What is AHU (Air Handling unit)?

What is AHU (Air Handling unit)?

An air handler, or air handling unit (often abbreviated to AHU), is a device used to condition and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system. An air handler is usually a large metal box containing a blower, heating or cooling elements, filter racks or chambers, sound attenuators, and dampers. Air handlers usually connect to a ductwork ventilation system that distributes the conditioned air through the building and returns it to the AHU. Sometimes AHUs discharge (supply) and admit (return) air directly to and from the space served without ductwork.

Small air handlers, for local use, are called terminal units, and may only include an air filter, coil, and blower; these simple terminal units are called blower coils or fan coil units. A larger air handler that conditions 100% outside air, and no recirculated air, is known as a makeup air unit (MAU). An air handler designed for outdoor use, typically on roofs, is known as a packaged unit (PU) or rooftop unit (RTU).

The design, installation, commissioning and qualification of clean rooms heating, ventilation and air conditioning (HVAC) systems is often one of the largest considerations in the design of a new pharmaceutical or biotechnology manufacturing facility. With high running costs (energy associated with the movement, cooling and heating of air) and the potential to impact upon safety and product quality, getting them right
is important for business, safety and good manufacturing practice (GMP) criticality.

The design of the HVAC system will be based upon the clean room suite that it serves, and will be affected by factors such as the number of rooms served, the layout of the rooms, the equipment within the rooms and, most critically from a qualification perspective, the environmental conditions that the rooms must achieve.

The air handling unit helps maintain each room's clean environment by providing an appropriate volume of clean air to each room at the correct temperature and humidity.

The air is filtered by pleated paper filters called high efficiency particulate air (HEPA) filters which, depending upon the classification of the rooms, are located either within the air handling unit or where the air enters each room. Cooling and heating coils are also located within the air handling unit, increasing or decreasing the air temperature to ensure that the room temperatures remain within specification.

Reliable operation of the air handling unit within established limits is critical, not only to prevent product quality from
being compromised by poor air conditioning, but also for the following reasons:

- to prevent cross contamination of products to maintain operator safety,
- where the HVAC is being used for this purpose to maintain product safety,
- where the HVAC is being used for this purpose.

Defining the Requirements

The cost of change during a project, based on the stage of the project.

Whereas other services and utilities can be (relatively) easily moved within a building's framework once the building work has been completed, the HVAC is much more integral with the building's fabric, making retrospective modifications much more time consuming and expensive. Getting the specification and design right first time is very important.

What are the problems?

If the design phase is completed without considering the compliance aspects of the clean rooms, then there is a high likelihood of incurring significant time delays and costs during the validation period, as a result of having to make mechanical changes to the installation or revisiting some of
the commissioning work.

Some typical examples of areas where problems can occur as a result of not designing for compliance are highlighted below, together with suggested actions to try to avoid these problems from occurring.

Operating tolerances. Design, commissioning and validation criteria must be determined for GMP-critical parameters such as air change rates, room differential pressures, temperature and humidity. For example, different tolerances may need to be applied at commissioning and validation to ensure that the facility will operate reliably within the validation acceptance criteria limits.

Air filtration. The level of air filtration will vary depending upon the classification of the clean rooms being served. For example, an ISO Class 5 room (Class 100) will require terminal HEPA filters, whereas an ISO Class 8 environment (Class 100000) may be achieved by using a high-grade (non-HEPA) filter within the air handling unit. To avoid failures during validation integrity testing it is important for the validation and design teams to discuss the in situ test requirements, and to agree upon appropriate grades of air filtration.

What are the criteria for validation?

During AHU validation, following tests shall be carried out

Filter efficiency test,
Air velocity & number of air changes,
Air flow pattern (visualisation),
Differential pressure, temperature and RH,
Static condition area qualification,
Dynamic condition qualification,
Non-viable count,
Microbial monitoring,
Area recovery and power failure study.

Why re-validation need to be performed?

AHU system shall be revalidated periodically as mentioned in the regulatory standards. AHU shall be revalidated in following cases also.

When basic design of AHU is changed,
When clean room volume is changed,
When new equipment is installed,
When a construction is carried out, that calls for reconstruction of AHU system.