The specific concept and design for an air handling system result from the requirements and local conditions placed on the cleanroom.
When selecting the type of system to be utilized, each of the following criteria can play a role:
For the manufacture of pharmaceuticals, the following types of air handling units (AHUs) are most commonly used:
The selection of the type of system to be used is often based on risk assessments of potential paths of airborne contamination. The introduction of contaminants by air is then only given and represents a risk if a stable aerosol is generated which can be carried by the air.
The AHU has the task to condition the air according to the calculated design requirements. An AHU system is comprised of the following main components:
Following the direction of the airflow, the system has the following layout, whereby the components shown can be varied as required (see Figure 1).
Figure 1 Layout of an air handling system (example with 100% fresh air)
The diagram legend is to be understood as follows:
These can be comprised of the following components, e.g.:
(2) fresh air louver flaps
(3) 1st filter stage (depending on location of the fresh air inlet and climatic conditions, a pre-heater may be necessary to protect the filter material from moisture)
(4) Heat recovery system for fresh air handling units with re-cycle composite systems, regenerative heat exchanger (also called a heat exchanger wheel) or cross-flow plate heat exchanger. For mixed-air systems, a mixing chamber for the addition of fresh air to the room air is installed if the recycled air is reused.
not shown: pre-heater – can be excluded in most cases for mixed air systems (mixing of re-cycled with fresh air)
(5) Silencer (to minimize the size of the AHU, a silencer with non-particle emitting design can also be installed directly within the duct system)
(6) Variable speed fan (to meet the demands at the actual design operating point or to control a constant or variable air flow rate using a frequency converter)
(7) Chiller with demister and fully draining condensate pan with adequate space for cleaning. At low air speeds the demister can be eliminated – this reduces the pressure loss in the AHU.
(8) Main heater with adequate space for cleaning
(9) Humidifier with fully draining condensate pan
(10) 2nd filter stage (for filters representing the final stage of the supply air treatment, these can be situated before the humidifier)
(2) louver flaps
(2) return air louver flaps
(3) optional filter stage for protection of heat recovery exchanger
(4) heat recovery system – coupled with feed air system
(6) variable speed fan (to meet the demands for the actual operating point or to control a constant or variable air flow rate using a frequency converter)
(5) silencer (to minimize the size of the AHU, a silencer with non-particle emitting design can also be installed directly within the duct system)
(2) exhaust louver flaps
As part of a risk assessment, it is evident that the “cleanroom” (production, process) lies between the inlet and return air grills. This means that the cleanliness of the inlet air as well as the air currents or flows within the clean/production room may have an influence on the product. The components outside the cleanroom are thus to be ranked as less critical.
A potential influence from the surrounding air is given if the product is exposed to the ambient air. The potential contamination depends upon the extent of the “contamination surface area”, the duration of the exposure and the following process steps (e.g. subsequent sterile filtration or sterilization).
To ensure the necessary air quality according to the clean room requirements of a pharmaceutical production facility, the acknowledged standard components are used for configuration of the air handling units.