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Radial Perimeter System
The radial perimeter system (Fig. 53) is also often used
in single story slab construction. In areas where heating is
of primary importance, ducts can be below the flow with
low wall outlets. In areas where cooling is a primary
concern, the heating/cooling equipment and ducts can be
located in the attic with high sidewall outlets. The system is
best used where the heating/cooling equipment is centrally
located and all the runs can be about the same length.
Because extra headroom is required where ducts must cross
floor joists, this system is not as popular for basement
applications.
Fig. 53—Radial perimeter system.
SYSTEM SIZING FOR FORCED
AIR APPLICATIONS
The key to providing even, comfortable environmental
control in any system, but especially in a zoned system, is
choosing the best combination of duct size, mechanical
equipment size, and fan size and type for the application.
The necessary steps are summarized below and explained
in greater detail in books on comfort conditioning system
design such as the Air Conditioning Contractors of America
Manual D, "Duct Design for Residential Winter and Sum-
mer Air Conditioning and Equipment Selection."
NOTE: Never undersize the ducts. Oversize to the next
damper size.
1. Calculate the sensible winter heat loss and the sum-
mer heat gain, both sensible and latent, for each room.
2. Add the loads for each room to obtain the total
system design load. In a zoned system, also add loads for
each zone.
3. Calculate the design cfm for each room, each zone
when the system is zoned, and for the system.
4. Choose heating and cooling equipment that meets
the design load. Depending on the zone layout and antici-
pated occupancy patterns, it may be possible to select
slightly smaller equipment for a zoned system. Make sure
that the blower cfm is in the range of the design cfm.
5. Locate enough supply outlets in each room to cover
the design heat loss/cooling gain and sketch the duct lay-
out. Avoid angles and abrupt changes in duct size where
possible.
6. Size the zone takeoff, branch ducts, and trunk to
provide the required cfm to each room, remembering that
velocity should not exceed 700 cfm in the main trunk and
600 cfm in each supply and that every run should have
the same pressure loss.
7. Locate the return inlets; sketch the return runs; and
repeat step 6 for the return system.
8. Choose outlet registers and inlet grilles to provide
the desired air distribution pattern.
9. Include a return for every room; include two returns
for rooms with three or more supplies.
DAMPER SELECTION
If at all possible, install dampers where they are acces-
sible for service. Models are available for side or bottom
insertion into existing rectangular ducts, for internal mount-
ing as the ductwork is assembled, and for use with round
ducts. The dampers can be mounted in any position, except
side and internal mount models used in horizontal ducts
must be mounted with the actuator toward the top of the
duct to reduce operating friction and minimize dirt accu-
mulation on the linkage.
Rectangular dampers are sized smaller to fit in the duct-
work. Choose a damper the same nominal size as the duct.
Round dampers are sized slightly smaller than the duct air
inlet and slightly larger on the air outlet so they will slip in
easily and be less likely to bind. Never force a damper into
an undersized duct because the resulting pressure will
M2286A
cause the blades to bind. When necessary, install two
rectangular dampers back-to-back; this application requires
U-channel mounting tracks, available from Honeywell, to
keep the damper stable under conditions of high velocity air
flow. Mounting tracks are also required with rectangular
dampers over 20 x 8 in. [508 x 203 mm], 18 x 10 in. [457 x
254 mm], and 16 x 12 in. [406 x 305 mm] unless they can
be secured from both sides of the duct.
When an internally mounted motorized damper is
used, install it just upstream from a register, or install the
damper just ahead of a right angle to allow access for motor
service.
Motorized dampers are usually installed close to the
heating and cooling equipment. They can be installed in a
divided plenum on a two-zone system; they must be
downstream from the manual balancing dampers.
For humidification, use evaporative type or return air
type humidifiers. Do not use spray or atomization type
humidifiers installed in the furnace plenum or air supply
duct.
SYSTEM SIZING FOR HYDRONIC/RADIANT
HEATING APPLICATIONS
The key to providing even, comfortable environmental
control in any system is choosing the best system type,
valves, and other components for the application. The neces-
sary steps are summarized below.
1. Size the piping for adequate water flow.
2. Size the system for adequate head pressure.
3. Determine the maximum valve operating tempera-
ture. The maximum operating temperature for motorized
valves depends on the maximum ambient temperature at
the valve location, and on the maximum fluid temperature.
53
W180 ZONE CONTROL SYSTEM
68-0139
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