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choosing Refrigerant Piping Selection Tips DETAILED TECHNICAL SPECIFICATION

Discussion in 'المنتدى التعليمي' started by mannan, 14/10/17.

  1. mannan

    mannan Administrator Staff Member



    الحمد لله والصلاة والسلام على رسول الله وعلى آله وصحبه أجمعين

    choosing Refrigerant Piping Selection Tips


    a) Refrigerant piping assembled must consist of copper tubing
    to ASTM specifications B.88, Type “K” hard drawn and soldered joints
    Fittings must be of wrought copper or fine cast brass. Where required
    for gauges, etc., tubing not larger than 10mm. Diameter may be of
    type “K” soft (annealed) with flared tube or double ferrule compression
    fittings suitable for high pressure. Flux and solder as recommended by
    the manufacturers of tubing and fittings only must be used during installation

    b) Refrigerant piping must be installed so as to ensure continuous and
    automatic return of oil to the compressor. Gauges and meters etc
    supported directly on piping must be properly leveled

    c) Refrigerant stop valves must be back seating, key operated
    seal cap type. Valves, which are to be in constant use, must
    have hand wheels and must be packless type
    Valves connected in copper tubing must have solder type ends or
    flanged end and soldered flanged adapters

    d) Accessories for field-assembled system like oil separators
    liquid receivers, heat exchangers, expansion valves, etc
    must be installed as per manufacturer’s recommendations and specifications

    e) Replaceable core type filter drier with by pass valves and
    liquid sight glass must be provided

    f) Pump down system must be provided for each unit

    Pressure Tests

    After installation is completed, but before piping is furred in or
    before insulation is applied, all piping and equipment must be
    tested for leaks using Nitrogen or an approved gas

    Vacuum Test

    Before charging the system with the refrigerant, it must be
    dehydrated thoroughly, using a high efficiency vacuum pump
    and vacuum indicator. Dehydrating operation should continue
    until a reading of 35 FWB at a pressure of 5.2mm HG absolute is reached

    Return Air Plenum

    Return air plenum must be an integral part of the unit, factory assembled
    Plenum must be suitable for accommodating 50 mm. thick metallic cleanable
    filters with a face velocity not exceeding 1.8 m/sec
    However, equal and approved field installed filter plenums are also acceptable

    Control Wiring & Protection Devices

    The thermostat control voltage must be 24 volts
    The A/C units being offered must feature the following minimum
    requirements of safety interlocking and protective devices

    Safety electrical and mechanical interlocking of evaporator fan motor
    with compressor / heater operation and interlocking through an airflow switch
    wherever duct heaters are provided

    Where multiple compressors are incorporated in the units their
    operation must be in sequence in accordance with return air temperature

    Manually reset and adjustable oil pressure differential cutout
    of 90-sec/120 sec. trip time rating for compressors of 25 HP and above

    Manually reset and adjustable high pressure and adjustable
    automatic low-pressure cutout for compressor protection

    Time guard circuit for preventing compressor rapid recycling
    preferably of adjustable range from 5 minutes to 15 minutes

    Time delay relay for sequence starting of multiple
    compressors system of minimum 15 sec. delay rating

    Separate single phasing preventor suitable for three phase
    415 volts, 50 Hz. power supply to prevent the whole unit from
    single phasing phase shift and under voltage with a response
    time rating of maximum 2.0 sec

    Inherent thermal protection for compressor motor winding
    three phase evaporator fan and condenser fan, motor windings

    Inherent thermal protection or manually reset thermal or magnetic overloads
    for single-phase condenser and evaporator fan motors

    External thermal overload with manual reset or MCCB of
    suitable rating for all three phase motors in addition to (h) above

    The unit must be controlled by a duct thermostat housed in a
    suitable perforated transparent casing with a lock. Control
    voltage of the circuit to which thermostat is connected must be 24 V

    The control panel must be IP 54 at least

    Return Air and Fresh Air Filters

    1) Return air filters must be permanent and washable type made of aluminium
    or G.I. sheet designed for heavy duty and must be sized for maximum
    air velocity of 350 ft. per minute with initial pressure drop of not more
    than 0.25 inch W.G. at the rated air flow. Filter media must consist of
    cripped G.I. or aluminium arranged to give maximum area for airflow
    2) Return air filters must be enclosed in a separate filter frame
    integral unit.
    3) Fresh air filters must be of the same specification as return
    air filters.
    4) Thickness of return air filters must be 2" and that of fresh air filters must be of 4"

    Drain-pipe sizes must be minimum 19-mm. diameter and
    the material must be GI. The drainpipe must be
    connected to the drain point of the unit with transparent
    plastic flexible hose and jubilee clips

    Thermostat must be provided for each unit

    All mountings, brackets, bolts, fixtures, etc. for installing
    the condensing unit and fan coil unit must be provided

    All mini-split A/C units must be provided with proper earthing

    في أمان الله



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