While centralized cleanroom HVAC systems have become more and more popular in practice due to their major cost advantage. Decentralized air handling systems filter and control the air locally with fan filter units (FFUs), meaning that the clean area can be broken up to several smaller clean rooms of different cleanliness classes (ISO 14644 classification levels) to save operational costs. The following outlines how such FFU controlled clean spaces work in practice and what you should absolutely consider before opting for a centralized vs decentralized cleanroom HVAC system.
BASICS OF AIR HANDLING SYSTEMS
No wonder that cleanroom HVAC systems usually make up the largest portion of the clean room installation budget since they are the most critical system of any controlled environment with a standard, playing a key role in ensuring compliance with ISO 14644 air cleanliness requirements. Still, what makes them so essential?
Air handling systems are responsible for complying with the given clean room standard. Should the system not meet the requirements of a certain ISO class, miss to filter particles above a certain size or guarantee the required number of air exchanges per hour, compliance of the entire clean space could be questioned.
Moreover, ensuring an adequate air exchange rate (ACH) usually results in high operational costs. Thus, smooth operation and regular maintenance of the air handling system both enjoy special attention.
When clean room manufacturers and contractors face the decision of choosing the suitable air handling system, they weigh a number of factors such as
- performance,
- cost,
- reliability,
- sustainability.
It only adds to the importance of the decision that it is rather troublesome to modify the system once it is in operation. If your cleanroom’s air handling system doesn’t meet critical requirements—like filtering particles above a certain size, maintaining the right air exchange rate, or supporting pressure differentials—you risk losing compliance with ISO 14644 standards. Optimization should always precede commissioning.
CENTRALIZED OR DUCTED HVAC SYSTEMS – THE STANDARD CLEANROOM AIR SUPPLY METHOD
Centralized HVAC (Heating, Ventilation and Air Conditioning) systems are controlled by a central air handling unit (commonly abbreviated as AHU). Air is delivered and removed from the clean space through the ducts and generally circulated back to the central air handling unit. Central or ducted solutions are considered as the conventional approach to supplying air.
This ducted HVAC setup remains the industry standard for cleanroom environments, especially where tight control and consistent airflow are critical. It’s a proven solution that works well in pharmaceutical, biotech, and high-end manufacturing facilities.
WHAT ARE THE BENEFITS OF A CENTRAL HVAC SYSTEM?
The greatest advantage of a centralized HVAC system is that all relevant metrics can be controlled very precisely: temperature, humidity and pressure. Consequently, the highest levels of cleanliness of cleanroom air quality standards can be achieved with a centralized system. Of course, the superior precision of the system is reflected in both installation and maintenance costs.
Expert advice:
If the clean environment consists of multiple ISO classes or GMP zones of different cleanliness classes, it is advised to maintain a pressure differential between the zones, in order to avoid less clean air leaking into a zone of a higher cleanliness class or cross-contamination.
Of course, this precision comes at a cost: both installation and maintenance tend to be more complex and expensive than in decentralized systems. But that extra investment pays off in reliability and long-term compliance.
DECENTRALIZED AIR HANDLING WITH FAN FILTER UNITS (FFUS)
Installing individual Fan Filter Units (FFUs, also called integrated blower modules) in your clean environment can eliminate the need for a central air handling unit. These stand-alone units are installed locally in the clean space and can control temperature and humidity sectionally, zone by zone. The clean and filtered air enters the clean room through the ceiling mounted fan filter units equipped with HEPA filters.
FFUs are individually equipped with all essential parts of an air handling system:
- a HEPA or ULPA filter,
- a fan for ventilation,
- an electric motor.
WHAT ARE THE BENEFITS OF FAN FILTER UNITS (FFUS)?
Due to lower installation costs and modular design, decentralized solutions have become more and more common in clean room practices. FFUs can be installed in both small and large spaces of as low as ISO 5 class.
HOW MANY FAN FILTER UNITS DOES A CLEANROOM NEED?
Depending on the required air exchange rate and cleanliness class, the number of fan filter units (FFUs) a given clean room can be calculated. Of course, there are several other factors that play a key role such as the physical properties of the clean room. Also, the system cannot be changed retrospectively, therefore, clean room experts should be consulted for the precise calculation for achieving the required cleanliness level.
