Liebert DM User Manual page 62

Suction Pressure
The compressor may stop when the suction pressure drops below the setting of the low-pressure switch. On the other
hand, too high suction pressure will undermine the cooling effect the refrigerant does to the compressor motor, leading
to the damage of the compressor. The minimum (pressure switch action point) and the maximum (allowed by the
system operation) suction pressure are listed in Table 6-1.
System
Air-cooled (stepless fan speed controller)
Water-cooled
Note:
The maximum operation LP of single system HG bypass should be lower than 700kPa
Exhaust Pressure
The exhaust pressure may change with the load or the condenser efficiency. When the exhaust pressure rises to the
setting of the pressure switch, the high pressure switch will act to stop the compressor. See Table 6-2 for details.
System design
Air-cooled
Water below 65° F ~ 75° F
Water-cooled
Water at 85° F
Suction Superheat Degree
The Thermal Expansion Valve (TXV) can regulate the suction superheat degree. Follow the procedures below to
determine the system suction superheat degree.
1. Measure the temperature of the suction pipe at the TXV thermo bulb.
2. Sample the compressor suction pressure at the needle valve of the suction pipe.
3. Evaluate the pressure difference between the two locations: thermo bulb and needle valve of the suction pipe.
4. Add the sum of the preceding two pressures with the standard local air pressure to find out the saturation
temperature corresponding to the saturation pressure.
5. The difference between the suction temperature at the thermo bulb and the saturation temperature is the suction
superheat degree.
The suction superheat degree is critical to the compressor lifespan. If the compressor runs with little or no suction
superheat degree for a long time, slugging may occur to the compressor, crashing the scroll plate of the scroll
compressor.
Expansion Valve
The auto-regulation of the expansion valve guarantees sufficient refrigerant for the evaporator in order to meet the
needs of the load. The superheat degree is an indicator of the operation state of expansion valve. If the refrigerant to
the evaporator is insufficient, the superheat degree will be high; and if the refrigerant to the evaporator is too much, the
superheat degree will be low. The proper superheat degree is 5.6℃～8.3℃.
Follow the procedures below to regulate the superheat degree setting.
1. Unscrew the bonnet at the bottom of the expansion valve.
2. Rotate the rotary switch counter clockwise to reduce the superheat degree.
3. Rotate the rotary switch clockwise to raise the superheat degree.

Note
1. Before delivery, the refrigerant of water-cooled unit has been charged, and the expansion valve has been adjusted. If you need
to adjust the expansion valve, please contact Emerson.
2. Every time you rotate the rotary switch, do not rotate it for more than one round, and it may take up to 30mins to reach a new
balance.
Table 6-1 Suction pressure
Min. pressure kPa (PSIG) R-22
Table 6-2 Exhaust pressure
KPa (PSIG)
1750 (251)
1400 (203)
1450 (210)
Liebert_DM 16kW Air Conditioner User Manual
Chapter 6 System O&M
138 (20)
138 (20)
System design
Maximum pressure
High pressure switch action
point
Max. pressure kPa (PSIG) R–22
620 (90)
620 (90)
KPa (PSIG)
2275 (330)
2760 (400)
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