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2.0 System Design Considerations
2.1 Air-Conditioning System Design Criteria
2.1 .1 Condensing Pressure and Evaporating Pressure
The recommended condensing pressure and evaporating pressure for R22 systems at standard conditions
are shown in the table 2-1 according to JIS standard.
Table 2-1 Recommended condensing and evaporating pressure
Pressure
Cooling
Heating
High side MPa(G)
1.8
2.0
Low side MPa(G)
0.45
0.40
It is necessary to adjust the system if the high side pressure or low side pressure has more than 0.1MPa
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
2.1.2 Sub Cooling Degree
The sufficient sub cooling degree can not only increase the cooling and heating capacity but also can keep