Clean room design

In this article, we try to explain the design of a clean room in 10 sensitive steps.
Of course, as you are aware, using the word "easy" to design a sensitive environment for a clean room is not consistent with the concept that comes to mind. However, this does not mean that you can not create a standard clean room design by following certain issues and standards in a logical sequence. This article has completely covered the basic steps and carefully stated the necessary points, to useful points, especially for adjusting air pressure calculations, planning air routes and angling the mechanical space of a clean room relative to the clean room class.Due to the fact that a clean room has different and special systems and the cost of maintenance and maintenance is high and many production processes have very strict environmental conditions that require the need to use a clean room, It is necessary to design a clean room in accordance with the principles and standards of the world. In this paper, a step-by-step method for evaluating and designing a clean room based on factorization in individuals / material flow, space cleanliness classification, space pressure, space supply airflow, air blast, space air balance, variables evaluated, mechanical system presented. Load, heating / cooling calculations and support space requirements are provided.

Step 1: Design the layout of the people / material flow

It is very important to design people and material flow in a clean room complex. Employees who move around in a clean room can be the biggest source of pollution in a clean room, and all salons and production rooms that are of particular importance should be separated by a door and staff access routes should be distinguished.The most important parts of the production should have a single access to prevent space as a way for other less important spaces and the movement of other employees to other parts of the site. Some pharmaceutical and bio-pharmaceutical processes are subject to cross-contamination with other pharmaceutical and bio-pharmaceutical processes. Mutual contamination of the process must be carefully considered in terms of inputs and inhibition of raw materials, separation of process materials and outputs, and inhibition of output of the final product. Figure 1 is an example of a bone cement facility that has both critical spaces ("Solvent Packaging", "Bone Cement Packaging") with a single access and an air lock as a buffer in busy personnel areas.

Step 2: Classify the cleanliness of the space

When designing a clean room, in order to be able to choose the right classification for a clean room, it is important to know the basic standard of clean room classification and how many particles are in each clean classification. Standard 14644-1 of the Institute of Environmental Science and Technology (IEST) provides different classifications of cleanliness (1, 10, 100, 1000, 10000 and 100000) and the permissible number of particles in different particle sizes.

For example, a clean room of class 100 is allowed to have a maximum of 3500 particles per cubic meter of size 0.1 microns and larger, 100 particles per cubic foot of size 0.5 microns and larger and 24 particles per cubic foot of size 1.0 micron and larger . This table provides the permissible air particle density in each clean classification table:

In the design of a clean room, the clean classification of the space has a significant impact on the construction, maintenance and energy cost of the clean room. Accurate assessment of the amount (rejection / contamination) is very important in different cleaning classifications and regulatory agency requirements, such as the Food and Drug Administration (FDA). Typically, the more sensitive the process, the more accurate the cleaning classification should be used. The following table provides a clean classification for different production process.

When designing a clean room, keep in mind that your product may require a more precise cleaning class, depending on your unique needs. When assigning a clean classification to any space, strictly follow the required instructions and standards. There should be no more than two grading differences in the clean classification between connection spaces. For example, entry from a 100,000 class clean room into a 100 class clean room is not acceptable, but entry from a 100,000 class clean room into a 1000 class clean room is acceptable.
Now look at Figure 1, as you can see in the diagram. "Bone Cement Packaging" has a higher sensitivity and is designed in the class of 10000 times ISO7.Step 3: Determine the pressure of the spaces

