Cleanroom energy efficiency

Cleanrooms are among the most energy-intensive spaces in any building. Large recirculation airflows, conditioned makeup air, process exhaust and continuous operation can make a cleanroom use many times more energy per square metre than an office. Most of it goes to HVAC.

Much of that energy is avoidable. Cleanrooms are frequently designed with conservative air change rates, run at full airflow around the clock and left unchanged for years. ISO 14644-16, published in 2019, provides a framework for improving energy efficiency in cleanrooms without compromising cleanliness. This guide explains where the energy goes and which measures work.

Where the energy goes

Fan power rises steeply with airflow. Under the fan laws it approaches the cube of airflow where duct losses dominate; HEPA filter pressure drop rises more nearly in proportion to velocity, so the real exponent is usually somewhat lower, but a modest airflow reduction still produces a large reduction in fan power. That makes air change rate the most powerful lever.

Measure 1: right-size air change rates

Many cleanrooms are designed at the high end of historical air change ranges without calculation. Rooms often meet their class with a wide margin. A structured review can safely reduce airflow:

1. Gather particle monitoring and certification data for each room.
2. Calculate the required airflow from particle generation, target concentration, recovery time and heat removal, as described in air change rates and airflow in cleanrooms.
3. Reduce airflow in steps, testing particle counts, recovery and pressures at each step.
4. Set a new design airflow with a documented margin.
5. In regulated facilities, manage the change through change control and requalification.

Measure 2: setback during unoccupied periods

People are usually the largest particle source. When a cleanroom is unoccupied, it can maintain its class with much less airflow. ISO 14644-16 recognizes reduced airflow during non-operational periods.

A typical setback strategy:

• Reduce recirculation airflow to a predetermined level when the room is unoccupied, often based on a schedule or occupancy sensing.
• Maintain pressure relationships at all times, which usually means keeping exhaust and makeup air offsets constant.
• Return to full airflow far enough before occupancy to allow the room to recover to its class, proven by testing.
• Monitor particles continuously during setback where possible.

In GMP facilities, setback must be validated and is usually limited to non-critical grades or to periods when no product is exposed.

Measure 3: demand-based airflow control

Some facilities use real-time particle counters to vary airflow based on measured cleanliness. When counts are low, airflow drops; when counts rise, it increases. This is common in semiconductor and electronics facilities and is being adopted in pharmaceutical non-critical areas with appropriate risk assessment.

Measure 4: shrink the cleanest zones

Providing ISO 5 unidirectional flow across a whole room is extremely expensive. Using isolators, minienvironments or local unidirectional hoods to protect only the exposed product can cut airflow dramatically, while allowing the background room to run at a less demanding class.

Measure 5: reduce pressure drop

Fan power is proportional to airflow multiplied by pressure. Ways to lower system pressure include:

• Low pressure drop HEPA filters, with deeper pleats or larger face area, and lower face velocity.
• Better prefiltration to slow HEPA loading.
• Generous duct sizing and low-loss fittings.
• Removing unnecessary dampers and obstructions.
• Changing filters on a pressure drop basis chosen by life-cycle cost, not just at the maximum allowed.

Measure 6: efficient fans and motors

Replace older AC-motor fan filter units with EC-motor units, and use high-efficiency fans or fan arrays in air handlers. Variable speed drives allow airflow to be set precisely and enable setback. Systems should be compared using specific fan power, such as watts per L/s. The trade-offs between distributed and central fans are covered in fan filter units vs ducted HEPA systems, and general strategies in reducing fan energy.

Measure 7: minimize makeup air and exhaust

Every litre per second of air exhausted must be replaced with conditioned outdoor air. In Canadian climates, heating and humidifying that air in winter is expensive.

• Review process exhaust volumes against actual needs, and close unused exhaust connections.
• Seal the cleanroom envelope so less makeup air is needed to maintain pressure.
• Avoid excessive pressure differentials, which increase leakage.
• Use variable exhaust where processes allow.

Measure 8: heat recovery

Heat recovery from exhaust to makeup air can greatly reduce heating and cooling energy. In cleanrooms, systems that keep the two airstreams completely separate, such as runaround glycol loops, are often preferred because they eliminate cross-contamination risk. Other opportunities include recovering heat from chiller condensers or process cooling water to reheat or preheat makeup air. See heat recovery strategies in commercial HVAC.

Measure 9: smarter temperature and humidity control

• Widen tolerances where product and process allow.
• Use a deadband between humidification and dehumidification.
• Separate dehumidification in the makeup air unit from dry sensible cooling in recirculation, so recirculation coils can use warmer chilled water.
• Use dedicated higher temperature chilled water for sensible loads to improve chiller efficiency and extend free cooling.
• Eliminate simultaneous heating and cooling found during commissioning or trending.

Measure 10: commission and keep commissioning

Controls drift, sensors go out of calibration and overrides are left in place. Trending airflows, pressures, temperatures and humidity, and comparing them with design, often finds savings without capital cost. Retro-commissioning of existing cleanrooms is one of the most cost-effective first steps.

Managing risk

Energy measures in cleanrooms must never compromise cleanliness, pressurization or product safety. Good practice includes:

1. Assessing risk for each measure before implementation.
2. Testing performance at each stage of change.
3. Monitoring particles and pressures continuously after changes.
4. Documenting changes under the facility's quality system.

Key takeaways

• Recirculation fans and makeup air conditioning dominate cleanroom energy use.
• Right-sizing air change rates and setting back airflow when unoccupied are the most powerful measures, because fan power falls steeply with airflow.
• Shrinking ultra-clean zones with isolators or minienvironments reduces airflow dramatically.
• Lower pressure drop, efficient EC fans, tighter envelopes and heat recovery cut energy further.
• Every change should be risk assessed, tested and documented, following ISO 14644-16 principles.