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2.0 Refrigerating Circuit Design Considerations
2.1 Condensing Pressure and Evaporating Pressure
The recommended condensing pressure and evaporating pressure for R407C systems at standard conditions
are shown in the table 2-1:
Table 2-1 Recommended condensing and evaporating pressure
Pressure
Cooling
High side MPa(G)
1.85~1.90
Low side MPa(G)
0.45~0.5
It is necessary to adjust the system if the high side pressure or low side pressure has relatively large
deviation
from the recommended pressure. Some reasons are listed in Table 2-2 for pressure deviation.
Table 2-2 Reasons of pressure deviation
Item
Low Side Pressure
Lower
Middle
Higher
High Side
Pressure
Higher
<a>
--
<c>
Same
--
OK
--
Lower
<d>
--
<b>
Note: Higher: The tested pressure is higher than recommended pressure.
Lower: The tested pressure is lower than recommended pressure.
Same:The tested pressure is approximately same as recommended pressure.
<a> Too big of compressor size
<b> Too small of compressor size
<c> Too high of dry bulb temperature in the condenser side
Excessive refrigerant has charged in the system
Uneven refrigerant distribution in the circuits of condenser
Too low rotation speed of condenser fan
<d> Too low wet bulb temperature in the evaporator side
Uneven refrigerant distribution in the circuits of evaporator
Too low rotation speed of evaporator fan
Lack of refrigerant charge in the system
Too big superheating degree caused by improper size expansive valve or capillary
2.2 Suction Temperature
The suction temperature shall be higher than evaporator outlet temperature. (If there is a specific description
in the compressor specification regarding to superheat, follow the contents.)
In order to prevent compressor from flooded back operation, a minimum suction superheating degree of 5K
[10F] should always be maintained.
