Compiled by Benjamin Brits

Cleanrooms, as controlled environments, are primarily designed to limit the amount of particulate or a contaminant from entering or leaving a space – be this dust, chemicals, vaporised droplets or biological organisms, or facilities that are highly sensitive to any form of foreign object or debris entering a process.

The idea of a cleanroom may take your thoughts directly to those films or documentaries where a room is filled with bright white stations, microscopes and scientists wearing lab coats working on sensitive elements behind a safety glass and using intense-looking gloves. Now, although such environments do indeed exist, the use of cleanrooms has become broad as ‘contamination-control’ has become essential in many fields. Cleanrooms in the context of this article are not to be confused with a generally clean space as they serve different purposes.

Factors around cleanrooms also include the types of equipment as well as occupant safety and protective wear.Factors around cleanrooms also include the types of equipment as well as occupant safety and protective wear. Image credit: LN | Unsplash

Different types of cleanrooms require a particular discipline to lead the design and layout process as each industry has many nuances to contend with. Cleanrooms typically involve complex operational systems and procedures, and most often high construction, operating, and energy costs are associated too. From the conceptual stage it is vital to take all relevant factors into account pertaining to the industry segment in question, as neglecting any elements would have significant implications down the line.

Cleanrooms are used in sectors including food production, medical, laboratory testing, industrial nano-scale production facilities, pharmaceuticals, information technology, and some horticultural applications to name a few. Each industry involves specific criteria or a set of requirements or standards, and cumulatively integrates many more factors than what meet the eye – such as the HVAC systems, space design, types of construction materials used, installed components, occupant attire and protective equipment use, and even consideration of necessary cleaning protocols based on the particular activity in the space.

Other factors that may come under question for cleanrooms are things such as specific and overall air movement or flow, service, and maintenance of mechanical or service equipment, facility sampling and testing frequency, building control systems, lighting, de-contamination processes, monitoring systems, traffic flows, and various equipment failure testing.

In some high-specification facilities, entering and exiting a cleanroom receives further special attention as contamination both inside or outside the space could have devastating consequences – such as a pathogen entering or exiting a laboratory, or bacteria affecting a sensitive operation that could result in stock loss, or operating rooms passing an organism onto a vulnerable patient. Here, measures typically involve variously configured airlocks and may also include portable air purification systems. Although an HVAC system and its operation would be well engineered, it would be an unrealistic expectation that such a system would be able to cater to every single possible air-occurrence within a space, and therefore certain other mitigating measures would be available to be included.

Interestingly, the concept of the cleanroom was another major that came about in the 1960s during World War II while advances in military products required the elimination of various contaminants in both production lines and scientific testing that were hindered in more accurate techniques at the time. Since its ‘invention’, the base methodology of a cleanroom has remained largely unchanged but has brought great innovations to the world at large – from electronics right through to the biological realm.

Without cleanrooms, we would in fact not have such things as advanced computing or even the smart phones on everyone’s desks today. Not only did cleanrooms revolutionise many industries, but they also made new processes possible, opened up better methods in research and development, and continue to offer far safer environment on many levels.

Cleanroom classification

Operational sizes of facilities range from tens- to thousands of square metres – most with unique design and operational characteristics based on their function. The development of cleanrooms has involved rapid expansion and progress for several decades now, mirrored by an increasing energy demand that can be as much as 10 times higher than that of offices of an equivalent size.

This considerable amount of energy used is to provide large amounts of filtered and conditioned air. Air movement could account for up to 50% of the HVAC consumption owing to the energy required to overcome high pressure differential on the high-efficiency filters, and other circulation components in the system. Production of high-quality air can account for up to 80% of the total energy used in a typical manufacturing facility, as an example.

Additional energy demand is then allocated to meet specific temperature and relative humidity for the particular process in the cleanroom, for comfort conditions, to achieve the correct laminar flows and pressurisation of the space. There is therefore significant potential for energy savings by well thought out designs of new facilities, by retrofitting improvements and upgrades to existing facilities.

Cleanrooms are classified according to the cleanliness level of the air inside the controlled environment. Cleanliness relates to the quantity and size of particles per cubic meter of air, ranging from 0.1 microns to 0.5 microns. A cleanroom rating is determined by the ISO classification system: ISO standard 14644-1.

The standard includes classes: ISO 1 to 9 – ISO class 1 being the ‘cleanest’ and ISO class 9 being the ‘dirtiest’. Even stated as the ‘dirtiest’, the ISO class 9 cleanroom environment is far cleaner than a regular room or space. Prior to the ISO classification, what was commonly referred to and used, was the Federal Standard 209 (FS 209E), which was replaced in 1999.

