Electronic Expansion Valve Pi Control - Daikin REYQ-XA Service Manual

SiUS371901E
5.4

Electronic Expansion Valve PI Control

Main electronic expansion valve EVM control
When the outdoor unit heat exchanging is performed via the condenser (Y5S or Y6S is set to OFF),
this function is used to exert PI control on the electronic expansion valve (Y1E or Y3E) so that the
condenser outlet subcooling degree (SC) will become constant.
SC = Tc – Tf
When the outdoor unit heat exchanging is performed via the evaporator (Y5S or Y6S is set to ON),
this function is used to exert PI control on the electronic expansion valve (Y1E or Y3E) so that the
evaporator outlet superheating degree (SH) will become constant.
SH = Tg – Te
Subcooling electronic expansion valve EVT control
In order to make the maximum use of the subcooling heat exchanger, this function is used to exert
PI control on the electronic expansion valve (Y2E, Y5E or Y3E) so that the evaporator-side gas
pipe superheating degree (SH) will become constant.
SH = Tsh – Tm
Functions and Control
SC: Condenser outlet subcooling degree
Tc: High pressure equivalent saturated
temperature
Tf: Liquid pipe temperature detected by heat
exchanger liquid pipe thermistor R4T,
R5T
SH: Evaporator outlet superheating degree
Tg: Suction pipe temperature detected by
heat exchanger gas pipe thermistor R8T,
R9T
Te: Low pressure equivalent saturated
temperature
SH: Evaporator outlet superheating degree
Tsh: Suction pipe temperature detected by
the subcooling heat exchanger outlet
thermistor R5T
Tm: Low or middle pressure equivalent
saturated temperature
Basic Control
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