Typical solutions for ventilation and air conditioning for clean rooms. Clean rooms Ventilation scheme for clean rooms

Raymond K. Schneider, Senior Cleanroom Consultant and CEO of Practical Technology, USA, Fellow of the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE)

The design of ventilation and air conditioning systems for clean rooms has a number of features. Below is an article by a well-known American cleanroom specialist, Mr. Raymond K. Schneider, which analyzes the requirements for ventilation systems for rooms of various cleanliness classes: from 1 to 9. The solutions proposed by the author, based on his extensive practical experience, deserve careful study and use where possible.

Air conditioning systems for clean rooms must supply purified air in a certain amount in order to maintain a given level of cleanliness in the room. Air is supplied to clean rooms in such a way as to prevent the formation of stagnant zones where dust particles can settle and accumulate. The air must also be conditioned in terms of temperature and humidity in accordance with the requirements for the parameters of the microclimate of the room. Moreover, additional quantity conditioned air is supplied to the room to create excess pressure.

This article discusses the design of air conditioning systems for clean rooms. In order to simplify the presentation of the material, the level of maintenance of cleanliness in the premises is divided into three categories: hard, medium and moderate (see table).

Air exchange

The calculated value of the supply of purified air is maximum for premises with a strict cleanliness regime and decreases as the requirements for purification decrease. Air exchange in rooms is usually expressed either in terms of air mobility in the room, or in terms of multiplicity (rpm / h).

Average indoor air mobility is usually used when the air is supplied through a filter ceiling. For many years, an air mobility of 0.46 m/s ± 20% was accepted as the highest level of purity. This was based on the first clean room designs carried out as part of the 1960–1970 space programs.

V Lately experiments were carried out with lower speeds, which showed that air mobility in the range of 0.35–0.51 m/s ± 20% is quite acceptable, depending on the type of activity and the installed equipment. The upper limit of air mobility corresponds to the high activity of personnel and the presence of dust-producing equipment. Lower values ​​are accepted if there is little sedentary work and/or no dust-generating equipment.

Frequently knowledgeable customers with experience in cleanrooms will set low level air mobility values. And customers and novice designers, unaware of the feasibility of lower speeds, set air mobility at the upper end of the scale. There is no unambiguously defined average level of air movement or air exchange rate accepted in the industry for clean rooms according to this classification. The only exception is the air mobility value of 0.46±0.1 m/s defined by the FDA (Food and Drug Administration). medicines, USA) for sterile areas in the pharmaceutical industry.

The standard air exchange values ​​for clean rooms with medium and moderate air cleanliness are more common. For rooms with an average level of cleanliness, the recommended air exchange is between 30 and 60 rpm / h, while for a moderate level, air exchange can be reduced to 20 rpm / h. The designer chooses the air exchange value based on his experience and understanding of the dust generation in the production process. Recently, there has been a tendency to take lower values ​​of air exchange; leading design and construction firms and prudent customers have successful experience in working with such parameters.

V practical advice Microclimate Institute (IEST-CC-RP.012.1) has a table of recommended air exchange values ​​for each cleanliness class; similar values ​​were later published in ISO 14644-1, clause 4. These data are given in the table. Both documents are consistent with each other and represent the joint recommendations of designers, builders and users, proven by years of successful work. In all these documents, the responsibility for the choice of parameters rests with the "sellers" and "buyers" of clean rooms, so it is advisable to exercise some caution when using the above recommendations.

Picture 1.

Figure 2.

Filters

For many years, clean room technology has been developed to serve the microelectronics industry. The need for high efficiency air filters is dictated by the needs of this industry and related industries. The ULPA (Ultra High Purity) filter, which has an efficiency of 99.9995% on 0.12 micron particles, has been successfully used in harsh cleanrooms. Higher efficiency filters exist, but they are expensive and not widely used. Filters with 99.99% and 99.999% efficiency are available from several manufacturers; experience shows that they can also be used for hard mode.

HEPA (High Efficiency Purification) filters with 99.97% efficiency on 0.3 micron particles have been the workhorse of the clean room industry for many years. They are still widely used in the pharmaceutical industry, where the requirements for air purity are even more stringent.

When filters were laboratory tested with accurate particle counts, HEPA/ULPA filters were found to generally pass 0.1-0.2 microns. At the same time, the passport efficiency of filters for fractions of 0.12 and 0.3 microns was confirmed, and an even higher efficiency was found for particles that are larger and smaller than the indicated sizes. For the strict regime of purity standardization, when setting the filter efficiency, it is customary to indicate not the values ​​of 0.12 and 0.3 microns, but the particle size of the fraction that is filtered worse than the others (MPPS). MPPS values ​​vary slightly between filter manufacturers. Specifying the efficiency by the size of the worst filtered particles is considered by some designers and manufacturers to be the most convenient.