Cleanroom design and installation may also need to comply with other related international standards where applicable, such as standards applied to pharmaceutical production or related to food safety protocols.

HVAC design aspects

The HVAC system will, in most cases, be found to be the most significant component of a cleanroom design and must provide sufficiently clean and conditioned air to the space no matter what percentage of operation capacity is in effect. For clients, it may also be an area that is the least understood, resulting then in either under-sizing or over-sizing. Given the cost of this particular element in cleanrooms, getting the specification right would be very necessary.

Something that is highlighted quite often from a client-perspective is that a request comes through for an ‘ISO 7 cleanroom’ as an example. An ISO classification does not define a cleanroom in terms of function and layout. It only defines the cleanliness level of the air that needs to be met, or the maximum quantity of air particles allowed in a space.


The cleanroom classification will, however, influence the layout of a facility. For instance, you can enter certain classed rooms directly from an uncontrolled environment. Conversely, you will need at least one airlock before entering an ISO 6 environment, and so on. These aspects of facility design are important to keep in mind from the planning phase as well as to ensure the correct pairing of air filtration.

A cleanroom is also not simply the floor, walls, and ceilings. Cleanroom HVAC systems differ from conventional commercial systems due to significantly increased air supply, specific engineered airflow patterns, the use of high efficiency filtration, room pressurisation needs (positive or negative), and air extraction.

In order to meet the required ISO class, air must pass through either high efficiency particulate air (HEPA*), or ultra-low particulate air (ULPA*) filters. Essentially, the lower the ISO class, the more often the air need to pass through the filter(s) – the air changes per hour (ACH). The required air flow from the HVAC system is then calculated using the ACH and room volume. In comparison with a conventional commercial HVAC system, cleanrooms can reach as many as 250 air changes per hour, or more. It has been said in illustration, the effectiveness of these filter’s efficiency is extremely high, and the very next best thing is a brick wall. No matter what type of classed room an engineer is dealing with, the filter configuration will be of great importance.

* Some references state: ‘particulate absorption or particulate arrestor’

 Table 1: Example of required air changes per hour (ACH) per ISO Class

 ISO Class

 Approximate air changes per hour needed (ACH)

 ISO 8

 10 to 25

 ISO 7

 30 to 50

 ISO 6

 60 to 150

 ISO 5

 150 to 250+

Once the ACH requirement is known as well as the room size, the air flow can be calculated as well as the filter configuration, and how many filters are required. Each filter (and there are several types and configurations of filters too) will be different, so it is recommended to check maximum performance/airflow of the intended filters to be used in system design. If your calculation requires 1 000m3 per hour and your filter capacity is 500m3 per hour, two filters would be required in the filter bank in this simple example.

The filtration, however, is not the only main consideration in a cleanroom. Air volume and psychometric calculations are paramount. An application may require an extremely low relative humidity (RH) figure of 2.5% at -6°C. This adds significantly to the complication level of the system. The fresh air quantities and cooling requirements can also become tricky to balance. -6°C continuous operation must take into account allowing periodic defrosting.

It is not uncommon to design cleanroom HVAC systems to be able to supply a slightly higher number of ACHs and a slightly higher airflow considering that the filters will accumulate ‘particulate’ over time that will result in a higher need to maintain the air flow rate and in turn consume more energy.

Depending on what will occur within the cleanroom, another major up-front design consideration will be the introduction and exhausting of air. Some chemicals and fumes are lighter or heavier than air and so this factor will determine either introducing clean air at a high level or a low level, and whether the extract point would be at a low level (most common) or a high level.

Each facility will further have its own configuration around the return air – some of which will include additional filtration, while others will include only single pass and exhaust (possibly with filtration in between depending on the process/use of the room).

Cleanrooms are further held in either positive pressure or in negative pressure. Positive pressure will force the air flow out of the room instead of into it. This means that the air in the cleanroom will continually be pushed out of the space, thus preventing any unfiltered air or contaminants from entering. As mentioned, the barrier between the uncontrolled space and the classified area is known as an airlock. This barrier may also include a number of airlocks or double door systems. Here the pressure cascade will force any particulate or contaminants to a lower pressure zone.

With hazardous processes or particulate, the opposite is applicable: the pressure is negative in order to prevent particulates from escaping the room.

Depending on the facility, ultraviolet lights may also form part of the HVAC system needs – particularly in medical and laboratory environments where these devices are used to kill (or neutralise) micro-organisms and pathogens. Some facilities may use high heat treatments for certain similar functions.

