27
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 3 - 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
Heating Coils
One or two row hot water and steam heating
and preheating coils can be factory installed.
These coils are supplied from a building hot
water source. All valve controls for heating
coil operation are field supplied and field
installed. Hot water and steam coil
connections are spun copper tube.
Connect the steam heating supply to the top
of the coil and the return to the bottom.
Figure 14 - Steam Distributing Piping
Table 4 - Steam Distributing Coil Sweat
Connection Sizes
Model (V3-)
Supply and Return
Connection Size (OD)
A-E
2 1/8"
Air handling units with steam heating coils
MUST BE
installed high enough to allow for
a minimum of 1 foot condensate drop leg off
of the steam coil, or as recommended by the
steam trap manufacturer. Lines should be
insulated with approved insulation and be
properly fastened, sloped, and supported
according to local code requirements.
Table 5 - Hot Water Coil Sweat Connection
Sizes
Model (V3-)
Supply and Return
Connection Size (OD)
A
7/8"
B
1 1/8"
C
1 3/8"
D & E
1 5/8"
Steam in
Steam out
