Free Virtual Router software
Free Virtual Router software


الحمد لله والصلاة والسلام على رسول الله وعلى آله وصحبه أجمعين 

choosing D.X. UNITS Selection Tips 



All units must be rated in accordance with the ARI Standard and must be 
designed to conform to ASHRAE 15 latest revision and in accordance with UL 1995 

All units must be manufactured in a facility registered to ISO –9001 

All insulation and adhesive must meet NFPA 90A
requirements for flame spread and smoke generation

All units located outdoors near sea side or subjected to a
highly polluted and corrosive atmosphere (see duty) must be
coated with a special coat suitable for the following 
1) Highly concentrated acidic and alkaline atmosphere
2) Solvent resistance
3) Moisture
4) Ultra violet rays
5) Abrasion resistance
6) Salt spray tests according to ASTM B117.85 2000 hours 
and must be repairable in the field 

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

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″

Split System Direct Expansion Units

The units must be of internationally reputed have undisputed
record of performance.and must be approved 

The unit must consist of a remote air-cooled condensing unit and a matching air-handling unit 
Condensing units and air handling units must be of the same make 

The condensing unit must be of the air-cooled type, suitable for outdoor installation
constructed of heavy gauge, galvanized sheet with baked enamel finish
special coat to be applied. The unit must be complete with its own compressors
air-cooled condenser, motors, fans, starters, relays and 
other standard accessories and controls 


Compressor must be of the reciprocating/scroll type direct coupled
to an electric motor and complete with vibration isolators and crank case oil heater.
Compressors 15 HP and below, can be of hermetic sealed 
type preferably with oil level sight glass 
Compressors above 15 HP must be of Semi-hermetic semi-sealed multi cylinder
type with service valves and oil level sight glass
All compressors above 15 HP must have suitable capacity control arrangement 
For multi-compressor units, each compressor must have its independent refrigerant circuit 


Condenser coil must be constructed of seamless copper tubes with copper or aluminium
plate fins mechanically bonded to the tubes 
Spiral or round fins are not acceptable. Maximum number of fins not 
exceeds 14 per 25 mm. Condenser coil tubes and fins must be coated 
with special coating suitable to the working conditions 
The condenser fan must be propeller type with aluminium or steel blades direct driven
upward or sideward discharge, provided with protective screens mounted to the casing
Frame, blades, protective screens must be coated with special coat suitable for the environment 


Evaporator coil must be of the same construction as of the condenser coil 
Evaporator coil face velocity must not exceed 2.8 m/sec 
Evaporator blower must be of the forward curved design and
sized to suit the system pressure 
Fan motors must be installed on an adjustable base and secured by a locking device
Fan drive must be through adjustable pitch pulley. Fan must be provided with sealed
permanently lubricated ball or sleeve bearings and the entire fan assembly must 
be statically and dynamically balanced 

Motor Enclosure and Insulation 

The following are the minimum requirements of enclosure and insulation for motors 
Type of Motor Enclosure
Insulation Compressor Motor
Hermetic / Semi-Hermetic Special
Condenser Fan Motor Drip-Proof Class “E” 
Evaporator Fan Motor Drip-Proof Class “A”

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 

في أمان الله 


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