Fan-Filter Unit (FFU) is a combination of blower and high efficiency filter (HEPA / ULPA) of the air circulation and filtration equipment (see Figure 1), a large number of currently used in various types of clean room , As the clean room secondary side of the main loop filtration system equipment, but also the whole clean room air handling terminal equipment (see Figure 2). FFU clean room, generally according to their laying density is divided into laminar (laminar) clean room and turbulent type (turbulent) clean room two categories, laminar flow clean room FFU is 100% coverage On a ceiling grid, while the turbulence clean room depends on design requirements. Laminar flow clean room generally within the Class 1000, turbulence clean room is in Class 1000 outside, and whether laminar or turbulent clean room, indoor re-process can be required, the use of machine ( (FFU) or local space (such as clean tunnels) to create a cleaner environment, the so-called mini-environment, and fully demonstrated FFU-type clean room in the creation of clean space on the flexibility And advantages. The use of fan-screen units began around the 1980s, and almost all of the new clean rooms (especially in the Asia-Pacific region) in the 1990s were of the FFU type, and the technology was evolving as a result of extensive use.
The early clean room is a so-called central system, the work area above or the side of the laying of only filter or blank plate (blank panel), airflow must be directly by the fan (Figure 3) or air conditioning system through the duct system indirect As shown in Figure 4). From the energy efficiency point of view, the central fan system is superior to the air conditioning duct system due to the absence of piping losses and the high fan efficiency. Compared with the FFU system, large central balance of the system more difficult, but maintenance is mainly targeted at a few large blower or air conditioning box, the target is clear and easier to implement, but the central system as long as a fan or air conditioning box Problem, unless the standby unit can be immediately on-line (on line), otherwise the clean room will probably have to shut down, and FFU system in this area the risk is relatively small. Recently, due to the development of motor and network control technology, FFU system due to the number of maintenance inconvenience caused by the situation has been improved, through the network monitoring, more units can also be fully displayed on a monitor. FFU clean room system As the fan directly above the work area, so the work area relative to the return air duct and the ceiling is a positive pressure air space, outside the work area contaminants can not leak into the work area; the contrary, the central System work area is negative pressure space, so the risk of leakage than the FFU system. Figure 5 shows that in addition to process equipment, peripheral (factory) system to the most energy-efficient refrigeration and air conditioning systems, which again in the air flow, circulation, filtration system is the largest, therefore, is the central or FFU clean room, Refrigeration and air conditioning system of energy-saving and air flow, circulation, filtration system selection and design of a significant relationship.
Fan-screen unit technology fan ─ ─ filter unit is basically an extension of the blower technology, but because of the reliability of the clean room on the vibration and noise issues are quite sensitive to the motor, fan and duct design and overall assembly quality Of the requirements of the fan than the general high; In addition, due to a large number of clean space and the machine on the pavement, coupled with continuous use of the characteristics of the energy use of the multiplication effect is considerable, so energy efficiency can not be ignored performance. In fact, the traditional large-scale HVAC system operation, if the energy-consuming equipment can be broadly divided into two main categories of mainframe and air supply systems, statistical data show that the total energy consumption of the air system is much larger than the host, one of the mainframe and But the air supply system as long as the HVAC system is turned on, it almost non-stop operation. Clean room is also a kind of HVAC system, naturally there are similar operating characteristics, and research and measured data also show that the air circulation system is indeed the most energy-consuming equipment outside the system equipment. From the design point of view, aerodynamic efficiency (aerodynamic efficiency) of the fan and the air duct design, with the use of high-efficiency motors and assembly on the strict quality control, can simultaneously achieve vibration, noise suppression and enhance energy efficiency , The reliability of multiple purposes.
FFU is currently on the market the brand is gradually increasing, but there is no standard performance testing methods, and because the cost of FFU system and clean room as a whole (including manufacturing process) the cost of disproportionate, so users are not able to pay attention to its performance It is possible that the fan-screen unit system will become a heavy burden on the future operation and will have an additional negative impact on the environmental protection. Since the FFU is an extension of the blower technology, the reference test method of the blower performance is reasonable, not only as the basis for product technology development, but also provide a consistent basis for performance comparison between different products. Figure 6 shows the performance of the FFU at the AMCA Laboratory of the Industrial Technology Research Institute (ITRI). Figure 7 shows the performance of the FFU at the IELI's CNLA certification. Figure 8 is the FFU in the maximum air flow operation (zero pressure point) to do the vibration measurement of the situation, if necessary, can do other points of vibration of the operating point of the amount of vibration, Measure. Many domestic and foreign manufacturers have commissioned the two laboratories FFU research and development, product validation or technical audit test, the test results show that, from the principle or practical application of the surface, the current international air blower aerodynamic performance and noise standard test methods are in line with FFU aerodynamic performance testing requirements, FFU filter efficiency, uniformity of the wind (uniformity) and parallelism (inclination) and other features, according to IEST recommended method of testing.
