Modular Cleanroom Design: Complete Guide to Layouts, HVAC & FFU Placement

A modular cleanroom is not simply a cardboard box with filters built into the ceiling. It is a system that requires coming up with three engineering solutions, which are layout design, HVAC air handling system and ffu ceiling grid. If these three elements are not considered simultaneously in the proper way, the cleanroom will not meet its ISO standards when running. This guide includes descriptions of all three elements of modular cleanroom design — layout planning, cleanroom HVAC design which allows air movement and conditioning, and cleanroom ffu design which gets filtered air from the ceiling to the air-handling unit.

Once the three mentioned elements are designed well enough, facilities would save money on cleaning operations. According to the experience of Deiiang™ with over 60 completed projects in the field of modular cleanroom, facilities which successfully integrated layout, HVAC and FFU design in one project cycle demonstrated savings of over 31–34% of 10-year operational costs compared to the facilities which designed the elements separately.

HVAC and FFU position along with layout needs to be thought of as one design issue rather than three different purchases.

Strategic Layout Design

Layout is where one can either gain or lose money on modular cleanroom layout design. After designing the module for every FFU, the designer has to work with three kinds of flows — of people, materials, and air — so that every area gets designated its classification that goes along a continuum and is not treated like separate islands. A design that makes clean air pass a gowning exit or a cart transfer hatch will completely fail to fulfil the necessary particle count no matter how much filtration is applied at the exit side.

The rule of thumb is that contamination travels along with materials and people, so space should be arranged in a way that makes the dirty path longer and the clean one shorter. In practice, it means placing the cleanest zone deep inside the module, away from exterior walls and personnel entry.

Separation of Flows of Personnel, Materials, and Air

The layout must be done in such a way that the three kinds of flow stay separate. The most common design involves a single airlock for personnel on the side of personnel along with a material or pass-through airlock on the production side, so that the cart comes into the room without touching the gowning path.

• Personnel flow: Unclassified corridor → gowning (iso 8) → airlock (ISO 7) → production (ISO 5–7).
• Material flow: Receiving → wipe-down / pass-through → staging → production without sharing doors with personnel gowning.
• Airflow: Introduce clean airflow into the cleanest area while venting back through the most contaminated part, so the pressure gradient will always be clean through less clean.

Human Factors: Hidden Load to Cleanroom Performance

While the engineering drawings will most probably omit the most significant contaminating variable in any cleanroom — the people. The sitting operator produces around 100,000 (0.3 micron) particles per minute only; once the operator starts walking, the rate jumps significantly. The overall behavior style with gowning, moving and working determines if the airflow is designed correctly or not — if the air changes happen or not.

That is why Deiiang™ considers the gowning protocol to be an input design solution rather than just an operational process. The gowning room sizes, the location of the benches, mirrors and airflow will have to ensure that all operators get dressed in the right order (coverall, hood, mask, gloves, boots). If the environment is so that following the proper sequence is an easy procedure, that solves the problem.

The rule of thumb is that each extra operator in ISO 7 will call for roughly 5–8% more airflow to cover particle load. If you are designing the premises for six operators and have ten in work, the facility will fail the pressure test before it fails the particle count.

Quantifying Space Efficiency

The Deiiang project employed modular technology to create a 1,850-square-meter shell in which the clean area amounted to 1,312 square meters, representing a net-to-gross ratio of 70.9 percent against the industry average rate for comparable stick-built ISO 7 buildings of 62 percent.

Its calculation is simple:

Net-to-gross ratio = usable clean area ÷ total building area

In particular, 1,312 ÷ 1,850 = 0.709. The figure is higher by 8.9 points due to space lost to interstitial areas which would have been otherwise occupied due to the ducted system.

Pressure Cascade and Classification

Classification is a gradient rather than a text. Each pair of rooms has to maintain pressure differential. There must be sufficient value to overcome door opening turbulence and not too high in order not to overspend on HVAC fan energy.

Table 1 — Classification gradient and pressure cascade for a typical modular suite. Values are design targets; iso 14644-4 requires verification by measurement, not by assumption.

