The TXI2 is an injection valve for desuperheating
in 2-stage refrigeration systems operating on
R22/R407C and other similar refrigerants where
the hot gas temperature and the intermediate
pressure are the controlling variables.
Application
In principle there are two dierent ways in which
to setup 2-stage refrigeration systems as far as
temperature signal to the liquid injection valve is
concerned.
2-stage refrigeration system built up with a
combined LP/HP compressor.
In this case the discharge gas temperature on
the HP side is used as temperature signal and the
Fig. 1
Example 2
2-stage refrigeration system with 2 separate
refrigerating compressors in series. In this set up
a solution with injection valve type TXI 2 can be
used, because the discharge gas temperature on
intermediate pressure as pressure signal to the
injection valve.
In this example a TXI 2 injection valve is used, see
g. 1.
LP: Low pressure
HP: High pressure
PI: intermediate pressure
the HP side can be used as temperature signal
and the inter mediate pressure as pressure signal
to the injection valve, see g. 2.
Fig. 2
Example 3
Same setup as in example 2 with 2 separate
refrigerating compressors in series. As in this
setup there is an accessible control signal where
there is correspondence between pressure
and temperature, regulation of the strongly
superheated condition of the refrigerant can
be undertaken by a traditional thermostatic
expansion valve e.g. Danfoss type TX 2 for
R22/R407C refrigeration systems, see g. 3.
The valve function is controlled by the
intermediate pressure (PI) acting under the
diaphragm and the bulb pressure derived
from the discharge gas temperature across the
diaphragm (g. 4).
The intermediate pressure (PI), setting spring and
bulb temperature form a working range which,
expressed in a co-ordinate system, makes up a
working area, see g. 5.
Within the limits of this area, the working point
required is found (PI/t
bulb
).
The location of the working point depends
on the spring force set and in addition to that
dependent on the proportional band (the
superheat) and the valve capacity (size of orice).
Therefore, the sizing is decisive for a satisfactory
result.
DKRCC.PD.AV0.A3.02 | 520H10558 | 4
Data sheet | Injection valve type TXI 2
Sizing
To size TXI 2 the refrigerating capacity required to
remove the superheat at the intermediate stage
must be known as well as the required discharge
evaporating temperature t0 (PI) of the
intermediate stage and the pressure drop across
TXI 2, the correct orice size can be determined.
gas temperature on the discharge side.
Besides this the pressure drop ∆p across the
injection valve must be determined as the
dierence between the condensing pressure and
the pressure at the intermediate stage.
With the values for the required capacity, the
Example:
Required refrigerating capacity Q = 5 kW
Evaporating temperature
at intermediate state t0 = –25°C
Pressure drop across TXI 2 ∆p = 12 bar'
Discharge gas temperature (HP) = 110°C
TXI 2 cannot be set until the refrigerant system
is started up. Setting after start-up is carried
out when the discharge gas temperature has
been recorded and the intermediate pressure is
known or measured. By means of the diagram,
g. 5, the actual working point is found. From the
location of the working point in the diagram, g.
Perm. working pressure PS/MWP: 34 bar
Capillary tube: 1.5 m.