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Fresh air application is an important link in the central air-conditioning system
In the air-conditioned environment, due to artificial heat preservation and moisturizing measures, the air inside and outside the environment cannot be exchanged naturally. It is necessary to artificially transport natural air into the outside to maintain the air quality requirements in the environment. The incoming air is called fresh air.
Attention must be paid to the fresh air because the air in the air-conditioning environment is tempered, humidified or purified. The addition of external air must also be cleaned in a warm and humid manner to maintain a constant parameter value of the original ambient air. Therefore, the feeding of fresh air is no longer just a problem of energy consumption of the air supply equipment, but a problem of a large amount of power that is continuously fed to the fresh air to regulate the temperature and humidity. It occupies a considerable proportion in the energy consumption of the entire air conditioner. Fresh air must not only consume energy but also strive for less energy, so analysis must be emphasized.
The necessity of fresh air
I. Air pollution
In the environment where air conditioners are actually applied, including human settlements or industrial production process plants, they cannot be kept fresh even under closed conditions, because various environments have different sources of pollution, such as:
(1) In the living environment or the environment in which other living things exist, there will be a process of inhaling and deflating in the cycle of life, such as a person inhaling oxygen
Exhale carbon dioxide, exhale odors, smokers emit smoke, etc.
(2) Harmful gases and volatile substances are released from furniture and four-wall decoration in the environment.
(3) Hazardous gas or oxygen consumption in the production process.
温湿死角滋生的霉变物质散发异味。 (4 ) The moldy substance that breeds in the dead corner of warm and humid odor.
Long-term accumulation in confinement will be the deterioration of the original air and anoxia. People feel dizzy and uncomfortable in a closed air-conditioning environment. The so-called air-conditioning disease is caused by the deterioration of the original air quality.
Second, ways to improve air quality
There are two ways to solve air deterioration. One is through various methods such as artificial oxygen production and chemical supply, chemical decomposition, physical adsorption, ionization and photocatalysis to eliminate harmful gases and supplement oxygen. However, this method has a complicated process and consumes a large amount of energy, which is only suitable for small space such as spacecraft, submarines and submarines for special needs. Secondly, a more suitable method for large civil spaces is to replace or dilute the original excess air with the endless air of the natural environment, so as to improve the overall air quality in the air-conditioned environment. This method is relatively easy to implement and consumes less energy, so it is widely used, and it is also a common method for fresh air system engineering in our air-conditioning environment.
Energy consumption of fresh air
The fresh air project in the air-conditioning environment is basically a welcome and old project in a closed environment. Because the air in the original air-conditioning environment has been adjusted according to people's requirements for temperature, humidity, and purification to maintain a specific state. The outside air must be treated in the same way to ensure that the fused ambient air remains constant. 。 Continuously entering a large amount of fresh air treatment will consume a lot of energy, which may reach 25% ~ 40% of the total energy consumption of the air conditioning system .
Application of fresh air
The input of fresh air to meet the requirements of the air-conditioning environment can be implemented in three ways.
(1) Total replacement, replacing the original ambient air with continuous fresh air from outside. In the air-conditioned environment, this method is only used in small environments with special needs. For example, environmental laboratories and special wards have fewer applications. However, non-air-conditioning conditions such as the ventilation system in mine tunnels are often used.
(2) Partial replacement. In areas where large air-conditioning needs to be focused on ensuring higher requirements, directional fixed posts are used to blow fresh air. For example, in some industrial production processes, fresh air is blown to the work station on demand to ensure higher requirements. This method can improve the utilization rate, reduce the fresh air consumption, and reduce energy consumption.
(3) Mixing and adjusting. For the air that exceeds the standard in the original large air-conditioning environment (such as low oxygen content and excessive harmful gas content, etc.), mix it with fresh air to keep the diluted large ambient air stable. Qualified content range.
This method is easy to implement and easy to calculate, so it is a commonly used method.
However, a detailed analysis of this method is like to ensure that the entire pool of water in the pool does not exceed the standard when drinking and drinking, and the whole pool of water is diluted with fresh water to pass, the fresh air volume is large, the time to reach the standard is slow, and the consumption Can be larger.
Therefore, a new theoretical measure has been developed, that is, when selecting the fresh air value, the fresh air distribution mode can be determined according to its environmental function, instead of simply multiplying the volume of air by the theoretical unit fresh air volume value.
V. Determination of fresh air volume
The selection of the fresh air volume value is based on three major premises. The aim is to reduce the amount.
(1) According to the functions and requirements of the air-conditioning environment
）。 If there are few or unmanned spaces such as production workshops, cold storage warehouses, etc., you can determine whether the ventilation volume is necessary or a small amount ( m3 / h ) according to the environmental conditions . m3/h 。 If it is a living environment, the air volume value m3 / h should be determined according to the person's normal needs and comfort requirements . To ensure the oxygen supply and reduce the harmful gas concentration ratio to meet the requirements.
