Supply and exhaust ventilation in clean rooms. Air conditioning systems for hospitals, pharmacies, clinics. Development and implementation of clean room ventilation projects

Clean room (clea nr oom) is a room in which the concentration of airborne particles is controlled, constructed and used to minimize the entry, release and retention of particles within the room, and allowing other parameters, such as temperature, humidity, to be controlled as necessary and pressure.

In such premises the contents pollutants in the air, on the surfaces of walls and ceilings must be kept to a minimum level.

The indicated particles may include materials such as dust, anesthetic waste gases, and microorganisms.

Extremely clean indoor air can only be achieved by removing indoor air and introducing filtered displacement conditioned air.

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

Technology clean rooms serves to perform the following tasks:

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

A clean room requires a clean atmosphere, clean gas, clean surfaces, clean equipment, clean products and clean technology.

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

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

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

The basic approach should be to meet hygiene requirements, where necessary, in the most cost-effective manner and maximum efficiency, but only to the extent necessary for a particular premises.

The parameters influencing the implementation of the necessary conditions can be divided into two groups: support parameters comfort and hygiene.

The criteria for comfortable air parameters are:

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

These parameters are important for assimilation of heat generation from external and internal sources, as well as for compensation of heat loss and for ensuring comfortable indoor conditions.

Criteria for hygienic air parameters:

• ensuring the concentration of microorganisms within specified limits;
• removing pollutants such as off-gases from the premises;
• controlling air movement in the room.

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 a minimum required level, air movement between rooms must be controlled.

However During design, these parameters should be considered in their entirety. To assimilate excess heat to ensure the required air quality, the amount of conditioned air should be checked, as well as the amount of displacement air required to maintain the concentration of microorganisms in the room below a certain level.

Cleanroom Applications

Clean rooms 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 cleaned of solid particles and microorganisms.

Cleanrooms are used in microelectronics, space technology, thin film technology, the printed circuit manufacturing industry and related areas where the removal of contaminant particles is necessary.

In the food industry from production premises Both pollutant particles and microorganisms are removed.

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 the air, water and especially in cracks and 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 wind, earthquakes and volcanic activity. These are usually called dust or aerosol. This group includes particles of smoke resulting from industrial processes, building heating systems and vehicle exhaust emissions. The same group also includes suspended particles, the sources of which are moving parts of machines in clean rooms. In addition, the activities of people in a clean room release approximately 100,000 particles smaller than 3 microns into the air of that room.

Sterility. This is how one can characterize a situation in a room in which there are no microorganisms in products and devices.

Sterilization. A technique for breaking down or killing microorganisms in products or devices.

HEPA filters (high efficiency particulate air filter - highly efficient aerosol filter). These filters are a type of high-efficiency air filters. They are used directly in air handling units, as well as at the end points of air supply to the room as a final cleaning stage. The efficiency of these filters for 0.3 micron particles ranges from 97.8 to 99.995%. Such filters are intended 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 particles measuring 0.3 microns ranges from 99.999 to 99.99995%. Such filters are intended for rooms with a cleanliness class of 1-100.

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

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

Clean rooms with laminar air flow. In this method, air flowing at a constant speed carries contaminants into the return air duct and then into the air handler. This method is suitable for rooms with cleanliness classes 1, 10, 100, 1000

Clean rooms with laminar air flow

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

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

In a cleanroom, all equipment and systems (including air handlers, ductwork, and duct equipment) must be capable of cleaning, replacement, and service.

In rooms where a high degree of sterility is required, three-stage filtration is used:

• First stage filter. Designed to keep the air treatment unit clean, located in the inlet section of this unit. (Class F4-F5).
• Second stage filter. 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 polluting particles into the room, and, on the other hand, must prevent the formation and accumulation of foreign substances in its design.
2. The systems must have a high degree of tightness; the proportion of air entering the room, bypassing the filter cassettes, must be very small.
3. Another location in the system that is susceptible to microbial intrusion is the drain connection and the drain line leaving the air handler system. A siphon system with two bends should be installed in this place, which does not have a connection to the city sewerage system.
4. To eliminate the need to open the door once again, an inspection peephole must be installed in it, in addition, a lighting system must be provided.
5. To prevent the accumulation of microorganisms and contaminants, air handling units must have very smooth surfaces without cracks or wavy shapes.
6. Hygienic sealing elements must be used at panel joints to prevent the accumulation of contaminants in these areas and to facilitate service procedures. In addition, to be able to visually monitor the degree of filter clogging, differential pressure gauges should be used.
7. Air ducts must have smooth surfaces and be made of galvanized steel, of stainless steel and similar materials.
8. The possibility of condensation is eliminated the right choice thickness of thermal insulation. It is important that the duct system has a sufficient number of service openings with good sealing.
9. Devices for measuring air flow parameters must have service openings with easy access. These devices should provide data on air flow and pressure in the room, 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 clean room.

