2-18
(1) Set point temperature and control sensor
™
Chilled operation
When the set point temperature is –5.0˚C (–41˚F) or higher, the suction modulating valve (SMV) is
controlled sensing the supply air temperature in order to adjust the cooling capacity.
(2) Control
(a) Pull-down operation
Pull-down operation is carried out with fully opened suction modulating valve when the control
temperature is higher than the set point temperature for 1.5˚C or more (point
q
).
(b) Capacity control operation
When the control temperature reaches the point
w
, the in-range lamp is turned on. At the same
time, the suction modulating valve is activated to conduct the capacity control operation.
The control temperature 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 is lower than [set point
tempe1.5˚C] (point
r
), the heat-up operation
using hot gas is conducted in order to raise the return air
temperature to the [set tempe1.5˚C] (point
t
).
(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
2
6
5
3
4
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