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f ans or pumps cycling at low load and more. To evaluate the risk of liquid f loodbac k, p lease
ref er to the oil dilution chart in
be checked.
The bottom shell temperature together with the evaporating temperature gives an indication
whether liquid refrigerant is returning or diluted in the compressor oil sump. The compressor s ump
temperature must remain in the (green) safe area, as shown in the oil dilution ch art in Fi gure 16
below. In case of operation in the (red) unsafe area, adjustments are required in order to modify the
system design, refrigerant charge or superheat setting of the expansion device(s). The bottom shell
temperature should be measured accurately. The thermo-probe must be positioned on the opposite
side of the sight glass or at an angle of 90° clockwise from the suction inlet with view on the top.
Figure 16: Oil dilution chart (tb = bottom shell temperature; te = evaporating temperature) and oil temperature
3.13 Suction line accumulator
Due to Copeland scroll's inherent ability to handle liquid refrigerant, for example in f looded st art
and def rost cycle operation, an accumulator is not required in most systems.
To determine if a suction line accumulator is required, the system designer must check this with an
appropriate test scenario. See section 3.11 "Compressor oil return, oil balancing and
floodback tests".
If an accumulator is used, the oil-return orifice should be from 1 to 1.4 mm in diameter for all ZH(I)*
models depending on compressor size and compressor floodback results. To prot ect t his small
orif ice from plugging with system debris a large-area protective screen no finer than 30 x 30 mes h
(0.6 mm openings) is required. Tests have shown that a small screen with a fine mesh c an easily
become plugged causing oil starvation to the compressor bearings. The size o f t he accumulat or
depends upon the operating range of the system and the amount of sub-cooling and s ubsequent
head pressure allowed by the refrigerant control. For the correct selection and size of t he suct ion
line accumulator, ref er to the manufacturer's specifications.
16
Figure
16. Liquid level and superheat at compressor inlet have to
AGL_HP_ST_ZHK1P_EN_Rev00
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