Danfoss PSH052 Application Manual page 9

Scroll compressors PSH052 to PSH105 | Injection system
Figure 5: Upstream exaction
P
SC
Pc
Pi
Pe
ΔT IntX
P Pressure
E Enthalpy
The injection mass ow must be regulated through an EXV, the injection superheat must be above 5 K.
For single compressor, it is highly recommended to install an additional solenoid valve on the injection line to
prevent the refrigerant to come back directly into the compressor scroll set in case of power shortage.
For manifolding, it is mandatory to install an additional solenoid valve on each compressor's injection line in case
of they are interconnected. When the compressor is OFF, the related solenoid valve must shut o the branch
injection line to avoid refrigerant owing into the stand by compressor.
Sol V
Injection
flow
Sol V
Interconnected
The vapor injection must not be activated during inversion cycle of defrost mode
For compressor start-up, vapor injection valve opening must delay than compressor start-up at least 5 seconds.
Wet injection
Whenever the vapor is no longer enough to cool the scroll and the application requires more envelope then the
controller must reduce the injection SH down to zero and control the injection by reading the compressor DGT. This
part is called wet (to di erentiate from liquid). There is no gain in e ciency and capacity, only envelope.
Considering the distance between sensor and scroll set, the wet injection is activated for when discharge
temperature exceeds 121°C (250°F) at the measurement point (the surface of discharge pipe with 40mm away from
the compressor discharge port). A minimum 4K (7.2°F) subcooling is necessary to ensure correct wet
injection.Injection temperature at measurement point set point is 121°C (250°F), maximum safety value is 135°C
(275°F).
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Inj SH
(m + m )
Inj
m
Inj
m
SH
Discharge flow
Suction flow
Figure 6: Downstream exaction
CC-000546
E
Danfoss
WD-00017
AB466745380281en-000201 | 9
Danfoss
OE-000107