(II) Layout and adjustment form based on fresh air
According to different forms of total displacement ventilation, partial displacement ventilation, or mixed adjustment ventilation and jet air supply, different values of fresh air supply should be used.
人）值。 (3) Determine the average fresh air volume ( m3 / h.person ) per person according to the density of the air-conditioned environment crowd and the activity status of the personnel .
VI to control the carbon dioxide content to determine the amount of fresh air
法则，即是“按需控制通风” DemandControlVentilation 这是近年来采用的节能通风策略，原则是以控制环境空气中的 CO2 浓度值，以及室外 CO2 浓度差值来确定新风量值。 In recent years, the United States and other countries have implemented the DCV rule, which is "control ventilation on demand." DemandControlVentilation is an energy-saving ventilation strategy adopted in recent years. The principle is to determine the fresh air volume by controlling the CO2 concentration value in the ambient air and the difference in outdoor CO2 concentration. value.
Generally, the air conditioning and ventilation system uses a mixed air supply method to send outdoor fresh air to dilute the original indoor air to ensure that the air quality does not fall below the required index.
There are many indicators of indoor air quality, including the necessary value of oxygen content and the maximum limit of various harmful gases. 策略是以“ CO2 浓度差”来确定新风量。 The DCV strategy uses the " CO2 concentration difference" to determine the fresh air volume.
ppm ，表示为每 106 个的单位体积空气中含有 CO2 气体相同单位体积的数量。 CO2 is derived from the exhaust gas released from the life cycle of humans and other animals and plants. The physical unit representing its content is ppm , which is expressed as the same unit volume of CO2 gas per 106 unit volumes of air . 10-6 。 Visible is a dimensionless value of 10-6 .
值不同，一般是在 200ppm 至 1000ppm 范围。 The ppm values at different heights in different regions of the earth's natural environment are generally in the range of 200 ppm to 1000 ppm . 400ppm 。 The fresh air in natural environment is about 400ppm . CO2 量也会相差数倍。 The indoor environment is related to functional occasions, and the amount of CO2 emitted will be several times different between people in static and dynamic . CO2 含量可能有 1000~3000ppm ，空调环境宜取小于 1000ppm 。 In buildings, the CO2 content may be 1000 ~ 3000ppm , and the air-conditioning environment should be less than 1000ppm .
标准，室内为 1000ppm ，而室外空气是 CO2 为 300ppm ，即差值为 700ppm 时，作为惯例取新风值为每人 25.5m3/h. 人。 According to the American ASHARE standard, the indoor air is 1000ppm , and the outdoor air is 300ppm CO2 , that is, when the difference is 700ppm , as a rule, the fresh air value is 25.5m3 / h. Person.
VII Principles of Actually Taking New Wind Value
的浓度差值也不同，其时可按下值选取： (1) The difference in CO2 concentration is different for different indoor and outdoor environments .
8.5m3/h. 人 2000ppm corresponds to 8.5m3 / h.
25.5m3/h. 人 700ppm corresponds to 25.5m3 / h.
34m3/h. 人 500ppm corresponds to 34m3 / h.
50m3/h. 人 350ppm corresponds to 50m3 / h.
(2) The actual selection must also be modified according to the actual environmental use requirements and the actual air quality and other harmful gas content.
(3) When selecting fresh air, we must pay attention to the actual outdoor environment. If the external air pollution is serious and the quality is bad, introducing fresh air will lead the wolf into the house. At that time, the comprehensive application of purification measures and appropriate amount of fresh air should be adopted.
Comprehensive analysis to draw value from examples
人作为参考基准，根据不同要求而上下延伸选取，在保证功能条件下，力求节能。 The fresh air volume in the actual engineering design can be selected based on 25.5m3 / h. Person , and can be selected up and down according to different requirements. Under the guarantee of functional conditions, strive to save energy. The following are the recommended values of various types of engineering cases:
人 Grand stadium, theater 8.0 ~ 8.5m3 / h. People
人 Department stores, classrooms 8.5 ~ 10m3 / h. People
人 Playgrounds, common rooms 17 ~ 20m3 / h. People
人 Restaurant, meeting room 20 ~ 25m3 / h.
人 Office 25m3 / h. People
人 Superior hotel room 30m3 / h. Person
人作为参考基准。 If the function is not clear, 25.5 ~ 30m3 / h. Person is selected as the reference benchmark.
Fresh air application is an important part of the central air-conditioning system, which is related to the use effect and operating energy consumption of the entire central air-conditioning system. We must strive for correct solutions, appropriate values, and reasonable layouts to achieve good results and energy savings.
Related links: Dongguan air-conditioning purification project, Dongguan dust-free purification equipment, Changan central air-conditioning project, low-voltage power distribution project, Dongguan purification ventilation project, Dongguan dust-free purification project, hydropower installation project, Dongguan 100,000-level dust-free workshop, Dongguan City Power Xiang Air Conditioning Purification Engineering Co., Ltd.
Article source: http://jimesale.com Tan Yuming 13751461639