AAON RL-240 - Manual (Page 60)

60
Figure 38 - Water Makeup Valve
Makeup water supply pressure should be
maintained between 15 and 60 psig for
proper operation of the valve. The makeup
water valve assembly should be inspected
monthly and adjusted as required. Replace
the valve seat if leakage occurs when the
valve is in the closed position.
Water Treatment System
All AAON evaporative-cooled condensers
come equipped with a water treatment
system that should 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 de-scaling 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 makeup 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.
The water meter measures the quantity of
makeup water used by the condenser.
Any water treatment program must be
compatible with stainless steel, copper,
aluminum, ABS plastic and PVC. Batch
feed processes should never be used as
concentrated chemicals can cause corrosion.
Never use hydrochloric acid (muriatic acid)
as it will corrode stainless steel.
Sequence of Operations
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.