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Design Scheme of Fresh Air System for Clean Workshop

Author: Shenzhen ZhongJian South Environment CO., LTDissuing time:2017-02-21 16:55:56Pageviews:2591smallinBig

With the rapid development of China\'s information technology, in recent years, large-scale, high-level clean plant (or super clean factory) have been built. This plant is characterized by a large area of clean production areas (or technological layer), the region arranged a specific craft area and the central corridor...
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With the rapid development of China's information technology, in recent years, large-scale, high-level clean plant (or super clean factory) have been built. This plant is characterized by a large area of clean production areas (or technological layer), the region arranged a specific craft area and the central corridor, the key set of high cleanliness of the product walkway and micro-environment devices. The upper layer of the huge space used to arrange the air duct or used as a hydrostatic tank; its quasi-clean area (or facilities layer) is used to arrange from the clean area out of the equipment, process facilities and central public facilities Pipe network; between the facility layer and the process layer with a return air space; clean area around the shaft for the return air. By the independent fresh air handling system, focus on the fresh air directly to the internal state of the dew point, and then into the circulating air system. The dry air duct is provided in the circulating air passage to handle the sensible heat load in the room. The difference is only the design of the cycle of wind system ideas, which have a corresponding solution.


无尘车间净化工程新风系统设计方案

  1, clean room purification project fresh air system design
 
The main support system of Zhongjian South Clean Factory is central public facilities, often concentrated around the clean area or set up in a separate dedicated building. In addition, a safety system is set up, which includes fire detection and forecasting system; HCF, CO2 gas fire extinguishing and sprinkler systems; smoke detection and smoke extraction systems, chemical testing, emergency control systems, and storage systems.
 
Due to critical process requirements and constant replacement of the environment is very harsh, especially the system reliability, flexibility and safety, equipment capacity and energy efficiency, margin and standby and the environment, health and safety are strict requirements The In order to meet critical production requirements, a very high degree of cleanliness (level 1 of 0.1 μm) can be achieved in the microenvironment set in the process layer, and the cleanliness level of other production areas must also reach 1000 or higher. The core of its technology is the use of one-way flow of air technology (the ability to exclude dust pollution) and isolation technology (isolation of the outside world on the process environment). The unidirectional flow rate is typically 0.35 m / s. In response to the low cost of use, the use of short time to achieve technological transformation and renewal, with particular emphasis on air supply mode flexibility, reliability and security, embodied at any time can be simply based on the process of distribution and process environment to make the latest changes. As the process updates quickly, the production equipment of the production capacity is not only a large proportion, but also changes frequently. So the design concept and the corresponding air supply system mode pay special attention to the system margin and spare.


  2, Clean room ventilation and air conditioning system model

 
In recent years, there are three system models of clean room, the main difference is that the circulating air system, usually a decentralized fan unit, fan shaft and fan filter unit (referred to as FFU). China's current extensive use of the fan filter unit model characteristics, as well as with the other two air supply model for further analysis and comparison.
 
(2.1) decentralized circulating fan units
 
This circulating fan unit is a distributed, air-conditioned unit consisting of a dry cooler and a centrifugal fan. Directly installed in the upper part of the clean process layer, the return air shaft is arranged on both sides of the building, the centrifugal fan can produce enough pressure head (650Pa or so) to meet the air flow through the air return through the various components of the static pressure, Greatly extending the life of the end filter. However, when the total flow increase is too large, the fan size, cost, fan noise generated by a corresponding increase. The air supply pressure chamber is provided between the blower unit and the filter ceiling, so that the pressure in the air supply chamber is still higher than that of the clean process layer.
 
(2.2) fan shaft
 
Can be used on both sides of the building (or tunnel) space to install the cycle unit, the axial fan is most appropriate. And the muffler together, very compact and efficient, and therefore very economical. As the roof do not have to withstand the cycle unit, the load can be reduced, the building structure is also reasonable. Between the roof and the filter ceiling between the layout of the air pressure box, air pressure chamber pressure is higher than the clean process layer, which had to use the liquid tank seal. That is, in the ceiling grille in the tank filled with non-Newtonian liquid sealant, round with a knife edge of the air filter into the sealant, resulting in a sealed with the liquid ceiling between the airtight seal. It is also convenient to install and change the air filter (or blind plate). The advantage of an axial fan is that it can deliver more air efficiently with a relatively low hydrostatic pressure and can easily and efficiently change the air volume. It produces static pressure and flow than the full compliance with the typical high-level clean room operating conditions.
 
