Mainly has the following characteristics.
1. Concentrate the air in the machine room and send it to each clean room.
2, because the equipment is concentrated in the computer room, it is easier to deal with noise and vibration.
3. One system controls multiple clean rooms, and each clean room is required to have a high utilization factor.
4. The clean air after centralized treatment is sent to each clean room, and different cleanness of each clean room is realized through different air exchange times and air flow forms.
Centralized clean air conditioning system is suitable for clean workshop with continuous production process, large clean room area, centralized location and strict noise and vibration control requirements. Generally speaking, there are three forms:
1. once-through type: all the air processed by the system comes from the outside, and then it is sent into the room after being processed, and then it is completely discharged outside. The system is cold, consumes the most heat, and the project investment and operation cost are high. When the clean room emits a lot of harmful gases and local ventilation cannot be solved, this method is adopted.
2. Closed: All the air handled by the system comes from the air-conditioned room itself and goes back and forth. When there is no one in the clean room for a long time, it is only to store or ensure the normal operation of precision instruments, or in some special occasions where fresh air is not needed, a closed system can be used. There is no outdoor fresh air in the closed system, and the system consumes the least cold and heat, but the sanitary conditions are the worst.
3. Hybrid: The system not only absorbs part of outdoor fresh air, but also uses part of return air. According to the return air form, there are primary return air system and secondary return air system. This system can not only meet the health requirements, but also be economical and reasonable, and is the most widely used.
Decentralized 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 merge into one system, or each clean room cannot be equipped with a conveying system and a machine room, a decentralized clean air conditioning system should be adopted, and the machine room, conveying system and clean room should be merged into one system. In the decentralized clean air conditioning system, clean air conditioning equipment or clean air conditioning equipment is installed in each clean room or adjacent room. Purification air conditioning equipment can be a complete set of products with purification function, but it can not meet the air demand of clean room with high cleanliness, and the system treatment process is often a primary return air system.
Because the fan in air conditioning equipment needs to overcome the resistance of heat exchange coil, channel and several filters, it needs a lot of pressure. In order to be installed in equipment, the volume cannot be very large; If a higher number of revolutions is used to achieve the required pressure, the noise vibration will be greater. Domestic equipment, the development of such units is slow. As we all know, in the clean room, except some necessary equipment, the equipment should be set outdoors as far as possible and the number of people should be strictly controlled. The heat and humidity load of clean room is usually smaller than that of ordinary air-conditioned room, but the demand for air is larger than that of ordinary air-conditioned room, which limits the application scope of clean air-conditioning equipment from another angle. In order to solve this problem, local purification equipment such as fan-filter unit can be placed in the clean room, or in adjacent rooms, suites, ceilings and other places connected with the clean room. Or use adjacent rooms, suites, ceilings, etc. As a static pressure box, an ordinary air conditioning unit is set in it for air mixing and air conditioning treatment. The treatment process can be regarded as secondary return air. The air conditioning unit is actually a small air conditioning system, and its cold source is usually a compression refrigeration unit. In the case of small capacity and flexibility, the heat source can be electric heating. Air treatment equipment mainly includes refrigerator evaporator, electric humidifier and electric heater. When the temperature and humidity control precision of the clean room is high throughout the year, a constant temperature and humidity unit can be used, which can automatically adjust the air temperature to maintain a certain temperature and humidity in the room. When the clean room only requires comfortable air conditioning in summer, that is, only refrigeration and dehumidification in summer, the cold air unit can be used. The main difference between it and the thermostatic unit is that there is no automatic control (manual control), electric humidifier and electric heater. If it is a small-capacity air conditioning unit (refrigeration capacity is less than 7kW, air volume is less than 1200m 3/h), it can be made into a window sill type. Large capacity (refrigerating capacity less than 70kW, air volume less than 20000m3/h) is cabinet type.