The most important tests for a clean room are: tests of air ducts for density, air handlers for ensuring required flow rate, diffusers - to ensure the specified temperature and humidity values, pressure testing and measurement of the content of particles of foreign substances. Instruments used for these purposes must be recalibrated before testing.

Outdoor air intake devices of air treatment systems, exhaust dampers, rating plates, filter labels and all sections of the air treatment system must have easy access and the ability to be visually inspected and serviced.

Another important issue is the training of cleanroom personnel. It is mandatory for staff to wear sterile clothing.

Same as for many engineering systems, the cleanroom should undergo regular maintenance procedures to ensure continuous operation without accidents or problems. To maintain hygienic parameters at all times, it is necessary to regularly check the filters for clogging before any problems occur in the system.

Air preparation systems for clean rooms

INTECH company carries out the full range of work related to the design, supply of equipment and materials, as well as direct installation of engineering equipment complexes and “clean room” systems for heating, ventilation and air conditioning with a multi-stage, high-quality air filtration (purification) system. Using specialized climate control equipment to service clean rooms in the following industries:

• Pharmaceutical industry;
• Microelectronics;
• Medicine;
• Biotechnology;
• Laboratories and scientific research;
• Aviation and space industry;
• Medical industry;
• Food industry;
• Optics.

Cleanliness classes

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

Using the example of clean rooms in medical institutions, 3 classes of cleanliness have been 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 burn wards, and leukemia therapy;
2. The second class of cleanliness includes rooms with a low level of microbial contamination - in the range of 50-200 bact/m3. These are operating rooms for urgent operations, operating rooms (including corridors), maternity, prenatal wards, wards for premature and injured children;
3. Third class premises have a bacteria concentration of 200-500 pcs/m3. These are intensive care wards for people with heart disease, newborns, sterilization rooms, children's dressing rooms 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 germs and microparticles contained in the air, as well as preventing the flow of air from neighboring less “clean” rooms;
• Monitoring the required air parameters: temperature, humidity, mobility, as well as the concentration of harmful impurities not exceeding the maximum permissible concentration;
• Eliminates the generation and accumulation of static electricity to prevent the associated risk of explosion.

Problem solving

The task of ensuring cleanliness in the premises is most effectively solved on the basis of a comprehensive approach that takes into account both the specific features of each specific 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 premises. This position is reflected in the creation of clean room complexes, the main design principles of which are:

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

Design of the complex is determined by the specific purpose of the cleanrooms, their configuration and size, and current regulatory requirements for the air environment. IN general view the complexes offered by INTECH are carried out on a modular basis and include the following functional systems and elements:

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

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Raymond K. Schneider, Senior Cleanroom Consultant and Principal at Practical Technology, USA, Member American Society 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 the famous American specialist in the field of clean rooms, 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 large practical experience, deserve careful study and use where possible.

Air conditioning systems for clean rooms must supply purified air to a certain amount in order to maintain a given level of room cleanliness. 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 for temperature and humidity in accordance with the requirements for the microclimate parameters of the room. In addition, additional conditioned air is supplied to the room to create excess pressure.

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

Air exchange

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

Average indoor air mobility is usually used when 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 cleanliness. This was based on the first clean room designs carried out as part of the space programs of the 1960–1970s.

Recently, experiments have been carried out with lower speeds, which have shown that air mobility in the range of 0.35–0.51 m/s ± 20% is quite acceptable, depending on the type of activity and installed equipment. The upper limit of air mobility corresponds to high personnel activity and the presence of equipment that produces dust. Lower values ​​are accepted if a small number of personnel perform sedentary work and/or there is no dust-producing equipment.

Often, knowledgeable customers with clean room experience will set air mobility values ​​at the lower level. And customers and novice designers who do not know about the admissibility of more low speeds, set the air mobility at the upper end of the scale. There is no clearly defined average level of air mobility 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 determined by the FDA (Food and Drug Administration) for sterile areas in the pharmaceutical industry.

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

The Institute of Microclimate Practice Guidelines (IEST-CC-RP.012.1) contains 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 joint recommendations of designers, builders and users, proven over years of successful work. In all of these documents, responsibility for the choice of parameters is placed on 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

Over the years, clean room technology has evolved 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 Purification) filter has an efficiency of 99.9995% for 0.12 micron particles and 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 duty.

HEPA (High Efficiency PA) 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 air cleanliness requirements are even more stringent.

When laboratory tests were carried out on the filters with an accurate count of the number of particles passed, it turned out that HEPA/ULPA filters mainly pass the 0.1-0.2 micron fraction. At the same time, the passport efficiency of filters was confirmed for fractions of 0.12 and 0.3 microns and even higher efficiency was discovered for particles that are larger and smaller than the specified sizes. For a strict purity standardization regime, 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 others (MPPS). MPPS values ​​vary slightly among different manufacturers filters. Setting efficiency by the particle size that is least filtered is considered by some designers and manufacturers to be most convenient.

