Control Of Electronic Expansion Valve - Daikin VRV-WIII RWEYQ72PTJU Service Manual

SiUS30-1301
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 subcooling 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 condensing 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 (Tl) 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 temperature.
• Subcooling 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 condensing unit, and the subcooling degree (SC), which is
calculated from the detected temperature (Tl) of the liquid temperature thermistor (R2T) in the
indoor unit, will come close to the target subcooling degree (SCS).
At that time, corrections to the subcooling degree are made according to differences (
set temperature and suction air temperatures.
Function and Control
SH = Tg - Tl
SHS (Target SH value)
• Normally 41°F.

• 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 - Tl
SCS (Target SC value)
• Normally 41°F.

• 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 (°F)
Tg: Indoor unit gas pipe temperature (R3T)
Tl: Indoor unit liquid pipe temperature (R2T)
SHS: Target superheated degree
SC: condensing outlet subcooling degree (°F)
Tc: High pressure equivalent saturated temperature
detected by the high pressure sensor (S1NPH)
Tl: Indoor unit liquid pipe temperature (R2T)
SCS: Target subcooling degree
Outline of Control (Indoor Unit)

T)

T) between
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