In pharmaceutical AHU and HVAC play an essential role in controlling microorganism-free environments by supplying fresh air. In this article, we discussed components of AHU in detail.
AHU (Air Handling Unit) construction and components:
It consists of a rectangular box containing the following parts:
- Mixing box
- Cooling coil
- Blower (to generate pressurized air)
- Fine filter
- Plenum HEPA (An enclosed, typically positive pressure section of an air supply system)
- RH control
HVAC (Heating, Ventilation, and Air Conditioning):
The whole set of AHU units with air carriers (duct), air distribution and collection in the room (riser/ grill and diffusers, volume control system (dumper), terminal filters with, cooling and heating coil for temperature and humidity control.
The surrounding system to work the HVAC system in operation ranges is utility, for example, DG set, boiler, chiller, air conditioning compressor, air compressor, cooling tower, vacuum, refrigerant gas, and outdoor heating.
Components of Pharmaceutical AHU and HVAC:
It consists of a rectangular box with single skin( without insulation) and double skin (with PUF insulation of 25,50, and 60 mm thickness or as per requirements).
MOC ( Material of construction):
Pharmaceutical AHU and HVAC rectangular boxes are made of GI, MS, and SS with AL, MS, and SS supporting frames.
Filters are used to remove air contamination, so they help in the prevention of cross-contamination. filters types based on micron are:
Mesh or 40 microns for insects and birds control.
They are about in size of 20, 10, 5 microns. It may vary based on system and air quality requirements. These are washable and cleanable. The material of construction is HDPE(high-density polyethylene), nylon, and polymeric fibers. Five-ply and three-ply are used for construction.
About 5 and 3 microns in size may vary based on the system and air quality required. These are cleanable, non-woven, non-washable. The construction material is HDPE (High-density polyethylene), nylon, or polymeric fibers( 150 mm- 300 mm depth of fold are generally used, also called micro v filter. If HEPA is not used after this, these are also called fine filters. These are tested by dust arrestance capacity.
4. Fine filter:
HEPA/ ULPA/ SULPA:(types based on efficiency) Filter of 0.3 microns. The construction material is Glass fiber, PTFE( poly tetra fluoro ethylene), available in various sizes and CFM capacities. They are tasted by particle count and DOP Penetration, non-washable and non-cleanable.
Another type of HEPA is mini pleat HEPA: In the same box, the maximum surface is provided with the pleat, and hence CFM is more and pressure drop is also less in mini pleat( 15 mmwg as compared with HEPA [25 mmwg]). Mini pleat HEPA may provide about 25 to 40% are more than general HEPA.
B. Heating coil:
Pharmaceutical AHU and HVAC are provided to heat the air ( recirculated and fresh air) to raise the dew point for humidity control. These are electric heaters or steam coils based on heating requirements and Air volume,two-row deep and four-row deep. Coil shall be fitted in AHU.
- DIDW (double inlets double width): this air section is from the horizontal side and air delivery from the upper side.
- SISW (single inlet single width): this air section is from only one horizontal side, and air delivery is from the side.
D. fan( blade type):
- BDA-backward angle( for high static above 100- 125 mmwg)
- FDA-forward angle( for low static below 100 to 125 mmwg)
- Efficiency: for this use, performance curve between;
CFM Vs. static pressure, CFM Vs. Efficiency.
Based on the room temperature requirement, chilled water (7 °C inlets) or DX coil is provided in AHU. If heating is provided, then cooling is after the blower. If there is no heating coil, then the cooling coil is placed before the blower. The aluminum fine is provided on the coil to increase the dwell time on the coil.
Some time split air conditioners are used to cool the non-production unit, consisting of the compressor, condenser, and FCU.
FCU (fan coil unit) is fitted in the room, and the compressor is fitted outside of the room. Cold air from the compressor is supplied to FCU, AND FCU supplies the cold air in the room.
F. VCD( Volume control dumper):
These are useful for pressure balancing. The material of construction is aluminum and GI. Capacity is in CFM.
G. Gasket and RTV:
A rubber gasket is used between the joints of the duct and VCD to avoid air leakage.
RTV is a sealant( room temperature vulcanized) used to seal the joints in the air path of the duct.
The duct is used for the carrier of air, rectangular or round shaped) MOC is GI or SS(22, 24, 26, 22 gauge are thick, and 26 gauge is thin sheet). A different standard is available for construction. Smackna is generally used standard size is on volume and velocity of air to be carried by duct.
Sq.ft area of duct= CFM of air/ FPM of air in the duct.
I. Insulation of Pharmaceutical AHU and HVAC:
To avoid temperature, drop ducts are insulated by suitable insulation material. Types of insulation are as follow;
- SCP ( Send cement plaster: EPS( Extruded polystyrene or thermocouple) 25 mm, 50 mm thickness is pasted on duct with the help of melted tar. Then fine mesh is applied, and the send cement plaster is applied on it.
- Aluminum: instead of mesh and SCP, aluminum tin cladding10 micron thick aluminum foil is covered on the EPS insulated duct.
- Nitrile rubber: nitrile rubber foam with or with outer aluminum foil coating is pasted on duct surface with the help of chemical base rubber adhesive.
J. Distribution system:
These are parts through which air through the duct is distributed in the room. Air distribution system comprises:
- Terminal HEPA with filter screen: HEPA box is fitted at the terminal side in the ceiling with a cover plate screen, through which air is supplied in the room.
- Diffusers: these are square-shaped, partitioned units with or without a volume control facility.MOC is GI powder-coated, aluminum, stainless steel grade 304. capacity in CFM.
- Grills: rectangular, GI or MS, or SS made frames with or without air guide or volume control facility.Capacity in CFM.
K. Return air Risers:
These are boxes with filters and mesh covering fitted in the wall at the bottom side to collect the air from the room, and these are connected to the return air duct.
MOC is aluminum, stainless steel, and GI powder coated. Capacity in CFM.
- Monitoring equipment:
- Thermometer: to monitor the temperature.
- Hygrometer: to monitor RH.
- Pressure Gauge:(Magnehelic gauge)- to indicate room pressure and filter pressure drop.
- Inclined Manometer: A manometer filled with red ink is installed. Now it is not recommended.