Most hard and medium clean rooms are equipped with filters in the ceiling. The filters can be grouped and connected to a common supply unit for easy installation in the ceiling, or they can be installed individually with individual supply air ducts. This arrangement, resembling an inverted "T", forms a honeycomb structure under the ceiling. At the same time, the filters are carefully sealed in the housing to prevent the passage of uncleaned air. In addition, filters built into supply chambers are still used. However, the modular schemes that displace them make it possible to better ensure the regulation of air parameters and mobility.

Blocks "filter-fan" are widely used. In some designs, the filter is replaceable, in other cases, the entire unit is replaced at the end of its service life. Various standard sizes are offered for delivery for embedding in a honeycomb structure. The fans are equipped with electric motors designed for different voltages, which makes it possible to use various schemes power supply. Some sophisticated control systems include the ability to individually control each unit, register power consumption, signal motor failures, control groups of filter fans, and change the speed of fans according to the time of day. Blocks "filter-fan" are used for all classes of clean rooms.

Frontal air velocity for ceiling filters can be from 0.66 to 0.25 m/s, depending on the project. Since the system with cellular placement of filters of the “T” type occupies 20% of the ceiling area, the frontal speed of the filters of 0.51 m/s corresponds to average speed in the working area of ​​the room 0.41 m/s.

Installing HEPA/ULPA filters directly in the ceiling of cleanrooms is dictated by the intention to minimize or eliminate the possibility of dust accumulation on any surfaces (for example, on the walls of air ducts) along the path of air from the filter to the cleanroom. The remote placement of HEPA filters is typical for moderate-mode clean rooms, since the number of particles blown off the walls of the air ducts after the filters is in acceptable limits. The exceptions are situations where standard system an air conditioning system not certified for clean rooms is converted for this purpose in accordance with ISO 14644. In this case, all air ducts after filters must be thoroughly cleaned.

For moderate duty cleanrooms, fan boxes or mixboxes with HEPA filters on the discharge side are often used. At the same time, the frontal air velocity in the HEPA filters reaches 2.54 m/s, which corresponds to a greater pressure drop than with a ceiling installation. The aerodynamic resistance of a clean HEPA filter with a size of 600x600 mm is 375 Pa at a frontal speed of 2.54 m/s. With a ceiling installation, the frontal speed is 0.51 m/s, the aerodynamic drag is 125 Pa.

Air circulation in clean rooms

The air entering the clean room after being cleaned with HEPA and ULPA filters is practically free of suspended particles. The air supply to the room is made for a dual purpose. Firstly, the “dissolution” (reduction of concentration) of dust pollution arising from the presence of people and the performance of production processes. Secondly, the capture and removal of these contaminants from the premises.

There are three types of indoor air circulation:

1. Unidirectional ordered flow (previously called "laminar"), when the streamlines of all air jets are parallel.

2. Disordered flow (previously called "turbulent"), when the streamlines are not parallel.

3. Mixed flow, when in one part of the room the air jets can be parallel, but not in the other part.

Hard mode cleanrooms typically use unidirectional flow. This is achieved by installing HEPA / ULPA filters throughout the ceiling area and installing a perforated raised floor. The air moves vertically from the ceiling to the floor, is removed through the perforation into the exhaust chamber under the floor. The recirculated air is then fed back into the room through the peripheral recirculation ducts.

If the cleanroom is narrow (4.2-4.6 m), wall-mounted exhaust grilles installed at the bottom are used instead of a raised floor. Air is supplied from above and moves vertically to a level of 0.6–0.9 m, then the flow spreads towards the gratings. Such circulation is considered acceptable for rooms with a strict regime, especially in cases where there has been a conversion of the room into a clean room in the presence of dust in the upper zone.

In rooms with an orderly circulation, the placement of furniture and equipment affects the structure of the air flow. To reduce the impact of these items on the cleanliness of the room, it is necessary to place them in such a way that stagnant zones with dust accumulation do not form.

Random air movement is common in medium duty clean rooms. HEPA filters are placed evenly over the ceiling surface. The air flow is generally directed from top to bottom. However, the direction of individual jets is different and does not fit into a certain pattern. While the supply air contains practically no suspended particles, their appearance and accumulation in the working area of ​​clean rooms depends on the amount of particles generated in the room itself; from reducing the concentration of dust due to air exchange; the intensity of entrainment of particles from the working area. In general, it can be said that the greater the air exchange, the cleaner the air in medium-mode rooms, however, the structure of the air flows in the room also plays a role.

The air removal scheme for rooms with disordered circulation is very important. In such rooms, wall-mounted exhaust grilles are widespread. They should be evenly distributed around the perimeter of the room. This requirement may conflict with the accepted layout of equipment along the walls. Where possible, equipment should be moved away from walls to allow air to flow behind it. It is also advisable to raise the equipment above the floor, placing it on a platform so that the air passes from below. In most cases, clean room designers aim to direct airflow away from work surface table to the floor and then to the low exhaust grilles. With this scheme, particles are removed from the room and sent to the filters, where they are captured. An exception may be such cases when particles of pollution are generated by equipment above the working area. Then some device should be used to catch the removal and particles at the top. In the general case, it is recommended to use a top-down air distribution scheme.

