The unit base is designed to provide strength and rigidity and the overall size of the unit will determine the type of base the unit will require. The smaller units have bases fabricated from galvanised or stainless steel sheeting and the larger units are manufactured from heavy duty structural steel sections. These sections are welded together and either painted or hot dipped galvanised.
The casing for the smaller units are constructed by a modern aluminium profile framing system with insulated sandwich type panels (double skinned). The larger units are constructed with tongue and groove type sandwich panels and trimmed with Aluminium angles. These sandwich panels are insulated using either fire retardant polystyrene, polyurethane, mineral wool or calcium silicate. The insulation is selected based on production costs, thermal characteristics, acoustic attenuation. The finish of the sandwich panels are either AluZinc, Chromadek or Stainless Steel depending on the clients requirements.
Fans and Motors
The fans are either single or double inlet, forward or backward curved centrifugal or axial type or Plug Fans. These fans are static and dynamically balanced. The fans are either belt driven or direct driven. The motors on the belt driven fans are squirrel cage TEFC type and the speed can be varied by the use of an external Variable Speed Drive or changing the belts and pulleys. The fans have removable belt guards, to provide the required safety from moving parts. The EC Plug Fans have an electrically commutated facility which allows for the fan speed to be varied.
Filtration is always provided within an Air Handling Unit, however the type of filters that are used is dependant on the application and climate. Some filters that are generally used are Panel washable filters, Bag filters, Compact Cassette filters, Carbon Filters, Electrostatic filters and HEPA filters
Dampers are generally located within the mixing plenum of the Air Handling Units, where there is a requirement to control the amount of air passing into and out from a certain opening. The dampers are either manually or motor-driven type and can vary the control of either Outside Air, Return Air, Exhaust Air etc. The Outside Air dampers can be controlled automatically via a C02 sensor. These dampers are generally supplied in extruded aluminium section construction.
Cooling, Heating and Steam Coils
These coils are selected using the latest supplier computer selection software to achieve the desired thermal and psychrometric efficiency with minimum air and fluid pressure drops. The bypass factors are also taken into account to ensure the optimal efficiency. These coils are generally copper tubes mechanically bonded to aluminium fins, with copper headers, all contained in a galvanised steel frame. These coils are provided with airvents and drain connections. All the coils are factory leak tested based on the fluid that is passing through the coil. The wall thickness of the tubing is also selected based on the fluid that passes through the coil. The cooling coil assembly is fitted into a stainless steel drain pan, for condensate removal. The material used to manufacture the coils is based on the application and climate the coils will be used and therefore there is a choice of copper fins, coated fins, stainless steel fins, aluminium fins. The tubing and frame material can also vary
Humidifiers are used to add moisture to the conditioned space, to maintain comfort and protect the contents of the space . The type of humidifier depends on the psychrometric process and the associated economical factors. The choice of steam humidifier could be either steam generated in a large central boiler and distributed into the Air Handling Units via a network of steam piping with it’s associated pressure reducing stations or it could be a portable boiler for each Air Handling Unit all with dispersion tubes and nozzels. Steam humidification is a isothermal process, i.e. it does not change the air temperature. The alternative humidification process is adiabatic process, so that the air is cooled while moisture is added into the airstream. This is achieved by either High Pressure Atomizing, Air/Water Atomising or Wetted Media Evaporative
Heat Recovery Wheels / Air to Air Heat Exchangers
PThese recovery methods are used extensively within the industry to achieve the required energy savings, by removing both sensible (heat) and latent (moisture). The wheel or Plate heat exchanger is positioned in an Air Handling Unit, so that it is divided into two sections, where the stale exhaust air is drawn through one half and the outside air through the other in a counter flow arrangement. The transfer of energy occurs.
Maintaining acceptable acoustics in a space is an important component of Indoor Environmental Quality (IEC). The application in which the Air Handling Unit is installed will determine the acceptable noise level. Sound levels can be reduced by selecting the appropriate fan i.e. use of direct drive fans can reduce vibration and drive noises by eliminating the belt and pulley mechanisms. After selecting the correct equipment the noise levels can be reduced further by using sound absorbing material in the walls of the discharge plenum section.