An air handler, or air handling unit and often abbreviated to AHU, is a device used to condition and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system. Usually, an air handler is a large metal box containing a blower, heating and/or cooling elements, filter racks or chambers, sound attenuators, and dampers. Air handlers usually connect to ductwork 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 rooftop unit (RTU).

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Baseframe Construction:

The baseframe of the RMI DS range of air handling units is fully welded from cold-rolled structural mild steel 'C' channel. The baseframe is hot dip galvanised after contruction for weatherproofing. The baseframe provides lifting points and structural support. Nominal height is 150, 100 and 50 mm.

Housing Construction:

The housing of the RMI DS range of air handling units consists of aluminium penta post frame and a double skin door and panel construction. The outer skin is 1.0 mm thick polyester coated galvanised steel sheet. The inner panel skin is 1.2mm galvanised steel sheet. The double-skin panels and doors are provided with fibreglass insulation (48 kg/m3 density), which gives the panels excellent thermal and acoustic properties. Doors are provided with a full height stainless steel piano hinge, double glazed window and polyamide lockable handles.

Mixing Box Section:

Standard mixing box sections are provided with opposed or parallel blade multi-leaf dampers. The dampers have airfoil section extruded aluminium blades mounted within a rigid, flanged galvanised steel frame. This construction provides the basis for a low leakage, high performance volume control damper. The blades have santoprene tip seals and stainless steel side jamb seals to ensure class-leading leakage performance. Low friction bearings and substantial blade linkages afford quiet operation and low torque requirements. Linkage outside the air stream.

Panel Filter Section:

Full cell: 595 x 595 x 50 mm
Half cell: 595 x 287 x 50 mm
Each panel filter is provided with an individual sealed filter frame. The filter frames are manufactured from 1.2mm thick galvanized steel with a foam gasket and spring clip mechanism for air on side fitting. The stainless steel retaining clips force the filter in the direction of air flow against the foam seal. Galvanised bulkhead framework seals the filter frames to the interior skin of the housing panels. Panel filter grades G3, G4 pleated fibreglass construction with wire reinforcement. 100mm panel filter depth is also available. A Dwyer series 2000 magnehelic gauge is provided for differential pressure measurement across each panel filter bank.

Bag Filter Section:

Full cell: 595 x 595 x 600 mm
Half cell: 595 x 287 x 600 mm
Each bag filter is provided with an individual sealed filter frame. The filter frames are manufactured from 1.2mm thick galvanized steel with a foam gasket and spring clip mechanism for air on side fitting. The stainless steel retaining clips force the filter in the direction of air flow against the foam seal. Galvanised bulkhead framework seals the filter frames to the interior skin of the housing panels. Filter grades F6, F7, F8, F9 pleated fibreglass construction. Rigid minipleat filters of the same grade are also available in 300mm depth. A Dwyer series 2000 magnehelic gauge is provided for differential pressure measurement across each bag filter bank.

Absolute (Hepa) Filter Section:

The absolute filter cells are high efficiency filters for the separation of suspended particles, aerosols, toxic dusts etc. These filters may be used in supply or extract air systems for applications demanding high standards of air purity in the electronic, research, medical, pharmaceutical and nuclear industries. Standard filter grades H10, H12, H13. Each hepa filter is provided with a matching frame from the filter manufacturer in both gel-seal and neoprene seal types. The filter bank of hepa filter frames is sealed to the inner skin of the housing panels using a rigid galvanised steel bulkhead. Appropriate caulking sealant is used to ensure no particle bypass. A Dwyer series 2000 magnehelic gauge is provided for differential pressure measurement across each hepa filter bank.

Cooling Coil Section

Chilled Water/Direct Expansion The chilled water or water/glycol mix cooling coils are constructed from a 1.5mm thick galvanised steel frame. Copper tubes are bonded to aluminium fins. The tubes are brazed to copper headers with brass BSP threaded male flow and return ends. Cooling coils are pre tested for 2 hours at 20bar. Max service pressure 10bar.Direct Expansion - R407C, R134A. Cooling coils are constructed from 1.5mm galvanised steel frame. Copper tubes are bonded to aluminium fins. The tubes are brazed to copper distributers and liquid collectors for refrigeration pipework. Cooling coils are pre tested for 2 hours at 20bar. Coils can be provided with 2 or more stages for step control. RMI also offer full refrigeration and condensing unit packages.Condensate Trays: All non sensible cooling coils are provided with a fully welded stainless steel tray with connection to the outside for trapping to drain. Trays are pitched at 1:20 towards the drain connection. Mist eliminator banks: Polypropylene blade 100mm deep rated to velocities of 3.5 m/s. Blades framed in stainless steel.

Heating Coil Section:

LPHW, MPHW, SteamThe LPHW and MPHW heating coils are constructed from a 1.5mm thick galvanised steel frame. The copper tubes are bonded to aluminium fins. The tubes are brazed to copper headers with brass BSP threaded male flow and return ends. Heating coils are pre tested for 2 hours at 20bar. Max service pressure 10bar.The steam coils are constructed from galvanised steel or stainless steel frame 1.5mm thick. The carbon steel or stainless steel tubes are bonded to aluminium or stainless steel fins. The carbon steel or stainless steel tubes are welded to carbon steel or stainless steel headers with male BSP threaded steam and condensate ends. The steam coils are self draining. The steam coils are pre tested for 2 hours at 20bar. Max service pressure 10bar.

