Daikin VRV RXYQ72-384XAYCA, Service Manual

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SiUS342004EB Outline of Control (Indoor Unit)
Part 4 Functions and Control 118
9.6 Control of Electronic Expansion Valve
Electronic expansion valves in indoor units have the functions of conducting superheating 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 outdoor unit, the units will give a priority to the control command.

Superheating degree control in cooling operation
This function is used to adjust the opening of the electronic expansion valve so that superheating
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 superheating degree (SHS).
At that time, correction to the superheating degree is made according to the differences (

T)
between set temperature and suction air temperature.

Normally 5°C (9°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.

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 outdoor 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 (

T) between
set temperature and suction air temperatures.

Normally 5°C (9°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 smaller, SCS becomes
higher.
SH = Tg – Tl
Where,
SH: Evaporator outlet superheating degree
Tg: Indoor unit gas pipe temperature (R3T)
Tl: Indoor unit liquid pipe temperature (R2T)
SHS: Target superheating degree
SHS (Target SH value)
SC = Tc – Tl
Where,
SC: Condenser outlet subcooling degree
Tc: High pressure equivalent saturated temperature detected by the high pressure sensor (S1NPH)
Tl: Indoor unit liquid pipe temperature (R2T)
SCS: Target subcooling degree
SCS (Target SC value)