Modern industrial product production and modernization scientific experiment activities require miniaturization, precision, high purity, high quality and high reliability, bringing clean technology to the healthy and rapid development with the development of science and technology and the rapid development of industrial products. In the food, cosmetics, military and other industries outside the three major strategies have better performance. To create a good clean room micro-environment, a set of efficient, safe, reliable, practical and simple air cleaning system is the core part of all its complementary systems, while the air handling unit completes heat exchange, filtration, humidification and air supply. Important components such as functions; there are many differences between ordinary comfort air handling units. This article talks about the application of air handling units for clean rooms from the perspective of clean rooms.
1. Characteristics of clean room air conditioning system
1.1 large air volume
The clean room mainly filters the dust and bacteria in the air through the circulation of air, and realizes the control of non-biological particles and biological particles in the air to achieve the standard of cleanliness. Therefore, it is necessary to have sufficient air volume to ensure the cleanliness of the room. The air volume of the clean room is generally calculated according to the number of indoor air exchanges, usually 10 times or even dozens of times, especially the one-way flow clean room, and the number of air changes reaches several hundred times of the room volume.
The high air volume is a test for the strength of the air handling unit. At present, the air handling units commonly used in the market are all made of aluminum alloy frame structure and square steel structure. If the thickness of the panel and the strength of the frame are not enough, it is easy to cause the air handling unit. Deformation, especially for medical air handling units, generally requires a positive pressure design. If the panel and frame are not adequately fixed, there may be a phenomenon in which the panel flies out. Therefore, the clean air handling unit must first meet the high-strength requirements. Currently, the common panel thickness on the market is 30mm and 50mm. Some manufacturers have also introduced the 60mm panel high-end unit. It is believed that it will be widely used in clean places.
1.2 The head of the fan is high
The clean room should generally be filtered by at least three stages of primary, middle and high filters. The resistance of the three-stage filter is about 700 to 800 Pa. The clean room should also be concentrated and sent back. It is guaranteed to maintain the requirements of positive and negative pressure regulation of the clean room, so the pipeline resistance of the clean room is generally more than double that of the ordinary air conditioner. In order to overcome these resistances, the blower of the air treatment unit is required to have sufficient pressure head, so the blower unit of the air treatment unit of the clean room generally adopts a fan of a back bend airfoil or a fan without a shell to achieve a high enough height. Return the wind pressure head. In the case of such a large air volume and large indenter, the air leakage rate of the unit is also a test. The lower the air leakage rate of the air treatment unit in the clean room, the more energy saved for the customer, and the lower the operating cost.
1.3 high temperature and humidity control accuracy
Different from the comfort requirements of ordinary comfort air conditioners, the accuracy of temperature and humidity control of clean rooms is to meet the process requirements. For example, in the manufacture of some electronic products, the control of temperature and humidity is very strict, in medical and experimental. Animals and other aspects, there are clear requirements for the accuracy of temperature and humidity control. In order to achieve constant temperature and humidity, the air handling unit is required to have at least cooling, heating, humidifying, dehumidifying and other functional sections, and requires precise control; for example, heat exchangers should use high-efficiency hydrophilic fins, and water The flow rate is controlled by proportional integral, and the humidification amount should also be proportional integration or PID adjustment to achieve higher control accuracy.
1.4 Positive and negative pressure control is strict
Whether it is an electronic factory or an isolation ward, a pharmaceutical factory, an experimental animal room, etc., in order to prevent dust and bacteria from spreading to other clean areas, or to prevent cross-infection caused by the spread of viral bacteria, the positive and negative pressure control of clean rooms is very important, especially It is necessary to prevent radioactive dust, harmful gases, odors and bacteria from spreading out in medical applications. It is extremely important to accurately control the positive and negative pressures. In practical engineering applications, industrial clean rooms and general biological clean rooms are maintained with positive pressure, but negative pressure control is used for the use of toxic, harmful gases or the use of flammable and explosive solvents and other biological clean rooms with special requirements. In order to have an accurate differential pressure control value, the air handling unit in the clean room requires a lower air leakage rate to have higher control accuracy. At the same time, the split section with concentrated return air will be widely used in air conditioners.
1.5 has a good filtration system
Whether it is an industrial clean room that meets the design requirements of the process, or a bioengineering for medical, pharmaceutical, laboratory animals, etc., the common feature is to meet the dust-free, which will be done by a good air filtration system. The degree of control of microorganisms, dust, etc. by clean technology depends mainly on the performance of the filter. The clean room generally has to pass at least three stages of filtration, the air treatment unit is equipped with a primary and medium efficiency filter, and the air supply end is equipped with a high efficiency filter. Air filters need to be of good quality, and once a leak occurs, it is no longer possible to achieve cleanliness. In addition to the fact that there can be no leakage, the sealing of the filter in the air-conditioning box should also attract attention.