Most hard and medium duty cleanrooms have filters in the ceiling. Filters can be grouped and attached to a common module supply system, which facilitates installation in the ceiling, or can be installed separately, with individual supply air ducts. This placement, reminiscent of an inverted "T", forms a honeycomb structure under the ceiling. In this case, the filters are carefully sealed in the housing to prevent the passage of untreated air. In addition, filters built into the supply chambers are still used. However, displacing them modular schemes allow better regulation of parameters and air mobility.

Filter-fan units have become widespread. 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 for installation in a cellular structure are offered for delivery. The fans are equipped with electric motors designed for different voltages, which allows the use of different power supply schemes. Some complex control systems provide the ability to individually adjust each unit, record energy consumption, signal faulty electric motors, regulate groups of filter fans, and change the fan speed according to the time of day. Filter-fan units are used for all classes of clean rooms.

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

Installing HEPA/ULPA filters directly in the ceiling of clean rooms is dictated by the intention to minimize or completely eliminate the possibility of dust accumulation on any surfaces (for example, on the walls of air ducts) along the air flow from the filter to the clean room. Remote placement of HEPA filters is typical for moderate-mode clean rooms, since the number of particles simultaneously blown from the walls of the air ducts after the filters is within acceptable limits. The exception is when a standard air conditioning system that is not cleanroom certified is converted for this purpose in accordance with ISO 14644. In this case, all ductwork downstream of the filters must be thoroughly cleaned.

For moderate-duty cleanrooms, fan units or mixing and distribution plenums with HEPA filters on the discharge side are often used. At the same time, the frontal air velocity in HEPA filters reaches 2.54 m/s, which corresponds to a greater pressure drop than with a ceiling installation. The aerodynamic resistance of a pure HEPA filter measuring 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 resistance is 125 Pa.

Air circulation in clean rooms

The air entering the clean room after cleaning in HEPA and ULPA filters contains virtually no suspended particles. Air supply to the room is carried out 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 said contaminants from the premises.

There are three types of indoor air circulation:

1. Unidirectional ordered flow (formerly called “laminar”), when the streamlines of all air jets are parallel.

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

3. Mixed flow, when in one part of the room the air streams can be parallel, but in another part they are not.

Heavy duty cleanrooms typically use unidirectional flow. This is achieved by installing HEPA/ULPA filters throughout the entire ceiling area and installing a perforated false floor. Air moves vertically from the ceiling to the floor and is removed through perforations into the exhaust chamber under the floor. The recirculated air is then returned to the room through peripheral recirculation ducts.

If the cleanroom is narrow (4.2–4.6 m), wall-mounted exhaust grilles installed below 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 grilles. Such circulation is considered acceptable for rooms with strict conditions, especially in cases where the room has been converted into a clean room and there is dust in the upper zone.

In rooms with orderly circulation, the placement of furniture and equipment affects the air flow structure. 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.

Disorganized air movement often occurs 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 orientation of individual jets is different and does not fit into a specific pattern. While the supply air contains practically no suspended particles, their appearance and accumulation in the work area of ​​clean rooms depends on the number of particles generated in the room itself; from reducing dust concentration due to air exchange; intensity of particle entrainment from the working area. In general, we can say that the greater the air exchange, the cleaner the air in medium-duty rooms, but the structure of air flows in the room also plays a certain role.

The air removal scheme for rooms with disordered circulation is very important. In such rooms, wall-mounted exhaust grilles are widely used. 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, cleanroom designers aim to direct airflow from the worktop to the floor and then to low exhaust grilles. With this scheme, particles are removed from the room and directed to filters, where they are captured. An exception may be cases where contaminant particles are generated by equipment above the working area. Then some kind of device should be used to catch the removal and particles at the top. In general, it is recommended to use a top-down air distribution scheme.

In environments with an average level of cleanliness, it is a sound practice to limit horizontal sections of air flow. The recommended values ​​for horizontal sections are no more than 4.2–4.8 m. Thus, in a room no more than 8.4–9.6 m wide, it is permissible to install exhaust grilles along the perimeter of the walls. This limitation is dictated by the fear of secondary contamination due to deposition or other transfer of particles into work area from extended horizontal flows.