Humidifier Section:

In the DS range of air handling units the following types of humidifier can be fitted; Direct steam: Stainless steel injection lance(s) provided with modulating steam valve and separater kit: Evaporative Humidifier: Direct or recirculating cold water cascaded from top to bottom of absorption media for evaporation into the air steam. Tray and pump included, controls optional. Electrode Boiler Humidifier: Three phase power heated electrodes for cold water supply. Steam boiled from tank connected to SS lance(s) inside the air stream. Modulating control included. Resistive Boiler Humidifer: Three phase power heated elements for cold water supply. Steam boiled from SS tank connected to SS lance(s) inside air stream. Modulating control included. Cold water spray: Adiabatic absorption of cold water spray into the air steam. Atomisation of supply using compressed air or high pressure water through nozzle orifices. Modulating control included. All humidifying sections are provided with a fully welded extended stainless steel tray.

Fan Section:

The DS range of air handling units provide a range of different fans (belt and direct driven) fixed to a galvanised steel base and isolated from the AHU structure through spring isolation mounts and a flexible sleeve connection to a bulkhead. Belt Drive Fans: RZR 15-0400:1000 The standard fans are Gebhardt, double or single inlet. Lap jointed scroll of galvanised sheet steel with discharge flange and heavy duty reinforced side frames. High performance impeller with 12 hollow section true aerofoil blades inclined obliquely to the shaft axis, welded in position and epoxy coated. Throat plate inclined obliquely in opposition to blade inclination. Inlet cones matched to the impeller reduce entry losses to a minimum. Impeller and shaft balanced as an assembly in according to DIN ISO 1940. Self aligning double row ball bearings secured by adapter sleeve, mounted within a cast iron housing packed with long life, high performance grease. Can be relubricated when not in service. Performance data to DIN 24166 Class 1 / BS 848 Class "A").Direct Drive Fans: RLM 55 2528:1214. All impellers are balanced statically and dynamically according to DIN ISO 1940, specification G 2.5, based on the maximum speed from size 4550. The line 50 impellers with backward curved blades made of sheet steel, are welded and coated.

Housing Construction Options:

For pharmaceutical (GMP), Microelectronic, Biomedical, and Heathcare projects, RMI offer the following AHU casing options;
   - Thermal break aluminium extrusion penta post frame combined with standard or special finish panels.
   - Internal stainless steel lining
   - Internal lining and wash down floor trays
   - 3mm thick aluminium floor tread plate (non-slip maintenance flooring)
   - Stainless steel welded box section frame with the option for internal and external stainless steel panels.
   - Heavy duty housing panels (50 or 100mm thick) using 1.5mm thick external and 1.2mm internal skin. These housing panels can be offered with the various options listed above.

Heat Recovery Sections

RMI DS air handling units have a number of different heat recovery options incorporated between supply and exhaust air streams. Heat Recovery Coils: Coils similar in construction as described in the previous paragraphs can be twinned to recovery up to 40% of the available exhaust heat. A glycol mix is used for frost protection. Circulating water circuit design and installation is not offered. Plate Heat Exchanger: Heat exchange between supply and exhaust streams is achieved through a non air mix on each side of an aluminium or plastic plates. Thermal Wheel: Non hygroscopic exchange of heat through two sides of a rotating wheel with optimised speed of rotation using a control signal.

Filter Section Options:

For Panel and Bag filters, the frames can be constructed from stainless steel. For critical absolute (Hepa) applications, RMI provide a fully welded hepa filter bank which we recommend for H14 applications. In addition, the bulkhead can be continued to the outside of the AHU section giving further guarantee against particle bypass.

Coil Section Options:

For pharmaceutical (GMP), Microelectronic, Biomedical, and Heathcare projects, RMI offer the following AHU casing options;
   - Coil casings in stainless steel
   - Coil tubes in stainless steel
   - Coil fins in stainless steel, treated aluminium or electro-tinned copper.
   - AHU includes removable coil panels and access for cleaning to air on and air off sides of each coil

Fan Section Options:

Treated and heavy duty fans can be incorporated to provide additional corrosion resistance and durability. Typically fans will have welded casings with plumber block bearings. Fans are epoxy coated with heavy duty reinforced side frames, access panels and drain points. The impellors and shafts are balanced as an assembly in accordance with DIN ISO 1940. The self aligning double row ball bearings are housed in split plumber block housings mounted on robust pedestals.

Atex 95

RMI has a long history of providing units suitable for explosive environments. In conjuction with our fan supplier Gebhardt, we are offering units suitable for Zone 1 category 3G and 2G in accordance with ATEX 95. Both centrifugal belt drive and direct drive plug fan options are available. Gas group IIB is the nominal environment, gas group 11C is possible using direct drive fan types.

Documentation/ Traceability:

For GMP and other highly critical processes, our clients demand from us an extensive documentation package which we can tailor to each individual project. We assist our clients with the required validation documents for any part or sub part we supply. These packages include: Scaled AutoCAD drawings, Extensive operating and maintenance manuals for every part and sub part of the assembly, certification for coil hydrostatic tests, calibration certificates for all instruments used in testing as detailed above and general FAT certification.

AHU Testing:

For pharmaceutical or other critical applications, RMI provide a testing service in their factory for client witnessing and approval. AHU Leakage Testing: The leak tightness of the air handing unit housing can be demonstrated in accordance with EN 1886 class B. The sections under positive or negative pressure in service are tested accordingly. Higher test pressures can be demonstrated on request. AHU Air Flow Testing: The fan duty can be demonstrated at full or over design resistance to prove the design data using a test duct traverse with a pitot tube. Motor starting current and running current are demonstrated. AHU Sound Testing: RMI can provide an acoustic test in their factory or in the site location to verify sound level criteria for any particular noise requirements.