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Refrigerant circuit
One circuit on sizes 250 and 300, and two circuits on
sizes 400, 500 and 600. Single circuit units will have
two compressors manifolded. Both circuits of the four
compressor units are manifolded. Refrigerant connections
not connected are sealed and plugged.
Refrigerant pipe connections
Determination of the size of the pipe connections.
Liquid line
Size the liquid line on the basis of:
1. Full load operating conditions.
2. A pressure drop of 100 kPa maximum.
3. A liquid velocity not exceeding 3 m/s (to avoid
hammer).
Suction line
Design the suction line to provide sufficient gas velocity
in both horizontal and ver tical runs to carry the
compressor oil and ensure a uniform rate of return to
the compressor. Size the hot gas line on the basis of:
1. Producing gas velocity in horizontal runs at least
2.5 m/s at minimum operating conditions.
2. Producing gas velocity in vertical risers at least 5
m/s at minimum operating conditions.
3. Gas velocity should not exceed 20 m/s under
maximum load conditions.
4. Maximum pressure drop in suction line should not
exceed 20 kPa.
Pitch the horizontal run of suction line toward the
evaporator.
Refrigerant line isolation
Isolate the refrigerant lines from the building to prevent
normal vibration in the lines from the building structure.
Also avoid bypassing the isolation system on the unit by
attaching the refrigerant piping or electric conduit too
rigidly.
Any unit vibration can travel along rigid pipes or conduits
to the building.
Installation
Pressure and leak testing
When pressure and leak testing, these safety precautions
must be adhered to:
1. Do not work in a closed area where refrigerant may
be leaking- a sufficient quantity of vapors may be
present to cause personal injury. Provide adequate
ventilation.
2. Do not use oxygen or ecetylene in place of refrigerant
and dry nitrogen for leak testing- a violent explosion
may result.
3. Always use a pressure regulator , valves and gauges
to control drum and line pressures when pressure
testing the system. Excessive pressures may cause
line ruptures, equipment damage or an explosion
resulting in personal injury.
Pressure test the liquid line , and suction line at pressures
dictated by local codes.
Caution: Do not exceed the high pressure control
setting plus 0.7 bar. Test pressures on liquid line and
on suction line must comply with local and national
codes.
Charge enough refrigerant into the system to raise the
pressure to 1 bar. Using oil-pumped dry nitrogen, build
the system pressure to 7 bar.
Check the piping and the evaporator unit for leaks with
a leak detector. Be very thorough in this test, checking
every possible point of leakage. If leaks are found
during the testing, release the test pressure, break the
connection and make a new joint. Retest to make sure
the connection is solid.
Field evacuation
For field evacuation , use a rotary-style vacuum pump.
Determine the pump size required for proper unit
evacuation.
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