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

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

According to the “top to bottom” circulation scheme existing in practice for clean rooms, bottom installation of wall-mounted exhaust grilles is also recommended here. Placing exhaust grilles overhead in a clean work area can create areas with high concentrations of suspended particles, especially during periods of intense work. In known cases of installation of ceiling exhaust grilles in moderate cleanrooms, 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 with critical and non-critical air cleanliness requirements is carried out in the same room. If it is not possible to carry out critical work in a separate room, then a shared clean room with zoning for cleanliness can be used. Zones are created by appropriately grouping ceiling filters. In an area with critical cleanliness conditions, the number of filters is greater, in an area with non-critical conditions - fewer. In addition, supply air can be supplied in such a way that it is first supplied through air ducts to the critical area and then flows to 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 exhaust grilles in such a way as to prevent the transfer of contaminants throughout the room. A raised floor with an exhaust air collector installed underneath it will be very effective in this case. However, the use of such a solution may be hampered by the limited budget of the customer, who chooses a zoned clean room project with mixed circulation precisely because of its low cost.

The disadvantage of disordered air circulation in clean rooms is the creation of areas of high dust content. Such areas may exist for a limited time and then disappear. This occurs through the interaction of air flows resulting from industrial activities and disordered supply jets. Attempts were made to reproduce unidirectional circulation by installing a false ceiling-air distributor and creating a high-pressure zone between the 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 orderly unidirectional flow was formed in the room at speeds much lower than in clean rooms with a strict regime. The displacement effect created by the supply air flow prevents the formation of areas with increased dust content and generally achieves a higher level of cleanliness. The specified result, as noted above, is achieved at a lower air mobility than specified in the standards for strict and medium cleanliness regimes (Fig. 1).

Thermal load

The share of sensible heat in the heat load of clean rooms usually exceeds 95%. Typically, year-round cooling is required because heat generated by process equipment and circulation fan motors enters the room. A small proportion of latent heat is generated by the presence of personnel. Each cleanroom has a unique design, so all factors affecting the heat load must be carefully analyzed.

In rooms with strict and medium levels of cleanliness, a significant part of the supply air is not processed by air conditioners - it is recirculated air. The required sensible heat removal is carried out in mixing and distribution chambers, where part of the total flow is cooled in surface heat exchangers and then returned to the general flow to recirculation fans (Fig. 2). The inlet air temperature into high-pressure cleanrooms may be only a few degrees lower than the exhaust air temperature due to the large influx volume. This temperature difference allows the use of ceiling-mounted HEPA/ULPA filters with air supply from top to bottom without compromising the comfort requirements for workers.

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

Outdoor air supply

An influx of outside air is necessary to compensate for exhaust and exfiltration, which always occurs in pressurized cleanrooms. External supply air is expensive, since before supplying it to clean rooms it must not only be cleaned, but also subjected to temperature and humidity treatment. Since it is impossible to completely eliminate the supply of outside air, for reasons of general economy and energy conservation, its amount should be reduced to a minimum.

The air pressure in clean rooms is usually higher than in the surrounding rooms. As a rule, a pressure drop of 12 Pa is recommended. Higher excess pressure causes a whistling noise in cracks and difficulty opening doors. In cleanroom blocks with different cleanliness classes, it is customary to maintain a pressure difference of 5 Pa between adjacent rooms, while 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-tested calculated amount of air for selecting air conditioning system equipment. The actual amount of outside air will vary depending on door openings, leaks and the actual operating schedule of the hood.

The outdoor air conditioner is designed to bring its parameters into compliance with clean room standards. This means 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 made: preliminary - an ASHRAE filter with an efficiency of 30%, an intermediate - a filter with an efficiency of 95%, and a final - a HEPA filter. In clean rooms with medium and moderate conditions, there are usually two stages of cleaning: preliminary (30%) and final (95%). From the name it is clear that the final cleaning filter is placed at the outlet of the air conditioner.

Preheating is necessary when the outside temperature in winter drops below 4 °C. If the air dew point temperature in the clean room is ≥5.6 °C, the surface heat exchanger cools and dehumidifies the supply air. Since workers in high-security cleanrooms always wear protective clothing, the dry-bulb temperature can be maintained no higher than 19 °C, while minimum value relative humidity for setting the regulators is 40%. 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 input from recirculation fans is taken into account. This is a significant value for clean rooms with strict regimes.

Reducing the surface temperature of the heat exchanger to the level required to maintain a room dew point below 5.6°C can be difficult. When it is necessary to dehumidify supply air below 40% relative humidity, various desiccant agents are usually used.

In the system described here, the outdoor air conditioner is subject to the load associated with latent heat and moisture in the room. It is assumed that the supply air parameters meet the requirements for the assimilation of latent heat generated by the room personnel and moisture input through the cleanroom enclosures. It is also assumed that the latent heat load is more or less constant. These assumptions must be verified on a project-by-project basis. It is necessary to take into account the conditions in the premises surrounding the clean room, the parameters of the external climate, and the possibility of moisture release from production processes in the room.

