Daikin RZQ100B8V3B Service Manual page 144

Outdoor Unit Functional Concept
3.4.2 General Expansion Valve Control
1
Outline
2
Details
3
4
Control
5
Calculations RZQ71
Calculations
RZQ100~140
2–60
After the start up control function has been terminated the general expansion valve control function will
regulate the expansion valve opening in function of the target suction SH value.
The discharge SH value will be used to set the target SH value.
The measured suction SH value will be used to control the opening of the expansion to the target SH
value.
When the unit is in cooling or heating operation the opening of the expansion valve will be controlled
in order to keep the amount of superheat at the evaporator outlet constant. This way the evaporator
can be used at maximum efficiency under all conditions. The initial target heat exchanger outlet
superheat value = 5°C.
The target heat exchanger outlet superheat value can be increased in case the discharge superheat
value decreases.
The target heat exchanger outlet superheat value can be decreased in case the discharge superheat
value increases.
During normal control 2 situations can decide on the expansion valve opening degree:
1 Target superheat amount:
When the target heat exchanger outlet superheat > actual heat exchanger
outlet superheat --> the expansion valve will close.
When the target heat exchanger outlet superheat < actual heat exchanger
outlet superheat --> the expansion valve will open.
The superheat amount is checked every 10 seconds.
2 Frequency change: At the time of compressor frequency change, the expansion valve opening will
be changed with a fixed value. This value will be in function of the amount of compressor frequency
change.
The heat exchanger outlet superheat value is calculated from the saturated suction temperature
Te(using LP sensor) and the suction pipe temperature R4T : SH = R4T-Te
The discharge superheat value is calculated from the saturated discharge temperature Td (HP value
calculated out of PI, frequency and LP) and the discharge pipe temperature R3T : SH = R3T-Td
The heat exchanger outlet superheat value is calculated from the saturated suction temperature
Te(using indoor coil sensor in cooling, outdoor coil sensor in heating) and the suction pipe temperature
R4T : SH = R4T-Te
The discharge superheat value is calculated from the saturated discharge temperature Td (HP value
calculated out of PI, frequency and Te) or Tc and the discharge pipe temperature R3T : SH = R3T-Td
or R3T or SH = R3T-Tc (whichever is the lowest)
ESIE05-03
Part 2 – Functional Description