Cleanroom applications, although most commonly associated with high tech or precise environments could also include more simple processes where for example coatings are applied to products or spray booths need to maintain a clean air to avoid spoiling or possible blistering. For such applications it is common to have a “water trap” that will catch the overspray or an air scrubber – a wet or dry device typically functioning by a centrifugal force. Where moisture (water or a chemical) is introduced, this will adhere to any particulate. The whirlpool motion will then naturally separate the heavier particles that fall down into a hopper mechanism and is thus extracted from that air. The downside to this method is that an effluent will be the by-product of the process that must be disposed of in the correct way.

Typically, when toxic fumes are generated within a space this is normally handled by standalone fume cupboards or fume hoods. These fume cupboards or hoods directly exhaust to an allocated outside point in a safe area via the HVAC system. The HVAC system feeding the room must also control pressure cascading, so that there is no backdraft. Some facilities that deal with harsh odours or dangerous chemicals would require the inclusion of suitable carbon filters to neutralise such factors. This would be another important aspect to know up front as different carbon compounds would be required for mercury droplets versus chlorine versus plant oils.

Fume extractor air and pressurisation air quantities change the cooling and heating capacities as well as supply air quantities. Some extract canopies require a separate air supply for short circulating outside air to extract air. The resulting performance required from the HVAC system inevitably requires rather unusual coil selections and sometimes creative methods of achieving that performance is required.

Cascading and pressure drops in the cleanrooms also affect fan selection. A materials lab may require positive and negative spaces adjacent to one another as they could use aggressive acids that cannot tolerate possible contamination from the outside. It does occur that different spaces such as this are fed from the same unit. Fans selection must frequently have high static pressures available in order to allow for the rooms to be cascaded. Sometimes the fan curves from conventional plug fans are not adequate and a custom-built fan is required. Occasionally the motors may have to be fitted outside air handling unit casings. Fortunately, direct drive fans have replaced the old belt driven units as belts actually shed quite a bit of debris themselves.

Cleanroom4An illustration of various filter types and configurations used in cleanrooms.An illustration of various filter types and configurations used in cleanrooms. Iamge credit: Freudenberg

Cleanrooms in agricultural research are also vital in the production and development of seeds, pesticides, feed, and other products that help produce food around the world. Some agricultural cleanrooms however are not used for research purposes, but for growing plants. These types of facilities cater to highly controlled growing environments that are free from pests, cross pollination, spores, and other opportunistic pathogenic contaminations. Another interesting factor with these agricultural growing cleanrooms is that they may even be required to meet ISO Class 5 levels – far cleaner than you would expect. A cleanroom environment in this setting is also required for the protection of occupants that may be exposed to harmful and deadly spores produced by the crop within the space, or chemical reactions with skin, as another example, that over time can cause various other health-related outcomes (irritation to loss of nerve function and sensations).

Some other less common applications may even require extremely precise accuracy, down to parts per billion rather than million. These applications require far more sophisticated AHUs that may also be required to be made out of a particular material – such as polypropylene. The reason for this could be the reactive nature of the processes involved within the space.

Achieving the required cleanroom status is relatively easy for commissioning and handover, however the overall design must take into account maintaining that status day after day, which in turn requires further considerations than just the HVAC. These include processes such as room flushing, wall, floor, and ceiling cleaning to name a few.

GMP as the foundation for design methodology in processing plants

The World Health Organisation (WHO) has established detailed guidelines for good manufacturing practice (GMP) although many countries have formulated their own requirements for GMP, based on these guidelines.

GMP is an international system for ensuring that products are consistently produced and controlled according to set quality standards. Poor quality in foodstuffs or medicines are not only a health hazard but land up being a waste of money for the entire supply chain as these goods must be discarded. GMP is therefore designed to minimise risks involved in production that cannot (and should not) be eliminated through testing of the final product.

Ultimately, unmanaged risks can cause detriment to health, or even again result in death. GMP covers all aspects of production from materials, premises, and equipment to the training and personal hygiene of staff. Detailed, written procedures are essential for each process that could affect the quality of any product. There must be systems to provide documented proof that correct procedures are consistently followed at each step in the manufacturing process – every time a product is made. Without GMP it is impossible to be sure that every production unit would be of the same quality as the units prepared and tested in a laboratory.

Each relevant industry would have a GMP standard for facilities that would be established by sector experts and technical committees, and this standard would influence all aspects of design, including appropriate cleanroom requirements.