In rooms with a medium level of cleanliness, it is reasonable practice to limit the horizontal sections of airflow. The recommended values ​​of horizontal sections are no more than 4.2–4.8 m. Thus, in a room with a width of no more than 8.4–9.6 m, it is permissible to install exhaust grilles along the perimeter of the walls. This limitation is dictated by the fear of secondary pollution during deposition or other transfer of particles into the working area from extended horizontal flows.

In wider rooms, it is customary to install exhaust grilles and air ducts in ducts mounted along the columns. If there are no columns in the room, vertical shafts are created from a suitable material.

In rooms of moderate cleanliness with remote installation of HEPA filters, standard ceiling air outlets of air conditioning systems can be used. The air circulation scheme is also similar to that adopted in air-conditioned rooms.

According to the “top-down” circulation scheme in practice for cleanrooms, the bottom installation of wall-mounted exhaust grilles is also recommended here. When the exhaust grilles are placed at the top, areas with a high concentration of suspended particles can form in the working clean area, especially during periods of intensive work. In the known installations of ceiling exhaust grilles in moderate duty cleanrooms, the success was most likely due to the low level of particle generation in the room, rather than the efficiency of the air distribution system.

Mixed circulation is used when work is performed in the same room with critical and non-critical requirements for air purity. If it is impossible to ensure the performance of work with critical requirements in a separate room, then a common clean room with cleanliness zoning can be used. Zones are created by appropriate grouping of ceiling filters. In the zone with critical conditions for purity, the number of filters is greater, in the zone with non-critical conditions - less. In addition, submission supply air can be carried out in such a way that it is first supplied through the air ducts to the critical zone, and then enters the rest of the room. Depending on the height of the clean room, a 0.6 m high plexiglass shelter or a plastic curtain that does not reach the floor by 304–457 mm can also be installed.

The direction of the exhaust air flows is regulated by the appropriate placement of the exhaust grilles in such a way as to prevent the transfer of contaminants throughout the room. A raised floor with a prefabricated exhaust air collector installed under it will be very effective in this case. However, the application of such a solution may be hindered by the limited budget of the customer, who chooses the mixed circulation zoned clean room design precisely because of its low cost.

The disadvantage of disordered air circulation in clean rooms is the appearance of areas with high dust content. Such areas may exist for a limited time, then disappear. This occurs due to the interaction of air flows resulting from production activities and disordered supply jets. Attempts have been made to reproduce unidirectional circulation by installing a false ceiling-air distributor and creating a zone high blood pressure between main and false ceiling. For this, perforated plastic or aluminum panels and a screen made of woven and non-woven materials were used.

As a result, an ordered unidirectional flow was formed in the room with velocities much lower than in clean rooms with a hard regime. The displacement effect created by the supply air flow prevents the formation of dusty areas and, in general, allows you to achieve more high level purity. The specified result, as noted above, is achieved at a lower air mobility than indicated in the standards for hard and medium cleanliness (Fig. 1).

Thermal load

The share of sensible heat in the heat load of clean rooms is typically over 95%. As a rule, year-round cooling is required, since the heat generated by the technological equipment and electric motors for circulation fans. A small proportion of latent heat generation is generated by the presence of personnel. Each clean room has a unique design, so all factors that affect heat load must be carefully analyzed.

In rooms with strict and medium levels of cleanliness, a significant part of the supply air is not treated by air conditioners - this is recirculated air. The required sensible heat removal is carried out in the mixing and distribution chambers, where part of the total flow is cooled in surface heat exchangers and then returned to the general flow to the recirculation fans (Fig. 2). The inlet air temperature to severe cleanrooms can only be a few degrees lower than the exhaust air temperature due to the large inflow volume. This temperature difference makes it possible to use ceiling installation top-down HEPA/ULPA filters without compromising worker comfort.

In rooms with a moderate cleanliness regime, the requirements for air distribution in the room are in some cases the same as in ordinary refrigerated rooms. Thus, the temperature difference between supply and exhaust air can be 8–11 °C. In these cases, standard ceiling diffusers or other means are used to prevent unpleasant blast and ensure comfortable conditions in the room.

Outside air supply

The supply of outside air is necessary to compensate for the exhaust and exfiltration that always occurs in pressurized cleanrooms. Outdoor supply air is expensive, because before being supplied to clean rooms, it must not only be cleaned, but also subjected to temperature and humidity treatment. Since it is not possible to completely eliminate the supply of outside air, for reasons of overall economy and energy saving, its amount should be kept to a minimum.

The air pressure in clean rooms is usually increased relative to the surrounding areas. As a rule, a pressure drop of 12 Pa is recommended. Higher overpressure causes whistling noise in the gaps and difficulty in opening the doors. In blocks of clean rooms with different cleanliness classes, it is customary to maintain a pressure difference of 5 Pa between adjacent rooms, while a higher pressure is maintained in a room with a higher cleanliness class.