HOW DOES CLEANROOM AIRFLOW CALCULATION LOOK LIKE?
Computational fluid dynamics can help with modelling before the manufacturing begins to estimate air supply and exhaust vents on airflow models. Using this modelling technique, you may be able to decrease the amount of FFUs needed and plan your HVAC layout more precisely, reducing the initial investment.
USE THIS RULE OF THUMB FOR ESTIMATION
You can easily estimate how many fan filter units (FFUs) you will need with a single metric called ceiling coverage.
The required coverage depends on your target ISO class: the cleaner the environment, the more coverage you’ll need. Use the chart below as a general guideline when planning your cleanroom HVAC design.
| Cleanliness class | Ceiling coverage (%) |
| ISO 8 | 5-15% |
| ISO 7 | 15-20% |
| ISO 6 | 25-40% |
| ISO 5 | 35-70% |
COST BENEFITS WITH SMALLER ZONES?
FFUs have a great operational cost saving potential, as well. By breaking up the clean environment into smaller zones of different cleanliness classes and minimizing the area of the cleanest zone, a significant proportion of expenses can be cut. Fan filter units allow for individual control of these different zones. Fan filter units allow for individual control of these different zones, making them an energy-efficient alternative to centralized HVAC systems. This decentralized approach to cleanroom air handling also simplifies maintenance and supports more flexible system scaling.
FLEXIBILITY AND SCALABILITY BENEFITS OF SMALLER CLEANROOM ZONES?
Obviously, this solution adds some complexity to the system, but most times the savings are far worth the additional design effort. In fact, when implemented as part of a modular cleanroom HVAC strategy, decentralized systems can offer long-term efficiency and scalability advantages. This approach also allows for greater flexibility in cleanroom layout and future expansion, which is particularly valuable in pharmaceutical and high-tech manufacturing environments. To illustrate the role of flexibility, consider the rapid scale-up of COVID-19 vaccine production, where manufacturers had to set up additional cleanroom production units almost overnight.
Integration with Building Management Systems (BMS) and IoT
Decentralized FFUs can connect seamlessly with building management systems and IoT platforms, enabling real-time monitoring and control of individual units. This integration allows for dynamic optimization of airflow, energy consumption, and filter maintenance schedules, enhancing overall cleanroom efficiency and reducing operational costs. With granular data from each FFU, facility managers can proactively address issues, extend equipment lifespan, and adapt quickly to changing production needs.
SAVINGS DO NOT WORK THE SAME WAY WITH A CENTRAL HVAC SYSTEM
What happens if you insist on breaking up the clean space into smaller zones, but would rather opt for a centralized HVAC system? The central system controls to the lowest denominator and will then locally heat up the air to the required level. Such a HVAC solution would result in wasting a lot of energy. In addition, centralized cleanroom air handling limits zone-level control, reducing both flexibility and long-term operational efficiency.
ADDITIONAL OPERATIONAL BENEFITS OF FFUS
Increased operational stability
From an operational point of view, fan filter units (FFUs) can be extremely useful because they increase the operational stability of the system, offering system stability and reliability. If a single FFU were to fail, other units could compensate by working at an increased rate.
Setback mode saves costs when in downtime
Moreover, fan filter units can be set to two different states: operation mode and setback mode. The latter is convenient when the zone is not in operation but cleanliness, according to ISO 14644 standard, should be maintained regardless. Setback mode can still assure compliance during out of shift periods and result in cost saving at the same time.
Staff comfort & noise levels
An additional advantage of decentralized FFU systems is their ability to significantly reduce noise pollution by placing air filtration units directly at the point of use. This eliminates the need for large, centralized HVAC equipment that often generates high noise levels. When noise sources are confined to smaller, localized units, they help lower the overall sound levels within the cleanroom environment. This enhances staff comfort, roves concentration and reduces fatigue, especially during long shifts.
KEY TAKEAWAYS ON FAN FILTER UNITS (FFUS)
Given the high complexity of every clean room project, we recommend getting cleanroom HVAC specialists’ consulting before making an investment. It might be very handy to know about the cost benefits of FFUs, but the air handling system will have to be adjusted to the unique circumstances. We are currently working on a major implementation project with FFUs, which will serve as the basis of a detailed and practical case study. We are very much looking forward to reporting on our experiences.
