Daikin VRVIII-S, Service Manual

Page: 54 / 266

SiENBE34-703 Basic Control
Function 43
2.3 Electronic Expansion Valve PI Control
Main Electronic Expansion Valve EV1 Control
Carries out the electronic expansion valve (Y1E) PI control to maintain the evaporator outlet
superheated degree (SH) at constant during heating operation to make maximum use of the
outdoor unit heat exchanger (evaporator).
The optimum initial value of the evaporator outlet superheated degree is 3°C, but varies
depending on the discharge pipe superheated degree of inverter compressor.
Subcooling Electronic Expansion Valve EV3 Control
Makes PI control of the electronic expansion valve (Y3E) to keep the superheated degree
(SH)
of the outlet gas pipe on the evaporator side for the full use of the subcooling heat exchanger.
SH = Ts1 - Te SH : Evaporator outlet superheated degree (°C)
Ts1 : Suction pipe temperature detected by
thermistor R3T (°C)
Te : Low pressure equivalent saturation temperature
(°C)
SH = Tsh -Te SH : Outlet superheated degree of evaporator (
°
C)
Tsh : Suction pipe temperature detected with the
thermistor R4T (
°
C)
Te : Low pressure equivalent saturation temperature
(
°
C)