OM WGS-5
WGS 130A to 190A
61
Manual Slide Control Mode
The slide position on each circuit can be controlled manually. A setting on the compressor
setpoints screen in each circuit controller allows the operator to select manual slide control.
On the same screen, a slide target can be selected, from 0% to 100%.
Anytime a circuit is in manual slide control, it is considered to be at full load in the staging
logic. It also will not be considered in load balancing calculations. None of the capacity
limits outlined above will apply in manual slide control, but all stop alarms are still
applicable.
Slide control will revert back to automatic control if a stop alarm occurs on the circuit or
unit, or the slide control has been manual for four hours.
Slide Pulse
The slide pulse output moves the compressor slide in order to reach the capacity requested
by the slide position target. The output will pulse for 200 ms every 6 seconds while the
Slide Pulse flag is true, that is, whenever there is a difference between the actual slide
position and the requested position.
Expansion Valve Control
The EXV can be in one of four control states. Each state is described below.
Preopen
At the time of a start request, the EXV will perform a pre-open function. This mode applies
to both remote air cooled and packaged water cooled condenser operation and helps prime
the evaporator prior to starting as well as getting the EXV in a better starting position. For
remote air-cooled condenser operation, this function is disabled should the condenser
pressure be less than the evaporator pressure at start. For remote air-cooled condenser
operation, the liquid line solenoid shall remain closed until the compressor starts. During
pre-open, the EXV signal is held at 3000 steps.
For remote condenser configuration units that come equipped with a factory mounted liquid
line solenoid, a post-open logic has been added to prevent hydraulic lock between the liquid
line solenoid and the electronic expansion valve. After the compressor performs a pump
down and cycles off, the electronic expansion valve will re-open for 30 seconds and then
return to its closed position.
Pressure Control
In pressure control, the evaporator pressure is controlled by the EXV position. The
pressure target varies based on evaporator LWT and discharge superheat values. PID logic
will be used to control the pressure to the target value.
The base pressure target is calculated using the following formula:
Base target = 0.6(LWT) – 2
The base target is limited to a range from low pressure inhibit set point + 2 psi, to 52 psi.
The pressure control target may be adjusted if the discharge superheat is not within an
acceptable range. If the superheat is less than 22oF, the base pressure target will be
reduced by a value equal to the low superheat error. If the superheat is more than 40
F, the
base pressure target will be increased by a value equal to the high superheat error. At any
time, the adjusted target pressure cannot go below the low pressure inhibit set point or
above 52 psi.
When the EXV transitions to the pressure control state, the target will start at the current
evaporator pressure value. The pressure target will then decrement 0.2 psi every second
until reaching the normal calculated target. If the pressure at transition is less than the
calculated target, then pressure control will start immediately with the calculated target.
Содержание WGS130AA: WGS140AW
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