The amount of outside air is determined by summing the exhaust volume for all production processes and increasing the resulting multiplicity by 2 rpm/h. This semi-empirical value is a practice-proven calculated amount of air for the selection of air conditioning equipment. The actual amount of outside air will be variable, depending on door openings, leaks, and the actual operation schedule of the hood.

The outdoor air conditioner is designed to bring its parameters in line with the standards for clean rooms. This means that it must be possible to clean the air, preheat, cool, reheat, dehumidify and humidify.

In clean rooms with a strict regime, three stages of outdoor air purification are often done: preliminary - an ASHRAE filter with an efficiency of 30%, an intermediate filter with a 95% efficiency, and a final one - a HEPA filter. In clean rooms with a medium and moderate regime, as a rule, there are two stages of cleaning: preliminary (30%) and final (95%). From the name it is clear that the final filter is placed at the outlet of the air conditioner.

Preheating is necessary when the outside temperature drops below 4 °C in winter. If the dew point temperature of the air in the clean room is ≥5.6 °C, the surface heat exchanger cools and dehumidifies the supply air. Since workers in strict cleanrooms always wear overalls, the dry bulb temperature can be maintained as low as 19°C, with a minimum relative humidity setting of 40% for regulators. The second heating is necessary in order to increase the temperature of the supply air after cooling and dehumidification in the heat exchanger. When calculating the amount of heat for the second heating, heat inputs from recirculation fans are taken into account. This is a significant value for clean rooms with a strict regime.

Reducing the surface temperature of the heat exchanger to the level required to keep the room dew point below 5.6°C can be difficult. When dehumidification of supply air below 40% RH is required, various desiccant agents are commonly used.

In the system described here, the outdoor air conditioner is loaded with latent heat and moisture in the room. It is assumed that the parameters of the supply air meet the requirements for the assimilation of latent heat emissions introduced by the room staff and moisture ingress through the clean room fences. It is also assumed that the latent heat load is more or less constant. These assumptions must be checked for each specific project. It is necessary to take into account the conditions in the rooms surrounding the clean room, the parameters of the outdoor climate, the possibility of moisture release from production processes in the room.

In small volume cleanrooms with little outside air demand, the recirculation air coolers in the mixing chambers discussed above can also be used to treat outside air. In this case, a mixture of outdoor and recirculated air is processed. The proportion between these supply air components is controlled by mixing valves depending on the pressure in the clean room. If the pressure drops, the outside air valve opens and the recirculation valve closes. The air from the mixing and distributing chambers is supplied to the circulation fans.

In moderate cleanrooms, the total supply air required can be close to the conditioned air flow. In this case, additional circulation fans are not installed; air is moved through the system only by the fans of one or more air conditioners.

table

Classi- fiction ISO Federal Standard 209E Federal Standard 209E Recommendations Room air mobility, ft/min (1 ft=0.305 m) Air- exchange, rpm/h 1 No equivalent No equivalent Hard 70-100 2 No equivalent No equivalent Hard 70-100 3 1 1,5 Hard 70-100 4 10 2,5 Hard 70-100 5 100 3,5 Hard Medium 70-100 225-275 6 1 000 4,5 Average No rules 70-160 7 10000 5,5 Average No rules 30-70 8 100000 6,5 Moderate No rules 10-20 9 No equivalent No equivalent Moderate No rules By calculation

The new ISO classification of clean rooms is shown on the left. The classification according to US Federal Standard 209E in Anglo-American and metric units is also given. The "Recommendations" column contains three categories according to the classification of the author of this article. Note that "Class 100" can be assigned to a hard mode when the design provides for ordered circulation, or to an average mode if disordered circulation is designed for non-critical conditions. The two columns on the right give recommendations for indoor air mobility (ft/min) and air exchange (rev/h) for medium and moderate modes.

conclusions

V normative documents In clean room design, there is a tendency to entrust the designer with the functions of a general expert, capable of fulfilling all the wishes of the customer (as far as he knows). The manuals usually use the expression "a matter of agreement between the buyer and the seller" in order to involve the customer in the decision-making process, since each developer can offer his own version of the project. The effectiveness of the design principle discussed in this article has been proven in practice; This approach, in the opinion of the author, makes it possible to harmonize technical requirements and the possibility of their implementation. These recommendations, like any others, must be adapted in each case to the specific conditions of use.

Reprinted with abridgements from the magazine ASHRAE.

Translation from English O. P. Bulycheva.

Scientific editing performed by Ph.D. tech. sciences A. P. Inkov

Clean room (clea nr oom is an airborne particle control room designed and used to minimize the intake, emission and retention of particles within the room, while allowing other parameters, such as temperature, humidity, to be controlled as needed. and pressure.

