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 tempe1.5˚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 tempe1.5˚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
02̲LXE10E100以降(16-28)̲E.qx 08.8.13 4:40 PM ページ 2-20
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