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The Opti-Mist
®
Adiabatic pre-cooling system is designed to
help fluid coolers, gas coolers and condensers keep their
outlet temperature or pressure under control during high
temperature waves or to increase cooling capacity when a
smaller than desired unit is installed due to limited space.
The system is controlled by the G RC-A controller
(PLC) to ensure a fully automatized operation and to run the
system only when necessary. It atomizes water at the air
inlet of the coils (of cooler or condenser) to absorb the heat
and increase its cooling capacity. The amount of atomized
water can be easily adjusted according to the unit needs.
On most systems, once the maximum ventilation capacity
of the cooler is reached, a signal is sent to the adiabatic
system, allowing it to run. If the temperature controlling
the system (either fluid or outside) reaches a certain point
and if the piping from the pump to the nozzles is empty, the
controller starts the pump, opens the valve on the pump’s
outlet, closes the drain valve, energizes the water treatment
system and after a delay (to purge the air and easily fill the
pipes), closes the air vent valve.
If the piping from the pump to the nozzles is already filled,
then only the pump and its outlet valve will resume operation.
If the outside temperature drops to a preset point (adjustable
by the user, set to 6
o
C by default), the system stops and
drains the pipes from the pump’s outlet valve to the air vent
valve, to avoid freeze damage to the pipes, nozzles and air
vent valve. The system will not restart until the temperature
reaches a preset point (adjustable by the user, set to 10
o
C
by default).
If there is no demand during a predetermined period
(adjustable by the user, set to three days by default ), the
controller drains the same pipe section to avoid bacterial
growth.
The system is also equipped with a water treatment system
which includes a water particle filter, a demineralizer (anti-
scale) and a UV light.
WATER INLET LOW PRESSURE SWITCH (LPS) OR
LOW LEVEL SWITCH (LLS)
IMPORTANT: In the event of a water shortage, the
controller stops the adiabatic system and triggers an
alarm. For this alarm to take place, a low pressure switch
(LPS) or a low level switch (LLS) must be installed. This
switch is not provided by RefPlus and must be field
installed on the inlet pipe if the system uses city water
(LPS) or on a water tank if the system uses a tank or
a receiver (LLS). When using city water, the minimum
inlet pressure must be 40 psi. The low pressure switch
should be adjusted to open below 40 psi. The Dwyer
A1PS-34
switch
is an appropriate switch model.
The system will not restart if the condition persists. Also, it
determines, by reading the pressure drop across the filter
of the water treatment system, if it needs to be replaced. It
monitors the pump outlet pressure and stops the system if
it increases to an abnormal level (with modulating pump). It
allows the user to set service alarms for the water particle
filter, demineralizer, UV light and pump oil (if modulating
pump is used).
The software can adjust the behaviour of the system using
two main configurations: Pulsing Valve or Modulating Pump.
For the sake of simplicity, they are often called PV and MP,
respectively, in this manual. Some parameters are only used
for one of these configurations. They are labeled “only for
PV” or “only for MP”, as needed.
COOLING DEMAND
The cooling demand is the percentage of the temperature
range reached by the temperature reading.
Example:
Setpoint = 28
o
C
Band = 5
o
C
Temperature range = 28
o
C to 33
o
C
Temperature reading = 31
o
C
Cooling demand = 60%
(as
demonstrated in Graph 1)
In this example, the cooling demand is 60%, since it is the
value on the Y axis that corresponds to the temperature
reading on the X axis (Graph 1).
0%
27
o
C
28
o
C 29
o
C
30
o
C
31
o
C
32
o
C 33
o
C 34
o
C
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
CD
TEMP.
Graph 1 Cooling Demand
The temperature reading used for determining the cooling
demand depends on the setting ‘’Control by’’, which can be
set to Fluid Temperature or Outside Temperature under the
System Specifications sub-menu (see page 17).
SYSTEM SELECTION: PULSING VALVE
If the
Pulsing Valve
has been set (see page 17), two
control options are available, either Ladder or Scaler.
The Scaler and Ladder methods allow the user to configure
a ratio between the pulse length and the cooling demand
(in %) as well as between the pulse length and the outside
temperature (OT).
With the Scaler method, when the cooling demand varies
ever so slightly (i.e. from 10% to 11%), the pulse length will
vary instantly.