In such premises, the content pollutants in the air, on wall and ceiling surfaces should be kept to a minimum.

Specified particles may include materials such as dust, anesthetic waste gases, and micro-organisms.

Extremely clean indoor air can only be achieved by extracting indoor air and supplying filtered, conditioned expellant air.

In addition, as in the classical system, comfort parameters such as temperature, relative humidity, noise level, air pressure and velocity, as well as the minimum outdoor air flow must be controlled.

Cleanroom technology serves the following tasks:

• protection of products from contamination;
• protection of the environment from pollution;
• creating a protective environment for people in the room;
• protection of indoor occupants from human-borne microbes;
• protecting the environment from hazardous products;
• protection of the environment from microbes carried by humans.

A clean room means a clean environment, clean gas, clean surfaces, clean equipment, clean products and clean technology.

No projects or investments should be carried out until the hygiene requirements to a clean room.

It is necessary to ensure guaranteed hygienic quality and maintain the required degree of cleanliness of the air in the room (not necessarily the highest possible).

High hygienic quality can be ensured by implementing an expensive protection project.

The basic approach should be to meet hygiene requirements where necessary, most inexpensive ways and with maximum efficiency, but only to the extent that it is necessary for a particular room.

Implementation Affecting Options necessary conditions, can be divided into two groups: provisioning parameters comfort and hygiene.

The criteria for comfortable air parameters are:

• acceptable temperature range;
• acceptable moisture content;
• required flow rate of supplied air (l/s);
• permissible noise level.

These parameters are important for the assimilation of heat releases from external and internal sources, as well as to compensate for heat loss and to ensure comfortable conditions in the room.

Criteria for hygienic air parameters:

• ensuring the concentration of microorganisms within the specified limits;
• removal of pollutants from the premises, such as escaping gases;
• control of air movement in the room.

The parameters for maintaining hygienic conditions are the concentration of microbes and polluting gases, as well as the movement of air between rooms.

In this regard, the concentration of pollutants should be at the minimum required level, the movement of air between rooms should be controlled.

but during design, consideration of these parameters in their totality should be carried out. For the assimilation of heat surpluses, providing required quality air, the amount of conditioned air should be checked, as well as the amount of displacing air required to keep the concentration of microorganisms in the room below a certain level.

Areas of application for cleanrooms

Cleanrooms are used in areas such as medicine, microelectronics, micromechanics and the food industry.

In medicine, operating rooms, drug preparation rooms, biochemical and genetic laboratories are cleared of particles and microorganisms.

Cleanrooms are used in microelectronics, space technology, thin film technology, the printed circuit industry and related areas where the removal of contaminants is required.

In the food industry, both pollutant particles and microorganisms are removed from production facilities.

Clean room with turbulent air flow

Terms used in cleanroom literature

living microorganisms. Bacteria, fungi and viruses fall into this category. Microorganisms can develop in the form of colonies in air, water and especially in cracks and on rough surfaces. The most common source of microorganisms is the human body, which spreads about 1,000 types of bacteria and fungi.

Contaminants other than microorganisms. Atmospheric substances and substances other than microorganisms are present in the atmosphere as a result of the action of wind, earthquakes and volcanic activity. These are usually referred to as dust or aerosol. This group includes smoke particles from industrial processes, building heating systems and vehicle exhaust emissions. The same group also includes particulate matter, which originates from the moving parts of machines in cleanrooms. In addition, as a result of the actions of people in a clean room, about 100,000 particles smaller than 3 microns are released into the air of this room.

Sterility. This is how you can characterize the situation in the room, in which products and devices are free of microorganisms.

Sterilization. A technique for destroying or killing microorganisms in products or devices.

HEPA filters (high efficiency particulate air filter - high efficiency aerosol filter). Such filters are a kind of high efficiency air filters. They are used directly in air handling units, as well as at the end points of the air supply to the room as the final purification stage. The efficiency of these filters for 0.3 µm particles ranges from 97.8 to 99.995%. Such filters are designed for rooms with a cleanliness class of 100-100,000.

ULPA filters (also known as ULTRA-HEPA). These are very effective special air filters. The efficiency of these filters for 0.3 µm particles ranges from 99.999 to 99.99995%. Such filters are designed for rooms with cleanliness class 1-100.

DOP test. Testing the effectiveness of HEPA filters in real conditions after installation.

Clean rooms with turbulent air flow. In such cleanrooms, conditioned air is supplied through HEPA filters located directly in false ceiling. The air return openings are at floor level. This cleaning method is designed for rooms with a cleanliness class of 10,000-100,000 (Fig. 1).

Clean rooms with laminar air flow. In this method, a stream of air flowing at a constant speed carries the contaminants to the return air duct and then to the air handling unit. This method is suitable for rooms with cleanliness class 1, 10, 100, 1000

Clean rooms with laminar airflow

Airlock. At the entrance to the cleanroom, there must be an air lock that allows access to the room in accordance with current regulations. The airlock is a small chamber with two doors, which is supplied with conditioned air through two HEPA filters.