1.6 using frequency conversion technology
The characteristics of large air volume in clean air conditioning systems bring high energy consumption, and various energy saving technologies are widely used in clean air conditioning systems. Among them, frequency conversion technology is widely used in clean air conditioning systems. Since clean air conditioners generally have to pass at least the primary filter, the medium efficiency filter (sub-high efficiency filter), and the high-efficiency filter, the filter is getting longer and longer as the use time is longer. The blower of the ordinary air handling unit is selected according to the calculated resistance of the filter. The power of the blower motor selected in the clean room is selected according to the final resistance of the filter, and is operated in the air conditioning system. In the initial stage, the pressure of the fan is absolutely enough to overcome the resistance of the system to meet the requirements of use. At this time, the inverter can reduce the speed of the fan, reduce the power consumption, and achieve good energy-saving purposes. As the system operates, the filter The resistance is getting bigger and bigger, the air volume of the air conditioning system will be reduced, and the variable data will be supplied to the frequency converter through the air volume or static pressure change in the air duct, and the frequency converter will increase the speed of the fan to meet the requirements of the system air volume. At the same time, it can also adjust the fan speed to maintain a good regulation of the positive and negative pressure of the room. In addition, the inverter fan can also be used to reduce the speed of the unit when the clean room is not in use, and the air volume of the blower is reduced, which is equivalent to the use of the duty fan.
1.7 considerable stability and reliability
The high development of modern industry makes industrial products have the characteristics of small size and high value. If the clean air conditioner fails, it will bring thousands of losses, especially in the medical clean room, if it is in the operation or the delivery room. If the air conditioning unit fails, it will bring life safety. Therefore, the air conditioning unit is required to have considerable stability and reliability. It is required that each component of the air handling unit should be purchased with a manufacturer with good quality management, such as In the unit, AMCA-certified high-quality fans and high-quality motors should be used. The filter should be used with great caution. Especially for high-efficiency filters, if there is a small hole, it will bring countless bacteria. The result is Unimaginable. In addition, the production and testing of air handling units must also be manufactured in strict accordance with national standards.
2, the characteristics of industrial clean room
The industrial clean room mainly controls pollution and guarantees the qualified rate of products. The main features are as follows:
2.1 high requirements for cleanliness
The industrial clean room needs to meet the process requirements, the performance index of the product is continuously improved, and the cleanliness of the clean room is required to be continuously improved. The ultra-high efficiency filter is required. Therefore, the air treatment unit is required to be equipped with at least initial effect, medium efficiency and sub-high efficiency filtration. The system is so strong that the strength of the unit is higher and the head of the air handling unit blower is larger.
2.2 temperature control priority
Industrial clean rooms generally require personnel to operate, so the air handling unit should try to give priority to temperature control, ensure a certain humidity control, and meet the temperature and humidity requirements of personnel to ensure the quality of the products.
2.3 meet the requirements of special processes
For some products, chemical preparations are needed, so the unit requires corrosion resistance, and some require the use of explosive gas. This requires the air treatment unit to be explosion-proof and anti-static. Some processes have high requirements for vibration, so the air handling unit is Have better anti-shock measures.
3. Characteristics of biological clean room air conditioning system
3.1 A significant feature of the biological clean room air conditioning system is to prevent cross-infection. This performance is on the air handling unit, mainly for the air cleaning unit of the biological clean room. The full positive pressure design is required, that is, the air blower of the air handling unit is placed. At the forefront, the remaining functional sections are placed in the positive pressure section of the airflow to prevent outside airflow from entering the air handling unit, causing cross-contamination. To prevent cross-infection, it is necessary to pay attention to: heat recovery of the runner, heat recovery of the plate, etc. are not suitable for use in hospitals. Although the hospital is a large energy consumer, the working principle of the runner heat recovery is to exchange between the exhaust and the fresh air through the runner, which is easy to produce cross infection. In the biological clean room, heat pipe heat recovery, coil heat recovery and other technologies It is widely used because there is no new wind contact.
3.2 The second significant feature of the biological clean room air conditioning system prevents secondary pollution of the air conditioning system. This feature is mainly reflected in the air handling unit:
3.2.1 The air handling unit should be kept clean and smooth, and it should be corrosion resistant. It is advisable to use stainless steel plate and change the right angle of the bottom of the unit to rounded corners for easy cleaning.
3.2.2 The air treatment unit adopts humidity control priority to prevent the humid air conditioner from breeding bacteria on the surface of the air duct and the high efficiency filter.
