Daikin EWAD620-C17C-SS Service Manual Download

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Functional Control

ESIE10-01

2–48

2.3.5

EXV Control

The EXV moves at a rate of 150 steps per second, with a total range of 3810 steps. Positioning should
be determined as described in the following sections, with adjustments made in increments of 0.1% of
the total range.

Preopen operation

The EXV control should include a preopen operation that is used only when the unit has liquid line
solenoids. The unit will be configured for use with or without liquid line solenoids via a set point.

When a circuit start is required, the EXV should be opened before the compressor starts. The preopen
position should be defined by a set point. The time allowed for this preopen operation should be at
least enough time for the EXV to open to the preopen position based on the programmed movement
rate of the EXV.

Startup operation

When the compressor starts if no liquid line solenoid valve is installed, the EXV will start to open to an
initial position that allows a safe start up. The value of LWT will determine if it is possible to enter the
normal operation. If it is higher than 20°C then a pressure control will start to keep the compressor into
the operating range. It goes in normal operation as soon as the suction superheat drops below a value
equal to the suction superheat setpoint.

Normal operation

Normal operation of the EXV can be used when the circuit has completed startup operation of the EXV
and is not in a slide transition conditions.

During normal operation, the EXV should control suction superheat to a target that can vary from 4°C
to 8.5°C.

The EXV should control the suction superheat within 0.8°C during stable operating conditions (stable
water loop, static compressor capacity, and stable condensing temperature).

The target value should be adjusted as needed to maintain discharge superheat within a range from
15°C to 25°C As the discharge superheat approaches 15°C, the suction superheat target should be
adjusted up. As the discharge superheat approaches 25°C, the suction superheat target should be
adjusted down. The control will apply a 0.5°C maximum reset every 5 minutes to the base target.

Maximum operating
pressures

The EXV control must maintain the evaporator pressure in the range defined by the maximum
operating pressure.

If the leaving water temperature is higher than 20°C at startup or if the pressure becomes higher than
3.5 bar during normal operations, then a pressostatic control will be started to keep the compressor
into the envelope.

Maximum operating pressure should be 3.5 bar.

It switches back to normal operation as soon as the suction superheat drops below 4°C suction
superheat setpoint.

Response to
compressor
capacity change

The logic will consider transition from 50% to 60% and from 60% to 50% as special conditions. When
a transition is entered the valve opening will change to adapt to the new capacity, this new calculated
position will be kept for 60 seconds. The valve opening will be increased during 50% to 60% transition
and decreased in 60% to 50% transition. Purpose of this logic is to limit liquid flood back when
changing from 50% to 60% if the capacity increases above 60% due to slides movement.

Daikin EWAD620-C17C-SS, Service Manual

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