Cleanliness class. Depending on the type of production that must be carried out in a clean room, the class of cleanliness of this room is determined. Various standards are used to classify cleanrooms. Currently, Germany uses VDI 2083, France uses US 209 in AFNOR 44001, and England uses BS 5295.

In a cleanroom, all equipment and all systems (including air handling units, air ducts, duct equipment) must be able to be cleaned, replaced and after-sales service.

In rooms that require a high degree of sterility, three-stage filtration is used:

• First stage filter. Designed to keep the air handling unit clean, located in the inlet section of this unit. (Class F4-F5).
• Second stage filter. It is used as a final element for keeping the air duct clean. (Class F7-F9).
• Third stage filter. Placed at the entrance to a clean room to ensure hygienic conditions. (Class H13-H14).

1. A hygienic air handling unit must, on the one hand, prevent the penetration of microorganisms and pollutants into the room, and, on the other hand, must prevent the formation and accumulation of foreign substances in its design.
2. Systems must have high degree tightness, the proportion of air entering the room, bypassing the filter cassettes, should be very small.
3. Another point in the system that is susceptible to microbial entry is the drain connection and drain line from the air handling system. At this point, a siphon system with two bends should be installed, which does not have a connection to the city sewer.
4. To eliminate the need to open the door once again, a viewing eye should be installed in it, in addition, a lighting system should be provided.
5. To prevent the accumulation of micro-organisms and contaminants, air handling units must have very smooth surfaces without cracks or undulations.
6. Panel joints should use hygienic sealing elements to prevent the accumulation of contaminants in these places and facilitate maintenance procedures. In addition, differential pressure gauges should be used to enable visual control of the degree of clogging of the filters.
7. Air ducts must have smooth surfaces and be made of galvanized steel, stainless steel and similar materials.
8. The possibility of condensation is eliminated by the correct choice of the thickness of the thermal insulation. In the duct system, it is important to have a sufficient number of service openings with a good seal.
9. Devices for measuring air flow parameters must have service openings with easy access. These devices must provide airflow and room pressure data, even when the filters are clogged.

Cleanroom components

Start-up procedures for cleanrooms. After completion of the testing procedures and commissioning, if the results of these procedures are positive, work can begin in the cleanroom.

The most important tests for a cleanroom are: duct density tests, air handlers to achieve the desired flow rate, diffusers to maintain temperature and humidity setpoints, pressure tests and measurement of foreign particles. Instruments used for these purposes must be recalibrated before testing.

The outdoor air intakes of the air handling systems, exhaust dampers, rating plates, filter labels and all sections of the air handling system must be freely accessible, visually inspected and serviced.

Another important issue is the training of cleanroom personnel. The use of sterile clothing by staff is mandatory.

Just like for many engineering systems, the cleanroom should be subject to regular maintenance procedures to ensure continued operation without accidents or malfunctions. In order to maintain hygienic parameters at all times, the filters must be regularly checked for blockage before any problems occur in the system.

Air treatment systems for clean rooms

INTECH company performs the whole range of works related to the design, supply of equipment and materials, as well as direct installation of complexes engineering equipment and systems of "clean rooms" for heating, ventilation and air conditioning with a multi-stage, high-quality air filtration (purification) system. Using specialized climatic equipment for maintenance of clean rooms in industries:

• pharmaceutical industry;
• Microelectronics;
• The medicine;
• Biotechnology;
• Laboratories and Scientific research;
• Aviation and space industry;
• Medical industry;
• Food industry;
• Optics.

Purity classes

Room cleanliness class- these are clearly regulated requirements for the level of various kinds of impurities and particles in the air. Purity classes differ in the number of colony-forming bacteria per unit volume.

On the example of clean rooms medical institutions- 3 cleanliness classes are established:

1. Premises with the first class of cleanliness must have the lowest concentration of bacteria - no more than 10 bacteria / m3. First-class facilities include operating rooms for transplants, complex orthopedic and cardiac surgery, intensive care and burns, leukemia therapy;
2. The second class of cleanliness includes premises with a low level of microbial contamination - within 50-200 bact/m3. These are operating rooms for emergency operations, rooms for operating blocks (including corridors), maternity, prenatal wards, wards for premature and injured children;
3. Premises of the third class have a concentration of bacteria of 200-500 pcs/m3. These are intensive care wards for people with heart diseases, newborns, sterilization, children's dressing and treatment rooms.

The task of the climate system for "Clean Rooms"

Technological requirements for ventilation and air conditioning systems for "clean rooms" are as follows:

• Reducing the spread of pathogens, which means removing air pollutants, supplying clean air, protecting the room from microbes and microparticles contained in the air, as well as preventing air from entering neighboring less “clean” rooms;
• Control of the required air parameters: temperature, humidity, mobility, as well as the concentration of harmful impurities that do not exceed the MPC;
• Elimination of the generation and accumulation of static electricity to prevent the associated risk of explosion.

