Compressor Capacity Control - Daikin RXYQ-TA Series Service Manual

Basic Control
5.2

Compressor Capacity Control

Tc : High pressure equivalent saturation temperature
Te : Low pressure equivalent saturation temperature
Capacity steps
The compressor rotation speed is changed according to the control pressure.
Cooling: suction pressure sensor value is converted into evaporating saturated temperature (relation between
pressure and evaporating temperature based on characteristics of refrigerant R-410A). For detailed
explanation refer to chapter field settings (Description field settings (mode 2: m2) on outdoor unit main PCB
on page 145 and installation manual outdoor chapter "Energy saving and optimum operation").
Initial selection is made between Automatic, Fixed, or High sensible.
During operation, the outdoor target evaporating temperature can be changed based on the selected sub
function, taking indoor load into account.
Heating: discharge pressure sensor value is converted into condensing saturation temperature.
Initial selection is made between Automatic, Fixed, or High sensible.
During operation, the outdoor target condensing temperature can be changed based on the selected sub
function, taking indoor load into account.
The initial target saturated temperature can be changed. For details refer to Description field settings (mode
2: m2) on outdoor unit main PCB on page 145: for Cooling: Te set based on field setting 2-8, for heating: Tc
set based on field setting 2-9.
During operation, outdoor control will take into account the pressure drop so that at indoor units, the pre-set
target temperature is reached (average). The estimated pressure drop is calculated based on:
Pressure drop characteristics found during test-operation outdoor (step 7). At several evaporating
temperature, outdoor control stores difference between outdoor evaporating temperature and average of
indoor heat exchanger (indoor evaporating temperature).
To have judgement of gas speed in main suction pipe, control takes the capacity step of the outdoor unit
into account. In function of pressure drop characteristics at the different compressor capacity steps,
control concludes the category of system pipe lay out (long, medium, short).
Target Te outdoor (cooling) = Te set – estimated pressure drop – A.
Target Tc outdoor (heating) = Tc set + estimated pressure drop + A.
Correction factor A depends on the absolute value of the difference between indoor air inlet temperature and
a set temperature after startup period.
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SiUS341615E
Functions and Control