4
UNIT NO. 1
UNIT NO. 2
FAN COIL UNIT
FAN COIL UNIT
NO MORE THAN
60% OF CAPACITY
ON ONE SIDE
30% MAX. OF CAPACITY
MINIMUM 18"
MINIMUM 18"
Plenum Duct
The plenum duct can be run in practically any location
accessible for the attachment of the supply tubing (see
suggested layouts in Figure 1.2). The plenum is normally
located in the attic or basement, and it is usually more
economical to run the plenum where it will appreciably
shorten the lengths of two or more supply runs.
In some two-story split level homes, it may be advanta-
geous to go from one level to another with the plenum
duct. Whenever necessary, either between floors or
along the ceiling, the small size of the plenum makes it
easy to box in.
The fan coil unit is designed to operate with a total exter-
nal static pressure of 1.5 inches of water column (mini-
mum 1.2 - maximum 1.5). Excessive static pressure is
an indication of too few outlets and may cause the coil to
freeze and some or all outlets to be noisy.
For systems with a bullhead tee installed as on Unit No.
1 (Figure 1.3), the best results are obtained if not more
than 60% of the total number of system outlets are
attached to any one branch of the tee. For systems with
a branch tee installed as on Unit No. 2 (Figure1.3), not
more than 30% of the total number of system outlets
should be attached to the perpendicular branch of the tee.
The larger system capacities (WCSP-3642/4860) are
affected more by higher system static pressure than
the smaller systems. The four and five ton systems are
ideally designed as indicated by the diagram in the lower
left corner of figure 1.2. If this layout cannot be followed,
it is important to create some pressure drop in the
plenum run using elbows and tees. Installation of the
plenum tee closer than the minimum indicated in Fig. 1.3
will reduce performance of the system. No supply runs
should be installed between unit outlet and this tee.
Static readings on system should be taken before tee.
Supply Tubing
In the case of two-story or split-level applications, supply
tubing may run from one story to another. It is small
enough to go in stud spaces, but this is often difficult
in older homes because of hidden obstructions in stud
spaces. It is more common to run the supply tubing
from the attic down through second story closets to
the first story terminators.
Supply tubing runs in the corners of the second story
rooms can be boxed in and are hardly noticeable since
overall diameter is only 3-1⁄4" (Model Number AC-ST6-
100).
PLENUM
FAN COIL
UNIT
PLENUM
FAN COIL
UNIT
PLENUM
FAN COIL
UNIT
PLENUM
FAN COIL
UNIT
PLENUM
FAN COIL
UNIT
FIGURE 1.2: PLENUM/TUBING LAYOUT ExAMPLES
(FOR GUIDANCE ONLY)
FIGURE 1.3:
USE OF TEES
