Hello and welcome to the cleanroom HVC design webinar. My name is Wei Sun and I’m with an Cisco. It is basing Ann Arbor Michigan. In addition, I’m also very active in ISO cleanliness standards and the activities for iest and the ASHRAE. Today we are going to discuss about cleanliness standards, classification particles, design, consideration, airflow pattern, air flow quantity, pressurization and the typical HVAC systems.
As we know, cooling technology has been very widely utilized for multiple industry for a semiconductor micro, electronic pharmaceutical, biotech aerospace and many others. What is a clean, clean on is especially in poorer area in which particulates and the contaminants are kept within street limits. A single environment typically has the following control parameters or objects, common requirements, temperature humidity song and vibration and alighting. These are typical requirements for common commercial spaces, as well as for clean rooms, but for clean rooms. There is another special set of the requirements: for example, airflow pattern, room pressure, particle contamination, microbial contamination, electrostatic discharge, gas phase, contamination and many process.
Specifics before 2001 us utilized federal standard 209, 209 yi actually was the latest version before the ISO standards were introduced. So after 2001 US and a many other countries, the utilize ISO 14, six, four four series: power 1 through PI – a are basically four particles and the molecular contamination. Another ISO series, 14 698, including PI, 1, 2 and a 3. These are for pyro contamination. If we put a federal standard, 209 and ISO in a combine, the table federal standard has six classes, they are defined in five particle sizes.
Point one point two point three point: five and a 5.0 micron ISO has nine classes to a class cleaner, one class dirtier. They are defining six particle sizes, including additional one micron. If we put the two standards in an overlapping chart, blue lines are for the federal standards. Red dashed lines is for the ISO standard.
As we can tell these two standards, they are not identical, but in industry we roughly consider themselves equivalent under certain classes and a particle sizes. When we talking about clean air clean in its class, it is very important also to mention under which occupancy stay. There are three states for the industry as built at the rest and in operation 4s bill. Basically, we have no production equipment, no personnel for at the rest, there is a production equipment, but no personnel in operation. We have installation in function in specified manner and with specified number of working personnel for pharmaceutical industry.
There is another classification, the color grades, gray, a B C and D. They define the occupancy States into category at the rest and being operation. Typically, we consider gray a is equivalent to ISO Phi B, 2, 6 c 2, 7 and a D 2 a. However, if we look at the total particle count, we find out at a point Phi of 5.0 micron.
The total allow. The particle counts may not be fully identical, so ISO number based classification versus pharmaceutical database classification. They are not truly identical, in addition to particle counts for pharmaceutical and healthcare industries. There is another microbial contamination. Limits should be considered for gray, a b c and d.
Each of this gray have a maximum allowed c fu counts for air sample, which is airborne or for surface contamination which could be set up a counter plate or girlfriend’s. In addition to iso standards, we also have other standards, guidelines and certifications. Usb 797 USP 804 ase. We have our p 12.3, which is considerations in cleanroom design.
We also have a Sri handbook application 2015 chapter 18, another new book. We call it a shriek Lingam design guy which in progress and will be print in 2016. We have a few other Klingon and elaborated related procedures in a certification, any BB ABC and a sita for particles. Typically, we consider from paul 1 micron up to a hundred micron anything larger than 100 microns can be seen with the naked eyes. The iso definition.
Folks, more in the middle range from part 1 to 5 microns. So these are the iso definition for particle size, a larger than 5 micron. We call the micro particles less than point one micron. We call this as ultrafine particles. There are two major category for particle sources: one is what we call it external, including Andreea or indoor transfer year between rooms are indoors for arabic units.
Typically, we call a particle migration. Our farm to rooms which are adjacent together for internal. We have a particle generation, inform people from work, surface farm equipment form either wall or finish material found liquid from chemicals and even form room construction materials. Each of these sources. We have respective control methods for physical controls of airborne particles.
