AAON SA-070 - Manual (Page 37)

37
the dirt allowance pressure drop for the
filters to account for the worst-case scenario.
The height from top of the bottom bend of
the trap to the bottom of the leaving pipe
must be at least equal to one half of the X
dimension. This ensures that enough water
is stored in the trap to prevent losing the
drain seal during unit startup
Note: The absolute value of the fan inlet
pressure will always be greater than or equal
to the absolute value of the static pressure in
the drain pan on draw-through units, so the
fan inlet pressure is a safe value to use for
the drain pan static pressure.
Table 7 - Drain Trap Dimensions
Draw-Through
Drain Pan Pressure Trap Dimensions
Negative Static X X/2
(inches of water) (inch) (inch)
-0.50 1.50 0.75
-1.00 2.00 1.00
-1.50 2.50 1.25
-2.00 3.00 1.50
-2.50 3.50 1.75
-3.00 4.00 2.00
-3.50 4.50 2.25
-4.00 5.00 2.50
Waterside Economizer
Cooling
and pre-cooling waterside
economizer coil is factory installed upstream
of the evaporator coil. Factory tested and
field installed water piping kit includes fully
modulating waterside economizer valve and
fully modulating waterside economizer
bypass valve.
The waterside economizer circuit can
operate
in three modes: waterside
economizer only, waterside economizer with
mechanical cooling, and mechanical cooling
only.
During waterside economizer only mode of
operation condenser water flows through the
waterside economizer coil with modulating
valves maintaining supply air temperature
setpoint. The condenser water then passes
through water-cooled condenser.
During
waterside economizer with
mechanical cooling mode of operation
condenser water flows through the waterside
economizer
coil with the waterside
economizer modulating valve fully open.
The condenser water then passes through
water-cooled condenser.
During mechanical cooling only mode of
operation condenser water flows around the
waterside
economizer coil with the
waterside economizer bypass valve fully
open. The condenser water then passes
through water-cooled condenser.
Waterside economizer coil condensate drain
outlet drains into evaporator coil drain pan.
See the previous section on evaporator coil
condensate drain piping.
Mineral content of the condenser water must
be controlled. All make-up water has
minerals in it and as the water is evaporated
in the cooling tower, these minerals remain.
As the mineral content of the water
increases, the conductivity of the water
increases.
Field provided and installed 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) or chlorine as it will corrode
stainless steel.