In small volume clean rooms with little need for outside air, the recirculation air coolers in mixing and distribution chambers discussed above can also be used to treat outside air. In this case, a mixture of outside 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. Air from the mixing and distribution chambers flows to circulation fans.

In moderate-duty cleanrooms, the total amount of supply air required may be close to the conditioned air flow rate. 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.

conclusions

IN regulatory documents When designing clean rooms, there is a tendency to entrust the designer with the functions of a general expert, capable of fulfilling all the customer’s wishes (as far as they are known to him). Guides typically use the phrase “a matter of agreement between the buyer and the seller” to involve the customer in the decision-making process, since each developer can offer his own version of the design. The effectiveness of the design principle discussed in this article has been proven in practice; This approach, according to the author, allows us to agree 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 abbreviations from the magazine ASHRAE.

Translation from English O. P. Bulycheva.

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

Table 2. Optimal filter selection scheme used in Switzerland for cleanroom classes according to ISO 14644-1 (GOST R ISO 14644-1)

To date, engineering practice has developed standard solutions, following which allows you to avoid inaccuracies and avoid unnecessary capital and operating costs. These typical solutions relate to:

• principles of building ventilation and air conditioning systems;
• determining the necessary structure and parameters of the air conditioner;
• choosing the number of filtration stages and filter types;
• determining the air exchange rate;
• ensuring the required temperature and humidity conditions in the room;
• creating thermal comfort for personnel.

The experience of the Invar Cleanroom Testing Laboratory during the certification of projects (DQ stage) and constructed cleanrooms (IQ, OQ and PQ stages) also revealed characteristic errors.

Initial data when designing a ventilation and air conditioning system

Before starting design, you should clearly formulate its purpose and determine the initial data. Errors and inaccuracies at this stage will lead to incorrect completion of the entire work. Such initial data include:

• requirements for air cleanliness, and for clean rooms - specifying a cleanliness class in accordance with GOST ISO 14644-1 or GOST R 52249;
• microclimate parameters for the technological process (temperature and humidity with permissible limits deviations);
• number of workers in the room;
• heat and moisture release from equipment and processes;
• release of harmful substances;
• area and height of premises;
• technology requirements, based on the characteristics of technological processes and the materials performed, used and products manufactured;
• pressure differences between rooms and air flow speeds (if necessary).

Structure of ventilation and air conditioning systems

Several types of air flows are involved in the ventilation and air conditioning system:

• exhaust - air leaving the room through the system forced ventilation. Part of the exhaust air (L in) can be removed directly into the atmosphere by local hoods, while part can be recirculated;
• external - atmospheric air taken by the ventilation and air conditioning system for supply to the serviced room, L n;
• supply air - air supplied to the room by the ventilation and air conditioning system, L p;
• recirculation - air mixed with the outside air and again sent to the ventilation system, L p;
• removed - air taken from the room and no longer used in it, L y.

Air leaks from rooms with high pressure (air exfiltration, L e) and air infiltration into rooms with high pressure should also be taken into account. low blood pressure, L and. The simplest ventilation and air conditioning scheme is a direct-flow system, when 100% of outside air is supplied to the room (Fig. 1). This system is uneconomical, since all air entering the room passes full cycle preparation - from outside air parameters to the required clean room air parameters. This system is characterized by high energy consumption and reduced filter life.

where i is the room number. To a certain extent, the performance of this system can be improved by heat recovery (Fig. 2). Thanks to recuperation, heating energy savings of up to 60% are achieved.

L n = L p = ΣL рi = ΣL вi = ΣL вi + L e, L у = ΣL вi,

where i is the room number. Direct-flow systems, due to their uneconomical nature, are used only where they are needed and where air recirculation is unacceptable (working with harmful substances, dangerous pathogenic microorganisms), Ch. 17. Where possible, recirculation systems are used, which reduces energy costs several times compared to direct-flow systems. An example of a single-level recirculation system is shown in Fig. 3.

L в = ΣL вi , L у2 = ΣL вмi ,

L p = L n + L p = ΣL pk, L y = L y1 + L y2 = L in - L p + L y2 = ΣL in - L p - ΣL in mi, L p = L in - L y1,

where Lbmi is the air flow rate of the local exhaust unit from the i-th room; Lвi is the air flow rate supplied to the air conditioner from the i-th room. In conditions cold winter or hot summer, as well as when servicing clean rooms with several air conditioners, a two-level system is used. In it, outside air is prepared to certain parameters in a separate (central) air conditioner, and then supplied to recirculation air conditioners (Fig. 4).

Local filter ventilation or recirculation units (Fig. 5) are widely used to create zones with unidirectional air flow, for example, in operating rooms and other critical areas. The given diagrams give a general approach to the design of ventilation and air conditioning systems; they do not cover the entire variety of options for fundamental solutions, which in each specific case should be developed based on the task at the lowest capital and operating costs.

