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Air and Water cooled inverter chillers and heat pump
EWAD TZ - EWAD TZ B - EWWD VZ
Air and Water cooled inverter chillers
and heat pump
D-EOMZC00105-17EN
Operation Manual
51/84
1 Vfd by mean of a modulating 0-10V signal generated through a PID controller. The following graph
is an example of the modulating signal behavior in case of a PID control supposed to be purely
proportional.
5.5 EXV Control
As a standard, the unit is equipped with one electronic expansion valve (EXV) per circuit, moved by a stepper
motor. The EXV controls the thermodynamic cicle (evaporator) in order to optimize evaporator efficiency and
at the same time guarantee the proper operation of the circuit.
The controller integrates a PID algorithm which manages the dynamic response of the valve in order to keep
a satisfactory quick and stable response to system parameter variations.
In Pressure control, the EXV is positioned to control the evaporator pressure and avoid that it can go above
the MOP.
When the EXV transitions to the Superheat control, the superheat target is calculated to maximize the
evaporator surface used to exchange heat with the other medium. This target is constantly updated, and
averaged over a 10 second period.
Whenever the circuit is running, the EXV position is limited between 5% or 100% position.
Any time the circuit is in the Off or starts the shutdown procedure, the EXV shall be in the closed position. In
this case additional closing steps are commanded to guarantee a proper recovery of the zero position.
Expansion valve driver is equipped with UPS module to safely close the expansion valve in case of power
failure.
5.6 Economizer Control (A/C units only)
The circuit economizer will be activated if all the following conditions apply:
Circuit in Run state
Compressor speed > Econ En Spd
Circuit Pressure Ratio > Econ Act PR
Discharge Superheat > 22°C (This condition is ignored with the EWAD TZ B)
Percent RLA < 95%
The economizer will be deactivated if one of the following conditions apply:
Circuit in Off state
Circuit Pressure Ratio < Econ Act PR
– 0.3
Discharge Superheat < 17°C (This condition is ignored with the EWAD TZ B)