(2.3) Fan Filter Unit (FFU)
 
A typical fan filter unit consists of a built-in centrifuge, a silencer and a high efficiency filter (HEPA or ULPA filter), compactly assembled in a metal box. In the clean craft layer on the ceiling can be arbitrarily in accordance with the requirements of the process directly set the fan filter unit (or blind) to form a different level of clean area. The fan filter unit is very easy to use for circulating air circulation, but can not produce too much static pressure. The air through the unit within the silencer segment and the end of the filter after almost no power left to overcome the external system resistance.
  
The above three concepts have a high degree of flexibility, in the clean room are widely used. Can make the intermediate process layer can be very convenient to accept high clean air, change the clean area. The system return air is carried out by means of the next space, and all facility piping can be easily mated according to the equipment change or displacement. All potential sources of pollution can be closed or eliminated to prevent cross contamination. The following three models will be analyzed and compared, focusing on how to make the whole system to reduce costs, save operating costs and improve energy efficiency.


  3, three air supply mode comparison

 
The recirculating wind system has three purposes: temperature control, dust control and airflow control. The main purpose of removing clean room dust and heat. The amount of air blown by the circulating air system depends on the cleanliness level of the clean room. Although the three air supply modes can meet the requirements of the circulating air system. But because of the circulating wind transport system accounted for a large proportion of energy consumption, we have to pay attention to its energy efficiency.
  
In recent years, a large number of fan filter units in China mainly for the following reasons:
  
(1) fan filter unit's own superior characteristics, such as flexible settings, can adapt to process changes, the roof is not easy to leak, ceiling grille and low cost of sealing;
  
(2) bias on the axial fan, such as low wind pressure, noise and so on.
  
(3) Compared with the distributed circulating fan unit, can reduce the height of the building.
  
(4) With the use of micro-environment, the process level cleanliness level, fan filter unit cost competitive.
  
(3.1) In recent years, the performance of the south side of the fan filter unit has been greatly improved, to solve the wind speed uniformity, vibration, noise and failure rate and other issues. The new fan filter unit blower uses a carbonless brush, electronic rectifier DC motor, can be continuously variable. Hall-effect (Hall-effect) sensor to control the line can accurately align the motor voltage and fan torque required to match the motor effect increased to 75% to 80%. The efficiency of the increase to bring more quiet operation effect, enhance its competitiveness. The controller also allows the speed of the fan to be monitored and controlled remotely. Similarly, the switch status of each fan filter unit can be monitored and controlled remotely. Can accurately control and monitor each fan filter unit operation, is the other two programs can not and. But the fan filter unit expensive equipment costs, but also the other two programs can not be compared. Fan equipment, power distribution facilities and the highest cost of automation. Although its motor is much smaller, but its number is much more. Although the cost of automation of the fan filter unit can be reduced by reducing the monitoring function, doing so can compromise the operation and maintenance of the system. In contrast, the fan filter unit due to the external pressure is not large (100Pa or so), the need for a wider return air shaft, a larger cooling coil area to reduce the cross-section wind speed and reduce system resistance. It is difficult to add other filters. From the structural point of view fan filter unit can reduce the cost of the filter ceiling. But because the tank sealed roof has been very mature, and mass production, the price has repeatedly declined. The difference between the two costs is not big. The fan filter unit can indeed simplify the seal of the filter ceiling. However, due to the high pressure inside the filter inside the unit than the clean room area, the filter inside and outside the unit is still a big problem, dust particles still exist to penetrate the risk of clean areas. Of course this ("leakage") was the original construction problem, is now turned into product quality problems, but the hidden danger.
  