The above types of air flows must be determined for each room and the system as a whole. On this basis, the air exchange balance is calculated, the results of which are presented in the form of a table and plotted on the principle diagram of ventilation and air conditioning (Fig. 6). To regulate the balance of air exchange, it is advisable to install valves on the supply and exhaust.

The point of building an air exchange balance is to check that the total volume of air entering the room must be equal to the total volume of air removed from the room. Violation of this condition leads to the inability to provide the required pressure drops, difficulty in opening and closing doors, etc. For clean rooms, this plays a special role, since it is necessary to maintain different pressures in different rooms.

In the air exchange balance table, the total supply air flow rate and the total exhaust air flow rate must be equal for each room (for each row of the table). For each clean room, supply and exhaust air are calculated, and air leaks are also taken into account (exfiltration - air leakage into rooms with lower pressure, air infiltration - air flow from a room with higher pressure). high pressure). Basic initial data for developing a design for a ventilation and air system for clean rooms:

1. planning solutions indicating cleanliness classes and pressure drops;
2. purpose of clean rooms (clean zones): protection of the product and process, protection of personnel and the environment;
3. release of harmful substances;
4. heat and moisture release from equipment;
5. number of staff;
6. climate characteristics of the construction area.

Outdoor air flow is calculated based on the need:

• compliance with sanitary and hygienic standards;
• compensation of removed air (both from individual rooms due to the operation of exhaust units, and removed through the air conditioning system);
• compensation of leaks due to pressure differences in clean rooms and the environment.

The outdoor air flow rate for the entire ventilation system is equal to the sum of the air flow rates for each room. Air consumption for a separate room is equal to the sum of the volumes of air removed by local exhaust units, and losses due to leaks. This amount should not be less than the minimum outdoor air flow according to regulatory documents.

Calculation of supply air for each room

Supply air performs the following functions:

• ensuring the required cleanliness class;
• ensuring requirements for microbiological cleanliness of air where they are imposed;
• supplying the required amount of outside air;
• removing excess heat and moisture and maintaining the required microclimate parameters in the room;
• compensation of air leaks due to pressure differences.

The required air exchange rate is influenced by all the above-mentioned functions of the supply air. For each of them, the required air exchange rate is determined and the highest value is included in the project. Let's look at each of the listed functions.

Cleanliness class

This is achieved through multi-stage air filtration and the selection of filters of the appropriate classes, setting the air flow speed (for unidirectional air flow), and the air exchange rate.

Air exchange rate

Sets the air flow for clean rooms of ISO classes 6-9 (zones B, C, D). For zone A, the air flow is determined by the speed of the unidirectional flow. There are several approaches to determining the air exchange rate to ensure cleanliness:

• use of various recommendations, standards and rules;
• calculation method.

Removing excess heat and moisture

Process equipment and personnel produce heat and moisture that must be removed using the HVAC system. Providing the necessary microclimate with maintaining temperature and humidity is an important condition for ensuring the normal work of personnel in clean rooms. In addition, certain technological processes (for example, photolithography in the production of microcircuits) have stringent requirements for temperature and humidity.

Compensation for the operation of exhaust units

The total volume of exhaust air for of this premises. The quotient of dividing it by the volume of the room gives the air exchange rate necessary to compensate for the hoods.

Leak compensation

The pressure difference between different rooms causes exfiltration (leakage) of air from the room through cracks in the doors and various types of leaks. The amount of leakage must be calculated for each room and taken into account in the air exchange balance. Air leakage must be compensated by an equal amount of outside air in the supplied supply air. The air exchange balance must also take into account air infiltration, i.e. air intake from neighboring rooms.

Air exchange rates in general premises

In such rooms, the air exchange rate is calculated in accordance with sanitary standards and by calculations of excess heat and moisture. IN Western countries The following values ​​of air exchange rates are used (data from Airflow, England) for some rooms (Table 1).

Selecting filter types

Typically, air preparation systems for clean rooms are carried out in three stages:

• first stage: medium efficiency filter type F to protect the air conditioner from contamination;
• second stage: high-efficiency F-type filter to ensure clean air ducts;
• third stage: HEPA or ULPA filter to ensure guaranteed high quality air entering directly into clean rooms.

In addition, the use of a three-stage air filtration system guarantees a long service life for HEPA and ULPA filters. Recommendations for the optimal selection of filters are presented in table. 2.

Typical errors

Cleanliness classes

The most common misconception is the requirement for the production of non-sterile drugs in clean rooms. It was generated by the notorious and illiterate OST 42-510-98 and previous documents of the same type. Nowhere in the world is there a requirement to produce non-sterile forms in clean rooms! The only document that provides specific data on the cleanliness of supply air in the production of solid forms is the International Organization of Pharmaceutical Engineers (ISPE) Guidelines.