We have a three strategies: filtration. You can use a hepa or Appa filters delusion. You can pump in more air to dilute the contaminated air constitution inside a Klingon or you can use isolation to control the sources of particle generation and you can remove them before they migrate into the rest payroll, and you can use a combination of any of these. Three strategies: microbiological contamination, unlike non Bible particles, which cannot reproduce viable particles or we call the living particles – could reproduce at a rapid rate. If nutrient and an environment are favorable, we can control them by physical means, such as heat, radiation, filtration or by chemical means using sterilization or the same fashion.
One of the interesting phenomena for clean rooms is the seating filter coverage for ISIL class. For in a cleaner, you typically use upper filters for I so classify or cleaner. You may use HEPA filters. Virtually the cleaner class you have, a high percentage of the seating can be occupied by either HEPA filters or upper filters, for example, for I so class 3. You may have a hundred percent sitting cover by operators Lumiere for volume or quantity.
This table was published by est 12.1 as their recommended products before 2007. This is what we call a table. Methods in this table you can see. Eg cleanest class is responding to our recommended air change.
Our range and this table was published based on consensus of experts, but there is no scientific basis. So when you use this table, keep in mind, our precaution is necessary. Recently, ASHRAE has done some further research. Try to establish a mathematical means to calculate or to estimate here change upon our rates. There is a new trend for clean energy conservation, which is, we called the main base flow control.
The strategy is to adjust or to modulate supply Airways to maintain the same or acceptable cleaning discuss based on particle sensing during both occupied and unoccupied modes January. The higher room conversion rates you have the higher eh ng rate you’re gon na provide to maintain the required cleanliness class. You can use the stage of row control or you can use variable for control when we use the ahu or recirculation film. You can use the single fan with the two speed or three speed motor or you can use a single fan with the variable speed drive. If you use a fan war unit type, you can turn off a number of events to lower the air flow, or you can use variable speed drive for multiple fans at the same pace.
If you use a fan filter units, you also can turn off a number of fan field units to lower the air change rate and to maintain the maintain air flow as uniformly as possible. Also, you can use a variable speed drive for multiple files, airflow patterns. We have a for airflow patterns, typically utilized for kingdoms. The first is non unidirectional flow. You have a ceiling, supply, clean air and you have low sidewall return.
The second type is you need your rational flow. You have a high density seeding supply air and over two year, is to race for typically utilize perforate four panels. In this case you can achieve much higher or much cleaner, clean in this class, and the air change rate is much higher than the first case. The combination of non unidirectional and a unidirectional flow is what we call them mix from at the room level. You have a ceiling supply, you have a low sidewall return for the most critical area you can have HEPA, canopy and underneath of the canopy, you can achieve cleaner class for the most critical area.
The last one is called a meeting moment in this case. You have a ceilings, supply Lois. I will return for the general room, but for the most critical area you can have an enclosed small area with a HEPA filter and a ceiling with, inter at human contact, with the objects for arrangement. Three types typically utilized for cleaning industry paalam, which is the big open room for clean rooms. The second is, will be called a service chase.
In this case, you have a clean rooms. Design in a very narrow are many very narrow rooms and the both side of a communal you are going to have a sheer return chase to let air to return back to the ceiling space and also you can use the MIDI environment. In this case, the larger area you may have less clean cars cleaner, but for the most of the critical areas you can use the mini environment to save energy and also to reduce the cost pressure auditions. The purpose of a pressurization is to eat direct design for directions, end to minimize and desire airborne particles microbial and chemical field migrations. There are two conditions when door is a closed or we call it is called a static condition when the door is being open.
Our coast, we call a dynamic conditions both of these collision. You may see particle migration from dirty area to other clean rooms, but they are in door opening order operation. This particle migration level could be much higher model particle migrate between clean them in adjacent space. Particle can migrate through cracks, such as the minor leaks on wall ceiling joints dug in a private penetrations, and also the air gap between door and the door frame where a pressure differential exists across cling-on enclosure. We can look at these three scenarios.
