C6.2.15/0815/E
17
debris. Tests have shown that a small screen with a fine mesh can easily become plugged
causing oil starvation to the compressor bearings.
The size of the accumulator depends upon the operating range of the system and the amount of
subcooling and subsequent head pressure allowed by the refrigerant control. System modelling
indicates that heat pumps that operate down to and below -18°C will require an accumulator that
can hold around 70% to 75% of the system charge.
Ideally the suction accumulator should be
connected with a slope to the suction line of the compressor, as shown in
Figure 28
. A sight
tube fitted to the accumulator makes it easier to check the liquid level inside.
Figure 26: Suction accumulators
3.10 Screens
CAUTION
Screen blocking! Compressor breakdown!
Use screens with at least
0.6 mm openings.
The use of screens finer than 30 x 30 mesh (0.6 mm openings) anywhere in the system should
be avoided with these compressors. Field experience has shown that finer mesh screens used
to protect thermal expansion valves, capillary tubes, or accumulators can become temporarily or
permanently plugged with normal system debris and block the flow of either oil or refrigerant to
the compressor. Such blockage can result in compressor failure.
3.11 Mufflers
External mufflers, normally applied to piston compressors in the past, may not be required for
Copeland Scroll compressors.
Tests on individual system should be performed to verify acceptability of sound performance. If
adequate attenuation is not achieved, use a muffler with a larger cross-sectional area to inlet
area ratio. A ratio of 20:1 to 30:1 is recommended.
A hollow shell muffler will work quite well. Locate the muffler at minimum 15 to maximum 45cm
from the compressor for the most effective operation. The farther the muffler is placed from the
compressor within these ranges, the more effective.
3.12 Reversing valves
Since Copeland Digital Scroll compressors have a very high volumetric efficiency their
displacements are lower than those of equivalent capacity reciprocating compressors. As a
result, Emerson Climate Technologies recommends that the capacity rating on reversing valves
be no more than 1.5 to 2 times the nominal capacity of the compressor in order to ensure proper
operation of the reversing valve under all operating conditions.
The reversing valve solenoid should be wired so that the valve does not reverse when the
system is shut off by the operating thermostat in the heating or cooling mode. If the valve is
allowed to reverse at system shut off, suction and discharge pressures are reversed to the
compressor. This results in a condition of system pressures equalising through the compressor
which can cause the compressor to slowly rotate until the pressures equalise. This condition
does not affect compressor durability but can cause unexpected sound after the compressor is
turned off.
ZRD42K* to ZRD81K*, ZPD34K* to ZPD91K*
ZRD94K* & ZRD125K*, ZPD103K* to ZPD182K*
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