It provides recommendations for the effectiveness of final filters for various stages of the process. In world practice, these recommendations are widely used without specifying cleanliness classes. No one prohibits the use of clean rooms, and many specify the production of solid forms in zones D, and liquid non-sterile forms in zones C. But which path to choose - to use clean rooms or simply limit yourself to a certain level of purity of the supply air and the quality of the enclosing structure is up to you customer.

This logic is followed by EU GMP Rules (GOST R 52249) and US guidelines. If someone wants to force a company to use an optional cleanliness class, we recommend a simple and effective remedy: to legally formalize this coercion so that the costs of it are borne by the initiator himself. No arguments (like “this is what our “advanced” neighbors do”) should be taken into account.

Overestimation of cleanliness classes in sterile production is also widespread. There is one more factor to keep in mind. Other design organizations artificially inflate cleanliness classes and sizes of clean zones. The cost of the project and the fee of the performers directly depend on the cleanliness classes and the volume of costs. In the author’s practice, I encountered a project in which the emission of particles by staff was overestimated by 100 times!

Unreasonably stringent requirements for temperature and humidity

There are, for example, requirements to maintain an air temperature of 22 °C with an accuracy of ±1 °C and humidity within 45-50% without justification from the technological process. A simple expansion of the limits of regulation of microclimate parameters within the framework of existing standards can significantly simplify the entire system.

Unjustified use of direct-flow systems

Previously, under the conditions of a costly government funding mechanism, direct-flow systems were widely used, even where they were not needed. In world practice, air recirculation is used wherever it is permissible from a safety point of view. Otherwise, recirculation heats the outside air in winter and cools it in summer, i.e. significant costs literally go down the drain.

Excessive air exchange rate Incorrect choice of filters

Projects often include low filter classes (for example, G3) in the first filtration stage. This increases the dust load on the filters of subsequent stages and shortens their service life.

Absence schematic diagram and air exchange balance tables

Without them, it is impossible to judge the project. Their development is mandatory. These errors are typical examples and do not exhaust the entire list of shortcomings encountered in practice.

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Ventilation in rooms such as the operating room is necessary to maintain hygienic conditions. Clean rooms are an environment where there are no microorganisms and harmful substances that adversely affect human health. It is in these conditions that medicines are manufactured, patients are operated on and treated, blood is transfused, watches and optics are produced, microelectronics are assembled, and food is processed. Providing and maintaining sanitary and hygienic conditions, as well as a controlled climate in such premises, play a particularly important role. A favorable microclimate is achieved using ventilation systems. However, ventilation in clean rooms should not be standard. The choice of such a climate control device depends on the functional load, size and cleanliness class. The latter represents certain requirements for the level of particles and impurities in the air.

Clean rooms are divided into three classes, differing in the number of microorganisms per unit volume:

Ventilation in clean rooms reduces the spread of microorganisms, supplies clean air, prevents the entry of contaminated air, and controls temperature and humidity levels. Most effective system air distribution is considered to be the installation of filters along the entire perimeter of the ceiling area. As a rule, cleanrooms are divided into four main types, each of which has different air flow:

• Clean room with multi-directional air flow. This can be achieved using conventional ventilation, which features the classic method of supplying air through air distributors.
• Clean room with unidirectional air flow. This type involves supplying clean air using a filter system while maintaining the direction of movement. This flow is also called “laminar”, which provides a high value of air exchanges at low speed (0.3 m/sec through the entire zone).
• Clean room with mixed flow. In areas where the product is exposed to contamination, a laboratory cabinet with unidirectional flow is installed.

Supply and exhaust ventilation systems for clean rooms

Cleanrooms include those where microelectronics are assembled, medicines are manufactured, and watches are produced. The microclimate in these rooms must be stable
Supply ventilation of a clean room supplies clean air into the room with the specified parameters for a favorable microclimate. This ventilation system processes and purifies the air before supply, regulates the level of humidity and temperature. Exhaust ventilation of a clean room removes contaminated air, provides the necessary air exchange rate, and maintains negative pressure in certain areas of the room.

The specialists of our company “Vent-m” have necessary knowledge and practical skills for ventilation installation work in clean rooms. Taking into account all the features of such premises, they choose a certain type of device and install it on high level quality.

Without clean rooms it is impossible to imagine the production of electronic chips, the pharmaceutical industry, effective treatment patients, conducting research in various branches of medicine and cooking. A room in which the number of aerosol particles and the number of bacteria in the air is maintained at an acceptable level is considered clean. There are nine classes of cleanrooms depending on the concentration of dust and bacteria in the air. They are enshrined in GOST ISO 14644-1-2000, which is based on international standard ISO 14644-1-99 Cleanrooms and associated controlled environments.

