are widely used, Thousands of unprecedented volatile chemical pollutants have appeared in the indoor air. The concentration of these pollutants is very low, and it is difficult to measure them even with the most modern chemical analysis methods, but human nose can feel them. However, for a long time, people have taken these large amounts of low concentration pollution and its effects lightly

3.2 the reduction of fresh air volume and the decline of fresh air quality

the lack of fresh air volume is the main reason for the decline of indoor air quality. In buildings, the perception effects of building related pollution and personnel related pollution are superimposed, and the ventilation volume required by the two should also be superimposed. However, designers usually compare the two ventilation quantities in the design, and take the larger value of the two, which leads to the lack of ventilation in the room

there is no doubt that the quality of indoor fresh air is the main factor affecting indoor air quality. There are two main reasons affecting the quality of indoor fresh air: first, the quality of outdoor air; The second is the process of fresh air treatment

fresh air system is the key to ensure indoor air quality. For a long time, people have taken increasing the amount of fresh air as a natural way to improve indoor air quality. But in recent years, with the acceleration of urban construction, the population density is increasing, and the number of cars is also rising. People are constantly discharging exhaust gas in the process of production and life, resulting in the gradual deterioration of outdoor air quality. Some air quality indicators in the outdoor air have exceeded the control indicators of indoor air quality, such as the concentration of suspended particles. The indoor control standard is 0.15mg/m3, while the concentration of suspended particles in the outdoor air has reached 0.3mg/m3. Obviously, in this case, the introduction of fresh air can not only play a dilution role, but also deteriorate the indoor air quality

air conditioning system equipment is also easy to become a source of pollution in the process of humidification, dehumidification and other air treatment. In particular, the outdoor humidity is large. When cooling and dehumidification, the surface condensate of the surface cooler accumulates dust, and the drainage of the drip pan is not smooth, which is very easy to pollute the air; Components in the system, such as canvas soft joints and flange joints, are most prone to dust and mold, and are most prone to microbial pollution. Such factors worsen the quality of fresh air. Experiments show that almost all air handling components are pollution sources and odor sources. It includes filters, coils, heat recoverers, fans and silencers. The deterioration effects of each component on the air are different, among which the filter has the greatest impact. The main causes of pollution are oil, dust and dirty surfaces. Some components may be polluted by dust or oil in the production process

3.3 influence of ventilation system on ventilation efficiency of 3D printing filament produced by melting

different ventilation modes and air distribution modes affect ventilation efficiency, have different effects on dilution and elimination of indoor pollutants, and indoor personnel can feel different air quality

centralized constant air volume all air system, by adjusting the air supply temperature difference to meet the indoor and outdoor load changes, it is difficult to make the ventilation volume to eliminate the indoor heat and humidity load consistent with the ventilation volume required to ensure the indoor air quality

when the indoor and outdoor load of VAV air conditioning system changes, the air supply volume will change accordingly. When the air supply volume is small to a certain extent, it will increase the inequality of indoor flow field, and even produce cold air drop. In winter, hot air flow will rise, and local high-speed air flow or air flow dead corner will appear. Not only thermal comfort problems will occur, but also the indoor air quality cannot meet the requirements due to the corresponding reduction of fresh air volume. Therefore, for VAV air conditioning system, it is necessary to ensure the minimum ventilation volume and minimum fresh air volume of the system

the displacement ventilation system directly sends air at a low wind speed at the lower part of the room. Relying on the thermal effect of heat sources such as people and equipment, the air supply passes through the working area with a small disturbance, sucking up the surrounding hot air and pollutants, and rising directionally to the exhaust outlet set at the upper part for discharge. Driven by the fresh supply air in the lower part, the approximate displacement ventilation is formed indoors, which ensures the best air quality in the working area and the highest ventilation efficiency

fan coil system, coil unit is used to eliminate indoor heat and humidity load, and independent fresh air system ensures the ventilation of indoor air quality. However, the fan coil system uses water pipes instead of air pipes to move the heat and moisture treatment and filtration of air indoors, which has many negative effects on the indoor air quality: a. the number of coils of the unit is small, and the dehumidification capacity is poor, which improves the indoor relative humidity under the condition of large indoor and outdoor humidity load; B. The wet surface of the coil in the unit often becomes the source of indoor bacteria and odor, and the indoor air quality cannot be guaranteed; C. The pressure head of the fan is small, which cannot meet the requirements of the air filter; D. Because there is no indoor exhaust air, it is difficult to effectively eliminate indoor polluted air only by diluting the incoming fresh air; Often relying on the micro positive pressure formed by the fresh air, the diluted air seeps out from the building cracks, and the polluted air accumulates near the indoor ceiling, which is re inhaled by the fan coil unit and then sent indoors. Therefore, fan coil system will face severe challenges in ensuring indoor air quality

3.4 volatile organic compounds

in recent years, scholars at home and abroad have generally believed that in the past, people often paid more attention to obvious indoor pollutants, but ignored many low concentration volatile organic compounds (VOC). The concept of "molecular pollution" proposed recently means that indoor air quality control extends from particulate pollution to chemical pollution control. The most common molecular pollution in modern buildings is volatile organic compounds, which is the main source of all kinds of odors in buildings, determines people's feelings about the freshness of the air, and affects the acceptability of indoor air quality. Because the molecular diffusion rate is much higher than that of particles, controlling molecular pollution is a serious challenge to ventilation and air conditioning technology

there are about 250 kinds of volatile organic compounds in the indoor air, and the main sources of volatile organic compounds are: A. volatile organic compounds naturally emitted by the human body, such as acetone, isoprene, etc; B. Building materials such as cement, carpet, paint, glue, wallboard, floor tile and new furniture are releasing mixed organic compounds, such as formaldehyde; C. In order to save energy, insulation materials and sealing materials are widely used in buildings, which also release volatile organic compounds. Experiments show that when various volatile organic compounds are mixed together and chemically react with ozone, many invisible killers will appear in the indoor air

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