AAON SB-018 - Manual (Page 26)

26
Condensate Drain Piping
Unit may be equipped with more than one
condensate drain pan connection. A p-trap
and drain line must be installed on at least
one section’s drain connection, with the p-
trap not to exceed 6” from the drain
connection. The lines should be the same
pipe size or larger than the drain connection,
include a p-trap, and pitch downward toward
drain. An air break should be used with long
runs of condensate lines.
Draw-through cooling coils will have a
negative static pressure in the drain pan area.
This will cause an un-trapped drain to back
up due to air being pulled up through the
condensate drain piping.
Condensate drain trapping and piping should
conform to all applicable governing codes.
Note: The drain pan connection(s) is a 1”
MPT fitting.
Figure 4 - Drain Trap
The X dimension on the draw-through trap
should be at least equal to the absolute value
of the negative static pressure in the drain
pan plus one inch. To calculate the static
pressure at the drain pan add the pressure
drops of all components upstream of the
drain pan, including the cooling coil, and
add the return duct static pressure. Include
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 5 - 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
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.
Unit should not be operated without
p-traps. Failure to install a p-trap may
result in overflow of condensate
water.
CAUTION