Designing for ISO Class Cleanrooms: HVAC, Pressure, and Particle Control

Semiconductor, pharmaceutical, and battery manufacturers all depend on cleanrooms classified under ISO 14644, and designing those spaces goes well beyond installing HEPA filters. It takes airflow engineering, pressure zoning, and a contamination control strategy that holds together across all three.

HVAC Design: The Heart of Cleanroom Control

HVAC governs both air cleanliness and thermal conditions, so every other design decision works around it.

Air Change Rates

• ISO 5 rooms may require 240-480 air changes per hour (ACH).

• ISO 7 spaces can operate with 30-60 ACH.

• These high rates are achieved with powerful Fan Filter Units (FFUs) or centralized air handlers.

Filtration

• HEPA (99.97% @ 0.3µm) or ULPA (99.9995%) filters are standard depending on ISO class.

• Filters are often located at ceiling diffusers or within FFUs for modularity.

Temperature and Humidity

• Semiconductor fabs: 20-23°C with ±1°C tolerance and 40-55% relative humidity.

• Battery dry rooms: can require <1% relative humidity with dew points below -40°C.

Pressure Cascades: Zoning for Containment

Pressure differentials control which direction particles migrate. Pressure steps down from the cleanest room outward, so air always has somewhere less clean to go.

A common arrangement:

• ISO 5 process area: +15 Pa relative to the adjacent ISO 6 space.

• Gowning room: +5 to +10 Pa relative to the ISO 7 corridor it opens onto, buffering that corridor from the ISO 5 workspace.

• Airlocks: interlocking doors that hold the differential while personnel or materials pass through.

A cascade only holds if the air leaving is replaced. Fabs exhaust large volumes through process and scrubber systems, and all of it returns as conditioned makeup air. Sizing makeup air against total exhaust is what makes the scheme achievable.

Even a well-designed cascade sees brief reverse flows from doors, movement, and turbulence, which is why particle counts are monitored.

Particle Control: More Than Air Filters

Material Selection

• Use non-shedding, easy-to-clean finishes such as stainless steel, epoxy coatings, and vinyl floors.

Cleanroom Behavior Protocols

• Enforce strict gowning rules, limit entry points, and install sticky mats and air showers.

Room Layout

• Keep laminar flow zones obstruction-free.

• Separate clean and dirty corridors for material and personnel flow.

Verification and Monitoring

• Install real-time particle counters in ISO 5 zones and maintain calibration logs.

• Verify laminar flow with airflow visualization (smoke testing) at commissioning and after layout changes.

Coordination Across Disciplines

Designing for ISO class requires coordination between mechanical, electrical, architectural, and process teams. HVAC has to deliver high-volume clean air, pressure zoning has to be precise, and every material and protocol has to serve particle minimization.

Designing Cleanrooms the BBTech Way

At BBTech America, our cleanroom designs are integrated from concept stage through installation and commissioning, using digital simulation and modular construction to reduce field errors. We focus on:

• Integrating HVAC with process utility piping.

• Designing for flexibility and future upgrades.

• Meeting strict ISO standards without compromising energy efficiency.