Left side is a core away. The right side is a clean. The first case is we have the same pressure. The second is, the freedom is pressurized. The third case is the kingdom is depressurize when the cleanroom is paralyzed.
You push the particle in acronym to answer. When the cream is depressurize, you are actively to draw join the particles from a surrounding area to other kingdoms, so pressure differential can force particle to migrate, leading on through cracks on cleanroom enclosure. Particle can also migrate through these cracks when our particle concentration difference exists across the criminal enclosure due to mass diffusion and UN equilibrium is reached. We also have a three scenarios. The left one is hallway and the Coulomb has the same clean in this class.
There is no pressure differential for these three cases. The middle case is the hallway, is the one class dirtier than a cleanroom, so particle can migrate, not by the pressure, because there is no pressure difference but by the mass diffusion, because the hallway has a high Constitution, then the cleaner. The right case is that we have three castes particle concentration difference. How is much dirtier, so even there is no pressure difference. Much more particles could be driven or could be forced from hallway to clean rooms, so particle Constitution.
Difference can also force particle to migrate through cracks on the cleanroom enclosure. What is the net gain or loss through migration? There are two forces. One is under pressure differential, so air move by force, another is on a particle concentration. Difference particle can move by a mass diffusion based on the combination of these conditions.
These two forces could work in the same or opposite directions. So what is the combined effect? This is the table industry. The basic phenomena for the combined effect, three cases for particle concentration concentration between hallway and acronym are the same. Clinton has a lower Constitution or Clinton has a high concentration.
The pressure religion also have three conditions. Clinton has identical pressure as on side, so pressure differential is zero or if the cleanroom is a pearlized, criminal has a high-pressure or if a cleanroom is depressurized. Cling-On has a low-pressure so based on three conditions for concentrations and pressure differentials. You have nine possible combinations, and this chart this table basically indicated what would be the combined effect so sometimes will depends on the prevailing force. Basically, the prevailing force determines the particle net gain or loss through migration into Canaan pressure differential criteria.
This table listed the new ASHRAE research on come on the left column. It indicates the cleanliness difference between clinton and the surrounding area. The second column is the minimum pressure differential requirement when the door is in close condition, or we call a static condition. The white column indicates the dynamic consideration when the doors in operation is suggest. If an air lock is required, not let’s say if we have one class, the difference between clean room and surrounding area whole 4-inch pressure, the ratio is the consider adequate and the airlock is not required.
If the surrounding area is to cross dirtier than the cleaner, then Paul 4-inch pressure differential is required and also based on your door operation on daily basis. If more than 30 times a day, then the airlock will be required if less than 30 times airlock is optional, and when you use a airlock, you want to make sure that it, you have a two doors in series to constitute an airlock each door. You will have a poll, two inch pressure gap and the time delay between two doors is required. Let’S look further down if the Klingons is 3 cross cleaner than the surrounding area once again, Paul 4-inch pressure, differential is required and an airlock is definitely required. Particle migration control, as we talked about earlier, if you want to have the room pressurized, you want to make sure the incoming air or supplier is more than the departing here, which is typically the vitria and exhaust.
So the officer flow is a positive in this case. The air the room is pressurized. Air is pushing up from King on to answer. If the incoming here is equivalent to the departing here, then the room pressure we’ll be in neutral, you know with the room, is not paralyzed or depressurize. In this case, there is no particle migration based on the pressure differential particle Casteel mercury.
If there is a constitutional difference, if the room is depressurized, you want to make sure the income here is less than the departing here and the offset is minus. In this case. The loom is depressurized and you actively draw particles or air from one side into the kernel. Traditionally we have several methods what we call the rules of thumb method for offset design. The first is what we called fraud.
Percentage method example is the VA. You aus VA hospital standard. So in this method, if you want have the room have a neutral pressure, you want to make sure the income here is equivalent to departing here. One positive: we want to have 15 % more incoming to positives. You want to have a 30 % more positive surprise here, one negative 15 %, less two negatives, 30 % less.