The separation of air conditioning and purification functions not only solves the problems of small heat and humidity load and large air volume in clean room, but also makes the system more flexible. Because the suite or ceiling is used as the static pressure box, the cross section of the air loop is large-the transportation route is short, and the requirements for the fan head and purification equipment of the air conditioning unit are not high, so the corresponding noise and energy consumption are not high. Purification equipment can also meet the needs of clean rooms, taking many forms, which is almost irrelevant to air conditioning units. This form is widely used in China. However, the new phoenix of this system often only depends on the negative pressure generated by the suite or ceiling, which can not be effectively controlled and can not meet the indoor hygiene requirements. By controlling the difference of air supply, positive pressure can be established in the clean space, but the negative pressure in the suite does not necessarily make the outdoor fresh air enter the suite through the fresh air filter, but often penetrates through other channels (from corridors, windows, etc.). ), and the concentration in the suite is very unstable. This will not only affect the service life of the filter element, but also involve the cleanliness in the clean space, which is an easily overlooked problem. For example, the multifunctional clean laboratory of Shanghai Urban Construction College has added a sub-efficient fresh air purification unit to the suite. Because of the fan with adjustable air volume, it can not only maintain the positive pressure in the suite, but also stabilize the air concentration in the suite; But also ensure that supply of fresh air in the clean space. In some occasions, the medium-effect fresh air purification unit can also be used.
The biggest feature of fully distributed clean air conditioning system is flexibility and simplicity. Can meet the different air supply requirements of different rooms. When the indoor heat and humidity load changes, the regulating system responds quickly and does not affect the air intake parameters of other rooms. The clean space is small and single, which is easy to manage and ensure cleanliness. In addition, there is no pipeline system and special machine room, which saves transportation energy consumption, cold and heat loss and pollution along the way, and reduces the auxiliary floor space. In addition, the air-conditioning unit is small in size, with less on-site installation workload, convenient to operate and use, and does not need specialized skilled operators.
Semi-centralized clean air conditioning system
Semi-centralized clean air conditioning system is a system form which combines centralized air treatment with local air treatment. Like a distributed system, it can not only send air back to the clean room in situ to avoid round-trip transportation, but also adjust the air to a certain state as required and then supply air to the clean room, which is beneficial to the control of clean air parameters. With the development of production technology, people have different requirements for clean rooms. People hope to realize the partition control of different cleanliness in a clean room. Therefore, semi-centralized clean air conditioning system came into being. Semi-clean air conditioning system mainly has two forms of use, which are introduced as follows:
(1) Terminal device with heat and humidity handling capacity: When the clean room meets the following conditions, semi-centralized clean air conditioning system with terminal device with heat and humidity handling capacity can be considered.
1. When the heat and humidity load of the system clean room is large;
2. The load between clean rooms varies greatly;
3. Or the use time of each clean room is different;
4, or avoid mutual pollution between clean rooms.
Because the indoor unit has the heat and humidity treatment ability, it can adjust the indoor temperature and humidity (that is, the terminal equipment) as needed. For example, using this system in hospitals can avoid cross-infection between operating rooms and meet different aseptic requirements. The temperature and humidity of the operating room can be adjusted by itself according to the nature of the operation, the requirements of doctors and the feelings of patients, but the control accuracy of such air conditioning system is not high, and the uniformity of temperature field, humidity field and concentration field is also poor. For larger terminal equipment, the primary air can also be directly sent to the fan coil, and then mixed with the return air to enter the room through the coil. Because there is only one air supply outlet in the room, the interference of primary air on the local parallel flow area of the terminal device is avoided.
(2) End of purification device
The most widely used semi-centralized clean air conditioning system is the terminal device system with purification function. Most reconstruction projects adopt this form. When the original ordinary air-conditioning system is reformed, filter equipment is added to the original air-conditioning system, such as adding filter boxes in the proper position of the air supply pipeline, adding filters in the air supply outlets of each room, or replacing the filters of the original system, thus forming a terminal device system with purification function. The terminal device plays the role of self-circulation and self-purification indoors, and is an auxiliary means of indoor cleaning. When adjusting the air volume of terminal devices or changing the number of open terminal devices, different cleanliness can be achieved indoors.