Typical cleanroom site plan illustrating separate personnel and material routes with pressure falling down from the production core.

HVAC System Design for Modular Units

The fundamental difference in modular cleanroom HVAC system design is that the equipment to manage the air is part of the module, rather than a structure. It means that duct runs will be shorter, plenums shallower, and the system has to be considered as a packaged and pre-manufactured system, not a network system manufactured on the construction site. Time advantage is significant while careless design leads to a system unable to hold pressure when the door is opened.

The three questions which will extensively define the result are: how air is delivered in the room, how pressure is controlled between rooms, and how much air is required at all. All three questions directly answer the modular cleanroom FFU system design questions.

Air Distribution Strategy

Air delivery in a modular cleanroom usually is a combination of FFUs, suspended from the ceiling and low-level air return. The goal is to create unidirectional airflow in the critical zone.

The supply air volume is set by the required air change rate:

Q = ACH × V, where Q is supply airflow (m³/h), ACH is air changes per hour, and V is room volume (m³).

The volume of a ISO 7 room that has an area of 100 m² and the height of 3 m can be calculated by the formula V = 300 m³. The flow rate of air can be determined with the help of the following equation Q = 40 × 300 = 12,000 m³/h. This is the flow rate that will aid in working out the fans, ducts and filters for the space.

Pressure Cascade Management

Setting up a modular system usually allows keeping the pressure cascade in place due to the controllable balance between airflow to and from the room. It should be mentioned that a room is positive when airflow inside exceeds the return flow. Air that enters the room gets leaked through doors and openings. The modular system is able to manage the system using variable speed fans on the supplying side and motorized dampers in the return airflow system. The differences in pressure at boundaries in the modular system are controlled through the use of pressure sensors that continuously log the process.

• Variable-speed fans on the supply side, trimmed per room.
• Motorized return dampers that adjust to hold the target ΔP.
• Differential pressure sensors at every classification boundary, logged continuously.
• Door-position interlocks that temporarily boost supply when a door opens.

Fig. 3 — Pressure cascade ladder. All measurements must be accurate and last at least 30 seconds.

Temperature, Humidity and Return Path Selection

Generally, modular units do not need the same kind of precision as semiconductor fabrication facilities. However, pharmaceutical, optical and similar processes need to be controlled better than regular industrial facilities. The following table shows the setpoints that we use as our default setpoints adjusted to respective processes.

Table 2 — Standard HVAC settings according to the type of installation. Deiiang™ validates each parameter based on client process heat load.

Design of HVAC system in modular unit.

FFU Placement & Airflow Dynamics

The way of properly constructing the modular cleanroom FFUs is often neglected by the field specialists. Instead, they calculate the number of the units based on the area of the cleanroom ceiling. It is not correct as using this method will give either an over- or an under-filtered ceiling depending on the number of the units that can make the design invalid. The proper design involves determining how much airflow is necessary and transforming it into the number of FFUs required by calculating the actual airflow velocities and filter area.

Calculating the coverage ratio is a good way to check whether the number of unit matches the required standard. It provides an overall idea about the efficiencies of the number of FFUs being put into one place.

Calculating the Coverage Ratio and the Number of FFUs

The calculations are quite simple. If we consider a domestic FFU and assume that its size is 1200×600 mm at the face velocity of 0.35 m/s then:

Airflow per FFU = 1.2 m × 0.6 m × 0.35 m/s × 3600 s/h = 907 m³/h

In case of a 100 m² room being iso 7 cleanroom which would require 12,000 m³/h, so we can calculate the number of FFUs needed in the following way:

FFU count = 12,000 ÷ 907 ≈ 13.2 → 14 units

Total FFU footprint = 14 × 0.72 m² = 10.1 m². The coverage ratio = 10.1 ÷ 100 = 10.1%, which sits comfortably inside the 8–15% band that ISO 7 modules typically need when downflow is well organized.

Interactive Estimator: Airflow & FFU Count

Fig. 5 — Consider this estimate to double-check your calculations. It isn’t final since FFU counts must be validated with the help of CFD or physical airflow tests.

