Air Handling Concepts Cleanrooms

The Air Handling Unit (AHU) is a device for circulating and regulating air, as part of the heating, ventilating and air-conditioning (HVAC) system. It consists of a fan(s) and multiple equipment to perform the functions of cleaning, cooling, heating, dehumidifying, humidifying and mixing of air. It is used to control humidity, temperature, air movement and air cleanliness.

The primary function of the AHU is to recondition outside air and circulate it as fresh air into the cleanroom or controlled environment. For an acceptable quality of indoor air, exhaust air is removed. The fresh air is either heated by a heating coil, recovery unit or cooled using a cooling coil.

To save energy, cleanrooms with less stringent requirements for air quality use a mixing chamber to recirculate air from the cleanroom. Usually, the mixing chamber has dampers for controlling the ratio between outside, return and exhaust air.

Modular Cleanroom Benefits

  • Modular Construction
  • Quick Assembly Time
  • Versatility
  • Reconfiguration
  • Airflow Control
  • Inexpensive Modifications

Air Handling concepts for Modular Cleanrooms

Apart from contamination control in the cleanroom, HVAC also provides a comfortable work environment for cleanroom personnel. To control the amount of bacterial and particulate contamination entering a cleanroom, the air must be filtered.

To classify the level of contamination control administered to the controlled environment, different classes are subsequently defined. Below is listed the number of parameters used to determine cleanroom classification:

  • Number of air changes for each room
  • Type and position of filters
  • Temperature and relative humidity
  • Airflow and air velocity pattern
  • Facility workflow and layout
  • Air pressure differentials between rooms
  • Number of particles on the surface or in the air

In connection with AC units, the two basic air handling concepts for modular cleanrooms include fan filter unit concept and ducted air-supply concept with terminal end filters.

Cleanroom Design, Build & Validation

  • Budgeting and planning
  • Engineering, design & layout
  • Airflow and filtration design
  • Construction and Installation
  • Full Certification of our product
  • Industry-specific equipment installation
  • Validation

An FFU can run with an AC unit or on its own. The AC unit is used when the humidity and temperature control of cleanroom air is required.  A specific filter coverage and air-exchange are required, based on your cleanroom ISO classification. The FFU permits the placement of individual filter boxes, equipped with a filter and air fan (ULPA or HEPA) installed on the cleanroom ceiling.

THE FFU draws air from the surrounding environment and circulates it to the cleanroom in a filtered, laminar manner. The conditioned air is re-circulated through the FFU to the cleanroom if surrounding air is supplied from an AC unit. Where this is not suitable, a closed loop system can be created.

Ducted Filter Modules provide ULPA or HEPA filtered air when connected to an air source, such as an air handler. They include a 12 x 2 H collar to attach it to the air source that determines flow rate.

A diffuser plate and internal baffling system ensure uniform face velocity. Room-side replaceable filter models allow for cleaner, faster filter replacement. ULPA filters are rated 99.999% efficient at removing particles ≥0.12 µm. HEPA filters are rated 99.999% at removing particles ≥0.3 µm.

Issues to consider when specifying a cleanroom AHU

Where a cleanroom design is completed without consideration of compliance, there is a distinct possibility of higher costs and significant time delay during validation. This arises from issues such as revisiting the commissioned project or mechanical changes. Typical areas where problems occur include:

Operating tolerances

Design, validation and commissioning criteria should be established for GMP parameters, such as room differential pressures and air change rates, as well as temperature and humidity control. For instance, various tolerances might be applied at validation and commission for the facility to operate within the validation requirements.

Air filtration

Filtration levels depend on the cleanroom classification being served. For instance, an ISO Class 8 cleanroom will be achieved with a high-grade ULPA filter within the AHU. Meanwhile, an ISO Class 5 environment will require terminal HEPA filters. Total Clean Air can provide design teams to ensure your cleanroom meets all on-site test requirements. We follow a structured approach to ensure the cleanroom complies with all regulatory requirements.

Tips for saving energy in Cleanrooms with AHUs

  • Use of HVAC units, HEPA/ULPA filters with reserve power and reduced pressure drop
  • Avoid over-specifying a cleanliness class
  • Reduce heat loss/gain and provide heat isolation of cleanrooms
  • Limit the number of personnel and equipment in the cleanroom
  • When at rest, reduce airflow rate
  • Seal all leaks
  • Determine the exact required air flow rates during testing and operation,
    based on actual data
  • Use high-efficiency AHUs, ventilators and chillers
  • Remove excess heat load from process requirement
  • Reduce size of the cleanroom to the minimum
technician working in a clean room

Contact Total Clean Air for your high-efficiency, energy saving AHU systems

Total Clean Air is a leading UK provider of cleanroom solutions, such as HVAC units, ACs (with ceiling plenum and without ceiling plenum), HEPA filters, ULPA filters and high volume air handlers. We also advise you regarding air handling concepts and devices that meet your airflow requirements.

Phillip Godden

Phillip Godden is the Founder & Chief/Executive Officer at Total Clean Air.

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