Task 5-Choose Register And Return Locations; Determining The Number Of Returns; Selecting Return Locations; Selecting Register Locations - Bryant ZONE PERFECT PLUS ZONEBB2KIT Zoning Design Manual

maintain minimum airflow through the system at all times, it is
better to use slightly undersized equipment than slightly oversized
equipment in a zoning system.
Select heating and cooling equipment to meet the peak heating and
cooling block load estimates that you calculated in Task 3. Use the
Product Data Sheets for the equipment that you are considering to
determine whether the equipment can meet the system's needs.
Verify that the selected indoor air handler can meet the heating and
cooling airflow requirements, as well as the system's external
static pressure requirements.
NOTE: When you design the air distribution system, you need the
Product Data for the indoor air handler's performance character-
istics.
In a zoning system, it is especially important to select heating and
cooling equipment that is not too large. Equipment that is larger
than necessary compounds the problem of keeping the airflow in
the system above the minimum required by the equipment when
few zones require conditioning. Because the system shuts down
the equipment if the duct temperature falls outside the minimum or
maximum temperature limits, and limits the number of times the
equipment can restart to 4 times per hour, the actual capacity
provided by the system can be smaller with larger equipment.
To help avoid such problems, size the equipment based on the
calculated peak heating or cooling airflow (whichever is larger) of
the home. Do not add a fudge factor. Under even the heaviest
loads, the system has the capability to send its entire capacity to
less than the entire home. To redirect capacity where it is most
needed, the homeowner can easily set back some zones.
For information about the different types of heating and cooling
equipment that can be used with zoning systems, see the section
"Special Applications Using Zone Perfect Plus."
TASK 5—CHOOSE REGISTER AND RETURN
LOCATIONS

Determining the Number of Returns

Each zone should have a separate return with sufficient capacity to
return all of the air that is delivered to that zone. If you cannot
provide a separate return for a zone, use one of the following
methods to maintain airflow to that zone:
• Leave space under doors.
• Install grilles into or above doors.
• Provide a connection from the zone to another area that has an
adequate return.
When the air leaving a zone must pass into another zone, cross
conditioning occurs and it becomes difficult to maintain different
temperatures in the 2 zones. For this reason, a zone that is
significantly "set back" at times needs its own return.

Selecting Return Locations

The location of the returns for a zone significantly affects the
capacity that can be delivered to that zone. A high return removes
warmer air from the ceiling and a low return removes cooler air
from the floor. For a 2-story home, it is best to have both high and
low returns.
The location of the returns for a zone also has a significant effect
on the comfort in that zone. Because our feet are generally on the
floor and our heads are never closer than about 2 ft from the
ceiling. It is more important to keep the floor at a comfortable
temperature. In both cooling and heating, floors can become
uncomfortably cool and a low return can help alleviate this
problem.
In homes where the air handler is located in the basement, a return
near the basement floor will help avoid overcooling of the
basement. A low return also helps with the removal of dampness
and radon from the basement. However, a low return in the
basement lowers the return temperature cooling, increasing the
size of ducts required for proper operation of the system.
For homes with cathedral ceilings or multi-story rooms, a return at
the highest point can enhance both efficiency and comfort,
particularly during heating.

Selecting Register Locations

The general issues related to selecting register locations are the
same in zoned systems as they are in non-zoned systems. The only
exception is that the velocity of air leaving a register is likely to be
higher in a zoned system. Locate the register to take advantage of
the greater mixing of air that can be provided by the higher air
velocity and to minimize the discomfort caused downwind from
the register. As always, select register and return locations to avoid
stratification of air in the room and to maximize the mixing that
occurs when air swirls through a room.
Meeting Zoning Challenges in 2-Story Homes
In a 2-story home where cooling is the primary challenge, keep in
mind the principle of buoyancy—the tendency for cool air to sink
and warm air to rise. The lower level might tend to be over
conditioned or the upper level might tend to be under conditioned.
To help avoid such problems, on the upper level you can:
• Use high registers to mix the cooled air with the warm air near
the ceiling.
• For registers, direct or deflect the air upward and maintain high
grille velocity.
• Install returns near the ceiling.
• Close doors to rooms and minimize space below doors when
possible, but only if each room has its own return.
• Install a ceiling fan in each room.

Recording Return and Register Locations

You can mark the locations for returns and registers on the Floor
Plan Worksheet for the home. Indicate the approximate height of
each return and register.
TASK 6—DETERMINE BYPASS NEEDS
Bypass dampers have become a standard component in many
zoning systems produced today. When multi-stage equipment with
an ICM blower motor is used in a properly sized duct system, a
bypass is not always necessary.
The use of a bypass to add load to a system is most common in
commercial applications. In residential applications, a direct by-
pass is most common. Without proper precautions, the use of a
direct bypass can lead to poor comfort and/or equipment failure.
A direct bypass recycles either the coldest or hottest air in the
system back into the return air inlet when it is needed the least. In
cooling, the direct bypass can cause the coil to freeze and the
equipment to shut down due to the low temperature limit. In
heating, the direct bypass can cause overheating and the equipment
to shut down due to the high temperature limit. Either of these
situations reduces the comfort that the system can provide.
A direct bypass with Zone Perfect Plus using the out zone feature
is an excellent option. The bypass reduces air noise under
minimum load and the out zone feature keeps the equipment from
shutting down.
TASK 7—LAY OUT SUPPLY DUCTS AND
LOCATE DAMPERS
The supply air duct system for a zoning system has a different
layout than one designed for a conventional single zone system.
Provide a separate zone duct to carry all of the air for each zone.
The zone damper for each zone is located in its zone duct. Branch
ducts connect to each zone duct, downstream from the zone
damper. They supply conditioned air to individual rooms or areas
in the zone.
In some systems, it might not be convenient to connect all of the
branch ducts for a zone to a single zone damper. In such a case,
multiple branch ducts can be fed through multiple (up to 3) zone
dampers. All of the zone dampers for the zone are wired in parallel
so that they open and close the same amount at the same time.
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