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12
Dedicated Outdoor
Air System (DOAS) Installation and Operation Manual
PIPING
Figure 6: Drain Trap
Condensate Drain Piping
Condensate drain trapping and piping must conform to all applicable codes. A p-trap and drain line must be installed. The p-trap cannot
exceed 6 inches from the drain connection. The lines need to be the same pipe size or larger than the drain connection, include a p-trap, and
pitch downward toward the drain. An air break should be used with long condensate line runs.
Failure to install p-traps can result in an overflow of condensate water. This can lead to product
damage or property damage. Draw-through cooling coils will have a negative static pressure in
the drain pan area. This can cause an un-trapped drain to back up due to the air being pulled up
through the condensate drain piping.
The value of pressure in the drain pipe should be at least equal to the absolute value of
the negative static pressure in the drain pan plus one inch. Follow the procedure below to
calculate the static pressure.
Calculating Static Pressure
1. Add the pressure drops of all components upstream of the drain plan. This includes the
cooling coil.
2. Add the return duct static pressure. Include the dirt allowance pressure drop for the
filters to account for the worst-case scenario.
Draw-Through
Drain Pan Pressure
Trap Dimensions
Negative Static
X
Y
(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
Table 3:DOAS Drain Trap Dimensions
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 or
draw-through units so the fan inlet pressure is a safe value to use for the drain pan static pressure.
Condensate Drain Piping
Summary of Contents for ARND20BDAR2
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