Comparison of FFU Layouts: 50% versus 20%

The table shows two designs of the same 100 m² ISO 7 module: a fundamentally conservative version of 50% of coverage and CFD-optimized version of 20% of coverage. Both designs meet ISO 7 particle limits; however, only one is cost-efficient.

Table 3 — Comparison of two FFU designs in a cleanroom iso 7 setting: both pass the validation, and the optimized grid is 59% more energy efficient than the conservative one.

Fig. 6 — Distribution of FFUs by cleanroom classification standards.

Placement Patterns That Actually Work

Count is only half the problem; position is the other half. Users who place FFUs based on purely theoretical means create poorly functioning cleanrooms filled with dead spaces above the working space and exhausted returns located on the walls. Deiiang™ developed four rules regarding placement in this kind of modular system:

• Start with critical spaces. Place the FFUs in the area of active phases of the process as opposed to distributing them randomly across the entire ceiling.
• Align FFUs according to return flows. Supply and return should be stacked when possible, so the air will travel short and predictable paths.
• Maintain a distance of 300–600 mm from the wall. FFU placement close to the wall will create edge eddies without improving working zones.
• Group FFUs in switchable zones. The four-zone strategy will allow the facility to operate with diminished airflow during non-production time resulting in energy savings of 40–55%.

Deiiang Case Study: Retrofitting a High-Tech Cleanroom

Clean room theory is always neat; retrofit process is rather complicated. The case demonstrates how the whole task of designing modular cleanroom layout, HVAC system, and FFU installation was accomplished simultaneously under strict deadlines.

Project Introduction

A manufacturer of precise optics required an ISO 7 cleanroom with the floor area of 480 m² prepared for lens assembling and alignment purposes. The potential cleanroom was located in a facility with a ceiling height of 2.8 m thus making impossible the use of a traditional ducted air handling system without adjusting the structure. The completion period was limited to 48 hours.

The Constraints

• Available ceiling height: 2.8 m — a traditional air duct system would take away 1.1 m.
• Shutdown window: 48 hours with heavy fines for further delays.
• Existing chiller capacity: 180 kW. Already running at 70% load.
• Classification of the target: It is an ISO 7 standard when in operational condition. The process verifies compliance with ISO 14644-1.

Deiiang's Proposal

The composed HVAC system made by Deiiang™ is composed of ceiling-based elements functioning together as one unit. The FFU framework and exhaust system are put together before beginning to be installed at the construction site. The need to use ducting in the halls was fully eliminated and the assembly work was nearly restricted to connection and assembly of the system.

• Floor plan: In the presented solution three zones — ISO 8 dressing room, ISO 7 staging zone, ISO 7 assembly zone — are involved. The hall is equipped with isolated airlock for materials.
• HVAC: The hall has ceiling-mounted plenum operated by 350 mm systems and using independent chiller 120 kW capable of cooling rather than being connected to the existing cooling system.
• FFUs: 112 1200×600 mm units working in 4 different groups are delivering air into the room with ceiling coverage of 21 percent.
• Validation: Counting of particles with sizes 0.3 μm and 0.5 μm, as well as verification of pressure jump were accomplished.

Results

Table 4 — Measured performance after commissioning. Design and validation by Deiiang™, lead product designer Jason.peng.

Before and after images of the multifunctional cleanroom created by Deiiang.

Common Misconceptions

Most cleanroom budgets are exceeded due to a few design beliefs that seem plausible but fail when tested. Here are the top four beliefs that come into play during modular cleanroom projects.

Micro-Glossary

Here are four definitions of the terms which are being used in modular cleanroom design, HVAC and FFU specifications.

