SCOPE

The scope of this section comprises the supply, erection, testing and commissioning double skin construction air handling units, conforming of these specifications and in accordance with Drawings and of the Schedule of Quantities.

TYPE

The Air Handling Unit shall be double skin construction, draw – thru type comprising of various section such as mixing box (wherever the fresh air & return air are ducted), filter section, Coil section, fan section as per details given Drawings and Schedule of Quantity.

CAPACITY

The air handling capacities, maximum motor H.P., Static pressure shall be as shown on Drawing and in Schedule of Quantity.

HOUSING / CASING

The unit shall be Ceiling Mounted type. The housing/casing of the Air Handling Unit shall be of double skin construction.  The frame work shall be of Extruded Aluminum hollow sections.  All the frame shall be assembled using pressure die cast aluminum/nylon joints to make a sturdy, strong and self supporting frame work for various section.

25mm thick Double Skin Panels shall be made of 0.6mm Pre-coated GSS on outside and 0.6 mm Galvanized sheet inside with CFC/HCFC free Poly Urethane Foam of 38-40 kg/cum. in-house injected in between.  These panels shall be screwed from inside on to the frame work with soft rubber gasket in between to make the joints air tight. The unit shall be suitably insulated from inside to avoid condensation on outer surface.

Units requiring mixing boxes shall be complete with thermal break profile as well as double skin panels in thermal break construction.

FILTERS

Each unit shall be provided with a factory assembled filter section containing 25mm thick washable synthetic type air filters having extruded aluminum frame.  The media  shall be supported with HDPE mesh on one side and aluminum mesh on other side. Filter shall fit so as to prevent by pass. Filter face velocity shall not exceed 2.5m/sec Holding frames shall be provided for installing a number of filter

cells in banks.  These cells shall be held within the frames by sliding the cells between guiding channels.

COOLING/HEATING COILS

Multi rows deep chilled / hot water coil, as per requirement, shall have 12.5 mm to 15 mm dia tubes maximum 24 G thick with aluminum fins maximum 36 G thickness firmly bonded to copper tubes assembled in zinc coated steel frame.  Face & surface areas shall be such as to ensure rated capacity from each unit & such that air velocity across each coil shall not exceed 2.5m/sec.  The coil shall be pitched in the unit casing for proper drainage.   Each coil shall be factory tested at 21 Kg per Sq.cm. air pressure under water.  Tube shall be mechanically expanded for minimum thermal contact resistance with fins.  Fin spacing shall be 11 to 13 fins per inch (4 to 5 fins per cm). The drain tray complete with necessary double slope and drain connection for proper drainage of water shall be fabricated out of 18 G stainless steel with welded joints. The drain tray shall be externally insulated with minimum 12mm thick closed cell polyethylene. Necessary arrangement shall be provided to slide the coil in the drain pan. The computerized coil selection and test certificate for the cooling coil shall be submitted by the supplier.

FAN

The fan shall be AMCA certified forward/backward curved, double inlet, double width type.  The fan shall be imported, factory tested and assembled by original manufacturer. The Wheel & housing shall be fabricated from heavy gauge galvanized steel.  The fan impeller shall be mounted on a solid shaft  supported to housing spider frame and heavy duty ball bearings.  The impeller & fan shaft shall be statically and dynamically balanced.  The fan shall be selected for a noise level less than 80db(A). The fan outlet velocity shall not be more than 12.0m/sec.  Fan housing with Motor shall be mounted on a common extruded aluminum base mounted inside the air handling housing on anti-vibration mounts.  The fan outlet shall be connected to casing with the help of fire retardant fabric, mounted on aluminium extruded channels, acting as a flexible connection for anti-vibration.

MOTOR AND DRIVE

Fan motors shall be 415 ï 10% volts, 50 cycles, 3 phase, squirrel – cage, totally enclosed fan cooled with class F Insulation and IP – 55 protection.   Motor shall be especially designed for quiet operation and motor speed shall not exceed 1440 RPM.  Drive to fan shall be provided through belt drive arrangement.  Belts shall be of the oil-resistant type. 

FRESH AIR INTAKE

Air intake section shall be provided in the return air path. The air intake louvers shall be in extruded aluminium section mounted in extruded aluminium frame work.

SAFETY FEATURES

Each air handling unit must have safety features as under:

1. Fan and motor base shall be properly earthed from the factory.
2. All screws used for panel fixing and projecting inside the unit shall be covered with PVC caps to avoid human injury.

ACCESSORIES

Each air handling unit shall be provided with manual air vent at high point in the cooling/heating coil and drain plug in the bottom of the coil.  In addition, the following accessories may be required at air handling units, their detailed specifications are given in individual sections, and quantities separately identified in Schedule of Quantities.

1. Motorized three way mixing valves in chilled/hot water lines connecting to the coil.  This valve shall be operated by the cooling/heating thermostat & shall  control  the flow of chilled/hot water.  See the section “Automatic Controls and Instruments” for detailed Specifications.
2. Cooling/heating thermostats as per section “ Automatic Controls Instruments” shall be located in return air stream.
3. Insulated butterfly valves/balancing valves “Y” strainer, union & condensate drain piping upto sump or floor drain in air handling unit room, as described in section “Piping”.
4. Thermometers in the thermometer wells & pressure gauge (with cocks) within gauge ports in chilled/hot water supply and return lines as per the section” Automatic Controls and Instruments”.

PERFORMANCE DATA

The Air Handling Unit shall be selected for the lowest operating noise level of the equipment.  Fan performance rating and power consumption data, with operation points clearly indicating shall be submitted and verified at the time of testing commissioning of the installation.

TESTING

Cooling/heating capacity of various air handling unit models shall be computed from the measurements of airflow and dry and wet bulb temperatures of air entering and leaving the coil.  Flow measurements shall be by an anemometer and temperature measurements by accurately calibrated mercury in glass thermometers.  Computed results shall conform to the specified capacities and quoted ratings.  Power consumption shall be computed from measurements of incoming voltage and input current.