الحمد لله والصلاة والسلام على رسول الله وعلى آله وصحبه أجمعين choosing Refrigerant Piping Selection Tips DETAILED TECHNICAL SPECIFICATION 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
