Electronic Expansion Valve Control - Daikin VRV X RXQ6-48ANR Series Service Manual

Outline of Control (Indoor Unit)

8.10 Electronic Expansion Valve Control

Electronic expansion valves in indoor units have the functions of conducting superheating
degree control in cooling 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 (ΔT)
between set temperature and suction air temperature.
SH = Tg – Tl
where,
SH: Evaporator outlet superheating degree (°C)
Tg: Indoor unit gas pipe temperature (R3T)
Tl: Indoor unit liquid pipe temperature (R2T)
SHS (Target superheating degree)
• Normally 5°C.
• As ΔT (Remote controller set temp. – Suction air temp.) becomes larger, SHS becomes lower.
• As ΔT (Remote controller set temp. – Suction air temp.) becomes lower, SHS becomes larger.
80
SiME341909EA
Part 4 Functions and Control