AAON CL SERIES, Установка, эксплуатация и обслуживание

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Water Treatment System:
All AAON evaporative condensers come
equipped with a water treatment system that must
be maintained by a local water treatment
professional trained in the water treatment of
evaporative condensers. This system consists of a
controller, three chemical pumps and storage
tanks, a conductivity sensor, a motorized ball
valve for water bleed, and a water meter.
One chemical pump and tank is typically used for
a descaling chemical to prevent scale from
forming in the condenser. The other two pumps
and tanks are typically used for two different
biocides (to kill any microorganisms that could
grow in the condenser). Two biocides are used to
prevent organisms from becoming resistant to one
chemical.
The mineral content of the water must be
controlled. All make-up water has minerals in it.
As water is evaporated from the condenser, these
minerals remain.
As the mineral content of the water increases, the
conductivity of the water increases. The water
treatment controller monitors this conductivity.
As the water conductivity rises above set point,
the controller will open a motorized ball valve on
the discharge side of the condenser pump and
dumps water into the condenser drain until
conductivity is lowered. While the motorized ball
valve is opened, the controller will not disperse
chemicals.
The chemicals are dispersed by the water
treatment controller based on the scheduled input
by the water treatment professional. (See the
separate manual for the water treatment controls
for specific programming information.)
The water meter measures the quantity of make-
up water used by the condenser.
Any water treatment program must be compatible
with stainless steel, copper, aluminum, ABS
plastic and PVC. Batch feed processes must never
be used as concentrated chemicals can cause
corrosion. Never use hydrochloric acid (muriatic
acid) as it will corrode stainless steel.
Sequence of Operation:
On a call for cooling, the condenser pump is
activated. A pressure switch in the pump
discharge is bypassed for six seconds by a time
delay relay in order for the pump to establish
recirculating water flow. If flow is not proven
within the six seconds, the pressure switch opens,
breaking the safety circuit, thereby shutting down
the entire system. This pressure switch is set to
close at 3 psi and open at 1 psi.
A Johnson Controls S350C measures the water
temperature in the pump discharge line. If the
sump water temperature exceeds 105°F, the
cooling system will be shut down thereby
preventing damage to the evaporative condenser.
If a fault occurs in the evaporative condenser fan
motor VFD, normally closed fault terminals on
the VFD will interrupt the safety circuit, thereby
shutting down the system.
If the VFD does fault and cannot be reset, there is
a VFD bypass switch mounted near the VFD.
This switch has four positions—line, off, drive,
and test. The “line” position will bypass the VFD,
sending power to the motor. In this position, the
condenser fans will run at full speed. The “off”
position will not allow power to pass through the
switch. This functions as a disconnect switch.
The “drive” position runs power through the VFD.
This is the normal operation for the switch. The
“test” position routes power to the VFD but not to
the motor. This is useful for running tests on the
VFD without sending power to the motor.
A Johnson Controls A350P controls the VFD
speed. This device sends a 0-10 VDC signal to
the VFD. This controller is set to maintain a sump
temperature of 70°F. On a rise in sump
temperature, the controller increases the voltage to
the VFD, increasing the speed of the condenser
fans. Conversely, on a drop in sump temperature,
the controller will decrease the voltage to the
VFD, decreasing the speed of the condenser fans.
An outside air thermostat does not allow the
condenser to operate when the ambient
temperature is below 35°F.