AAON M3-094 - Manual (Page 50)

50
The following components should be added:
RA Opening 0.28”
12” Cartridge Filter 0.35”
Pleated Cartridge Filter 0.30”
Cooling Coil 0.45”
Preheat Coil 0.09”
Dirt Allowance
0.35”
These values should be added to the
absolute value of 1.5” to get a total of 3.32”
static pressure. Note that the heating coil
which is downstream of the drain pan and
the discharge opening static pressures are
not used in the calculation.
In this case the ‘X’ dimension of the draw-
through p-trap should be at least 4.32”,
which is the absolute value of the calculated
static pressure in the drain pan plus one
inch. The lower part of the p-trap should be
half that value, or 2.16”.
The total height of the p-trap would be 6.48”
measured from the bottom of the drain pan
connection to the top of the bottom bend, so
one diameter of the pipe needs to be added
to find the required clearance for the drain.
If the outside diameter of the pipe is 1.5” the
total clearance required would be 7.98”. If
the unit has a 6” base rail, accommodations
must be made for an additional 2” of drain
pipe to extend below the base rail.
Blow-Through Coils
Figure 26 - Blow-Through Drain Trap
The Y dimension of blow-through traps
should be at least equal to the value of the
positive pressure in the drain pan plus one
inch. This ensures that there will be enough
water stored in the trap to counter the static
pressure in the drain pan. To find the
pressure subtract any pressure drops
between the drain pan and the supply blower
from the blower discharge pressure. The
worst-case scenario for blow-thru coils is the
minimum pressure drop, so do not include
dirt allowance pressure drops for filters.
The bottom of the leaving pipe should be at
least one half inch lower than the bottom of
the drain pan connection. This ensures
proper drainage when the unit is not
running.
Note: It may be necessary to fill the trap
manually, or the trap can be filled
automatically by operating the unit until
enough condensate collects to fill the trap.
The trap will then be filled when the unit is
turned off.