So this is what we call the full percentage method. The second method is from differential method. Our typical example is for us CDC guideline, so for this method, if you want to design a loom with neutral pressure, you want to make sure incoming in the departing has about a sin far away. If you want to have the room in positive pressure, you want to make sure you have 125 CFM more incoming, then departing. If you want to have the negative pressure you want to make sure we have.
The incoming year is about 125 CFM less than the tea party, but there is a caution both of these rules of thumb, method, ignored, issue, Rome’s unique air tightness, our enclosure, our fixed, offset value. We don’t feel adjustment capacity could cause a problem in control and in balancing among multiple rooms. When you want to consider to can do part of migration on the to operation, then air lock is necessary. Air lock, basically is alone between adjacent areas, with different cleanliness. To minimize particle microbial of him migrations, there are four types of air lock, cascading bubble sink and a dual compartment for cascading air.
Lock, you want to make sure clean room. Has the highest pressure? Cleaning have a high pressure than air lock, and a log have has high pressure and corridor for bubble air lock. You want to make sure the air lock has the highest pressure for a sink air lock. Air lock should have the lowest pressure for do compartment, yellow virtually is a combination of bubble and Sinclair lock in series in this case, if you want to walk from the corridor into the cleaner, you need to go through three doors in series.
Typically do compartment. Airlock has the most stringent and the most effective means to prevent or minimize particle migration when do operation is under consideration how to select an airlock? If you can answer the following for crashes, is the room in positive or negative pressure? Do you have a fume or bio contamination if a containment is a necessary if personal attention is needed? If you can answer for these four questions based on this table, you pretty much can select the most proper airlock for your application.
There is an analogy between air filters and airlocks on the left side. We can look at the configurations if you have one photo and say if you the efficiency, 90 %, then 10 % of particle go to penetrate the filter. If you have a two filters in series each fill, they have their own efficiency, then the penetration rate of the second filter is lower. If you have a three filters in series, then the penetration rate after the very last filter is much lower. The similar observation for duo or airlocks, if you have a single door, if it’s a barrier, if that Venus is 80 %, then during the dual operation, you may have a 20 % or particle which can migrate from corridor to cleaner.
If you have a two doors in series, which is an airlock, then the particle migration way after the second wall is much lower. But if you have a three doors in series, the particle migration through the very last door is much much lower. So this is the very interesting observation between air filters and airlocks HVAC diagram for iso class 789 clean rooms. Typically, one ahu is adequate to provide heating, cooling ventilation and air clean is control. In this case.
A hu draws written here, combined with outside view, then provide supplier into each green ohms through HEPA filters in the middle category for ISO costs four five six and a seven you may want to use a primary secondary air handling system. In this case, you are going to have a two units. This is what we call a designated on-site unit. This will be called a recirculation unit, and the circulation unit typically have a much higher CFM or air flow rate. Then the secondary designate on-site unit and, in this case, you’re, going to provide a very high or much higher change rate into the clean rooms, typically for cleaner classes for ISO cross, one two three and four, which are the very end of the clingen design.
In addition to the primary secondary, you may also want to add a tertiary, our air system, into the entire loop. For this case, you have a designated side air unit, the supply air into a secondary unit. The secondary unit can do all the routing here from reservoir of acronym into the unit. Then they surprised into a recirculation fan. You can either pressurize the premium above the ceiling or you can use the duct.
Now you can use the ductwork connect to each HEPA filters. So for this case, you have three units to achieve very high air change rate. Some time could be 300 up to 600 air change rate and you may end up with more than one, but the two or three units like this. They are handling configuration strategies. There is a major design difference between commercial spaces and a clean rooms.
Typically indoor temperature humidity for clean homes. It could be little bit little bit colder and a dryer, but the major difference is on the air change array and airflow cooling ratio for general purpose of space, let’s say 70 or 80 percent about 6 to 15 years. Changeup an hour is kind of typical air fall versus a cooling ratio. Typically is around 250 to 550 CFM per turn, but for kingdom’s air, changing rate could be much higher majority of acronyms. They are design between 15 up to 600 air change panel under the airflow versus a cooling ratio current from 250 up to 10,000 CFM per turn.
