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Basic concepts of Clean air conditioning
1. Basic concepts of clean air conditioning
Clean air conditioning is a type of air conditioning engineering. It not only has certain requirements for the temperature, humidity and Wind speed of indoor air, but also has higher requirements for the number of dust particles and bacteria concentration in the air. For this reason, the corresponding technology is called air cleaning technology. A well-sealed space that controls air temperature, humidity, cleanliness, pressure, noise and other parameters according to needs is called A Clean Room.
2. The difference between clean air conditioning and general air conditioning
a. Main parameter control
General air conditioning focuses on the control of temperature, humidity and air freshness, while clean air conditioning also requires the control of indoor air dust content, wind speed, ventilation frequency, etc.
b. Air filtration measures
General air conditioning only has coarse-effect filtration and primary filtration, and the higher requirements are coarse-effect and medium-effect secondary filtration, while clean air conditioning requires coarse, medium and high-efficiency three-level filtration. In some clean rooms, there is also a filter adsorption filter.
c. Indoor pressure requirements
General air conditioners have no special requirements for indoor air, but clean air conditioners have different requirements for positive pressure values in different clean areas to avoid the infiltration of external polluted air or the mutual influence of different substances in different production workshops. There are also control requirements for negative pressure values in negative pressure clean rooms.
d. Requirements for the selection of materials and equipment for clean Air conditioning systems
The selection of materials and equipment for clean air conditioning systems, processing technology, processing and installation environment, and storage environment of equipment components have special requirements to avoid external pollution, which are also not available in general air conditioning systems.
e. Requirements for system air tightness
Although general air conditioning systems have requirements for system air tightness and air permeability, clean air conditioning systems have higher requirements, and their detection methods and standards for each process have strict measures and testing requirements.
f. Requirements for architecture and other professions
General air-conditioned rooms have requirements for building layout, thermal engineering, etc., but they do not pay much attention to material selection and air tightness requirements. In addition to the requirements for the appearance of general buildings, clean air conditioning also has strict requirements for dust prevention, dust prevention, and leakage prevention in the evaluation of building quality.
Forms of clean air conditioning system
In order to maintain the required temperature, humidity, wind speed, pressure and cleanliness parameters in the clean room, the most common method is to continuously send a certain amount of processed air into the room to eliminate various heat and humidity interference and dust pollution inside and outside the clean room. In order to obtain air with a certain state sent to the clean room, a complete set of equipment is needed to process the air, and continuously send it into the room, and continuously discharge part of it from the room. This complete set of equipment constitutes a clean air conditioning system.
1. Basic composition of clean air conditioning system
The equipment used in the clean air conditioning system is roughly divided into three categories according to its function:
Heating or cooling, humidification or dehumidification and purification Equipment:
Air conveying equipment and its pipelines that send the treated air into each clean room and circulate it:
Heat and cold sources and their pipeline systems that provide heat and cold to the system.
2. Classification of clean air conditioning systems
Clean air conditioning systems are generally divided into three categories:
a. Centralized clean air conditioning system
The purification and air conditioning equipment required for a single or multiple clean rooms in the system are concentrated in the machine room, and the clean air is distributed to each clean room using air supply ducts.
b. Distributed clean air conditioning system
In each clean room in the system, purification equipment or purification air conditioning equipment is separately set up.
c. Semi-centralized clean air conditioning system
In this system, there are both centralized purification air conditioning rooms and air handling equipment dispersed in each clean room. It is a form of centralized processing and local processing.
People generally name the system according to the cleanliness of each clean room in the system, such as 100-level purification air conditioning system, 1000-level purification air conditioning system, etc. Sometimes it is also distinguished according to the nature of the system's unfiltered filters, divided into high-efficiency air purification system, sub-high-efficiency air purification system and medium-efficiency air purification system.
Centralized clean air conditioning system
1. Features of centralized clean air conditioning system
The air is centrally processed in the machine room and then sent to each clean room.
Since the equipment is concentrated in the machine room, it is easier to handle noise and vibration.
One system controls multiple clean rooms, requiring each clean room to have a high simultaneous use coefficient.
The clean air after centralized processing is sent to each clean room, and different cleanliness levels in each clean room are achieved with different ventilation times and airflow forms.
2. Applicability of centralized clean air conditioning system
Centralized clean air conditioning system is suitable for clean workshops with continuous process production, large clean room area, centralized location, and strict noise and vibration control requirements.
