Daikin EWWD VZ Series, Installation, Maintenance And Operating Manual

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Compressor alternation
The water-cooled Daikin EWWD_ VZ units alternate the compressor start sequence (EWWD VZ dual
compressor) to balance the number of starts and operating hours. Compressors are automatically alternated by
the controller.
If the unit is in automatic mode, the compressor with the lowest number of starts is started first. If both
compressors are in operation and one compressor must be turned off, the one with most hours is switched off
High pressure condensation control
The microprocessor is provided with a transducer to monitor condensation pressure. Although the main purpose
of the high pressure transducer is to maintain proper control of the condensing pressure (by controlling the
cooling towers if connected), another purpose is to send a signal to the microprocessor which stops the
compressor in case the discharge pressure is excessive. If the unit is switched off for high condensing pressure,
the microprocessor must be reset manually.
High pressure mechanical safety pressure switch
The high pressure safety switch is a single pole switch that opens when the pressure exceeds the set limit. The
opening of the mechanical safety pressure switch directly triggers the compressor inverter, stopping the IGBT
bridge supply. This condition interrupts the compressor power supply inverter output in accordance with EN
60204-1 (stop category 0), as required by the PED directive (Pressure Equipment Directive).
The pressure switch(es) is mounted on the compressor discharge cap.
If the pressure switch triggers, once evaluated and resolved the cause that made it trigger, the alarm can be
reset by pressing the blue button on the pressure switch body itself and then resetting the alarm on the
microprocessor.
The high pressure pressure switch can be triggered by:
a) Lack of water flow to the condenser
b) Incorrect control of the cooling tower fan and/or of the condenser water temperature control valve (if
present).
c) Wrong measurement of the water temperature in the case of heat pump operation.
Compressor motor protection
The compressor motors are protected against overheating by the use of thermistors inserted on each motor
winding. Thanks to these three thermistors, the controller is able to constantly monitor winding temperature and
stop the corresponding compressor in the event that the temperature exceeds the safety value.
Repeated interventions of this protection, during normal operation, may indicate a potential problem with the
compressor motor or a high suction superheat value due to low refrigerant load. The inverter also has a
protective function against overload that stops the corresponding compressor in case of over-absorption. This
alarm is manually reset.