Draw-Through Coils; Table 10 - Draw-Through Drain Trap Dimensions (Metric); Figure 26 - Draw-Through Drain Trap - AAON RN Series Installation Operation & Maintenance

penetrate the roof external to the unit itself.
The drain line must be pitched away from the
unit at least 3.2mm (1/8 inch) per meter
(foot). On longer runs an air break must be
used to ensure proper drainage.
CAUTION
Unit must not be operated without a p-
trap. Failure to install a p-trap may
result in overflow of condensate water
into the unit.
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 must
conform to all applicable governing codes.

Draw-Through Coils

Figure 26 - Draw-Through Drain Trap

The X dimension on the draw-through trap
must 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 10 - Draw-Through Drain Trap
Dimensions (Metric)
Draw-Through
Drain Pan Pressure
Negative Static
(mmHg) (millimeters) (millimeters)
-0.93
-1.87
-2.80
-3.74
-4.67
-5.60
-6.54
-7.47
-8.41
-9.34
-10.28
-11.21
-12.14
-13.08
-14.01
-14.95
Note: 1 mm = 0.1 cm
Trap Dimensions
X X/2
38.1
19.1
50.8
25.4
63.5
31.8
76.2
38.1
88.9
44.5
101.6 50.8
114.3 57.2
127
63.5
139.7
69.9
152.4
76.2
165.1
82.6
177.8
88.9
190.5
95.3
203.2 101.6
215.9 108.0
228.6
114.3
49