3. Forms of centralized clean air system
a. Direct current type
The air processed by the system comes from the outside, is sent indoors after processing, and then all discharged to the outside. This system consumes the most cold and heat, and has high engineering investment and operating costs. This method is used when a large amount of harmful gases are emitted in the clean room and local exhaust cannot solve the problem.
b. Closed type
The air processed by the system comes from the air-conditioned room itself and circulates back and forth. When no one stays in the clean room for a long time, a closed system can be used only for storage or to ensure the normal operation of precision instruments, or some special occasions where fresh air is not required from the outside. The closed system has no outdoor fresh air, and the system consumes the least cold and heat, but the sanitary conditions are the worst.
c. Hybrid type
The system not only absorbs part of the outdoor fresh air, but also uses part of the return air. There are primary return air and secondary return air systems according to the return air form.
This system can meet the hygienic requirements, is economical and reasonable, and is the most widely used.
Distributed clean air conditioning system
For some occasions where the production process is single, the clean rooms are scattered, and it is impossible or inappropriate to combine them into one system, or the conveying system and machine room cannot be arranged in each clean room, a distributed clean air conditioning system should be used. In this system, the machine room, conveying system and Clean Room are combined to form a system. In the distributed clean air conditioning system, purification and air conditioning equipment or purification air conditioning equipment are installed on-site in each clean room or adjacent room. The purification air conditioning equipment can be a fixed unit product. It has a purification function, but the Air volume it processes is small, and it often cannot meet the air volume required for clean rooms with higher cleanliness. The system processing process is often a return air system.
Semi-centralized clean air conditioning system
The centralized clean air conditioning system controls more clean rooms, and the air volume it needs to process and transport is large, but most of these transported air volumes are indoor return air. When the system is working, in order to meet the requirements of noise control, the supply and return air ducts must use low flow rates to transport air, so the cross-sectional area of the air duct is large. In addition, the air handling equipment in the machine room is huge, and the entire air conditioning system occupies a large building area and building space. Semi-centralized clean air conditioning system is a system form that combines centralized air treatment with local air treatment. It has both the ability to return air to each clean room on site to avoid round-trip transportation like a decentralized system, and the ability to supply fresh air to each clean room as needed after air conditioning to a certain state like a centralized system, which is conducive to the control of clean air parameters. On the other hand, with the development of production technology, people have different requirements for clean rooms. People hope to achieve different cleanliness zoning control in a clean room. Therefore, semi-centralized clean air conditioning systems have emerged, such as tunnel or duct clean air conditioning systems.
1. Semi-centralized clean air conditioning system with terminal device with heat and humidity treatment capabilities
When the clean room is in the following conditions, a semi-centralized clean air conditioning system with terminal device with heat and humidity treatment capabilities can be considered.
When the heat and humidity load in the clean room of the system is large,
The load difference between each clean room is large,
Or the use time of each clean room is different,
Or avoid mutual contamination between each clean room.
Since the indoor unit has heat and humidity treatment capabilities, the indoor temperature and humidity can be adjusted according to the requirements of the unit (i.e. terminal device). For example, using this system in a hospital can avoid cross infection between operating rooms and meet their different aseptic requirements. The temperature and humidity in the operating room are adjusted by the terminal device according to the nature of the operation, the doctor's requirements and the patient's feeling, but the control accuracy of such an air-conditioning system is not high, and the uniformity of the temperature field, humidity field and concentration field is also poor. For larger terminal devices, the primary air can also be directly sent into the fan coil, which is mixed with the return air and enters the room through the coil. Since there is only one air supply port in the room, the interference of the primary air on the local parallel flow area of the terminal device is avoided.
2. Terminal device with simple purification function
The terminal device system with simple purification function is most widely used in semi-centralized clean air conditioning systems. Most reconstruction projects adopt this form. When the original ordinary air conditioning system is purified and renovated, a filtering device is added to the original air conditioning system, such as adding a filter box at the appropriate position of the air supply pipe, adding a filter at the air supply port of each room, or replacing the original system filter. In this way, a terminal device system with simple purification function is formed.
The terminal device plays a role of self-circulation and self-purification in the room, which is an auxiliary means for indoor cleanliness. When the air volume of the terminal device is adjusted or the number of terminal devices turned on is changed, different cleanliness levels can be achieved indoors.
