FILTERS

Each unit shall be provided with a factory assembled filter section containing 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.

Whenever fine filters are required to be installed, unit shall be provided with factory fabricated plenum in similar construction as described above for casing specifications.

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.

HUMIDIFIER

Each unit shall be equipped with pan type/steam humidifier located inside the unit. The pan type humidifier shall consist of water tank made of GSS with stainless steel perforated cover. Electronic water level sensor shall be interlocked with water heating element. The heating element shall work automatically with a humidistat. Spray type humidifier if specified in Schedule of Quantities shall consist of spray header, nozzles, vertical mounted spray pump. The water spray pump shall work automatically with a humidistat. The water pump shall be made of non-corrosive material with water strainer before pump. 2 bend PVC eliminator shall be provided after the spray to prevent water carry over to fan section.  

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

Extruded aluminium construction duly anodized (20 microns and above), fresh air louvers with bird screen and extruded construction dampers shall be in the clear openings in masonry walls of the air handling rooms having at least one external wall. Louvers, dampers, prefilters, ducts and fresh air fan with speed regulator shall be provided as shown on Drawings and in Schedule of Quantities.

SAFETY FEATURES

Each air handling unit must have safety features as under:

•  The fan access door shall be equipped with micro-switch inter locked with fan motor to enable switching off the fan motor automatically in the event of door opening.
• The Access Door shall further have wire mesh screen as on added safety feature bolted on to the unit frame.
• Fan and motor base shall be properly earthed from the factory.
• 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.

• 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.
• Cooling/heating thermostats as per section “ Automatic Controls Instruments” shall be located in return air stream.
• 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”.
• 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 air flow 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.