Control Of Electronic Expansion Valve - Daikin RTSQ20PY1 Service Manual

Outline of Control (Indoor Unit)
9.7

Control of Electronic Expansion Valve

Electronic expansion valves in indoor units have the functions of conducting superheated
degree control in cooling operation and subcooled degree control in heating operation.
However, if the indoor units receive any control command such as a protection control
command or a special control command from the outdoor unit, the units will give a priority to the
control command.
• Superheated degree control in cooling operation
This function is used to adjust the opening of the electronic expansion valve so that
superheated degree (SH), which is calculated from the detection temperature (Tg) of the gas
pipe thermistor (R3T) and the detection temperature (T1) of the liquid temperature thermistor
(R2T) of the indoor unit, will come close to a target superheated degree (SHS).
At that time, correction to the superheated degree is made according to the differences (
between set temperature and suction air thermistor temperature.
• Sub cooled degree control in heating operation
This function is used to adjust the opening of the electronic expansion valve so that the high-
pressure equivalent saturated temperature (Tc), which is converted from the detected pressure
of the high pressure sensor in the outdoor unit, and the subcooled degree (SC), which is
calculated from the detected temperature (T1) of the liquid temperature thermistor (R2T) in the
indoor unit, will come close to the target subcooled degree (SCS).
At that time, corrections to the subcooled degree are made according to differences (
between set temperature and suction air thermistor temperatures.
127
SH = Tg - T1
SHS (Target SH value)
• Normally 5°C.
∆
• As T (Remote controller set temp. - Suction air temp.) becomes larger, SHS becomes
lower.
∆
• As T (Remote controller set temp. - Suction air temp.) becomes smaller, SHS
becomes higher.
SC = Tc - T1
SCS (Target SC value)
• Normally 5°C.
∆
• As T (Remote controller set temp. - Suction air temp.) becomes larger, SCS becomes
lower.
∆
• As T (Remote controller set temp. - Suction air temp.) becomes lower, SCS becomes
larger.
SH:Evaporator outlet superheated degree (°C)
Tg:Indoor unit gas pipe temperature (R3T)
T1:Indoor unit liquid pipe temperature (R2T)
SHS:Target superheated degree
SC:Condenser outlet subcooled degree (°C)
Tc:High pressure equivalent saturated temperature
detected by the high pressure sensor (S1NPH)
T1:Indoor unit liquid pipe temperature (R2T)
SCS:Target subcooling degree
SiBE31-801_C
∆
T)
∆
T)
Function