C6.2.27/0716-0219/E
11
Special care has to be given to the design of the heat exchanger and of the thermostatic expansion
valve (TXV) to allow for part-load operation. Good refrigerant distribution is required in the common
heat exchanger as well as sufficient velocities for oil return, even at part load.
In the case of a large range of capacity modulation (more than 2 compressors in parallel), the use
of an electronic expansion valve (EXV) or two different TXV
’s controlled by individual solenoid
valves, may be necessary. It is important to ensure that the solenoid valves, vapour injection lines
and header(s) are adequately sized in order to keep pressure drop to a minimum. At the same
time, the layout should be such that excessive amounts of oil do not accumulate in the header.
NOTE: For further information about vapour injection please refer to Technical Information
C7.19.1 "Vapour Injection Scroll Compressors for Refrigeration".
4.3
ZF*K5E compressors with wet vapour injection
When using scroll compressors in low temperature applications with R407A, R407F, R448A or
R449A and an extended envelope (see Chapter 2.4.3 "Application limits"), additional liquid
injection with a DTC valve is required in conjunction with the vapour injection to protect the scroll
from higher discharge temperatures. A dedicated discharge gas thermostat must be installed on
the discharge line.
The full range of ZF*K5E compressors can be used with R407A, R407F, R448A, R449A and
vapour inj liquid injection.
The wet injection cycle showing the main components is shown in
Figure 8
.
Figure 8: liquid injection for low temp applications
NOTE: For further information about wet vapour injection please refer to Technical
Information C7.19.2 "Refrigeration Scroll Compressors using R407A, R407F, R448A or
R449A in Low Temperature Applications".