So this is the major difference between clean homes versus commercial spaces. Plenum airflow design, clean homes over require high air changing rate to dilute the luminaire in order to lower particle concentration is the air for rate versus recording low, is higher or much higher than those for commercial spaces? For I so price or cleaner cleans. This ratio may be beyond the reach of single AHQ can handle, but if there is a mismatch of the design rate to a relative, smaller cooling load, which could cause a cooling coil to have a sensible cooling only with a latent heat removal capacity, which will result Very poor, humidity control inside clean rooms when we design clean rooms, we also need to consider the on door ear property based on the locations. Things are the United States, some area could be are hot and dry, other areas could be cold and the web, so the outside air probably is very important for the clean room design, especially for those you have a high percentage of unsightly air intake.
If we look at the HVC diagram, as we talked about earlier, also cost seven, a nine single unit with the HEPA filter is adequate to provide heating, cooling ventilation and us particle confusion, control, CFM protein ratio. Typically, three hundred five hundred, sometimes will be lower, sometimes will be higher. Also, a percentage could be in a range of 15 to 30 percent based on the location and based on the percentage of once a year that you require for your clean room. You also can do some provision for the primary rule. For example, you can Bob has the supply here to mix with the return.
So if you have a high latent low for once a year, this will give you our pretreatment, often also here, and in this case your CFM protein ratio, usually toward the low end. Another provision is what we call a dual return. This is a conventional return. You also can split a portion of routing here, where pans heating, cooling, coil and to achieve a higher CFM per turn or for the case when the also air percentage is not too high. This is what we call the primary secondary system.
As we talked about early CFM, platon visual could be in a range of 800 to 5000 here for rate ratio between these two fans could be in a range of two to ten. There is another alternation, yes, you also can have New Britain pass for this configuration in this case CFM per ton, maybe stealing a hundred to five thousand range for ISO costs, one two, three four, as we talked about earlier. Typically, we use primary secondary and the tertiary units for this case. Cfm protein ratio could be twenty five hundred up to twenty-five thousand. The primary for all versus the second overall ratio is about the two to ten secondary to tertiary.
Flow ratio could be two to five. So, in this case, this span is much much bigger than the secondary secondary is much bigger than the Treasury fam. So that’s the another reason we do not want to combine twin units into one fan system. Otherwise, you are going to have a mismatch between cooling low and the TV air flow requirement to achieve high air change rate. The last configuration is what we call FEM filter units for primary recirculation.
In this case, you can draw a portion of written here mix. With answer here, their age, you can supply HEPA filter, declare into a Klingon to ensure the cleanliness this application or configuration you can use virtually for any class from I, so one to a zero seven and the CFM protein ratio could range from eight hundred up to Twenty-Five thousand the total fan filter unit flow rate over the ahu, for a could be between two to fifty. There are two types of air flow arrangement. This is what we called thin tower style in this case, you have a multiple stories. The first story is the Cleveland flow on the leaf, is the written airflow and that the first floor is the Rakata basement floor, which can house our process equipment.
In this case, you have a larger metal fan, draw the creamier foodways floor perforated for all panels, pressurize the ceiling space above the cleanroom that air can go through these HEPA filters in order to provide filter, cleaner air into the cleaner. The second arrangement is the film filter units. The space configuration is very similar as the previous slide. We have a basement, we have been written, for, we have a clean room floor and we have our space above the cleaner. In this case, we do not have consolidate with infants; instead, each of the HEPA or upper unit have its own fan, but that’s what we call the fan filter units, so they can draw the air from the return floor below and to push it here through the Hepa media’s in order to provide a cleaner into the cleaner, so this configuration can provide a very good flexibility.
You can relocate them filter units to the areas which demand a certain cleanliness level. Thank you for your attention and the disc concludes my presentation and I hope this presentation is valuable to your applications.
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