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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 20 - 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
38
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 - 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
Note: 1 mm = 0.1 cm
Table 8 - Draw-Through Drain Trap
Dimensions (Imperial)
Draw-Through
Drain Pan Pressure
Negative Static
(inches of water)
-0.50
-1.00
-1.50
-2.00
-2.50
-3.00
-3.50
-4.00
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
Trap Dimensions
X
X/2
(inch)
(inch)
1.50
0.75
2.00
1.00
2.50
1.25
3.00
1.50
3.50
1.75
4.00
2.00
4.50
2.25
5.00
2.50
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