Problem solving

The task of ensuring cleanliness in the room is most effectively solved on the basis of a comprehensive approach that takes into account both the specific features of each particular room (space-planning characteristics, technological purpose, requirements for cleanliness and climatic parameters), and the features that characterize the room as an element of a set of rooms. This provision is reflected in the creation of cleanroom complexes, the main design principles of which are:

• ensuring the required design air exchange;
• preparation of supply air with the required parameters for humidity, temperature and microbiological purity;
• rational organization of air flows from cleaner modules to less clean ones;
• air distribution in the modules with the organization of a given direction of its movement, taking into account the characteristics of the room and technological process;
• highly efficient indoor air purification.

Design of the complex is determined by the specific purpose of clean rooms, their configuration and dimensions, acting regulatory requirements to the air environment. V general view The complexes offered by INTECH are made according to the modular principle and include the following functional systems and elements:

• air preparation, disinfection and distribution system;
• indoor climate control system.

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For healthcare facilities, research centers, as well as enterprises for the production of microelectronics and medicines, they are suitable ventilation systems which are intended for "clean rooms".

Clean room concept

“Clean” is a room with all related structures in which the concentration of microorganisms and particles in the air is maintained at the level defined by SNiP 41-01-2003(8) and GOST ISO 14644-1-2002. Their cleanliness classes and sanitary standards are also available in the US and EU countries.

Depending on the number of suspended particles ranging in size from 0.1-5.0 microns per 1 m 3 in a clean room, 9 sterility classes have been established.

For example, class 5 iso has 2 subspecies:

• "A" - MPC of microorganisms maximum 1/m 3;
• "B" - MPC of microorganisms is not higher than 5/m 3 .

For cleanrooms, the appropriate iso category applies and one of these states: “equipped”, “built” or “in operation”.

Devices for creating a "clean" air exchange

The organization of air conditioning and blowing systems is a laborious process that requires specialized knowledge, the availability of certain tools and specific engineering solutions.

Air streams in such a room must be supplied already filtered from microorganisms, bacteria and pollution, therefore one of the main roles in creating a favorable microenvironment in clean rooms is assigned to the supply air purification system. The running filtration system is considered to be the installation after the blower of several groups of cleaning elements:

1. Rough cleaning of mechanical contaminants;
2. Fine cleaning and antibacterial filtration;
3. Absolute cleaning of supply air masses.

In addition to filtering devices, ventilation of clean rooms involves: air intake and air distribution units, gateways, devices for automatically maintaining the required temperature and humidity, fans, as well as shut-off and control devices. The choice of a certain set of equipment depends, first of all, on the purpose of clean rooms and the air mass purity class required for the operation of this facility.

In the process of developing clean room ventilation systems, great attention should be paid to the design and material of pipes and filter chambers, which must be systematically treated for the purpose of antimicrobial prophylaxis.

Features of air exchange

In order to maintain clean air in the premises, it is necessary to use ventilation with an excessive volume of inflow, compared with exhaust unit in adjacent offices.

• If there are no windows in the room, then the predominance of the inflow over the exhaust should reach 20%;
• If the room has windows that allow infiltration, then the performance of the air supply should be about 30% higher than the hood.

Such an air exchange system prevents the penetration of contaminants into the room and promotes the movement of air from a clean office to adjacent rooms. Much attention is paid to the options for the intake of air flows into clean rooms and, as a rule, depends on their purpose.

Air supply to rooms with cleanliness class 1-6 is provided by air distribution devices that evenly direct air masses with a speed of 0.2 to 0.45 m/s. In rooms with a lower level of cleanliness, the creation of a non-unidirectional flow is allowed, for this, ceiling diffusers are used. The frequency of air exchange in clean rooms is 25-60 times per 60 minutes.

Frequently used schemes

When developing air ducts, one of the most acute problems is the competent arrangement of air flows. Currently, 5 ways of arranging air distribution devices are most often used, the choice of which directly depends on the purpose of clean rooms. Consider these schemes:

• Unidirectional air flow is carried out by means of an inclined ventilation grille;
• Non-unidirectional inflow of air masses is carried out through the use of ceiling diffusers;
• Supply of supply air to the operating room is carried out through a perforated ceiling unit with the creation of a unidirectional flow of the air mixture;
• The intake of supply air occurs due to the ceiling air distributor, which creates a unidirectional air flow into the working area;
• The supply of non-unidirectional air is done by means of an annular air hose.

Exhaust ventilation of operating rooms is carried out by exhaust fans and supply grilles equipped with check valves.

Practice has shown that the best device for creating a unidirectional air flow in the operating room are ceiling mesh air distributors. For example, a laminar ceiling measuring 1.8x2.4 meters in the operating room, whose area reaches 40 m 2, will allow organizing a 25-fold air exchange at a speed of air mass exit from the device of 0.2 m/s. These indicators will be enough to assimilate excess heat from the operation of equipment and the number of health workers in the operating room.