• Laminar flow (unidirectional air flow): Air movement in a uniform direction at a definite velocity, about 0.35–0.55 m/s for minimizing turbulence and preventing any particles to settle on the important surfaces of the cleanroom.
• HEPA filtration: High efficiency particulate air filtration of 99.97% of efficiency for particles of diameter of 0.3 μm — the minimum requirement for supply air for ISO classes 5 to 8.
• Pressure cascade: A difference in pressure in adjacent cleanrooms that compels air to move from cleaner zone to less clean one and prevents reverse flow of contamination during the periods of doors opening.
• FFU coverage ratio: Percentage of ceiling area occupied by fan filter units, used as a primary indication of acceptable ISO class and expected energy consumption of the fan.

Operations, Compliance & Audit Readiness

It is clear that the importance of a good design is limited to how well it achieves compliance. The nature of the cleanroom layout, the HVAC/FFU decisions taken during the design phase may make the compliance checks and environmental monitoring extremely easy or vice versa.

The costs spent on validation and environmental monitoring on annual basis would be 15–25% more for those facilities which consider compliance issues after the cleanroom is delivered.

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Three Monitoring Parameters That Must Be Designed In

With Deiiang™ these features are supposed to be deemed as design outcomes, instead of something that is added by the validation contractor:

• Continuous monitoring of particles: There has to be at least one real-time particle counter present per critical area and installed in close proximity to the process, meaning that it has to be put not on the wall that is furthest away from the work. The 0.5 μm channel needs to be recorded at a frequency that will permit identifying any changes during one shift.
• Pressure alarm thresholds: Each of the classification boundaries has to have sensors with a specified alarm range — usually its value will be ±2 Pa from the set point manufacturer of the device. The alarm has to be recorded and not displayed only.
• Forecast of filter loading and replacement: Each bank of FFU has to be either equipped with devices or manually assessed so that the changes in parameters across HEPA filter can be seen. When the filter will reach the pressure drop limit during the work, it will require an emergency stoppage; however, this issue can be avoided with the help of monitoring data.

How the Design Solutions Help Cut the Costs

The most important advantage of complying the requirements is that the system will automatically collect necessary information. When HVAC set points and values of the rooms are controlled by one management system it means that information can be processed automatically making the revalidation easier. The method that was utilized in the design of the new Deiiang project has reduced the workload for completing the annual internal audit by more than sixty hours per year. This means an enormous saving of operations costs which is not displayed in the long-term financial plans of the project, but rather registered in operational logs each year.

The following table illustrates the link between the compliance benefits obtained in the process of the development of the design of the new project and the obligations needed to be undertaken.

Table 5 — Design-to-compliance mapping. Each design solution requires an obligation in operation; the best designs limit these burdens as much as possible.

Conclusion & CTA

The success of the modular cleanroom design depends on the simultaneous development of layout, HVAC and air conditioning grid as one overall task. The layout determines the access points for contamination; HVAC specifies whether the pressure will be maintained; and FFU provides protection for the working zone. By optimizing the work done in all the processes together, it is possible to achieve the result.

The order of actions should not be overlooked. First, you need to establish a classification gradient, determine the airflow based on the volume of the cleanroom, position the FFUs only above the critical zone and validate the pressure thresholds based on the measurements. After that, the monitoring and compliance systems need to be integrated in a proper way and made part of the continuous process so that they would not have to be done every year separately. Organizations applying this method have lower chances of failing their ISO 14644 test than those using the device catalog.

If you wish to design a cleanroom in accordance with the space plans, ventilation and FFUs' construction, Deiiang™ offers complimentary design consultation service. Jason.peng, the chief designer at Deiiang will consider your floor plan, production process and target classification and then prepare the package with calculated airflow level, pressure changes, FFU placement scheme and monitoring plan.

Get in touch with Deiiang™ to book your free consultation.

References

• ISO 14644-1:2015 — Classification of air cleanliness by particle concentration
• ISO 14644-4:2022 — Design, construction and start-up of cleanrooms
• iso 14644-3:2019 — Test methods
• EU GMP Annex 1 — Manufacture of Sterile Medicinal Products
• IEST-RP-CC002 — Unidirectional Flow Clean-Air Devices
• ASHRAE Handbook — HVAC Applications, Clean Spaces
• Deiiang™ — Modular Cleanroom Systems and Engineering Data