(3.2) According to past experience, axial fans should be the three types of fans in the noise and vibration of the largest static pressure generated enough to overcome the resistance of the purification system. Additional noise abatement measures must also be taken, which in turn increases system costs and additional static pressure losses. To this end in the field of air conditioning in the vast majority of occasions are used centrifugal fan. However, the performance of centrifugal fans and axial fans not only to see the static pressure or flow of the value, but to consider the resulting flow and static pressure ratio, high-grade clean room, the axial flow fan and static pressure ratio of the most reason. The comparison of performance between the two is relative. Usually the final choice of the two does not depend on their own strengths and weaknesses but on what concepts and ideas are used. It must be noted that the current axial fans have been completely not the concept of the past, and that advanced wind turbine engineering has been combined with aerodynamics and acoustically manufactured mufflers. In order to achieve the desired level of performance, the manufacture of axial fans must be within the strict tolerances; the fan body must be perfectly close to the cylinder, so that the gap with the fan impeller to a minimum. So the fan body is not only a sheet metal parts, but also the speed and blade spacing angle of the two variable flow device, can make the fan to achieve the best performance. Import and export muffler is also designed to be customized so that no high noise muffler is required to achieve maximum noise attenuation performance. In addition to improving these properties, the axial fan unit shaft equipment settings can be simplified, more convenient maintenance. Each fan is mounted on a movable trolley, which is generally fixed and connected to the muffler of the entrance and exit. Normally, these fans do not require service because they are only one moving part. When necessary to repair or replace the fan, you can unload the fan and the muffler connection, with a simple traction tape to roll it out from the air channel, sent to the adjacent maintenance area. If necessary, it is entirely possible to select an axial fan with external hydrostatic capability to overcome the resistance of components such as front filters or chemical filters. The more suitable external pressure is 400Pa.
  
(3.3) Now the decentralized circulation fan units are mostly used without a volute fan, the performance has also increased. But the new axial fan performance, more and more units in the non-clean area, in three programs in its installation and maintenance of the most convenient, minimal impact on the clean process layer. It requires the highest height of the plant, but without such a large building width. For the decentralized cycle unit, the building structure of the fan platform is essential, while the other two programs are not required. As the cooling coil area is set in the unit, the chilled water must be connected to each cycle unit of the roof. There is a hidden danger of water. This is the fatal weakness of the distributed circulating fan installed in the upper deck.


  4, Qualitative analysis of three air supply mode

  If we introduce the energy efficiency and investment cost as the evaluation index, this is the basis for the qualitative analysis of the three modes of air supply. The energy efficiency evaluation index mentioned in the literature is expressed as the energy consumed by the unit air flow [W / (m3 / h)]. Investment costs are expressed in terms of relative cost prices, including machinery, electricity, testing equipment and controls, and construction and construction costs.
In the past to adapt to the process of frequent updates, most of the use of a large area of clean room, the process layer filter full rate is often 100%; now a large number of production lines using micro-environment devices, external clean space cleanliness of only 1000, Reduced, the filter full rate can be reduced to 25%. For these two occasions to compare the above three programs.
  
(4.1) the relative total cost of each scheme. Reflecting its cost factors. The difference between the three schemes in the 100% filter full rate is obvious. Fan filter unit program, the highest cost of equipment, fan filter unit costs can be close to the decentralized cycle unit. But its superiority is also lost.
  
(4.2) For 25% of the filter full rate of the occasion, the fan-type shaft program in general did not change much. Due to the presence of the axial fan, the size of the fan shaft can not be changed. Fan filter unit is due to greatly reduce the amount of circulating air, so that the number of units to reduce the return air shaft narrowing. Investment costs can be reduced to the most. In contrast, the cost of the decentralized unit is slightly higher (the cooling water must still be fed into each decentralized unit). In addition, the required distribution costs and automation costs for the fan filter units are also reduced with the reduction in the number of units, and the cost of the equipment for the distributed cycle unit is maximized. The cost difference between the three programs is only reduced at 25% of the filter's full rate. Reflecting its cost factors. At this time the fan filter unit competitiveness increased. However, compared to the other two programs, still need a larger cooling coil area, to adapt to the process of changing the corresponding system margin (air volume or residual pressure) is still small, difficult to make a larger system changes. For the fan filter unit, the height of the upper layer only to meet the convenience of the maintenance of the static pressure box can be. If the plant height is too low, you can not use the fan shaft program. For decentralized units, the larger upper level is important for the placement of the equipment on the pressurized air supply. The architectural platform of the fan platform is also important for supporting decentralized circulation units.
  
(4.3) The higher the energy efficiency, the less energy required to move the air at a certain flow rate. Reflecting the energy efficiency of different filters at full rate. From this table, it can be seen that the shaft fan and its motor are essentially more efficient, whether the traditional fan, or the use of new fans in the filter full rate of 100% and 25% of the case, the energy efficiency is always better than the other two High program Even when the filter full rate is 25%, the energy efficiency of the CCF unit is greatly improved, but the energy efficiency of the fan filter unit is still the lowest. The traditional fan system energy efficiency is about 0.235W / (M3 / H) or so, usually IC clean room only the annual air system more than 5 million yuan electricity. Such as the use of new fan system energy efficiency increased to 0.118W / (M3 / H), the electricity can save half, considerable.

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