SiUS12-928_B Control Specification
Function and Control 56
Indoor Frequency Command (D signal)
The difference between a room thermistor temperature and the target temperature is taken as the
“D signal” and is used for frequency command.
Values depend on the type of indoor unit.
Th OFF = Thermostat OFF
Indoor Unit Capacity (S value)
The capacity of the indoor unit is a “S” value and is used for frequency command.
Frequency Initial Setting
<Outline>
When starting the compressor, or when conditions are varied due to the change of the operating
room, the frequency must be initialized according to the total of a maximum D value of each room
and a total value of Q (Q) of the operating room (the room in which the thermos is set to ON).
Q value: Indoor unit output determined from indoor unit volume, airflow rate and other factors.
PI Control (Determine Frequency Up / Down by D Signal)
1. P control
A total of the D value is calculated in each sampling time (20 seconds), and the frequency is
adjusted according to its difference from the frequency previously calculated.
2. I control
If the operating frequency is not change more than a certain fixed time, the frequency is
adjusted according to the D value.
When the D value is low, the frequency is lowered.
When the D value is high, the frequency is increased.
3. Limit of frequency increasing range
When the difference between input current and input current dropping value is less than 1.5 A,
the frequency increasing range must be limited.
4. Frequency management when other controls are functioning
When each frequency is dropping;
Frequency management is carried out only when the frequency drops.
For limiting lower limit
Frequency management is carried out only when the frequency rises.
5. Upper and lower limit of frequency by PI control
The frequency upper and lower limits are set according to the total of S values. When the indoor
unit quiet operation commands come from more than one room or when the outdoor unit quiet
operation commands come from all the rooms, the upper limit frequency is lower than the usual
setting.
Temperature
difference
D
signal
Temperature
difference
D
signal
Temperature
difference
D
signal
Temperature
difference
D
signal
–3.6°F (–2.0°C) Th
OFF
0°F (0°C) 4 3.6°F (2.0°C) 8 7.2°F (4.0°C) C
–2.7°F (–1.5°C) 1 0.9°F (0.5°C) 5 4.5°F (2.5°C) 9 8.1°F (4.5°C) D
–1.8°F (–1.0°C) 2 1.8°F (1.0°C) 6 5.4°F (3.0°C) A 9°F (5.0°C) E
–0.9°F (–0.5°C) 3 2.7°F (1.5°C) 7 6.3°F (3.5°C) B 9.9°F (5.5°C) F
Ex: Capacity S value Capacity S value
9 kBtu/h 25 18 kBtu/h 50
12 kBtu/h 35 24 kBtu/h 60
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