NATIONAL ALUMINIUM COMPANY LIMITED - Rites

17.5.22 Condenser capacity control shall be provided by means of variable speed fans and ‘head
pressure’ sensing.
17.5.23 The evaporator air blower(s) shall be centrifugal forward curved type belt driven by
individual motor(s) and suitable for the external static pressure. The fan assembly shall be
isolated from the casing by anti anti-vibration vibration mounts. The fan/motor drive shall be capable of
capacity adjustment by pulley changes within +15% of design duty.
17.5.24 High efficiency filters shall be pprovided
rovided in the main supply air duct and in the fresh air
connection to return air duct.
17.6 Construction Requirements
17.6.1 General construction details of various equipment under Contractor’s scope shall be as
elaborated in subsequent clauses below.
17.6.2 Roof Ventilators and accessories
Roof ventilators and accessories shall be provided as required.
17.6.3 Impeller shall be axial flow type, cast in one piece finished all over and carefully dynamically
balanced after final assembly. All impellers shall consist of high efficiency aerofoil blades.
Impellers shall be mounted directly on the motor shaft.
17.6.4 Casing shall be of heavy gauge construction and shall be properly reinforced for rigidity.
Access door with suitable locking arrang arrangement shall be provided.
17.6.5 Hood shall be of hinged type providing easy access to motor and impeller. It will also protect
them from rain and any other contingencies. Weather Weather-proof proof lockable type disconnect switch
shall be provided such that the hoods can be opened only when the disconnect switch is in
‘OFF’ positions. On larger sizes of roof ventilators, hoods shall be of split construction. 15
mm mesh galvanised bird screen shall be provided. The hoods will have low pressure drop
across it.
17.6.6 Suitable uitable arrangement shall be provided for mounting the roof ventilators such that ingress
of rainwater into the building will be avoided completely.
17.6.7 Axial Flow Fans
Axial flow fans shall be provided as required.
17.6.8 Impellers shall be axial fl flow ow type and single piece cast aluminum with aerofoil blades
construction. It shall be finished all over and balanced dynamically. Impeller shall be
mounted directly on the motor shaft.
17.6.9 Casing shall be of heavy gauge construction properly reinforced for rigidity. It shall be
provided with suitable supports. Access door shall be provided in the casing for easy access
to motor and impeller. Suitable arrangement for mounting of motor shall be provided.
Technical Specification:Sec-4,System System Parameters, Operation & Control Philosophy
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