As mentioned earlier, the current clean room air circulation design probably FFU-style, central air-conditioning and central air conditioning box-type three categories, each type of clean room itself can be further in the equipment and system design to improve, but the above Three types of clean room present in the world is not evenly distributed, generally the Asia-Pacific region with multi-purpose FFU-type clean room, the Americas is the central clean room, the European region is the central type FFU. In addition to the habits, experience and other non-technical factors, the energy efficiency (operating costs) is also the focus of consideration, but the current three types of clean room air circulation system energy efficiency evaluation is inconclusive, basically accustomed to that class , Said that the type of energy efficiency. Figures 15, 16 and 17 are the partial results of the three studies, showing the current energy efficiency comparison of the three types of air circulation systems except for the central air-conditioning unit with a higher energy efficiency than the central air conditioning unit , Can not FFU type and the central type between the obvious conclusion. In fact, the comparison between systems is not easy, the so-called "Apple and Apple than the orange and orange than" the principle we all know, but how to define the different system design of the apple or orange is not simple, but in the foregoing comparison Principle, the reality of comparable examples is almost impossible, the more feasible way is by comparison of laboratory and laboratory experiments.
In comparison with the FFU-type clean room, the fan efficiency of the large-scale axial-flow fan is 80% of ideal, and it is assumed that the motor The efficiency of up to 90%, the electrical efficiency is the product of the two 72%, if you consider the sound box on the fan losses, the fan pressure efficiency down to 70%, the electrical efficiency will be reduced to 63% (assuming motor Efficiency); fan - filter unit DC brushless motor efficiency can reach 90%, assuming the fan (including filter) full-pressure efficiency of 50%, the electrical efficiency of 45%. Of course, the actual operating point in the stand-alone, the motor efficiency may not be so high, so the electrical efficiency will not reach 63% and 45%, but in the best circumstances, axial fan single mechanical efficiency is higher than FFU is generally no doubt. But the situation on the system and how? As the brushless DC motor can be in a large operating range to maintain a high efficiency of output, and large-scale axial fan motor in the frequency of operation after the rapid decline in efficiency, so do the air in the clean room control, operation deployment (ie, non-design point Operation), FFU-type system will be more dominant should not be too controversial. The design point of operation (ie, fixed-frequency operation) how? Before answering this question, first of all to confirm how the two systems are relative? Only requires the size of the work area and the total air volume of the same cycle can be? Do you want to further require the work area above the air compartment, below the elevated floor and return air duct the same size? Do not require the same air flow within the work area or as long as both meet the requirements of cleanliness can be? Are there any inconsistencies between the requirements listed above? Are there other more important conditions to consider? At present, there is no answer to the above question. Therefore, the interpretation of the information contained in Figures 15, 16 and 17 must be answered first.
We can see the comparison of two different air circulation system energy efficiency group technology development, is also towards the establishment of experimental facilities, experimental techniques and analysis of the direction of forward, Figure 18 is a Class 10, with automatic measurement system Experimental clean room, hoping to provide effective in the near future to the measured data, as a comparison of evidence. Figure 19 is the analysis of small central and FFU-type system diagram, FFU for the market high efficiency 4'x3 '/ AC models, operating point of electrical efficiency of more than 20%, axial fan is a variable pitch (Variable pitch) type, full-speed operation point efficiency more than 80%, the two systems in addition to the work area height, depth and width of the same size, the rest of the size of the characteristics of the system to do the best design. In the system total air volume of 16560 CMH, the use of FLOVENT software and the actual reference FFU and fan performance curve, the two systems of air flow energy consumption simulation results shown in Table 2, Axla6 and FFU6 two cases show the energy situation and No significant differences in air flow in the work area, although not exactly the same state, but also in the IEST suggested range, so the current set, the fixed-frequency system energy consumption does not seem to be central or FFU type and obvious different.