In designing a clean room, you should pay attention to the fact that maintaining the pressure of the positive air space, in connection with spaces with different classifications in terms of cleanliness, is necessary to prevent the infiltration of contaminants from less clean rooms to more clean rooms. It is very difficult to maintain a clean classification and control the number of particles in space when the space has a neutral or negative pressure. Here is the important question, what should be the difference between the space pressure between the halls and the different level of cleanliness?Various studies have evaluated the penetration of contaminants in a clean room versus the space pressure differential between a clean room and an adjacent uncontrolled environment. These studies found a difference of 0.03 to 0.05 in the global pressure differential. To be effective in reducing the penetration of pollutants. Note that the spatial pressure difference of more than 0.05 inches is significantly proportional in the control of pollution penetration, so try not to provide a pressure difference of more than 0.05 percent.Remember, higher space pressure differences cost more energy and are more difficult to control. Also, a higher pressure difference in opening and closing doors requires more force. The maximum recommended pressure difference in the door is 0.1 inch. At 0.1 inches, a 3-foot, 7-foot door requires 11 pounds of force to open and close. To keep the static pressure difference in the doors within an acceptable range, it may be necessary to redesign the clean room completely and completely clean a site.Pay attention to photo number 1. In this clean room design, you can see that our bone cement packaging facility is available in a warehouse under construction that has a neutral space pressure (0.0 inches). Now see that the air lock between the warehouse and the "Gown / Ungown" hall does not have a clean classification of space and therefore will not have a specific space pressure and is equal to the normal ambient pressure. You will notice that the "Gown / Ungown" hall is designed with a space pressure of 0.03 inches. 0.06 inch space pressure is designed for "Bone Cement Air Lock" and "Sterile Air Lock" salon. The map shows that the "final packing" hall has a space pressure of 0.06 inches. For example, in the "Bone Cement Packing" hall, in order to control the dust produced during packing, the space pressure is 0.03 inches inside and the space pressure is less than "Bone Cement Air Lock" and "Final Pack". Is to prevent particles from moving from this space to the adjacent spaceCreating airflow in the "Bone Cement Packing" hall is designed from a space with the same clean classification. In designing a clean room, make sure that air intrusion should not be created from a clean classified space to a lower clean classified space, ie pollution should not be directed to a cleaner classification. "Solvent Packaging" will have a space pressure of 0.11. Note that the space pressure difference between spaces with a sensitivity of less than 0.03 inches and the space pressure difference between the sensitive "packing" and "sterile air lock" halls is 0.05 inches. In the design of a clean room, it is effective for the construction process that the 0.11 inch space pressure for walls or ceilings does not require special structural reinforcements. Space pressures above 0.5 should be considered for the possible need to reinforce additional structures.

Step 4: Determine the air flow in space

In the design of a clean room, the clean classification of the space plays a decisive role in determining the air flow provided by the clean room. Looking at Table 3, each clean room classification has a rate of change of air. For example, a clean 100,000 class room has a range of 15 to 30.When designing a clean room and determining the amount of air change in a clean room should take into account the projected activity in the clean room.

A 100000 class clean room (ISO 8) with low traffic, low particle generation process and positive space pressure in relation to adjacent spaces may use 15 times air circulation per hour, while the same clean room with high traffic, Frequent traffic inside and outside, having a process with the production of particles or neutral space pressure relative to adjacent rooms is likely to reach 30 times the air circulation per hour.In designing a clean room, you should use experienced professionals and determine the amount of air change to use. Other variables that affect the airflow in a clean room are the process airflow, the infiltration of air through the doors / openings, and the infiltration of air out of the doors / openings. IEST has published the recommended air change rates in standard 14644-4.Looking at Figure 1, you can see that the "Gown / Ungown" hall has the highest number of staff traffic, but it is not a vital space for the process, so 20 times an hour air circulation is designed for this hall, but two "Sterile Air Lock" and "Bone Cement Packing Air Lock" are important in the vicinity of production, and in the case of "Bone Cement Packing Air Lock", air flows from the air lock to the packing space. Although these air lacquers are limited in inlet / outlet traffic and have no particle production process in the hall itself, their vital importance as a buffer between the "Gown / Ungown" and "Bone Cement packing" processes results in 40 times air circulation. Be on the clock.In the design of the clean room in the next step, it is considered that the process in the "final packaging" hall is to simply put the product in a secondary package, which does not have a high risk of particle production and leads to a speed of 20 times. Air circulation is per hour. "Bone cement packing" is a vital process and has an air circulation rate of 40 times per hour. "Solvent Packaging" is a very critical process performed on Class 100 (ISO 5) laminar hoods in a clean Class 1000 (ISO 6) room. "Solvent Packaging" is very limited in incoming and outgoing traffic and the production of particles is low process, so it has a rate of 150 times air circulation per hour.Clean room classification and air changes every hour
Air purity is achieved by passing air through HEPA filters. The more air that passes through the HEPA filters, the fewer particles remain in the room air. The volume of filtered air per hour divided by the volume of the room gives the number of air changes per hour.Required air changes per hour (ACH).

The hourly air changes suggested above are just a general rule of thumb for a clean room design. They should be calculated by a clean room specialist, as many aspects need to be considered, such as room size, number of people in the room, equipment in the room, related processes, heat gain, and so on.

Step 5: Determine the flow of air out of space

The next step in designing a clean room is to pay attention to the fact that most clean rooms are under positive pressure, as a result of air to the adjacent space with lower static pressure and without filtering the air through electrical outlets, lighting fixtures, window frames, Door frame, wall / floor interface, wall / ceiling interface are inserted. It is important to understand that the rooms are not completely closed and are leaking. A well-sealed clean room has 1% to 2% air volume leakage. Is this leak bad? Is it necessary to consider this issue in designing a clean room?Note first, zero leakage is impossible. Second, when using supply, return, and exhaust air control devices, there must be at least a 10% difference between the supply and return air flow to separate the supply, return, and outlet air valves. The amount of air penetration through the doors depends on the size of the door, the door pressure differential and the amount of sealing of the door (washer, sagging door, closing). In the design of a clean room, we know that the calculated air goes from one space to another by infiltration.

