14
Air Handling Unit
Installation, Operation, and Maintenance Manual
April 2021
Figure 7-4. Positive Internal Static Pressure in Coil Section-
Fan On (Blow-Through Application)
H = Fan outlet pressure
(in. W.C.) + 1/2 in.
(minimum)
Sea level
with fan on
Fan outlet pressure
Recommendation:
1/2-in. minimum
Condensate drain pan
Trap for blow-thru unit, fan running and
condensate beginning to drain away.
H = Positive Internal Static Pressure in Drain Pan
Section (in W.G.)+.5”
Example:
Pos SP in Drain Pan Section=3.6 in/w.g.
H = 3.6+.5” = 4.1”
Total Trap Dimension=4.1+.5”=4.6”
8.0 Filters
Air filters are usually shipped loose, in boxes, inside
the air handling unit. Although they may be shipped,
in bulk, directly to the job site. It is essential air filters
be installed before putting the unit into operation, thus
making sure coils and ductwork are protected and kept
clean.
8.1 Slide Type Filter Rack
This filter rack uses horizontal channels into which the
filters slide. Filters are loaded in the frame through a
removable end or on the side where a portion of the
channel has been removed. Frequently, spacers are used
to make up the difference between the length of the
rack, which is governed by the cabinet width, and the
length of the standard sized filters.
8.2 Universal Holding Frames
The universal holding frame (Figure 8-1) surrounds each
filter and can accommodate a variety of filters from the
standard 2” filter, to a 2” filter plus a 12” high-efficiency
filter. The universal holding frame’s versatility allows the
use of many combinations of different filter types.
Filter clips are supplied with the frames to hold the filter
in place and are sized for the selected filter combination.
If a unit has multiple filter banks, associate the clips
with the correct bank before installing. Clips are shipped
loose and are to be attached to the frames as shown in
Figure 8-2.
Figure 8-1.
Figure 8-2.