3.2.3 Place the heat exchanger, filter, etc. in the positive pressure section. The fan should normally close the fresh air valve immediately during shutdown to prevent condensation on the inner surface of the unit. After the air cooler is closed, the air supply is still required, and the coil is blown dry. The water in the water tray, the temperature of the inner wall gradually rises to prevent the bacteria from breeding, and the filter is placed in the positive pressure section to prevent the air filter from being damp, effectively preventing the growth of bacteria.
3.2.4 The heat exchanger adopts hydrophilic red sheet, and the fins per inch should not be too much, otherwise the heat exchange fins are easy to accumulate dust. Use a non-condensing coil. As long as the inlet water temperature of the unit is higher than the difference between the indoor dew point temperature and the heat transfer temperature difference, the dry condition of the heat exchange coil in the air conditioning unit can be ensured, and this need can be realized by combining the air conditioning system, and the fresh air is used to bear the indoor humidity. load.
3.2.5 The air treatment unit for the biological clean room generally does not use the water deflector, which requires that the oncoming wind speed of the coil is generally less than 2.5 m / s.
3.2.6 Electric heating is made of stainless steel light pipe - smooth and finless, corrosion resistant, not easy to accumulate dust, easy to clean.
What should be noted to prevent secondary pollution is:
3.2.7 Wet film humidifier can never be used in hospitals. The initial investment and operating costs of wet film humidifiers are very cheap, and are widely used in civil buildings where humidification is required but humidity control requirements are not high. However, since the humidification principle of the wet film is exchanged on the wet film by air and water, the wet wet film is the environment where the bacteria are most likely to breed, so it is absolutely necessary for the biological clean air conditioner to pay special attention to prevent secondary pollution. Not allowed. Therefore, wet film humidification is absolutely not applicable to biological clean places such as hospitals and pharmaceuticals, and dry steam humidification, electrode humidification, and electric heat humidification generated by condensed water are widely used in biological clean room air conditioners.
3.2.8 Fan coils, hanging machines with cold and heat sources, and cabinets are not suitable for use in operating rooms, delivery rooms, ICUs, infection isolation rooms, various laboratories, radiology departments, etc. Fan coils, hooks, etc. all have a condensate pan, and the humid environment inside is also easy for bacteria to breed. By the same token, the air-conditioning host of the hospital also tries to use the air-cooled mainframe, because the cooling tower of the water-cooled mainframe is also a place where legumes and other bacteria grow easily.
3.3 The unit must have good sterilization and sterilization
3.3.1 The air handling unit must have at least two stages of filters. The filter can effectively remove dust from the air, and can also block the spread and spread of bacteria and viruses in the air conditioning system, especially high-efficiency filters for viruses floating in the atmosphere. The capture efficiency of bacteria can actually reach 100%, and it can also be used to effectively prevent the filter bacteria from breeding. For filters containing the antibacterial agent INTESEPT, titanium dioxide filters, etc., the filter should be replaced regularly.
3.3.2 Adding an electronic sterilization device to the return air inlet of the unit
3.3.3 The primary effect filter generally uses a disposable filter, which is directly discarded after a period of use, and should not be used again.
3.3.4 The unit is equipped with an ultraviolet germicidal lamp. The sterilization mechanism of ultraviolet irradiation is to cause chemical changes in the microbial bacteria, such as nucleic acid, protoplasmic proteins and enzymes, to die. UV disinfection has a broad-spectrum bactericidal effect, which can kill various microorganisms. Ultraviolet germicidal lamps are generally installed in the downstream section of the air-conditioning box, such as the windward side of the coil section and the filter section.
3.4 High degree of automatic control. Due to the use time of the various departments of the hospital, the required temperature and humidity, and the different loads, the air conditioning system partition should be refined, and each room should be independently controlled and adjusted. This requires the medical air handling unit to be equipped with a highly configured control system.
3.5 Prevent noise from air conditioning systems, vibration of equipment and large wind speeds to stimulate patients. Because the patient's resistance in the hospital is relatively weak, the noise and vibration of the equipment will cause it to be uneasy and affect the treatment effect. Therefore, the hospital air handling unit needs better damping and noise reduction measures.
3.6 The pollution and cross-contamination caused by the pharmaceutical factory to the production of special drugs will seriously affect other drugs and need to be strictly separated. Such as: penicillins, radioactive drugs, vaccines, blood products, etc., this is particularly important in the selection of air handling units, should know more about the process, for unreasonable air conditioning systems, should be reflected to the design institute and owners.
3.7 The exhaust fan should be placed at the end of the exhaust pipe as much as possible, so that the entire exhaust pipe is under negative pressure, and pollutants such as harmful substances and radioactive aerosols are discharged. HEPA filter should be installed at the exhaust inlet.
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