Step 6: Determine the air balance of the space

The balance of space air in the design of a clean room means that we calculate in such a way that the air flow entering the space (supply, infiltration) and the air flow out of space (exhaust, explosion, return) are equal. Looking at the balance of bone cement plant space (Figure 2), "Solvent Packaging" has 2250 cfm of supply air flow and 270 cfm of intrusive air, leading to a return of 1980 cfm of air. "Air Lock Sterile" has 290 cfm of air supply, 270 cfm of penetration from "Solvent Packaging" and 190 cfm of penetration to the adjacent hall "Gown / Ungown", which leads to the return of air flow of 370 cfm.We have already determined the amount of clean air flow, infiltration, vents, outlets and airflow in the design of a clean room. The final flow of air return to space is set during launch for unplanned air.

Step 7: Evaluate the remaining variables

Other variables that need to be evaluated are:Temperature: Clean room workers wear clean room clothes to reduce particulate matter and contamination. Due to the extra clothing, maintaining a low temperature is very important for the comfort of the worker. The temperature range of the space between 66 degrees Fahrenheit and 70 degrees provides comfortable conditions.Humidity: Due to the high flow of clean room air, a large electrostatic charge is created. When the ceiling and walls have a high electrostatic charge and the space has low relative humidity, airborne particles attach to the surface. When the relative humidity of the space increases, the electrostatic charge is discharged and all the captured particles are released in a short time, causing the clean room to go out of specification. Having a high electrostatic charge can also damage materials sensitive to electrostatic discharge. It is important that the relative humidity of the space is high enough to reduce the accumulation of electrostatic charge. RH or 45% + 5% is considered the optimal level of humidity.Luminosity: Vital processes may require gentle flow to reduce the possibility of airflow contamination between the HEPA filter and the process. IEST Standard # IEST-WG-CC006 meets airflow laminating requirements.
Electrostatic discharge: Beyond the humidification of the space, some processes are very sensitive to the damage of electrostatic discharge and the installation of a ground conductive floor is necessary.
Sound and vibration levels: Some precision processes are very sensitive to noise and vibration.

Step 8: Determine the layout of the mechanical system

In clean room design, a number of variables affect the layout of a clean room mechanical system: space availability, available budget, process needs, clean classification, required reliability, energy cost, building codes, and local climate. Unlike conventional A / C systems, clean room A / C systems provide significantly more than is needed to provide cooling and heating loads.Clean rooms in Class 100000 (ISO 8) and Class 10,000 (ISO 7) are low level and can pass air through the AHU. Looking at Figure 3, the return air and outside air are mixed, filtered, cooled, heated and humidified before being fed to the HEPA terminal filters on the ceiling. To prevent contaminants from re-circulating in a clean room, return air is collected by low wall return. For rooms with a class above 10000 (ISO 7) and cleaner rooms, the air flow is too high for air to pass through the AHU. Looking at Figure 4, a small portion of the return air is sent to the AHU for ventilation. The remaining air returns to the fan.

Step 9: Perform heating / cooling calculations

When designing a clean room, you should consider the following heating / cooling calculations:
Use the most conservative weather conditions (99.6% heat design, 4.4% dry bulb / medium bulb cooling, and 4.4% dry bulb / dry bulb cooling data).
Include filtration in the calculations.
Include the heat of the humidifier manifold in the calculations.
Include process load in calculations.

Step 10: Calculate the mechanical space of the room

In designing a clean room, it should be noted that as the cleanliness classification of the clean room becomes clearer, more mechanical infrastructure space is required to properly support the clean room. Using a clean room of 1000 square feet, for example, a clean room of 100000 class (ISO 8) needs 250 to 400 square feet of support space, a clean room of class 10,000 (ISO 7) of 250 to 750 square feet of support Requires support space, a clean 1000 class (ISO 6) room needs 500 to 1000 square feet of support space and a clean 100 class (ISO 5) room needs 750 to 1500 square feet of support space.The actual support material will vary depending on the airflow and the complexity of the AHU (simple: filter, thermal coil, cooling coil and fan; integrated: sound attenuator, return fan, soothing air part, outside air part, filter part, The heating section (cooling, humidifying, supply fan and drain plenium) and the number of supported clean room systems (exhaust, rotating air units, cold water, hot water, steam and DI / RO water) are important in the early stages. Clean room design, transfer the required mechanical equipment per square meter to the project architect.last word
Perhaps the design of a clean room can be compared to the design of a fighter jet. Properly covered, it will withstand a great deal of adverse conditions for many years to come. Otherwise, if the design of a clean room is not equal to the standard, it can not be used and can not be trusted and the product production process can begin in it. It is ready to save you from the exorbitant and irreparable costs of wrong design.