P
Pc
(m + m
Inj
)
Inj SH
SH
ΔT IntX
SC
m
Inj
m
Pi
Pe
E
CC-000546
P
E
Pressure
Enthalpy
EXV
E
CC-000547
C
Sol v
EXV
Control
(Injec SH)
IE
C
E
IE
Condenser
Evaporator
Intermediate Exchanger
Suct SH:
Superheat at compressor suction.
Inj SH:
Superheat of injected gas (at intermediate pressure).
SC:
Subcooling at intermediate exchanger inlet.
For system with vapor injection we should also consider, in addition of the suction superheat and the condenser
subcooling, the injection superheat and Intermediate exchanger DeltaT as key
influent
parameters on the
compressor performance.
The injection
massflow
must be regulated through an EXV piloted by the injection superheat which must be above
5 K.
It is 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.
The vapor injection must not be activated during defrost course.
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
differentiate
from liquid). There is no gain in
efficiency
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 set point is 130°C (266°F), maximum safety value is 135°C (275°F).
Scroll compressors, VCH115 | Introduction
© Danfoss | Climate Solutions | 2023.08
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