2-20
(1) Set point temperature and control sensor
If the set point temperature is
–
9.9
˚
C (
–
14.1
˚
F) or more, the suction modulating valve is controlled by the
supply air temperature to adjust the freezing capacity.
(2) Control
(a) Pull-down operation
Pull-down operation is carried out with fully opened suction modulating valve when the control
temperature (SS) is higher than the set point temperature for 1.5˚C or more (point q).
(b) Capacity control operation
When the control temperature (SS) reaches the point w (set point temperature +1.5˚C), the
suction modulation valve is activated to conduct the capacity control operation.
The control temperature (SS) converges to the set point temperature (point e) while repeats
temperature increasing and decreasing.
During capacity control, hot gas by-pass (HSV, DSV, BSV) and liquid injection (ISV) are conducted in
order to maintain the optimum operation condition of refrigerant system.
(c) Heat-up operation
When the control temperature (SS) is lower than the set point temperature for 1.5˚C or more (point r), heat-
up operation using hot gas is conducted in order to raise the equivalent return air temperature (RS) (point r)
to the set point temperature +1.5˚C or more (point t ). Then
the equivalent control temperature (SS) (point t) is controlled
to reach to the point w.
(d) Overcool protection operation
Although the unit's operation is in a stable state, if the
control temperature lowers below set point temp –3˚C
(point y), the compressor stops and only the evaporator
fan continues to operate.
'
'
–3˚C
–2˚C
–1˚C
+1˚C
+2˚C
SP
1
6
2
5'
5
4
4
3
02LXE10E100以降(16-28)E.qx08.8.134:40PMページ2-20
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