Why cleanrooms are required and how contamination occurs

Contamination causes compromise to a test, product, process, patient, environment, and potentially creates a safety risk for the people involved at any facility. You can image the risk when a contamination incident occurs at a nuclear testing facility. While maintaining high standards and air quality would be essential, prevention is always better than cure, as the saying goes.

The most common contaminants are categorised into different components – all of which would require an understanding in order to design the most suitable HVAC system. These could include, amongst others, either or a combination of the following:

Physical contaminants: chips, particles, material fibres

Chemical contaminants: moisture, gas, vapor, molecular particles

Biological components: micro-organisms, viruses, bacteria, fungi

It is crucial to also identify any possible sources of contaminants to be able to implement an appropriate system to manage these too. Often only the major factors are considered such as human error, while in reality several factors may lead to contamination that would affect the HVAC design. Some of these include:

  • Adherence to established standards
  • The link between divisions or stations within a facility where poor design could lead to cross contamination or particulate entering clean zone air
  • Affected airflow or filtration by equipment placement
  • Handling and storage of goods or materials
  • Use of materials or tools within the space
  • Degradation due to environmental conditions
  • Incorrect zoning
  • Cleaning requirements and cleaning chemical reaction in the space
  • System failure and maintenance management
  • Use of PPE within the space, incorrect use of PPE, or failure to clean re-useable PPE correctly
  • Supply of liquid or gaseous substances to the cleanroom (water/oxygen/etc.)
  • Packaging or storage units

Care and maintenance of cleanroom HVAC

The subject of cleaning and maintenance will always come down to what the system has to ultimately ‘deal with’ and if it is having to deal with what was agreed in the design and specification process. It is critical that the engagement between the client, engineering team and suppliers is transparent to provide the appropriate and correct solution. Designing and installing a standard cleanroom while the client intends to run secret chemical tests will of course result that the HVAC system will not be able to perform appropriately and this in return will create a heavy maintenance or repair burden onto the client that could have been avoided.

Depending on the function of the facility again, regular swabbing and testing may occur as well as air sampling that will in turn determine what ‘corrective measures’ need to be implemented. Some newer technology is available that can be installed within a space to provide continuous real time sampling of air quality. Here portable equipment such as what is seen in the HVAC sector has made significant progress owing to the Covid-19 pandemic conditions.

Protection of the HEPA/ULPA filters in a cleanroom has also long-been the priority as these particular products are costly to replace as the last line of protection in a facility. However, maintenance is quite impactful at such facilities to ensure a safe and consistent environment, or production line. It was common in past years to have a filter cleaning operation, but due to advances in technology and the significant health risks that exist, replacement has rather become the norm.

In applications where replacements can be done, the HEPA filter installation and service needs special attention. The old filters can (and do) drop debris when changed. Some of the well-known filter manufacturers provide innovative bagging solutions to minimise spillage from filters that are being changed.

The design of a system as well as the air handling units/packaged units that primarily drive HVAC systems in these applications is another development area that is ongoing, particularly as these types of facilities are usually established to have a high capacity and minimising downtime is further important, or multiple shifts may be run where time of day is irrelevant, or scheduling is erratic. The use of maintenance friendly design and components, where each room could have its own system, is therefore a key consideration too.

One of the most common and significant risks involved in cleanrooms comes down to pure lack of maintenance or pushing the system beyond its accumulation limit of particulate. This results in filter leaks in the structure or bursting due to the high pressures which then allows common or contaminated air into the space – this can have major implications for high-classed cleanrooms where shutdown will result, as well as additional flushing and cleaning will be required to again meet the room classification requirements.


Having that in mind, bacteria can also grow in moist areas inside units and the usage of materials like copper can mitigate this to a degree. Further, paying attention to how the unit is constructed and minimising areas where contamination could accumulate are important. Maintenance should be an easy and effective task and consideration must be made to simplify the sanitisation and cleaning of the equipment too. This should include the speed at which the unit can be cleaned, and it is not really practical to dis-assemble the entire unit to do this or have to remove the unit entirely from the plantroom.

One would always have to consider the fact of investing a significant amount of money into these facilities and then running them to failure. Although times have become tough and it is common practice to implement ‘sweating of assets’, this action must be avoided when cleanrooms are in question at all costs owing to the numerous risks that would exist.

Split systems for this topic are definitely not a solution, even though it is unfortunate that some customers still don’t understand why.


  1. 52 Engineering
  2. Angstrom Technology
  4. Cleanroom Technologies
  5. Filtaire SA
  6. HCM Contractors
  7. Hi Tech Manufacturing
  8. International Organisation for Standardisation (ISO)
  9. Spoormaker & Partners
  10. US Department of Energy
  11. World Health Organisation

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