The development of ventilation and air conditioning systems in cleanrooms is a complex process that requires a person to understand the processes of air exchange and the intricacies of using air distribution units. It is for this reason that in order to assemble the entire structure at such objects, it is necessary to contact only the masters of their craft.

With the increase in the volume of construction in our country of healthcare facilities, laboratories, enterprises for the production of microelectronics, medicines, etc., the demand for ventilation systems for "clean rooms", which will be discussed in this publication, has sharply increased.

Clean room concept

A clean room (CP) is usually called a room or a group of rooms with all related structures, in which the countable concentration of suspended particles and microorganisms in the air mixture is maintained at a strictly defined level, determined by GOST ISO 14644-1-2002; SNiP 41-01-2003(8); sanitary standards and the required purity class. The United States, Germany, France, Great Britain and the European Union have their own standards for the purity of the air mixture.

Depending on the counting amount of suspended particles, ranging in size from 0.1 to 5.0 microns per 1 m 3 in the CP, and the concentration of microorganisms in it, 9 classes of sterility were determined.

Based on the MPC of microorganisms, class 5 iso is divided into two subspecies:

• "A" - MPC of microorganisms, not more than 1/m3;
• "B" - maximum concentration limit of microorganisms not more than 5/m 3 .

For the PE, its iso class and state are used: "operated"; "built" and "equipped".

Equipment for creating "clean air exchange"

Creating competent ventilation and air conditioning systems for clean rooms is a complex process that requires knowledge of air exchange features, special equipment and specific technical solutions.

The air in such a room must be supplied already cleaned of contaminants, bacteria and microorganisms, therefore, the filtering system of the supply air mixture plays a special role in creating a sterile microclimate in "clean rooms". A popular cleaning system is the installation of three groups of filter elements after the blower:

1. The first group consists of a coarse filter from mechanical impurities.
2. The second group of filters consists of a set of fine filter elements and an antibacterial filter.
3. The third group consists of HEPA microfilters with absolute cleaning of the supply air.

In addition to filter elements, ventilation of clean rooms involves: fans, air intake and air distribution equipment, devices for automatically maintaining the required humidity and temperature, shut-off and control equipment, locks, etc. The choice of one or another set of equipment depends on the purpose of the emergency and the required object of air cleanliness class.

When designing CP ventilation systems, much attention is paid to the design and coating of air ducts and filter chambers, which must undergo periodic antimicrobial treatment.

Features of air exchange

To maintain the purity of the air, in process clean rooms, ventilation with an excess volume of inflow should be used, compared with the exhaust in adjacent rooms.

• If the room is without windows, then the inflow should prevail over the exhaust by 20%.
• If the emergency room has windows that allow infiltration, then the air supply capacity should be 30% higher than the exhaust.

It is this air exchange system that prevents the penetration of contaminants and ensures the movement of air from a clean room to adjacent rooms. Much attention of designers is paid to the methods of supplying the air mixture to such objects and depends on their purpose.

The inflow to the emergency room with a purity class from 1 to 6 must be supplied by an air distribution device from top to bottom, creating uniform unidirectional air flows of low speed, from 0.2 to 0.45 m/s. In rooms with a lower cleanliness class, it is allowed to create a non-unidirectional flow by means of several ceiling diffusers. The frequency of air exchange for PE is set depending on their purpose, from 25 to 60 times per hour.

The most common schemes

When designing ventilation of clean rooms one of major problems is an proper organization air mixture flows. To date, designers use several solutions for the location of air distribution devices, the choice of which depends on the purpose of the emergency. Consider the most common schemes for organizing ventilation in the operating room.

• A) air flow is unidirectional, through an inclined ventilation grille;
• B) non-unidirectional inflow of the air mixture is carried out through the use of ceiling diffusers;
• C) fresh air is supplied to the operating room through a perforated ceiling panel with the creation of a vertical unidirectional air flow;
• D) the supply air mixture is supplied through the ceiling air diffuser, which creates a unidirectional air flow to the working area;
• E) Air is not unidirectional through an annular air hose.

Exhaust ventilation of clean operating rooms is carried out by means of exhaust fans and overflow wall grates with check valves.

As practice has shown, the best device to create a unidirectional laminar air flow in the operating room, ceiling-type mesh air diffusers are used. For example, a laminar ceiling with dimensions of 1.8 by 2.4 m in an operating room with an area of ​​40 m 2 will allow creating 25-fold air exchange at an air outlet velocity of the device of 0.2 m/s. These indicators are sufficient to assimilate heat surpluses from the operation of the equipment and the number of personnel in the operating room.

Designing ventilation and air conditioning systems in an emergency is a complex process that requires knowledge of air exchange processes and the intricacies of using air distribution equipment. That is why to create ventilation at such facilities, you should contact only professionals.