Operating Manual
D-EOMCP00104-14_01EN
EWYD_BZ
25/35
up dead band (high condensing temperature error). In particular the stage up is executed when the integral of the
high condensing temperature error reaches the value 50 °C x sec (90 F x sec). At the same manner a stage down
is executed (the previous stage is activated) if the evaporating saturated temperature exceeds the target setpoint
by an amount equal to a stage down dead band by a time depending by the difference between th e reached the
target setpoint minus the stage down dead band values and the reached value (low condensing temperature error).
In particular the stage down is executed when the integral of the low condensing temperature error reaches the
value 14 °C x sec (25.2 Fxsec). The condensing temperature error integral is reset to zero when condensing
temperature is within the deadband or a new stage is activated. Each fan stage will have its own adjustable stage
up (default 3 °C (5.4F)) and stage down (default 3 °C (5.4 F) ) deadband.
5.23.1.2.2 Control of pressure ratio
The control will operate to keep pressure ratio equal to a target adjustable value (default 3.5). A stage up is
executed (the next stage is activated) if the pressure ratio exceeds the target pressure ratio b y an amount equal to
an adjustable stage up dead band by a time depending by the difference between the reached values and the target
value plus stage up dead band (high pressure ratio error). In particular the stage up is executed when the integral
of the pressure ratio error reaches the value 25 sec. At the same manner a stage down is executed (the previous
stage is activated) if the pressure ratio falls below the target setpoint by an amount equal to a stage down dead
band depending by the difference between the target setpoint minus the stage down dead band values and the
reached value (low pressure ratio error). In particular the stage down is executed when the integral of the low
pressure ratio error reaches the value 10 sec. The pressure ratio error integral is reset to zero when condensing
temperature is within the deadband or a new stage is activated. Each fan stage will have its own adjustable stage
up (default 0.2) and stage down (default 0.2) deadband.
5.23.1.2.3 Control of temperature difference
The control will operate to keep difference between the condensing temperature (saturated temperature at
discharge pressure) and evaporating temperature (saturated temperature at suction pressure) equal to an
adjustable target value (default 50°C (90 F)). A stage up is executed (the next stage is activated) if the pressure
difference exceeds the target pressure difference by an amount equal to an adjustable stage up dead band by a
time depending by the difference between the reached values and the target value plus a stage up dead band (high
pressure difference error). In particular the stage up is executed when the integral of the pressure difference error
reaches the value 50 °C x sec (90 Fxsec). At the same manner a stage down is executed (the previous stage is
activated) if the pressure difference falls below the target setpoint by an amount equal to a stage down dead band
depending by the difference between the target setpoint minus the stage down dead band values and the reached
value (low pressure difference error). In particular the stage down is executed when the integral of the low pressure
ratio error reaches the value 14 °C x sec (25.2 Fxsec). The pressure ratio error integral is reset to zero when
condensing temperature is within the deadband.
5.23.2
Variable Speed Driver
A continuous control is used; fans speed is modulated to keep saturated condensation pressure at a setpoint; a PID control
is used to allow a stable operation.A Fan Silent Mode function (FSM) is implemented on unit with Variable Speed Driver
(VSD) to keep fan speed below a set value during some periods.
5.23.2.1 VSD in cooling, cooling glycol or ice mode
When the system is operating in cooling mode, either if it is controlling the condensation pressure, the pressure ratio or
the pressure difference, the PID proportional gain is positive (the higher the input the higher the output).
Controlled
Variable
Action
Set Point
Dead Band
Regulation Band
Max
0
-Max
Fig. 15
– Proportional action of VSD PID in cooling/iced mode