As part of ordinary air (which we breathe in Everyday life) there is a large amount of impurities (smog, dust, pollen, viruses, fungi). The listed impurities are unacceptable for clean rooms, as they negatively affect the work. Therefore, the creation of ventilation and air conditioning systems in clean rooms is an essential component of ensuring a suitable microclimate.

Features of designing a ventilation system for clean rooms

Design and installation of ventilation and air conditioning systems for clean rooms requires skills in working with special equipment, as well as knowledge of the standards and requirements for clean rooms.

There are three schemes for organizing air exchange in clean rooms:

• all air flows move in parallel;
• disordered direction - clean air is supplied in different sides;
• mixed direction - observed in large rooms, when in one part the air moves in parallel, and in another part - in a disorderly manner.

Depending on the size of the room and the location of the work area, choose optimal project ventilation systems, but most optimal solution is ventilation with a unidirectional flow of clean air.

For clean rooms, only supply and exhaust ventilation and air conditioning systems are used. Its essence is as follows: a flow of clean air is supplied from above under pressure at a certain speed, which “squeezes out” the polluted air in the room down to the air intakes.

Cooled air is supplied at low speed, usually to the upper part of the room (approximately 1/4 of the room volume) through the ceiling panels. It seems to flow around the space, lowering the dust down towards the hood, while creating a minimal level of irritation. With such ventilation, drafts and whirlwinds of dust that settle on the floor do not appear. In addition, the supplied air is pre-conditioned to the required temperature and humidity.

The basis of the ventilation and air conditioning system is a supply and exhaust unit with recirculation, consisting of the following elements:

1. frame;
2. filters;
3. humidifier;
4. heat exchangers;
5. fans.

   General diagram of the cleanroom ventilation system.
   

Special requirements are placed on filters. The filtration system consists of three groups of filters through which the air flow sequentially passes:

• coarse filter (first degree of filtration) - removes mechanical impurities from the air;
• fine filter (second degree of filtration) - removes bacteria and other microorganisms;
• HEPA and ULPA microfilter with absolute purification (removes 99.999995% of microorganisms).
  

Coarse and fine filters are located in the central air conditioner, and HEPA and ULPA filters are located directly in the air distributors.

HEPA and ULPA filters

Depending on the size of the room, air pressure, and method of placing furniture, the number and characteristics of air intakes and air distributors are determined.

There are a number of rules that need to be taken into account when designing exhaust ventilation for clean rooms:

1. It is necessary to maintain a positive air pressure imbalance in clean rooms. The pressure drop must be at least 10 Pa with the doors closed.
2. At the design stage, it is important to take into account the height of the ceilings. If they are higher than 2.7 m, then it is more rational to use the method of local ventilation of the workplace. In this case, a stream of clean air flows directly to the place where the person works.
3. For rooms up to 4.5 m instead of a raised floor, wall gratings are installed at a height of 0.6 m to 0.9 m . A directed stream of air envelops the room and moves towards the grilles, gradually displacing polluted air.
4. “Clean” rooms should be located near those rooms in which the level of cleanliness is as high as possible.
5. For the construction of clean rooms, exclusively environmentally friendly materials with high tightness are used, which will maintain stable air circulation.
6. In clean rooms, it is necessary to use HEPA filters and CAV regulators: the former ensure high quality purification of the supplied air, and the latter determine the portion size of its supply.

Below are the most optimal systems ventilation and air conditioning of clean rooms.

A) Unidirectional flow is supplied through the ventilation grille.

B) Air is supplied in different directions due to diffusers located on the ceiling.

C) Unidirectional flow enters the room through a perforated panel on the ceiling.

D) Air is supplied directly to the work area through an air distributor located on the ceiling.

D) The flow of clean air moves in opposite directions due to the equipment of ring air hoses.

Cleanroom ventilation requirements

The following requirements apply to ventilation systems for clean rooms:

• Reducing the amount of harmful impurities and bacteria, which includes a number of such actions: removing polluted air and supplying clean air, protecting the workplace from harmful impurities and microorganisms, blocking the flow of air from other rooms.
• Providing the following air parameters: temperature, mobility, humidity, concentration of harmful impurities.
• Prevents the accumulation of static electricity.

In addition, the cleanroom ventilation system is aimed at “blocking” the occurrence of such effects:

• periodic turbulent eddies;
• dust formation in some areas;
• temperature deviation from the norm;
• different humidity levels different areas serviced premises.

Air exchange requirements

Air exchange in a room is determined through air mobility, which is measured in m/s. Only for sterile rooms in the pharmaceutical industry is there a clear definition of the required air exchange - 0.46 m/s ±0.1 m/s (FDA, USA). Recommended air mobility standards for clean rooms range from 0.35 to 0.52 m/s±20%.

The presence of windows also affects air exchange. So, in a sealed room without windows, the air performance should be 20% higher than the hood, and in a room with windows - 20%.